About all

How does heart pump: How the Heart Works | Michigan Medicine


How the Heart Works | Michigan Medicine

Topic Overview

The heart is at the center of your circulatory system, which is a network of blood vessels that delivers blood to every part of your body. Blood carries oxygen and other important nutrients that all body organs need to stay healthy and to work properly.

Your heart is a muscle, and its job is to pump blood throughout your circulatory system.

How does my heart pump blood?

Your heart is divided into two separate pumping systems, the right side and the left side.

  • The right side of your heart receives oxygen-poor blood from your veins and pumps it to your lungs, where it picks up oxygen and gets rid of carbon dioxide.
  • The left side of your heart receives oxygen-rich blood from your lungs and pumps it through your arteries to the rest of your body.

Your heart has four separate chambers that pump blood, two on the right side and two on the left.

How does blood flow through the heart?

Blood flows through your heart and lungs
in four steps:

  1. The right atrium receives oxygen-poor blood from the body and pumps it to the right ventricle through the tricuspid valve.
  2. The right ventricle pumps the oxygen-poor blood to the lungs through the pulmonary valve.
  3. The left atrium receives oxygen-rich blood from the lungs and pumps it to the left ventricle through the mitral valve.
  4. The left ventricle pumps the oxygen-rich blood through the aortic valve out to the rest of the body.

The left and right atria are smaller chambers that pump blood into the ventricles. The left and right ventricles are stronger pumps. The left ventricle is the strongest because it has to pump blood out to the entire body. When your heart functions normally, all four chambers work together in a continuous and coordinated effort to keep oxygen-rich blood circulating throughout your body. Your heart has its own electrical system that coordinates the work of the heart chambers (heart rhythm) and also controls the frequency of beats (heart rate).

How does my heart maintain its normal function?

The task of your heart is to pump enough blood to deliver a continuous supply of oxygen and other nutrients to the brain and the other vital organs. To do this, your heart needs to:

  • Regulate the timing of your heartbeat. Your heart’s electrical system controls the timing of the pump. The electrical system keeps your heart beating in a regular rhythm and adjusts the rate at which it beats. When the electrical system is working properly, it maintains a normal heart rate and rhythm. Problems with this electrical system can cause an arrhythmia, which means that your heart chambers are beating in an uncoordinated or random way or that your heart is beating too fast (tachycardia) or too slow (bradycardia).
  • Keep your heart muscle healthy. The four chambers of your heart are made of a special type of muscle called myocardium. The myocardium does the main pumping work: It relaxes to fill with blood and then squeezes (contracts) to pump the blood. “Contractility” describes how well the heart muscle squeezes. After pumping, your heart relaxes and fills with blood. The muscle must be able to relax enough so that it can fill with blood properly before it pumps again. The health of your heart muscle affects both its contractility and its ability to relax, both of which determine whether your heart is able to pump enough blood each time it beats. Problems with the contractility of your heart can be caused by problems with the muscle itself (such as a viral infection of the heart muscle or an inherited heart muscle disorder) or by problems with the blood supply to the heart muscle (such as reduced blood flow to the heart muscle, called ischemia). Your heart muscle needs its own supply of blood because, like the rest of your body, it needs oxygen and other nutrients to stay healthy. For this reason, your heart pumps oxygen-rich blood to its own muscle through your coronary arteries.
  • Keep blood flowing efficiently. Your heart has four valves that control the flow of blood in and out of the chambers. There are valves between the atrium and the ventricle on each side of your heart. There is also a valve controlling the flow of blood out of each of your ventricles. The valves are designed to keep blood flowing forward only. When each chamber contracts, a valve opens to allow blood to flow out. When the chamber relaxes, the valve closes to prevent blood from leaking back into the chamber and to allow the chamber to fill with blood again. A problem with your heart valves can disrupt the normal flow of blood and cause problems for your heart.


Other Works Consulted

  • Hoit BD, Walsh RA (2011). Normal physiology of the cardiovascular system. In V Fuster et al., eds., Hurst’s The Heart, 13th ed., vol. 1, pp. 94–117. New York: McGraw-Hill.


Current as of:
August 31, 2020

Author: Healthwise Staff
Medical Review:
Rakesh K. Pai MD, FACC – Cardiology, Electrophysiology
Martin J. Gabica MD – Family Medicine
Adam Husney MD – Family Medicine
Stephen Fort MD, MRCP, FRCPC – Interventional Cardiology

Current as of: August 31, 2020

Healthwise Staff

Medical Review:Rakesh K. Pai MD, FACC – Cardiology, Electrophysiology & Martin J. Gabica MD – Family Medicine & Adam Husney MD – Family Medicine & Stephen Fort MD, MRCP, FRCPC – Interventional Cardiology

How the Heart Works & Pumps Blood Through The Human Body

The heart is an amazing organ. It pumps oxygen and nutrient-rich blood throughout your body to sustain life. This fist-sized powerhouse beats (expands and contracts) 100,000 times per day, pumping five or six quarts of blood each minute, or about 2,000 gallons per day.

Your heart is a key part of your cardiovascular system, which also includes all your blood vessels that carry blood from the heart to the body and then back to the heart.

How Does Blood Travel Through the Heart?

As the heart beats, it pumps blood through a system of blood vessels, called the circulatory system. The vessels are elastic, muscular tubes that carry blood to every part of the body.

Blood is essential. In addition to carrying fresh oxygen from the lungs and nutrients to the body’s tissues, it also takes the body’s waste products, including carbon dioxide, away from the tissues. This is necessary to sustain life and promote the health of all parts of the body.

There are three main types of blood vessels:

  • Arteries. They begin with the aorta, the large artery leaving the heart. Arteries carry oxygen-rich blood away from the heart to all of the body’s tissues. They branch several times, becoming smaller and smaller as they carry blood further from the heart and into organs.
  • Capillaries. These are small, thin blood vessels that connect the arteries and the veins. Their thin walls allow oxygen, nutrients, carbon dioxide, and other waste products to pass to and from our organ’s cells.
  • Veins. These are blood vessels that take blood back to the heart; this blood has lower oxygen content and is rich in waste products that are to be excreted or removed from the body. Veins become larger and larger as they get closer to the heart. The superior vena cava is the large vein that brings blood from the head and arms to the heart, and the inferior vena cava brings blood from the abdomen and legs into the heart.

This vast system of blood vessels — arteries, veins, and capillaries — is over 60,000 miles long. That’s long enough to go around the world more than twice!

Where Is Your Heart and What Does It Look Like?

The heart is located under the rib cage, slightly to the left of your breastbone (sternum) and between your lungs.

Looking at the outside of the heart, you can see that the heart is made of muscle. The strong muscular walls contract (squeeze), pumping blood to the rest of the body. On the surface of the heart, there are coronary arteries, which supply oxygen-rich blood to the heart muscle itself. The major blood vessels that enter the heart are the superior vena cava, the inferior vena cava, and the pulmonary veins. The pulmonary artery exits the heart and carries oxygen-poor blood to the lungs. The aorta exits and  carries oxygen-rich blood to the rest of the body.

On the inside, the heart is a four-chambered, hollow organ. It is divided into the left and right side by a muscular wall called the septum. The right and left sides of the heart are further divided into two top chambers called the atria, which receive blood from the veins, and two bottom chambers called ventricles, which pump blood into the arteries.


The atria and ventricles work together, contracting and relaxing to pump blood out of the heart. As blood leaves each chamber of the heart, it passes through a valve. There are four heart valves within the heart:

  • Mitral valve
  • Tricuspid valve
  • Aortic valve
  • Pulmonic valve

The tricuspid and mitral valves lie between the atria and ventricles. The aortic and pulmonic valves lie between the ventricles and the major blood vessels leaving the heart.

The heart valves work the same way as one-way valves in the plumbing of your home. They prevent blood from flowing in the wrong direction.

Each valve has a set of flaps, called leaflets or cusps. The mitral valve has two leaflets; the others have three. The leaflets are attached to and supported by a ring of tough, fibrous tissue called the annulus. The annulus helps to maintain the proper shape of the valve.

The leaflets of the mitral and tricuspid valves are also supported by tough, fibrous strings called chordae tendineae. These are similar to the strings supporting a parachute. They extend from the valve leaflets to small muscles, called papillary muscles, which are part of the inside walls of the ventricles.

How Does Blood Flow Through the Heart?

The right and left sides of the heart work together. The pattern described below is repeated over and over, causing blood to flow continuously to the heart, lungs, and body.

Right Side of the Heart

  • Blood enters the heart through two large veins, the inferior and superior vena cava, emptying oxygen-poor blood from the body into the right atrium of the heart.
  • As the atrium contracts, blood flows from your right atrium into your right ventricle through the open tricuspid valve.
  • When the ventricle is full, the tricuspid valve shuts. This prevents blood from flowing backward into the atria while the ventricle contracts.
  • As the ventricle contracts, blood leaves the heart through the pulmonic valve, into the pulmonary artery and to the lungs, where it is oxygenated and then returns to the left atrium through the pulmonary veins.

Left Side of the Heart

  • The pulmonary veins empty oxygen-rich blood from the lungs into the left atrium of the heart.
  • As the atrium contracts, blood flows from your left atrium into your left ventricle through the open mitral valve.
  • When the ventricle is full, the mitral valve shuts. This prevents blood from flowing backward into the atrium while the ventricle contracts.
  • As the ventricle contracts, blood leaves the heart through the aortic valve, into the aorta and to the body.

How Does Blood Flow Through Your Lungs?

Once blood travels through the pulmonic valve, it enters your lungs. This is called the pulmonary circulation. From your pulmonic valve, blood travels to the pulmonary artery to tiny capillary vessels in the lungs.

Here, oxygen travels from the tiny air sacs in the lungs, through the walls of the capillaries, into the blood. At the same time, carbon dioxide, a waste product of metabolism, passes from the blood into the air sacs. Carbon dioxide leaves the body when you exhale. Once the blood is oxygenated, it travels back to the left atrium through the pulmonary veins.

What Are the Coronary Arteries of the Heart?

Like all organs, your heart is made of tissue that requires a supply of oxygen and nutrients. Although its chambers are full of blood, the heart receives no nourishment from this blood. The heart receives its own supply of blood from a network of arteries, called the coronary arteries.


Two major coronary arteries branch off from the aorta near the point where the aorta and the left ventricle meet:

  • Right coronary artery supplies the right atrium and right ventricle with blood. It branches into the posterior descending artery, which supplies the bottom portion of the left ventricle and back of the septum with blood.
  • Left main coronary artery branches into the circumflex artery and the left anterior descending artery. The circumflex artery supplies blood to the left atrium, side and back of the left ventricle, and the left anterior descending artery supplies the front and bottom of the left ventricle and the front of the septum with blood.

These arteries and their branches supply all parts of the heart muscle with blood.

Coronary artery disease occurs when plaque builds up in the coronary arteries and prevents the heart from getting the enriched blood it needs. If this happens, a network of tiny blood vessels in the heart that aren’t usually open called collateral vessels may enlarge and become active. This allows blood to flow around the blocked artery to the heart muscle, protecting the heart tissue from injury.

How Does the Heart Beat?

The atria and ventricles work together, alternately contracting and relaxing to pump blood through your heart. The electrical system of the heart is the power source that makes this possible.

Your heartbeat is triggered by electrical impulses that travel down a special pathway through the heart.

  • The impulse starts in a small bundle of specialized cells called the SA node (sinoatrial node), located in the right atrium. This node is known as the heart’s natural pacemaker. The electrical activity spreads through the walls of the atria and causes them to contract.
  • A cluster of cells in the center of the heart between the atria and ventricles, the AV node (atrioventricular node) is like a gate that slows the electrical signal before it enters the ventricles. This delay gives the atria time to contract before the ventricles do.
  • The His-Purkinje network is a pathway of fibers that sends the impulse to the muscular walls of the ventricles, causing them to contract.

At rest, a normal heart beats around 50 to 90 times a minute. Exercise, emotions, fever, and some medications can cause your heart to beat faster, sometimes to well over 100 beats per minute.

How the Heart Pumps Blood

The primary responsibility of the heart is to pump blood throughout the circulatory system. As the center of the circulatory system, the heart is an essential organ for maintaining the overall functioning of the body.

The cardiovascular system consists of many veins and blood vessels which ensure that all parts of the body are provided with an adequate amount of oxygen and nutrients to function efficiently.  Without a sufficient supply of oxygen, any bodily function would fail, causing organ damage or organ death.

How a Normal Heart Pumps Blood — The Children’s Hospital of PhiladelphiaPlay

Components of the heart

Fully understanding the heart’s vital function in the body entails the need to first understand its anatomy. As a busy and hardworking organ, the heart needs to closely monitor all of its components to ensure proper functioning. Even a minor cardiac dysfunction may result in significant functional challenges in the total body function of an affected individual.

Located at the center of the chest and in the thoracic cavity, the heart can be divided into four parts that are otherwise known as chambers, each of which contains several valves. Two of these chambers, which are called atria, are located in the upper portion of the heart and receive oxygen-free blood. The valves that separate these chambers are called atrioventricular valves, which are composed of the tricuspid valve on the left and the mitral valve on the right.

Meanwhile, ventricles, which are the chambers found in the lower portion of the heart, pump oxygen-enriched blood into the body. Similar to the atria, the ventricular chambers are also separated by valves called semilunar valves. These valves may be further divided into the pulmonary and aortic valves.

The heart is also composed of a protective layer that has three parts, which include the outer layer known as the epicardium, the middle layer known as the myocardium, and the innermost layer known as the endocardium. Both the outer and inner layers of the heart are thin; whereas the middle layer, makes up most of the heart and is comrpised of cardiac muscle fibers.

There are two types of blood vessels that facilitate the distribution of blood throughout the body. The vessels that bring oxygen-free blood back into the heart are called veins. Comparatively, the blood vessels that carry oxygen-rich blood away from the heart and to other body parts are called arteries. Originating in the left ventricle, the largest artery is called the aorta.

All these parts function together to ensure that all organs of the body are regularly supplied with a sufficient amount of oxygen and nutrients.

The pumping process

The heart’s blood pumping cycle, which is called the cardiac cycle, begins when oxygen-free blood returns to the heart through the right atrium, after distributing oxygen and nutrients to other parts of the body. The blood then moves into the right ventricle, which facilitates a transfer of blood into the lungs. Within the lungs, all waste gases, such s carbon dioxide, are released from the blood, while also reoxygenating the blood for its return to circulation.

The oxygen-rich blood returns to the heart through the left atrium and eventually into the left ventricle. This chamber then pumps blood to the other organs of the body through the aorta. After reaching each of the organs, deoxygenated blood leaves these organs through their respective veins until finally reaching the heart through the superior and inferior vena cavae, depending upon the organ. Several anatomical studies have estimated that a total of approximately 5.6 liters of blood circulate the body, with three cardiac cycles completed each minute.

Image Credit: Lightspring / Shutterstock.com

Generating a heartbeat

A normal heartbeat is evidence of the heart’s typical functioning, and each heartbeat is a manifestation of the oxygen-reloading process within the heart. As blood flows throughout the body in a single direction, any misdirection of the blood is avoided through the regulated closing and opening functions of the various cardiac chambers and valves.

The first phase of a heartbeat, which is known as systole, is a short period that occurs when the ventricles contract and initiate the closing of the tricuspid and mitral valves. The second phase, which is called diastole, is a relatively long period of ventricular relaxation, where the aortic and pulmonary valves close.

The heart’s “lub-dub” sound is produced by the continuous closing and opening of the valves. This process occurs in a way that the entry and exit of either oxygen-rich or oxygen-free blood into and outside the heart remain synchronized.

A complete and successful heartbeat is made possible by electrical impulses coming from the sino-atrial (SA) node that catalyzes the function of each component within the heart. The rate of systole and diastole are commonly used to quantify the rate of an individual’s blood pressure at a certain point in time. A normal adult heart rate of an adult is typically around 72 beats per minute.


Further Reading

How your heart works | NHS inform

Your heart is roughly the size of a fist and sits in the middle of your chest, slightly to the left. It’s the muscle at the centre of your circulation system, pumping blood around your body as your heart beats. This blood sends oxygen and nutrients to all parts of your body, and carries away unwanted carbon dioxide and waste products.

Structure of your heart

Your heart is made up of three layers of tissue:

  • epicardium
  • myocardium
  • endocardium

These layers are surrounded by the pericardium, a thin outer lining protecting your heart.

There are four chambers that make up the heart – two on the left side and two on the right.

The two small upper chambers are the atria. The two larger lower chambers are the ventricles. These left and right sides of the heart are separated by a wall of muscle called the septum.

Circulatory system

Your heart pumps blood around the body all the time – about five litres (eight pints) of it – and this is called circulation. Your heart, blood and blood vessels together make up your cardiovascular system (or heart and circulatory system).

The right side of the heart receives blood that is low in oxygen because most has been used up by the brain and body. It pumps this to your lungs, where it picks up a fresh supply of oxygen. The blood then returns to the left side of the heart, ready to be pumped back out to the brain and the rest of your body.

Blood vessels

Your blood is pumped around your body through a network of blood vessels:

  • arteries – they carry oxygen-rich blood from your heart to all parts of your body, getting smaller as they get further away from the heart
  • capillaries – they connect the smallest arteries to the smallest veins, and help exchange water, oxygen, carbon dioxide and other nutrients and waste substances between the blood and the tissues around them
  • veins – they carry blood, lacking in oxygen, back towards your heart, and get bigger as they get nearer your heart

Blood vessels are able to widen or narrow depending on how much blood each part of your body requires. This action is partly controlled by hormones.


Your heart has four valves. They act like gates, keeping the blood moving in the right direction:

  • aortic valve – on the left side
  • mitral valve – on the left side
  • pulmonary valve – on the right side
  • tricuspid valve – on the right side

Electrical system 

For your heart to keep pumping regularly, it needs electrical signals which are sent to the heart muscle telling it when to contract and relax.

The electrical signal starts in the right atrium where your heart’s natural pacemaker – the sino–atrial node – is situated. This signal crosses the atria, making them contract. Blood is pumped through the valves into the ventricles.

Where the atria meet the ventricles, there is an area of special cells – called the atrio-ventricular node – which pass the electrical signals throughout your heart muscle by a system of electrical pathways, known as the conducting system.

The muscles of the ventricles then contract, and blood is pumped through the pulmonary and aortic valves into the main arteries.

The heart’s natural ‘pacemaker’ – the sino-atrial node – produces another electrical signal, and the cycle starts again.

Blood pressure

This is the measurement of the pressure within the arteries. It plays a vital role in the way your heart delivers fresh blood to all your blood vessels. For blood to travel throughout your body quickly enough, it has to be under pressure. This is created by the relationship between three things:

  • your heart’s pumping action
  • the size and stretchiness of your blood vessels
  • the thickness of the blood itself

One heartbeat is a single cycle in which your heart contracts and relaxes to pump blood. At rest, the normal heart beats approximately 60 to 100 times every minute, and it increases when you exercise.

To ensure an adequate blood supply around your body, the four chambers of your heart have to pump regularly and in the right sequence.

There are two phases to your heart’s pumping cycle:

  • systole – this is when your heart contracts, pushing blood out of the chambers
  • diastole – this is the period between contractions when the muscle of your heart (myocardium) relaxes and the chambers fill with blood

Read more from Chest Heart & Stroke Scotland on how the heart works.

What can go wrong?


Some people are born with a heart that has not developed properly in the womb before birth – this is called congenital heart disease.

Sometimes you can inherit a heart condition from your family.

Cardiovascular system

Problems with your heart and circulation system include:

  • heart attack
  • angina
  • stroke

Heart disease can happen when your coronary arteries become narrowed by a gradual build-up of fatty material – called atheroma.

If your coronary arteries are narrowed or blocked, the blood supply to your heart will be impaired. This is the most common form of heart disease, known as coronary heart disease (sometimes called coronary artery disease or ischaemic heart disease).

Eventually, your arteries may become so narrow they can’t deliver enough blood to your heart. This can cause angina – a pain or discomfort in your chest, arm, neck, stomach or jaw.

If the fatty material breaks off or ruptures, a blood clot will form, which can cause heart attack (or stroke, if the artery affected is carrying blood to your brain).

Electrical system

Normally your heart will beat between 60 to 100 times per minute. This regular rhythmic beating is dependent upon electrical signals being conducted throughout your heart.

If the electrical signals within your heart are interrupted, your heart can beat too quickly (tachycardia), too slowly (bradycardia) and/or in an irregular way. This is called an arrhythmia – see Chest Heart & Stroke Scotland.

Conditions affecting the pumping of your heart

There are some conditions which can damage your heart muscle, making it weak and unable to pump as efficiently as before:

  • heart attack 
  • high blood pressure (hypertension)
  • heart valve problems – see Chest Heart & Stroke Scotland
  • cardiomyopathy – this is a general term for diseases of the heart muscle. Sometimes these diseases are inherited from your family. Sometimes they are caused by other things, like viral infections.

There are also conditions – like high blood pressure (hypertension) – which mean your heart has to work harder.

When your heart muscle can’t meet your body’s demands for blood and oxygen, you can develop various symptoms, like breathlessness, extreme tiredness and ankle swelling. This is called heart failure because of the failure of your heart to pump blood around the body and work efficiently.


Your heart can’t function normally if the heart valves aren’t working properly, as it can affect the flow of blood through the heart.

There are two main ways that the valves can be affected:

  • valves can leak – this is called valve regurgitation or valve incompetence
  • valves can narrow and stiffen – this is called valve stenosis

Further information

Try the British Heart Foundation’s Know your heart, an interactive tool narrated and presented by Dr Hilary Jones.

Heart: how your heart pumps blood around your body

The heart is a fist-sized muscular organ that sits in the chest cavity.

What does your heart do?

The purpose of your heart is to pump blood to the organs and tissues of your body that need the oxygen and nutrients it carries. Oxygen-rich blood is pumped out of the left side of your heart (shown on the right in the diagram) into the arteries to these tissues and organs.

Blood that has delivered its nutrients and oxygen and is in need of oxygen comes back to your heart in the veins and enters the right hand side of the heart (on left of diagram). This blood which is in need of oxygen (so-called deoxygenated blood) is sent to your lungs to pick up oxygen and get rid of carbon dioxide.

Your heart pumps all day to circulate blood around the body. On average, a red blood cell in the circulation will pass through the heart every 45 seconds. If you start to exert yourself your heart will start to pump faster to supply your working muscles with the increased amount of oxygen and nutrients they need. The heart is a muscle too, and to enable it to pump effectively, it has its own blood supply bringing it oxygen.

How does your heart work?

Your heart is made up of 2 pumps. The pump on the right hand side receives blood that has already delivered its oxygen round the body and sends this blood to the lungs to pick up more oxygen (and get rid of carbon dioxide).

The pump on the left hand side receives oxygen-rich blood and then pumps it out into the arteries to deliver its oxygen around the body.

Blood in need of oxygen enters heart

Blood in need of oxygen from around the body travels in the veins to the heart. This blood in need of oxygen (also called deoxygenated blood) is usually shown as blue or purple on diagrams.

This ‘deoxygenated’ blood enters the top right hand side chamber (shown on left in diagram) of the heart, which is called the right atrium, via two large veins. Blood from the upper body, e.g. the head and arms, comes in via the superior vena cava. Blood from the lower body, that is the trunk and legs, comes in via the inferior vena cava.

Blood passes from right atrium to right ventricle

When the right atrium fills, the blood then passes through a one-way door (valve) called the tricuspid valve into the right ventricle. The valve stops blood from flowing backwards into the right atrium once it’s in the right ventricle. The right ventricle relaxes and venous blood in need of oxygen flows in.

Right ventricle sends blood needing oxygen to the lungs

The blood needing oxygen is pumped out of the right ventricle, through the pulmonary valve into the pulmonary artery. The pulmonary artery then divides into the right and left pulmonary arteries, carrying blood to the right and left lungs. In the lungs the blood gives up its carbon dioxide and picks up oxygen.

Oxygen-rich blood from lungs enters heart

Fresh blood full of oxygen leaves the lungs and comes back to the heart in the pulmonary veins. This oxygen-rich blood enters the left atrium — the top left chamber of the heart (on right of diagram).

Blood passes from left atrium to left ventricle

When the left atrium is full it pushes the blood through the mitral valve into the left ventricle.

Left ventricle sends oxygen-rich blood around body

The left ventricle relaxes and fills up with blood before squeezing and pumping the oxygen-rich blood through the aortic valve into the aorta — the main artery that carries blood to your body. The muscle wall of the left ventricle is very thick because it has to pump blood around the whole body.

1. Tortora GJ, Derrickson BH. Essentials of Anatomy and Physiology. 9th International student edition. New York: Wiley; 2012.
2. Tracey DJ, Baume P. Anatomica: The Complete Reference to the Human Body and How it Works. Random House Australia, 2000.
3. Netter FH. Atlas of Human Anatomy. 6th ed. Saunders; 2014.

How the Heart Works – Heart Foundation

The human heart pumps blood to every part of your body. Learn about the different parts of the heart and watch our video about how a healthy heart works.

Your heart is the pump which powers your body. It supplies blood carrying oxygen and nutrients to every cell, nerve, muscle and vital organ in your body.

It sits in your chest between your lungs, slightly to the left of centre, and is protected by your rib cage.

Your heart is about the size of your clenched fist and weighs about 300 grams (that’s just over half a packet of butter).

Watch our step-by-step video of how the heart works

What are the parts of the heart?

Your heart is a bit like a house. It has:

Heart walls

The walls of your heart are made of powerful muscle tissue, which squeezes and relaxes to pump blood around your body. This muscle tissue is divided into three layers.

  • The endocardium (the inside layer).
  • The myocardium (the muscular middle layer).
  • The epicardium (the protective outer layer).
Heart chambers (rooms)

Your heart is made up of four chambers, two on the right and two on the left. These are like the rooms of your house.

The top two chambers are called the left and right atrium and the bottom two are called the left and right ventricles.

They are divided by a thin wall called the septum.

Heart valves (the doors between the rooms)

There are four heart valves, which act like doors between the chambers of the heart. They open and close as your heart pumps.

The valves only open one way. This stops blood flowing in the wrong direction between the chambers of your heart.

The two valves that sit between the upper and lower chambers of the heart are called the atrioventricular, or AV valves.

The tricuspid valve is the door between the right atrium and ventricle.

The mitral valve is the door between the left atrium and ventricle.

The other two valves are the doors out of the ventricles. They are called semilunar, or SL valves.

The aortic valve is the door out of the left ventricle into the aorta.

The pulmonary valve is the door out of the right ventrical into the pulmonary artery.

The blood vessels (the plumbing)

Blood travels between the heart and the lungs and the rest of the body, via a network of pipes called the blood vessels. There are three main types of blood vessels.

  • Arteries, which carry oxygenated blood from your heart to the rest of your body.
  • Veins, which carry the de-oxygenated blood back to your heart and lungs.
  • Capillaries, the small vessels where oxygenated and de-oxygenated blood is exchanged.
How the heart pumps

Your conduction system sends the electrical signals which trigger the heart to pump blood around the body, and to and from the lungs.

Blood which has used all its oxygen is returned to the right side of the heart, via large veins called the inferior and superior vena cava. From there it is pumped to the lungs, via the pulmonary artery.

Once the blood has received oxygen from the lungs, it travels through the pulmonary veins into the left side of the heart. From here it is pumped back out around the body, via the aorta.

The heart’s conduction system (the electrics)

Your heart has its own electrical wiring system (conduction system), which keeps it beating. This conduction system includes:

  • the sinoatrial (SA) node (or sinus node). This is your body’s own internal pacemaker, that produces electrical signals to make your heart beat
  • the atrioventricular (AV) node. This is a node that passes on the electrical signals from the upper chambers of the heart (artia) to the lower ones (ventricles)
  • the bundle of His, the left and right bundle branches, and the Purkinje fibres. These act like electrical wiring that communicate the signals around the heart.

The SA node sends an electrical signal that makes the upper chambers of the heart (atria) contract (squeeze). This pushes blood out of the atria and into the lower chambers of the heart (ventricles).

The electrical signal passes from the atria to the AV node. From there, it passes through the bundle of His and into the right and left bundle branches.

Finally, the signal travels down the Purkinje fibres, causing the ventricles to contract. This pushes blood out of your heart to your lungs and the rest of your body.

How the heart pumps

Your conduction system sends the electrical signals which trigger the heart to pump blood around the body, and to and from the lungs.

Blood which has used all its oxygen is returned to the right side of the heart, via large veins called the inferior and superior vena cava. From there it is pumped to the lungs, via the pulmonary artery.

Once the blood has received oxygen from the lungs, it travels through the pulmonary veins into the left side of the heart. From here it is pumped back out around the body, via the aorta.

The coronary arteries

The heart has its own network of blood vessels, which supply it with the blood it needs to keep pumping.

These vessels are called the coronary arteries. They branch off the body’s largest artery, the aorta, and lie on the outside of your heart.

Narrowing in one of the coronary arteries can lead to angina and a blockage can cause a heart attack.

Learn about heart conditions

What is your pulse?

The pulse you can feel, for example in your wrist or neck, is the heart pumping blood. You can measure the rate and rhythm of your heart by taking your pulse.

How to take your pulse

Heart Basics | Hoag Heart & Vascular Institute

How The Heart Works

The normal heart is a strong, muscular pump a little larger than a fist.
It pumps blood continuously through the circulatory system. Each day the
average heart “beats” (expands and contracts) 100,000 times
and pumps about 2,000 gallons of blood. In a 70-year lifetime, an average
human heart beats more than 2.5 billion times.

The circulatory system is the network of elastic tubes that carries blood
throughout the body. It includes the heart, lungs, arteries, arterioles
(ar-TE’re-olz) (small arteries), and capillaries (KAP’ih-lair”eez)
(very tiny blood vessels). These blood vessels carry oxygen- and nutrient-rich
blood to all parts of the body. The circulatory system also includes venules
(VEN’ yoolz) (small veins) and veins. These are the blood vessels
that carry oxygen- and nutrient-depleted blood back to the heart and lungs.
If all these vessels were laid end-to-end, they’d extend about 60,000
miles. That’s enough to encircle the earth more than twice.

The circulating blood brings oxygen and nutrients to all the body’s
organs and tissues, including the heart itself. It also picks up waste
products from the body’s cells. These waste products are removed as
they’re filtered through the kidneys, liver and lungs.

What is the heart’s structure?

The heart has four chambers through which blood is pumped. The upper two
are the right and left atria. The lower two are the right and left ventricles.
Four valves open and close to let blood flow in only one direction when
the heart beats:

  • The
    tricuspid valve is between the right atrium and right ventricle.
  • The
    pulmonary or pulmonic valve is between the right ventricle and the pulmonary artery.
  • The
    mitral valve is between the left atrium and left ventricle.
  • The
    aortic valve is between the left ventricle and the aorta.

Each valve has a set of flaps (also called leaflets or cusps). The mitral
valve has two flaps. The others have three. Under normal conditions, the
valves let blood flow in just one direction. Blood flow occurs only when
there’s a difference in pressure across the valves that causes them to open.

How does the heart pump blood?

A heart’s four chambers must beat in an organized manner. This is governed
by an electrical impulse. A chamber of the heart contracts when an electrical
impulse moves across it. Such a signal starts in a small bundle of highly
specialized cells in the right atrium — the sinoatrial (SI’no-A’tre-al)
node (SA node), also called the sinus node. A discharge from this natural
“pacemaker” causes the heart to beat. This pacemaker generates
electrical impulses at a given rate, but emotional reactions and hormonal
factors can affect its rate of discharge. This lets the heart rate respond
to varying demands.

Information provided by the American Heart Association.

All about the heart | Association of Cardiovascular Surgeons of Russia Section “Cardiology and Imaging in Cardiac Surgery”


The human heart is a strong muscle pump. Every day, the heart contracts and relaxes 100,000 times and pumps 7,600 liters of blood. Over 70 years of life, the average human heart contracts more than 2.5 million times.

The heart pumps blood through the circulatory system.The circulatory system is a network of elastic tubes that carry blood to the organs and tissues of the body. The circulatory system includes the heart and blood vessels: arteries, arterioles, capillaries (the smallest vessels), venules and veins. The arteries carry oxygen-rich blood to all parts of the body. Veins carry carbon dioxide and waste products back to the heart and lungs. If all the vessels of the human body are connected together and pulled out in one line, they will cover a distance of 96.5 thousand kilometers. This will be enough to grip the ground more than 2 times.Blood carries oxygen and nutrients to all organs and tissues, including the heart itself. Metabolic products enter the blood from the tissues. Metabolic products are removed by the kidneys, liver and lungs.

The heart consists of 4 chambers; 2 atria and 2 ventricles. The chambers are separated by valves that open and close as the heart contracts, allowing blood to flow in only one direction. The valves open when the pressure in the chambers increases as the heart contracts.

Heart valves:

– Tricuspid valve between the right atrium and the right ventricle

– Pulmonary valve between the right ventricle and pulmonary artery

– Mitral valve between the left atrium and the left ventricle

– Aortic valve between the left ventricle and aorta

Each valve has several leaves.The mitral valve has 2 leaflets, the other valves 3.

How does the heart work?

The heart pumps blood due to the coordinated sequential contraction of its chambers. Blood enters the right atrium from the veins. Venous blood is rich in carbon dioxide and contains almost no oxygen. Compared to arterial blood, it is darker in color. When the heart muscle relaxes, venous blood flows through the open tricuspid valve into the right ventricle.

Electrical impulse, starts the heartbeat, which begins with the contraction of the atria.The right atrium, by contracting, fills the right ventricle with an additional volume of blood. After contractions of the right atrium, the right ventricle contracts. At this point, the tricuspid valve closes, preventing blood from flowing back into the atrium, and all blood from the right ventricle enters the pulmonary artery and then into the lungs. In the lungs, carbon dioxide is released from the blood and the blood is saturated with oxygen. Oxygen-rich arterial blood flows from the lungs into the left atrium.

Synchronously with the right atrium, the left atrium contracts.From it, blood flows through the mitral valve into the left ventricle. The left ventricle contracts and pushes blood through the aortic valve into the aorta. Many arteries depart from the aorta, carrying blood to all organs and tissues.

All four chambers of the heart must contract in a certain way. The contractions of the heart are controlled by electrical impulses. The chambers of the heart begin to contract after electrical impulses pass through them. The impulses originate in a special part of the heart’s nervous system called the sinus node.The sinus node is the main pacemaker that makes the heart beat. The pacemaker regenerates the pulses at a specific rate. Emotional responses and hormonal influences can alter this frequency, causing the heart to beat faster or less frequently.

An electrical impulse originating in the sinus node travels through the right and left atrium, causing muscle cells to contract. After the atria have contracted, an electrical impulse travels along the nervous system of the heart further to the ventricles, forcing them to contract and expel blood into the vessels.The role of the electrical impulse is to provide the coordinated contraction of the heart that is necessary for it to function well.

Material prepared by E.Z. Golukhova.

Surprising facts about heart and blood

  • William Park
  • BBC Future

Photo author, iStock

The most complex creation of the universe is undoubtedly the human brain. But our heart and circulatory system are equally exciting.BBC Future has a few interesting facts about them.

The heart pumps a lot of blood

Our heart is a very hardworking organ.

Within five minutes, he pumps five liters of blood. In an hour, the heart makes an average of 4200 beats and pumps 300 liters of blood.

In one year, it pumps enough blood to fill the Olympic pool – more than 2.5 million liters – and makes 38.5 million reductions to do so.

Heartbeat Affects Behavior

When we have to make a difficult decision, we often say that we made this choice with our heart.

But did you know that this expression can have a literal meaning? Heart rate affects our feelings, emotions and even intuition – from pain and empathy for another person to the suspicion that your man may be cheating on you.

Researcher Agustín Ibanez of the University of Favaloro in Buenos Aires had a unique opportunity to test this assumption when he met a man with two hearts.Carlos (the man’s name has been changed) had another heart, a mechanical one, located in the chest just below his real heart. Carlos received a heart transplant, which helped his weak heart muscles work.

Photo author, SPL

Signs to photo,

Scientists have replaced the patient’s blood with saline, thus trying to prolong his life.

As a result, Carlos had a feeling that his heart “sank” into his stomach, and this began to influence his perception of reality and even his mind.

Scientists have found a way to live without blood

What happens when our heart stops? Is it possible to bring a person back to life from the moment of clinical death, when all the basic vital functions – heartbeat and brain activity – have stopped?

Surgeons today tried a radical new procedure. They replaced the patient’s blood with saline in an attempt to prolong his life.

This experimental study seems to blur the line between life and death.The patient’s body is cooled to about 10-15 C. Since the body’s metabolism has already stopped, blood is not needed in order to supply oxygen to the cells. Replacing blood with cold salt water is the best way to maintain an overall low body temperature.

We still don’t know why we have different blood types

One of the biggest mysteries of our circulatory system has remained unsolved for over a century.

We still do not fully know why people have different blood types.We know that they are determined by various molecules on the surface of red blood cells. And we realize the importance of this process, since enzymes in our body recognize red blood cells precisely thanks to these molecules.

That is why blood can only be transfused to a person of the corresponding group – enzymes cannot recognize another group.

Photo author, Science Photo Library

Pidpis to photo,

Why did nature endow us with different blood types?

But why do we have different blood types? Why didn’t nature make it so that we all have a universal set of molecules in our blood cells?

One day we will be able to live with an artificial heart… or a pig’s heart

Xenotransplantation – the use of animal tissue in the human body – dates back to at least 1682, when the Dutch surgeon Job Janszon van Meerkeren reported the successful transplantation of a fragment of a dog’s bone into the skull of a Russian soldier.

Researchers are now actively studying the possibility of transplanting hearts from other animals, such as pigs, to humans.

Another line of research aims to grow human hearts using tissue engineering.

Some people drink blood without any benefit

Perhaps the most surprising use of blood is to consume it internally, preferably fresh, to relieve a number of medical complaints.

In different parts of the world there are entire communities of people who drink fresh human blood for medicinal purposes. Doses of the red drink are kindly provided by relatives, friends or volunteers.

Photo by Olivia Howitt

Sign up to photo,

Blood tastes differently depending on blood type, diet and amount of fluid you drink

These “medical vampires” claim that regular blood intake helps them relieve symptoms such as headaches , fatigue, stomach pain that no other treatment works for.

However, scientists believe that drinking blood is unlikely to have any benefit, and the relief it brings is actually just a placebo effect. But the mere fact that people feel better attests to the powerful effect the ritual of consuming human blood has on the mind.


the original of this article in English you can visit the website

BBC Future.

Chronic heart failure

According to international statistics, the planet is home to 25 million people with heart failure.

What is chronic heart failure?

The main engine in our body is the heart – a pump that constantly pumps blood. When the heart muscle weakens for some reason (scar formation after a heart attack, rhythm disturbance, ischemia, the consequences of inflammation, etc.), the amount of blood passing through per unit of time decreases, and heart failure occurs. In other words, it is a disease in which the heart is unable to pump and distribute blood throughout the body in the right amount.

The heart consists of 4 chambers: two atria, ventricles on the right and left sides. The powerful left ventricle pumps blood, then expels it into the aorta, spreading it throughout the body. If the pumping function weakens at some point, heart failure occurs. However, in the early stages, it is not felt, and it may take years before the first symptoms appear.

The presence of CHF is also directly related to the age of the patient, since over time the cardiovascular system weakens, cardiac dysfunction appears – the inability of the heart to pump blood in sufficient quantities.According to statistics, more than 65% of patients diagnosed with CHF are persons over 75 years old. In these patients, heart failure is usually accompanied by a number of other diseases that overlap the main symptoms. This complicates diagnosis and further treatment.

The development of CHF is also influenced by hormonal changes in the body. At this moment, the load on the heart increases significantly, so the organ becomes vulnerable. Since periods of hormonal changes occur more often in women, they are more susceptible to disease, especially during pregnancy or menopause.In the first case, the situation is not so difficult and is usually treatable.

In men, heart failure is less common and is ultimately due to poor lifestyle choices such as smoking and excessive alcohol consumption. Other diseases also affect the development of heart failure, most often ischemic disease or arterial hypertension.

Types and symptoms

There are two types of CHF: systolic and diastolic with preserved blood ejection function.Even 20 years ago, the second type was difficult to diagnose, since the heart muscle did not weaken, and the symptoms of CHF still occurred. Thanks to the advent of ultrasound of the heart and echocardiography, the diagnostic problem was solved.

A characteristic feature of the second type of CHF is an increase in pressure in the left ventricle. Because of it, the muscle thickens and becomes rigid – unable to relax. When circulation occurs, the heart must not only throw out the blood and contract, but also come to a state of rest for the next portion to enter.If this does not happen, blood stasis is formed. And it turns out that the heart seems to pump blood well, but cannot relax.

There are four stages of chronic heart failure:

  1. The appearance of mild ailments during physical exertion, but there are no structural changes in the heart yet.

  2. The emergence of structural changes in the heart.

  3. The manifestation of the first symptoms.

  4. Manifestation of pronounced symptoms that are difficult to treat.

The first stage of the disease can appear decades before symptoms, so it often goes unnoticed. Basically, it makes itself felt in the form of rapid fatigue and heart palpitations during vigorous activity. In a calm state, it does not appear.

At the second stage of the disease, structural changes in the heart appear – the first signs of hemodynamic disturbances and blood stasis, which lead to an increase in the heart chambers.Symptoms appear in the same way as in the first stage.

The first symptoms of the disease – shortness of breath and constant heart rhythm disturbances – appear only in the third stage. They are felt during physical activity and are long lasting.

In the elderly, dyspnea can also occur at rest due to stagnation of blood in the venous bed of the lesser circulation. In the future, shortness of breath begins to be accompanied by a cough that appears at night or during physical exertion.It appears due to stagnation of blood in the vessels of the lungs and generates further edema of the bronchial mucosa – at this moment the period of the last stages of CHF begins.

With severe circulatory failure, the patient has:

  • persistent shortness of breath;
  • wheezing in the lungs;
  • chronic fatigue;
  • severe swelling of the limbs;
  • enlarged heart;
  • accumulation of fluid in the abdominal cavity.

Such symptoms indicate a severe case and require, in some cases, surgical intervention.


The main cause of CHF is ischemic heart disease, heart attack, rhythm disturbances and other acute diseases of the cardiovascular system. Their development is ultimately influenced by risk factors:

  • smoking;
  • aging;
  • overweight;
  • heredity;
  • high cholesterol and sugar.

Hypertension can also cause heart failure. According to statistics in Russia, 26% of people have this disease. Hypertension leads to hypertrophy of the heart muscle, and subsequently to CHF. Therefore, patients with this disease are recommended to undergo regular examination by a doctor in order to prevent the development of heart failure.

Other root causes can be: smoking, overweight and diabetes. Research shows that smoking affects the development of cancer and cardiovascular disease.And diabetes is potentially dangerous to health, as it contributes to the development of many pathological changes in the cardiovascular system. In any case, the same measures are applied to a diabetic to protect against heart attacks and strokes as to a patient with already proven angina pectoris. First of all, this is a correction of nutrition and lifestyle and, of course, adequate treatment. The Chernaya Rechka spa cardiology clinic has a special diabetes treatment program.

Diagnostics and treatment

As mentioned earlier, CHF symptoms appear only at the third stage of the disease.But how, then, to define the first and the second?

In order to detect heart failure in the early stages, it is necessary to be regularly diagnosed by a doctor. For example, in the center of heart medicine “Chernaya Rechka”, the following methods of diagnosing heart failure are carried out:

Remember that the absence of symptoms does not exclude the presence of disease. A decrease in pumping function is more often present in people with risk factors, which means that if you have them, you should undergo a diagnosis. Neglect can lead to the development of structural changes in the heart and a decrease in the ejection fraction.

To prevent the development of diseases of the cardiovascular system, try to lead a healthy lifestyle and listen to your body. Be healthy and have fun!

Concept of pressure, resistance and heart rate

Take a rubber bulb in your palm and fill it with water. Now squeeze it as hard as you can, being careful not to leave a drop inside. Water will pour out of the outlet, and the larger it is, the less effort you need to make.And vice versa. The narrower the hole, the more difficult it is to squeeze everything out of the pear cavity without a trace. Now let’s do the same, but let’s try to put two rubber pears together. We fill them with the same volume of water, but for one we will make a large hole for the exit, and for the other – a small one. From the first, when squeezed, water will pour out easily, from slight squeezing, and to empty the second, much more force is required. It is the same with the heart. With one important exception: there is no one to squeeze him, and all the work is done by his own muscular system .

Compressing, or “contracting”, in systole phase , it pushes out of its ventricles all the blood coming from the atria, and in the phase of diastole – rests, gaining strength for the next contraction, which will follow in fractions of a second.

The force with which the heart muscle compresses this volume of blood in the cavity of the ventricles creates pressure, as a result of which the blood is thrown into the great vessels. But the speed with which it leaves the ventricles will depend not only on the force of compression, but also on how difficult or easy it is for it to leave the ventricle into the lumen of the vessel.That is, if we return to our two rubber pears: it will go through a larger hole, or through a smaller one. In other words, it is also important what resistance will be to this surge from the side of , so to speak, receiving it, i.e. vascular bed . Here you and I came to an understanding of several main laws governing both the movement of blood in the heart and its movement in the body, i.e. to the fact, thanks to what forces and on what currents our kayak was moving.

So, a few new concepts: blood volume , pressure and blood flow resistance .

The simplest and long-known most important parameter that can be measured and expressed in numbers is pressure. But what is pressure? Believe me, if you want to understand what is wrong with your child, you need to know it clearly. Only then will you be able to understand what the doctors will tell you about. It’s actually very simple.

Blood pressure is a figure that speaks of two most important aspects of the movement of blood: its volume and resistance to its flow in each separate period of time. It can be measured in any vessel, in any cardiac chamber.And it gives a fairly accurate idea of ​​what is happening there, inside the chamber, every phase of the cardiac cycle.

So far we are talking only about the work of a healthy heart. And it is clear that the greater the volume of blood in the ventricle, the more effort is needed to eject it, i.e. put more pressure on it. And – the greater the ejection resistance, the more effort (pressure) is needed to empty the ventricle, preparing it for a new portion of blood.

The vascular bed resists blood flow as a whole, from the beginning, i.e.That is, from the ascending aorta, to the smallest arteries and capillaries – in the large circle, and the pulmonary arteries, arterioles and capillaries – in the small circle. Consequently, the powerful left arterial ventricle works against the resistance of the gigantic volumetric vascular bed of the entire body. The right ventricle, venous, more thin-walled, works against the same giant in volume, but much more elastic, short and “soft” vascular bed of the lungs. Accordingly, the pressure figures in the cavities of the ventricles are different, and in the vessels extending from them.In table 1, these figures are reflected, and it can be seen that the pressure in normal conditions in the right ventricle and pulmonary artery is approximately one third of the pressure in the left ventricle and vessels of the great circle. Remember that the quantity, i.e. the volume of blood ejected at each contraction from each ventricle is normally the same. So far, we have only talked about the compression of blood volume under pressure. This is the so-called systolic pressure , or – the maximum pressure created in the system at the time of contraction.

But there is also a second number – this is the blood pressure in the vessels during diastole, or a relaxed and filling heart. In this phase, the valves of the aorta and pulmonary artery are closed and, with their integrity, the blood in the vessels is under the pressure of the closed system of the vascular bed of the body (in the large circle) and lungs (in the small circle). Therefore, there are two pressure figures – the so-called “upper” (systolic) and “lower” (diastolic) pressure.

Average figures of normal pressure in the cavities of the heart and large vessels (mm.Hg)


Children (1 month – adolescents)

Right atrium

0 – 3

2 – 5

Right ventricle

35 – 65

15 -30 / 2 – 5

Pulmonary artery

35 – 65/20 – 40

15 – 30/5 – 10

Left atrium

1 – 4

5 – 15

Left ventricle

70 – 90

80 – 130/5 – 10


80 – 100 / 50- 60

90 – 130/60 – 90

Note that in newborns, the pressure in the right ventricle and pulmonary artery is significantly higher than in children even in the first month of life.This is due to the fact that the vessels and all 700 million alveoli of the lungs open gradually and are fully ready to receive the entire volume of blood from the right ventricle only a few weeks after birth.

Now let’s try to answer the question – what moves the heart , what causes its rhythmic contractions . Believe me, this is also very important.

A rhythmic, sequential, regular cycle of contractions and relaxation of the heart is controlled by electrical impulses .These impulses arise in special cells of the heart muscle, the so-called cells of the conducting system. The foci of a large accumulation of these cells are called “nodes”, and their branches along the muscle fibers are called “pathways”. There are two nodes of the conducting system: sinus and atrioventricular , and there are several paths. The peculiarity of the cells themselves that conduct electrical impulses is that they are able to be excited and transmit this excitation much faster than neighboring cells of the working, contracting myocardium, or heart muscle.Therefore, they are guides, showing the way to others, understanding faster than others where to go. In a normal heart, the upper sinus node is first excited. The impulse is transmitted along the pathways of the atrial walls to the lower, atrioventricular node, and then, along the thinner paths, it enters the ventricles, causing them to contract in response – phase of systole . This is followed by a pause period – diastole – and the myocardium prepares to receive a new impulse. The frequency of these impulses is the heart rate and pulse rate.In newborns – 110-120 beats per minute, in adults it is much less common – 65-75 beats per minute. These electrical impulses are easily recorded by fairly simple instruments. The recording devices are called electrocardiogram .

We are far from the idea of ​​teaching you to read it: this is the business of professionals. We just want to explain what it is and why it is being done. An electrocardiogram makes it possible not only to identify abnormalities in the normal conduction of the impulse, but also to determine which parts of the heart are abnormally enlarged, which constantly work with increased load, how they cope with it.If you suspect a heart defect, your child will have this test done many times. It is painless and very informative.

We can only be amazed at the incredible perfection of the cardiovascular system, which, for all its complexity, is surprisingly simple, logical and harmonious. However, it must be absolutely accurately and correctly created. Even not too large changes in its structure are enough to cause a violation of this constant, calm and synchronous work.

Quoted from book G. E. Falkovsky, S. M. Krupyanko. The heart of a child. A book for parents about congenital heart defects

The cardiovascular system and what it includes

The cardiovascular system is one of the most important systems of the body that ensures its vital activity. The cardiovascular system provides blood circulation in the human body. Blood with oxygen, hormones and nutrients is carried through the vessels throughout the body.Along the way, she shares these compounds with all organs and tissues. Then it takes away everything that is left from the metabolism for further disposal.


Blood circulates in the body thanks to the heart. It contracts rhythmically like a pump, pumping blood through the blood vessels and providing all organs and tissues with oxygen and nutrients. The heart is a living motor, a tireless worker, in one minute the heart pumps about 5 liters of blood through the body, in an hour – 300 liters, and in a day it accumulates 7,000 liters.

Circles of blood circulation

The blood flowing through the cardiovascular system can be compared to an athlete who runs at different distances. When it passes through the small (pulmonary) circulation, it is a sprint. And the big circle is already a marathon. The Englishman William Harvey described these circles as early as 1628. During a great circle, blood spreads throughout the body, remembering to provide it with oxygen and take carbon dioxide. During this run, arterial blood becomes venous.

The small circle of blood circulation is responsible for the flow of blood into the lungs, where the blood gives off carbon dioxide and is enriched with oxygen. Blood from the pulmonary circulation returns to the left atrium. The systemic circulation, beginning in the left ventricle, provides blood transport throughout the body. Oxygenated blood is pumped by the left ventricle into the aorta and its many branches – various arteries. Then it enters the capillary vessels of organs and tissues, where oxygen from the blood is exchanged for carbon dioxide.The systemic circulation ends in small veins that merge into two large veins (vena cava) and return blood to the right atrium. Through the superior vena cava there is an outflow of blood from the head, neck and upper extremities, and along the inferior vena cava – from the trunk and lower extremities.

Blood vessels

Blood vessels are elastic tubular formations in the human body, along which the force of a rhythmically contracting heart or a pulsating vessel moves blood through the body.Through the arteries, blood runs from the heart to the organs, through the veins it returns to the heart, and the smallest vessels – capillaries – bring blood to the tissues.


No cell can do without nutrients and oxygen. They are delivered by arteries. They carry oxygen-rich blood throughout the body. When breathing, oxygen enters the lungs. where further oxygen delivery begins throughout the body. First to the heart, then along a large circle of blood circulation to all parts of the body.There, the blood changes oxygen to carbon dioxide and then returns to the heart. The heart pumps it back into the lungs, which take carbon dioxide and give oxygen, and so on endlessly. And then there are the pulmonary arteries of the pulmonary circulation, they are in the lungs and through them blood, poor in oxygen and rich in carbon dioxide, enters the lungs, where gas exchange takes place. This blood then returns to the heart through the pulmonary veins.


Blood with carbon dioxide and metabolic products from the capillaries first enters the veins, and through them moves to the heart.The valves, which are found in almost all veins, make the blood flow one-way.

Even in the small circle of blood circulation there are the so-called pulmonary veins. Through them, oxygen-rich blood flows from the lungs to the heart.


  1. Kozlov V.I. Anatomy of the cardiovascular system. Practical medicine, 2011 – 192 p.

SARU.ENO. 19.06.1021

Interesting about physiology – Kazan State Medical University

Did you know?

That the organ that sets the blood in motion is the heart.The organ is about the size of a fist and weighs about 300 grams does a tremendous job. per day, the heart contracts even at rest over 100 thousand times, and with each contraction it throws blood into the aorta with such a force that could raise the blood column by almost 1.5 m. Pumping 150 cc with each systole. cm into the vessels (75 cc from the left ventricle to the aorta and from the right to the pulmonary artery), the heart pumps over 15 thousand liters of blood per day, and the frequency of its contractions can reach more than 240 beats per minute for an athlete at the finish line.

If at rest the heart throws out about 4 liters of blood into the aorta per minute, then in an athlete this minute volume of blood circulation reaches 25 liters in some competitions, and some outstanding sportsmen had record figures exceeding 40 liters per minute.

With continuous and enormous work, when does the heart restore its strength? If we compare the work of the heart with the brain, which works for two-thirds of the day and rests one-third, the heart rests in the process of its work.Each systole is replaced by relaxation, diastole, i.e. It works for 0.3 seconds, and then rests for 0.5-0.6 seconds. This means that it actually rests almost 2/3 of the time of one cardiac cycle.

An important property of the heart muscle is the automatism of the heart. This allows for a long time to study how various substances, for example, new drugs being tested, act on the heart of an animal extracted from the body. Based on this property of the heart, the Russian scientist A.A. Kulyabko performed in August 1902 his famous experience of revitalizing the human heart. A three-month-old baby died of pneumonia. 20 hours after his death, Kulyabko removed the heart from the corpse, revived it and made it contract for several hours.

Although the heart is automatic, it is subordinated to the leading role of the nervous system in the whole organism. The vagus nerve slows down the contraction of the heart, while the sympathetic nerve, on the contrary, accelerates them.


From the heart, blood enters the main vessels, large vessels – to the aorta and pulmonary artery.Arteries extend from the aorta to all organs of the body. Entering the organ, the arteries branch into ever smaller vessels: arterioles and capillaries, penetrating the entire organ with their networks, the capillaries collect into small veins, which, merging with each other, form larger and larger venous trunks. Thus, there is always a capillary network between the artery and the vein. Capillaries are the thinnest hair vessels (from the Latin capillaris-hairline). Although the capillaries are called hair vessels, they are incomparably thinner than a hair. So, the hair has a thickness of 1/10 to 1/20 mm, while the thickness of the capillaries is 1/100 – 1/200 mm, or 5-10 microns.In the body of these thinnest vessels, there are several billion. Their total length is 100 thousand kilometers, i.e. 2.5 times the length of the Earth’s equator. In a muscle at rest, only 1/10 – 1/50 of its capillaries (duty capillaries) are open. When working, with an increase in the blood supply to the muscle, the capillary network is completely opened. The capillary wall consists of only one layer of flat cells, which makes it easily permeable to substances and gases dissolved in the blood. Erythrocytes go through the capillaries one at a time, “single file” – two erythrocytes cannot fit next to each other.


Despite the fact that they are sometimes called red blood balls, in fact they resemble flat circles with a depressed middle, i.e. biconcave lenses, their dimensions are negligible: the diameter is 7 microns. This means that a chain of 140 red blood cells would fit 1 mm. 1 cubic millimeter of blood contains 4-4.5 million erythrocytes. The volume of a pin head will accommodate 15 million. If all the erythrocytes of one person are put in a row, their chain will surround the earth three times along the equator or take about a third of the Earth-Moon route.Red blood cells are extremely important for the body – they carry out the respiratory function of the blood, being an oxygen carrier. They contain a special compound of iron with a protein called hemoglobin, which gives blood its red color. Thanks to hemoglobin, the blood has an exceptional “capacity” for oxygen. 100 cubic meters cm would dissolve only 0.3 cubic meters. cm of oxygen, meanwhile hemoglobin binds up to 20 cc of this gas. Thanks to hemoglobin, the blood contains practically the same amount of oxygen as there is in the atmospheric air (20-21%).Where there is a lot of oxygen around, hemoglobin combines with it. Where there is little oxygen, hemoglobin gives it away. The total surface of erythrocytes of one person is 3400 square meters, which facilitates the saturation of oxygen in the blood and its return to the tissues.

Erythrocytes differ from all other cells in that they do not have nuclei in a mature state, therefore they are short-lived, they live no more than 4 months. This means that every day 1/3120 of all our erythrocytes die, i.e. more than 175 billion, and therefore the same amount should be formed. Erythrocytes are produced in the bone marrow, which, like other organs, is conducted by the nervous system.


Sometimes they are called white blood balls , although they are colorless, transparent lumps of irregular shape. This is one of the most important defenses of the body. The characteristic ability of leukocytes is their mobility. The number of leukocytes in the blood is much less than the number of red blood cells.1 cubic mm contains 5-7 thousand, i.e. one leukocyte for 700-800 erythrocytes. The discovery of the role of leukocytes belongs to the great Russian scientist II Mechnikov, who in 1882 established that leukocytes “devour” microbes that entered the body, as well as various dying pieces of body tissue. Mechnikov therefore called them phagocytes (from the Greek phagos – devourer). Approaching the microorganism, the leukocyte, as it were, envelops it, envelops it with its protoplasm and digests it with the enzymes of its body. If a large amount of foreign agents that have entered the body or the substances released by them upon death are toxic, then the leukocytes die in masses in the fight against this infection.Millions of their dead bodies form a well-known suppurative process: an abscess, an abscess.

Distinguish granular (granulocytes): neutrophils, basophils and eosinophils and non-granular (agranulocytes): lymphocytes, monocytes. There are two types of granulocyte reserve – vascular and bone marrow. The vascular granulocytic reserve is a large number of granulocytes located along the walls of the vascular bed, from where they are mobilized when the tone of the sympathetic part of the autonomic nervous system increases.The number of bone marrow reserve cells is 30-50 times higher than their number in the bloodstream.

Blood groups

Since ancient times, blood was considered the most important carrier of health, moreover, not only physical, but also mental. Doctors were constantly trying to find ways to transfuse blood. It was only in 1667 that several successful blood transfusions were made for the first time in Paris. In this case, a person was transfused with the blood of an animal – a lamb or a ram.Scientists (Denis and Emmerets) substantiated this by the fact that animals do not spoil their health either by excess in food and drink, or by strong passions.

However, after several successful transfusions, a number of deaths followed. Blood transfusion was prohibited and only after more than two centuries did it finally spread. A.A.Malinovsky was one of the pioneers of blood transfusion in Soviet medicine. What was the reason for the danger of this operation, which so often claimed the life of the patient and caused the death of the first director of the Institute of Blood Transfusion? The mystery has been solved by science.It turned out that the sudden death that occurs after blood transfusion is due to the destruction of the injected red blood cells. They stick together in columns and die, and the substances released during this massive decay of blood cells poison the body.

The result is a phenomenon that resembles in its mechanism an attack of malaria. There, a malaria parasite (plasmodium), having got into the blood of a person with a bite from a camara, penetrates into erythrocytes and feeds on their contents. Every 48-72 hours (depending on the type of plasmodium) the mass of parasites leaves the blood cells destroyed by them and is introduced into the next “portion” of them.At the same time, many decay products enter the blood from the destroyed erythrocytes, which causes an attack of malaria.

Bonding of erythrocytes during blood transfusion occurs because, due to the properties of the blood of both people, the erythrocytes of one of them are incompatible with the plasma of the other. Scientists have identified four main blood types. Of course, in addition to the four main groups, there are a number of other differences to consider.

In the European part, Group I has 35% of the population, Group II – about 40%, Group III – about 20%, Group IV – a little more than 5%.

Domestic scientists have developed methods of transfusion of not only whole blood, but also separately either the mass of erythrocytes or plasma. Moreover, methods have been developed to transport frozen plasma and even dry plasma or serum (plasma remaining after blood clotting). Such plasma can be stored for a very long time.

Bioelectric phenomena

With the development of physics, the doctrine of electricity and magnetism was born.In Europe, they became acquainted with electricity thanks to the observations of Thales of Miletus as early as 600 BC. He discovered that a piece of amber, if rubbed, acquires the ability to attract and then repel various small objects. For more than two millennia, this fact has not attracted much attention.

It is not known when they would have taken electricity seriously if Signora Galvani, the wife of the Bologna professor of anatomy, did not have to go to the butcher’s shop for a piece of beef for lunch herself.However, not only beef: the Italian people have always been distinguished by their open-mindedness and did not disdain such delicacies as frog legs.

It is said that it was the frog legs, hung in clusters on copper hooks attached to iron bars, that struck the imagination of Signora Galvani. To her great surprise and horror, the severed frog’s leg, touching the iron, trembled as if it were alive. They say that the signora is so tired of her husband, talking about the phenomenon that frightened her, explaining it by the proximity of a butcher with evil spirits, that the professor decided to go to the shop himself and find out what was happening there.

Naturally, Galvani explained the twitching of frogs’ legs in the butcher’s shop by the influence of discharges of atmospheric electricity. To calm his wife, the scientist decided to observe frogs at home. The experiment, staged on one of the stormy nights, was brilliantly successful: the legs of a dead frog, suspended on a copper hook from the balcony railing, twitched from time to time as if alive.

Galvani outlined in his famous book “A Treatise on the Forces of Electricity in Muscular Movement”, published in 1791., where he argued that electricity is generated in the spinal cord, which is transmitted by copper conductors and causes muscle contraction. Carrying out a number of other observations, the scientist came to the conclusion that ordinary, natural muscle contractions also occur under the influence of animal electricity, which is born in our body, but so weak that it is inaccessible to existing scientific instruments. It was a brilliant guess.

Galvani’s research interested Alexander Volta, his contemporary, no less famous than Galvani.At first, he was a supporter of the views of Galvani, but soon took the position of denying any “animal electricity”. The objections put forward by Volt were based on the fact he proved that when two different metals are combined, in Galvani’s experiment – copper and iron, a potential difference arises, which causes muscle contraction.

As this dispute developed, each of the parties resorted to new experiments to prove the correctness of their views. Galvani’s experiment, which he carried out without the participation of metals, was decisive.This experiment, called the second Galvani experiment, or contractions without metals, consisted in the following: in a frog, the dissected sciatic nerve pounces on the damaged area of ​​the muscle. The potential difference between the damaged and undamaged areas causes the muscle to contract.

If in the first case Volta’s assertion that Galvani observed electricity between two different metals raised doubts about the presence of “animal electricity”, then the second experiment was a decisive fact for confirming Galvani’s views.

Its correctness was additionally demonstrated in a very elegant experiment by the Italian physicist and physiologist Mateucci. Experiments called secondary tetanus, or secondary contraction, can be called classic in the full sense of the word

The nerve of another neuromuscular preparation was superimposed on the muscle of one neuromuscular preparation. Upon stimulation of the induction current of the nerve of the first neuromuscular preparation, the muscle of the second preparation also contracted, the nerve of which was thrown over the muscle of the first preparation.

In another experiment, the chest was opened in a frog attached to a cork plate. At the same time, it was seen how the frog’s heart was contracting, another frog was placed next to it, whose skin on the thigh was opened, the sciatic nerve was found, cut it and the end of the cut nerve was thrown, in the form of a loop, onto the contracting heart of the first frog. With each contraction of the heart, the foot of the neighboring frog also contracted. A simple movement of the nerve, even more energetic than from the movement of the heart, did not evoke any reaction.It became obvious that the nerve responds precisely to the electric currents that arise in the heart with each contraction.

In the course of this long-term dispute, which took an honorable place in the history of science, a current was discovered, which was called galvanic – by the name of Galvani, and the unit of voltage was called “volt”.

Nervous system

It is well known that the nervous system consists of the brain, located in the cranial cavity, and the spinal cord, which lies in a special canal of the spine, as well as a mass of nerves that leave the brain and spinal cord and are like multicore wires that connect the brain with all organs and tissues of our body.The main, higher part of the nervous system is the so-called cerebral cortex, or simply the cerebral cortex.

The central nervous system provides interconnection between cells, tissues and individuals

organs of our body and connects them into a single whole, and also carries out the connection of the body with the environment. The nervous system is made up of individual nerve cells. a nerve cell (neuron) has a body and processes: a long one – an axon that goes to the periphery, and short and branched – dendrites.

As we already know, the nervous tissue is built of cells similar to spiders, their size, like other cells of the body, is negligible. Only in the cerebral hemispheres there are about 100 billion of them. Interacting with each other, they form special contacts – synapses, the number of which is 100 trillion. Some scholars believe these numbers are underestimated. When several hundred thousand fibers, processes of different cells come together, they form the nerve trunks visible to the eye, connecting the brain with all parts of the body.No matter how small the nerve cells are, their thinnest processes running as part of the nerves have a considerable length – up to 1 meter and even more. So one fiber stretches from the cells of the spinal cord to the toe or from the cortex to the lumbar spine, etc.

Muscle contraction

Each skeletal muscle, consisting of fibers, attaches itself to one bone at one end and to the other at the other, throwing itself over the joint. Only in this way can she make movement.In this case, musculoskeletal levers are obtained, on which there is almost always a loss in strength. For example, flexion of the forearm at the elbow joint. The forearm in this case can be considered a lever of the second kind with a pivot point at the elbow joint. The biceps (biceps brachii) is attached to the ulna 3 cm from the axis of rotation of the joint, and the weight compressed by the hand is located 30 cm from it. The ratio of the lever’s shoulders is 10: 1, which means that in order to hold a load of up to 16 kg in a bent arm, the muscles must develop an effort of up to 160 kg.A similar relationship develops on the foot. The front part of the foot, on which we lean when walking, is six times longer than the back of the foot, where the gastrocnemius muscle is attached. The axis of the lever in this case is the ankle joint. If a person weighing 70 kg rises, then on the toe of one leg during normal walking, his calf muscle should develop an effort 6 times more, i.e. 420 kg. It is no coincidence that our Achilles tendon is so powerful. It is like a living cable that attaches the muscles to the heel bone and withstands a load of half a ton or more.However, losing in strength, we, according to the same law of leverage, gain the same amount in the speed of movement. The calf muscle will contract by 1 cm, and during this time the heel will fly 6 cm above the ground. For animals, gain in movement speed is more important than gain in strength.

Why do the eyes of a cat in a dark room “glow” with green light?

The retina functions under the influence of at least a weak light falling on it. Reflection from the deep layer of the retina of part of the incident light leads to the fact that this reflected light intensifies the irritation of the visual receptors, leading to an increase in visual acuity in low light conditions.The pupil of the eye can only glow with reflected light and, therefore, the “glow” of the eye is impossible in complete darkness, it can appear only under the condition of at least a weak illumination of the retina from the outside. But why, then, the cat’s eyes “glow” with a green light? This is due to the fact that the pigment layer of the retina of her eye reflects mainly green rays. This property is not required for all animals whose eyes “glow” in the dark. The presence of the retinal pigment layer, which reflects part of the light that has reached it into the eye, depends on the wavelength of the light rays, so the color of the glow will be different.For example, a raccoon’s eyes glow bright yellow in the dark, a bear’s eyes are orange, and a rabbit’s are ruby ​​red. The ability of the eyes to glow is especially well expressed in nocturnal predators. Sometimes the glow of the eyes in the dark can be noticed in humans.

A small part of the spectrum of electromagnetic waves is an irritant to the retinal receptors. For a person, only electromagnetic waves are visible, the length of which is in the range from 0.35 to 0.85 microns (microns is a thousandth of a millimeter).Light waves of different lengths are subjectively perceived by us as different colors of the spectrum from red to violet. Within these limits, the richest palette of colors is located, which, however, has its limits. Our color vision is due to the presence of three types of cones in the retina, each of which is tuned to one of the three primary colors – red, blue or green. Color vision disorder is called color blindness. Dalton amazed his friends by the fact that he had never found red rowan berries in the forest.They looked green to him. Having become interested in such a phenomenon, the researchers figured out and named this violation of color perception by the name of the scientist. About 8% of men suffer from various forms of it. There are significantly fewer women who are color blind. Medicine knows people who do not see green, they are called eranopes. In addition, there are people who do not distinguish colors at all. They define colors logically, based on the tonality of light and dark. This violation of color perception is known as macular degeneration with the phenomenon of hypermetric astigmatism.

Corneal refractive power

In humans and other “land” mammals, the cornea outside above the pupil, the surface of which is convex like a watch glass, has a very significant value in the refraction of light directed into the eye. Since the refractive indices of light in the cornea are almost the same as in water, immersion of the eyes in water causes visual impairment. You have probably noted more than once that when diving into the water while swimming, it is difficult to properly see the bottom of the reservoir and the fish swimming by, even in water with good transparency.It is much better to survey the bottom of the reservoir, being not in the water, but above it – on the shore, in a boat, etc. An air layer in front of the cornea significantly increases visibility in water, while maintaining the refractive power of the cornea. This is usually used when diving, wearing special masks on the face that protect the cornea from direct contact with water. The question arises, but what about animals living in water, and above all fish, whose cornea is constantly in contact with water? The cornea of ​​such animals cannot participate in the refraction of light directed into the eye.Therefore, it is usually flat, and all the responsibilities associated with the refraction of light rays are taken over by the spherical lens and the vitreous body of the eye. It is difficult for animals living both in water and on land. Then the eyes often provide the animal with sufficient vision only in one of these environments, and in the other environment the animal is guided with the help of other organs


The pupil of the eye is the opening in the center of the iris, located between the lens and the cornea.In humans and many animals, the pupil is round. The diameter of the pupil of the human eye in the dark reaches eight millimeters, and in bright light, it can decrease four times. But the round shape of the pupil in the animal kingdom is not at all necessary. In representatives of the feline family, in lizards and crocodiles, the pupil has the form of a vertical slit formed by peculiar curtains. There are animals with horseshoe-shaped pupils, hourglasses, tears, stars, and even, as the American naturalist K.Warner, in the form of a keyhole.

The relative and absolute sizes of the eyes of deep-sea animals are especially large. In some fish living at great depths, the eyes have a telescopically elongated shape and a very large pupil, which allows the maximum amount of light to penetrate into the eye. The eyes of the cuttlefish are only ten times smaller than themselves; in the giant octopus, the eyes reach forty centimeters in diameter.

The mysterious property of the auricle

Thanks to the funnel shape, the auricles are able to capture and concentrate sound waves.Old people with reduced hearing, listening to something, put their folded mouthpiece to their ear, as if increasing it. In the course of phylogenetic development, an increasingly highly organized sound-receiving apparatus hides in the thickness of the temporal bone, the auditory canal lengthens, and the auricle appears as a buffer against unforeseen damage, thus, the auricle has a protective function.

There is also a cosmetic function for the outer ear. At all times and all peoples have tried to decorate the auricle, realizing that it plays an important role in creating an external appearance.Some African tribes have a strange concept of beauty for us: they pull the earlobes to incredible sizes. In the oriental despotism of antiquity, there was a custom to cut off the ears of state criminals. Indeed, a person devoid of auricles takes on an ugly appearance.

But there is another mysterious property of the auricle, which quite recently even gave rise to a special area of ​​medical science called “ear acupuncture”.

In 1957, the French physician P.Nozhier, based on the data of ancient Chinese medicine, shared his experience of acupuncture. According to Nogier, the outer ear should be considered as an inverted embryo in the womb, and in the auricle the human body and all organs are projected in the same way as in the cerebral cortex. He described the topography of points and zones that are the projection of certain parts of the body and internal organs. If about seven hundred biologically active points are found on the human body, then there are over a hundred of them on the ear alone. The technique of acupuncture in the auricle differs only in the shallower depth of needle insertion – from two to five millimeters.Ear acupuncture is used not only for treatment, but also for the diagnosis of diseases. It is believed that in case of a disease of internal organs, pain points appear in the auricle, which are determined by the handle of a needle or with the help of an electrode.

It would seem that there is not a big problem: to pierce your earlobe and insert an earring. However, this procedure requires special care. On the earlobe there are 11 points associated with the eyes, teeth, tongue, facial muscles, inner ear. And if the shackle of the earring is not made of a noble metal or is soldered to another metal, irritation can be prolonged, as a result, vision deteriorates, and teeth hurt.

Often, doctors have to deal with defects in the auricles. One of them is macrotia – an enlarged auricle. Much more common is a less pronounced pathology known as lop-earedness: the shape and size of the auricle remain within the normal range, but it is located not parallel to the temporal bone, but at an acute angle approaching a right angle. There are also congenital deformities of the auricle, manifested in the form of microtia – one or another degree of underdevelopment of the auricles, and sometimes their complete absence.

The ability to determine the direction of sound is called ototopica. This ability in humans makes it possible to determine the direction of sound with an accuracy of one degree. Animals determine where the noise comes from by coordinating the movement of the auricles in the direction of the sound source. The hare has ears “on the crown”. “On the crown” ears of a dog, cat, horse. The function of human ototopics is ensured by the maximum distance of the auricles from each other. In the course of evolution, the auricles moved further and further away from each other until they were on opposite sides of the skull.Compare with technology: the farther the detecting locators are located from each other, the more accurately they are able to detect a passing object.

In the world of odors

The ability to see and hear developed in animals a long time ago, but a little earlier, primitive animals began to smell. For many of the most diverse animal creatures, it began to play a leading role in meeting such vital needs as protection, nutrition, the search for a sexual partner necessary for reproduction.

Since the irritants of the olfactory analyzer are molecules of an odorous substance in the inhaled air, the latter should have at least a slight ability to evaporate at ordinary temperatures. Since the receptor field is covered with a thin film of moisture, an odorous substance can penetrate through it only if it has at least an insignificant solubility in water. The olfactory receptors are covered with a lipoid (fatty) membrane, so the odorous substance should be somewhat soluble in fats.

Part of the odorous substances, acting on the nasal mucosa, causes not only the sensation of smell, but also a reflex change in breathing. When some substances are inhaled, a reflex cessation of breathing occurs. Such substances include ether, chloroform, ammonia, etc.

The sense of smell is an extremely keen and subtle sense. A person senses the smell of a substance with its very insignificant content in the air. For example, if 1 liter of air contains 1: 1,000,000 g, a person can smell it.The organ of smell is even more sensitive to the smell of hydrogen sulfide, the presence of which in 1 liter of air in an amount of 1: 1,000,000,000 g already causes the sensation of smell. The smell of musk is felt at a concentration of 1: 10,000,000 g in 1 liter.

For a person who has managed to actively change the conditions of his existence, the sense of smell is not of paramount importance. A person deprived of his sense of smell not only retains vitality, but, as a rule, also retains working capacity. However, its usefulness is beyond doubt.The sense of smell helps us to avoid poisoning with poor quality food, to identify impurities of various, including poisonous substances in the ambient air. The smell of smoke, burning sometimes helps to prevent a starting fire, the importance of smells in cooking, in perfumery, etc. is very important.


The receptors that perceive taste in mammals, like in humans, are located mainly in the mucous membrane of the tongue. In fish (carp, dwarf catfish), taste buds are located not only in the mouth, but also over the entire surface of the body.In insects such as meat flies, bees, butterflies, most of the taste-sensitive organs are located on the front legs in special formations on their lower segments. The forelegs of the blowfly are five times more sensitive to sugar than the gustatory organs found on the head. With their feet, butterflies feel the concentration of sugar in the water 200 times less than that from which the sweet taste becomes palpable to humans.


The skin and mucous membranes are a continuous receptor field.It contains nerve endings of various structures and functions, which provide the perception of external stimuli – tactile, or tactile (touch, touch), temperature (feeling of cold and warmth), pain (feeling of pain), which act directly on the receptors.

The sensitivity of different parts of the human body surface is not identical. On the entire surface of the skin there are approximately 500,000 receptors that sense touch and pressure; on average 1 sq.see there are about 25 receptors. However, these receptors are unevenly distributed over the entire surface of the body. For comparison, the following example can be given: there are 9-10 receptors per 1 sq. Cm of shin skin, and per 1 sq. Cm. cm of scalp – 165-300 receptors. The skin of the palms of the hands, especially the terminal phalanges, is very rich in receptors. This explains why when examining an object, when we need to find out the shape, the presence of roughness, etc., we stroke the object, i.e. we touch its surface with the skin of our palm.

The tactile sensation arises not only when touching the skin surface directly, but also when touching the hairs covering the skin. The hair bends and provides, according to the principle of a lever, stimulation of the nerve receptor located at its root. Tactile sensitivity is characteristic of animals and insects. So, feeling with its antennae – antennae every cell of the honeycomb intended for the future bee generation, the queen bee determines the size of the cell and, depending on this, lays a fertilized egg in it.A working bee develops from a fertilized egg, and drones develop from an unfertilized one.

Temperature sensitivity

Thermoreception (temperature sensitivity) of the skin includes two qualitative types – a feeling of coldness and a feeling of warmth.

Each organism can exist only under certain temperature conditions, while the optimal temperature and the tolerable limits of its fluctuations for different species of animals are very variable.In humans and warm-blooded animals, due to the presence of thermoregulatory mechanisms, the body temperature is always close to a certain indicator and its fluctuations have a very limited amplitude.

Observations show that ants take eggs and larvae from the nest during the day and place flat stones under the sun-warmed ones. At night, when the ground cools, the eggs and larvae are dragged back into the anthill. Bees, very sensitive to temperature shifts, are able to maintain an artificial microclimate in hives.On hot days, all worker bees leave the hive, and some of them are located near the entrance and, continuously working with their wings, drive fresh air into the hive, others bring water and regurgitate it to the surface of the combs. In cold weather, bees congregate in the hive, gather in a ball and generate heat, producing continuous vigorous movements. All this allows the bees to regulate the temperature in the hive and maintain it within the optimal range for the developing offspring.

Of large terrestrial animals with a pronounced ability to search for prey with the help of a “heat trapping” system, it is known in pit-headed snakes, in particular, in rattlesnakes living in America and in Asiatic snakes.They have conical grooves on either side of their heads in front of the eyes, containing special heat-sensitive receptors that can capture infrared rays radiating from a heat source in a radial direction. Thus, heat rays can enter each heat-sensitive fossa of a snake only if the heat source is located in a strictly defined fragment of space, which can be compared with the field of view. In this case, both such “fields of view” of both pits partially overlap if the source of thermal radiation is at a strictly defined distance – right in front of the snake’s head.This distance is such that a snake curled up in a ring can simultaneously hit a heat radiating source. The snake is alert if the heat source is 0.0018 degrees different from the environment. Such a high sensitivity to thermal radiation allows the snake, even in absolute darkness, to detect a motionless sitting frog or, moreover, a warm-blooded animal – a mouse, a bird. A person approaching it in the dark can also become a victim of a snake.

Venous return brings oxygen-depleted blood to the heart

Venous valve function

Venous valve function: oxygen-depleted blood returns to the heart through the venous system.The work of the heart plays an important role: it not only pumps blood under high pressure into the arteries, but also sucks blood from the veins into the right atrium. This is called venous return.

Non-return valves

However, the suction capacity of the heart is not strong enough to provide venous return from parts of the body distant from the heart.