What are endocrine glands and how do they work. Which glands make up the endocrine system. How do endocrine glands differ from exocrine glands. What hormones do major endocrine glands produce. How do endocrine glands regulate bodily functions.

The Fundamentals of Endocrine Glands

Endocrine glands are specialized organs that play a crucial role in maintaining the body’s homeostasis. These glands secrete hormones directly into the bloodstream, allowing for widespread effects throughout the body. Unlike exocrine glands, which release substances through ducts, endocrine glands rely on the circulatory system to transport their chemical messengers.

The endocrine system consists of several glands distributed throughout the body, including the hypothalamus, pineal gland, pituitary gland, thyroid, parathyroids, adrenals, pancreas, and reproductive organs. Each of these glands produces specific hormones that regulate various bodily functions, from metabolism and growth to sleep patterns and stress responses.

Key Characteristics of Endocrine Glands

• Direct secretion into the bloodstream
• Production of hormones
• Widespread effects on target tissues
• Regulation by the nervous system
• Ability to store hormones for future use

The Intricate Dance of Hormone Release

Hormone release from endocrine glands is a carefully orchestrated process. The nervous system plays a significant role in modulating hormone secretion, responding to various neural and hormonal stimuli. This delicate balance ensures that the body maintains appropriate hormone levels to meet its current needs.

How does the body regulate hormone release? The process involves complex feedback loops. For example, when hormone levels in the blood rise, they can signal the gland to reduce production. Conversely, low hormone levels can trigger increased secretion. This self-regulating system helps maintain hormonal balance and prevents excessive fluctuations that could disrupt bodily functions.

Factors Influencing Hormone Release

1. Neural stimuli
2. Hormonal feedback
3. Circadian rhythms
4. Stress levels
5. Nutritional status

The Pineal Gland: Regulator of Circadian Rhythms

The pineal gland, a small endocrine gland located in the brain, serves as an excellent example of how endocrine glands function. This tiny organ plays a crucial role in regulating our sleep-wake cycle, also known as the circadian rhythm.

How does the pineal gland influence our sleep patterns? The gland is connected to neurons in the eyes, which detect changes in light levels. When darkness falls, the pineal gland becomes activated and begins to secrete melatonin, a hormone that promotes sleepiness. This process helps synchronize our internal clock with the external environment, preparing our bodies for rest and recovery.

Functions of the Pineal Gland

• Melatonin production
• Regulation of sleep-wake cycles
• Influence on reproductive hormones
• Potential antioxidant effects

The Thyroid Gland: Master of Metabolism

Located in the neck, just below the larynx, the thyroid gland plays a pivotal role in regulating metabolism. This butterfly-shaped organ produces hormones that influence nearly every cell in the body, controlling how quickly cells convert nutrients into energy.

What hormones does the thyroid gland produce? The primary hormones secreted by the thyroid are thyroxine (T4) and triiodothyronine (T3). These hormones regulate metabolic rate, heart function, digestion, muscle control, brain development, and bone maintenance. The thyroid’s activity is controlled by the pituitary gland, which releases thyroid-stimulating hormone (TSH) to regulate thyroid hormone production.

Impact of Thyroid Dysfunction

Thyroid disorders can have significant effects on overall health. Hyperthyroidism, characterized by excessive hormone production, can lead to weight loss, rapid heartbeat, and anxiety. Conversely, hypothyroidism, or underactive thyroid, may cause weight gain, fatigue, and depression. These conditions highlight the importance of maintaining proper thyroid function for optimal health.

The Adrenal Glands: Stress Response Specialists

Perched atop each kidney, the adrenal glands play a crucial role in the body’s stress response. These small but powerful glands produce a variety of hormones that help regulate metabolism, blood pressure, and the body’s reaction to stress.

What are the main hormones produced by the adrenal glands? The adrenal cortex secretes cortisol, aldosterone, and small amounts of sex hormones. The adrenal medulla produces epinephrine (adrenaline) and norepinephrine. Together, these hormones help the body respond to stress, regulate blood sugar levels, maintain electrolyte balance, and influence sexual characteristics.

The Stress Response Cascade

1. Stressor detected by the brain
2. Hypothalamus signals the pituitary gland
3. Pituitary gland releases ACTH
4. ACTH stimulates the adrenal glands
5. Adrenal glands release stress hormones

The Pancreas: Dual-Function Powerhouse

The pancreas is a unique organ that functions as both an endocrine and exocrine gland. While its exocrine functions involve producing digestive enzymes, its endocrine role is crucial for regulating blood sugar levels and energy metabolism.

Which hormones does the pancreas produce? The endocrine portion of the pancreas, known as the islets of Langerhans, produces several important hormones. The two most well-known are insulin and glucagon, which work in tandem to maintain blood glucose homeostasis. Insulin promotes glucose uptake by cells and storage, while glucagon stimulates the release of stored glucose into the bloodstream.

Pancreatic Hormones and Their Functions

• Insulin: Lowers blood glucose levels
• Glucagon: Raises blood glucose levels
• Somatostatin: Regulates other pancreatic hormones
• Pancreatic polypeptide: Influences appetite and digestive functions

Reproductive Glands: Hormones Beyond Reproduction

While primarily responsible for producing gametes, the reproductive glands – ovaries in females and testes in males – also function as important endocrine organs. These glands produce sex hormones that not only regulate reproductive functions but also influence various other aspects of physiology and behavior.

What are the primary sex hormones and their effects? In females, the ovaries produce estrogen and progesterone, which regulate the menstrual cycle, support pregnancy, and influence bone density and cardiovascular health. In males, the testes produce testosterone, which drives the development of male sexual characteristics, supports muscle mass, and influences mood and cognitive function.

Sex Hormones and Their Wide-Ranging Effects

• Sexual development and function
• Bone density maintenance
• Muscle mass and strength
• Mood and cognitive function
• Cardiovascular health

The Intricate Network of Endocrine Communication

The endocrine system functions as a complex network of glands and hormones that work together to maintain homeostasis. This intricate communication system relies on feedback loops, where hormone levels in the blood can trigger or inhibit the release of other hormones from different glands.

How do endocrine glands coordinate their activities? The hypothalamus and pituitary gland act as master regulators, influencing the function of many other endocrine glands. For example, the hypothalamus releases hormones that stimulate or inhibit the pituitary, which in turn releases hormones that act on target glands such as the thyroid, adrenals, and gonads. This hierarchical system allows for precise control of hormone levels and bodily functions.

Key Endocrine Axes

1. Hypothalamic-Pituitary-Thyroid (HPT) axis
2. Hypothalamic-Pituitary-Adrenal (HPA) axis
3. Hypothalamic-Pituitary-Gonadal (HPG) axis
4. Renin-Angiotensin-Aldosterone System (RAAS)

Understanding the complex interplay between these endocrine axes is crucial for comprehending how the body maintains balance and responds to various physiological challenges.

Endocrine Disorders: When the System Falters

While the endocrine system is remarkably efficient, it can sometimes malfunction, leading to a variety of disorders. These conditions can result from either overproduction or underproduction of hormones, or from issues with hormone receptors on target cells.

What are some common endocrine disorders? Diabetes mellitus, perhaps the most well-known endocrine disorder, results from problems with insulin production or function. Other common conditions include hypothyroidism, hyperthyroidism, Cushing’s syndrome, and growth hormone deficiency. These disorders can have wide-ranging effects on health and quality of life, highlighting the importance of a well-functioning endocrine system.

Factors Contributing to Endocrine Disorders

• Genetic predisposition
• Autoimmune conditions
• Tumors or growths on endocrine glands
• Environmental toxins
• Nutritional deficiencies
• Stress and lifestyle factors

Early detection and proper management of endocrine disorders are crucial for maintaining overall health and preventing complications. Regular check-ups and awareness of symptoms can help identify potential issues before they become severe.

The Future of Endocrine Research

As our understanding of the endocrine system continues to grow, new avenues for research and treatment are emerging. Advances in molecular biology, genetics, and imaging technologies are providing unprecedented insights into the workings of endocrine glands and the actions of hormones at the cellular level.

What are some promising areas of endocrine research? Scientists are exploring the potential of stem cell therapies to regenerate damaged endocrine tissues, such as insulin-producing cells in the pancreas. Gene therapy approaches are being investigated to correct genetic defects that lead to endocrine disorders. Additionally, researchers are studying the complex interactions between the endocrine system and other bodily systems, such as the immune system and the gut microbiome.

Emerging Topics in Endocrine Research

1. Endocrine disruptors in the environment
2. Chronobiology and hormonal rhythms
3. Epigenetic influences on endocrine function
4. Hormonal therapies for age-related conditions
5. Personalized medicine approaches for endocrine disorders

These exciting developments hold promise for improving the diagnosis, treatment, and prevention of endocrine disorders, potentially leading to better health outcomes and quality of life for millions of people worldwide.

The Endocrine System: A Marvel of Biological Engineering

The endocrine system stands as a testament to the intricate design of the human body. Through its network of glands and hormones, it orchestrates a myriad of physiological processes, from the basic functions of metabolism and growth to the complex realms of mood, cognition, and behavior.

Why is the endocrine system so crucial for human health? Its ability to maintain homeostasis through precise chemical signaling allows our bodies to adapt to changing internal and external environments. From regulating our sleep-wake cycles to coordinating our stress responses, the endocrine system plays a vital role in every aspect of our lives.

Key Takeaways on Endocrine Glands

• Endocrine glands secrete hormones directly into the bloodstream
• Hormones act as chemical messengers, influencing target tissues throughout the body
• The endocrine system works closely with the nervous system to maintain homeostasis
• Endocrine disorders can have wide-ranging effects on health and well-being
• Ongoing research continues to uncover new insights into endocrine function and potential therapies

As we continue to unravel the mysteries of the endocrine system, we gain not only a deeper appreciation for the complexity of our bodies but also new tools to promote health and treat disease. The study of endocrine glands and their functions remains a vibrant and essential field in biomedical science, promising continued advances in our understanding of human physiology and pathology.

Endocrine Glands – Definition, Examples, Function

Definition

Endocrine glands are tissues or organs that excrete chemical substances (hormones) directly into the blood. Common endocrine glands are the hypothalamus, pineal, and adrenal glands. Endocrine glands secrete hormones directly into the bloodstream or into the intercellular space, allowing the hormones to reach their target.

Overview

Endocrine system glands are spaced throughout the entire body. They release a wide number of hormones which control the metabolism and function of other cells. Exocrine glands, by comparison, secrete substances inside and outside of the body using ducts. These two methods of transport mark the difference between exocrine and endocrine glands.

While in the bloodstream, the hormones are able to travel through the body’s circulatory system to reach distant targets. Hormones, in turn, will carry out varied functions in the body depending on the receptors they bind and the quantity of the hormone that is present. These changes will reflect the balance of secretion and excretion of hormones in the body. Their duration will depend on the hormone’s inherent half-life and activity levels.

Endocrine Glands Diagram

As you can see in the image above, men and women share all of the same endocrine glands, besides the reproductive organs. While reproductive organs have the primary function of creating and releasing gametes, they also release a number of hormones which affect the body in different ways.

Examples of Endocrine Glands

Pineal Gland

The pineal gland is a small gland located within the brain that serves as a great example of endocrine glands in general. The pineal gland is activated by neurons connected to your eyes. When these nerves are activated by light, the pineal gland is repressed. When nighttime comes, and the light reaching your eyes decreases, the pineal gland becomes activated.

The pineal gland secretes melatonin, a hormone which activates our sleep cycle. By releasing this hormone when it gets dark, the pineal gland is helping your body coordinate for sleeping. This includes changing your respiratory rate, brain patterns, and even digestive patterns.

Thyroid Gland

The thyroid gland is found in your throat, just below the jaw. This gland secretes a number of hormones that act on your metabolism. Thyroid hormones can increase the rate of your cellular metabolism, or decrease it. These activities are in part directed by another endocrine gland, the pituitary, which signals to the thyroid which hormones to release. In turn, your metabolism is regulated. In fact, a nonfunctioning thyroid gland often leads to drastic weight gain or loss, depending on the malfunction.

Function of Endocrine Glands

Releasing Hormones

The endocrine system derives its power from coordinating the interactions that take place between the hormones that are released by this network of glands. Endocrine glands themselves will inherently be able to make, secrete, and store hormones for future use. This ability to store hormones for later release is useful for modulating responses to certain stimuli. Depending on our developmental needs at whichever stage in life we are in, our endocrine system will ensure that a proper hormonal balance is in place so that we release more or less of certain hormone based on these needs. Many factors can compromise this balance, however, resulting in endocrine disease.

One such instance is when too much or too little hormone is released from a given endocrine gland. Another problematic scenario is if an afflicted patient’s blood supply is not strong enough to carry the hormones the distance they need to be carried to reach their target organs. Furthermore, once the hormones reach their target site, the tissue must have an adequate number of hormone receptors to maintain this intricate balance.

Responding to the Nervous System

The actual release of hormones by endocrine glands is tempered by the nervous system. Hormone release will be directly tied to the body’s response to certain neural or hormonal stimuli. Hormones come in various forms; some may present as fatty steroids or long-chained amino acids. These substances will travel through our bloodstream to reach specific tissues or organs.

The endocrine system will regulate our metabolic processes, our appetite, our growth, and even our sleeping patterns. Our endocrine glands will essentially help regulate our body’s energy distribution in order to wire all of these varied processes. Many tissues in our bodies have the ability to release chemical substances into our blood, but we will discuss the most major endocrine glands in more detail.

List of Endocrine Glands

Endocrine system

The figure depicts the major endocrine glands of the human body.

Within the Brain and Neck

Among the most important endocrine glands in the human body is the hypothalamus. In spite of its small size, this part of the brain releases crucial chemicals that influence the body’s internal homeostasis as well as the pituitary gland. Its hormones include oxytocin and growth hormone, among many others.

The pituitary gland, in turn, is another endocrine tissue that releases hormones related to growth, mental development, and sexual reproduction. Moving on to the pineal gland in the brain, the pineal body will create and release various hormones, including melatonin, which regulates our sleep and waking cycles and eventual sexual maturation. The thyroid is an endocrine gland in the neck that releases thyroid hormones that help maintain our body’s metabolic and energetic processes. The parathyroid gland, on the other hand, lies behind the thyroid gland and secretes chemicals that allow for normal bone development.

Within the Body

The thymus has much more important roles in immune health during our childhood (via T cell production), as it is eventually phased out by fat in post-pubescent children. The pancreas is another endocrine gland that releases insulin in the body, which importantly allows for sugar in the blood to be metabolized.

Moving southward to the kidneys, the adrenal glands that lie above each will secrete adrenaline hormone during strenuous fight or flight situations. This modulation will likewise influence the way our bodies use energy.

Lastly, our sex organs are a major type of endocrine gland. Ovaries in women will create estrogen and progesterone derivatives that help with our sexual development and will aid in the release of eggs for future fertilization. Thus, all of these glands orchestrate large processes that keep our species alive and thriving. Hence, the evolutionary importance of having endocrine tissue!

Major Endocrine Glands:

• Hypothalamus
• Thyroid
• Parathyroid
• Pituitary gland
• Adrenal glands
• Pineal gland
• Pancreas

Quiz

1. Which of the following is not an endocrine gland property?

A.Production of hormones

B.Regulate wake and sleep processes

C. Expel primarily to local receptors

D.Secrete to blood

2. Which of the following is not an endocrine gland?

A.Adrenal Glands

B.Salivary Glands

C.Pineal Glands

D.Pancreas

3. Which is not a complication of the endocrine system, as posed by the article?

A.Too little hormone is expelled

B.The patient does not have adequate blood flow to allow adequate passage of substances

C.The incorrect hormone is transmitted through a target tissue

D.Not enough hormone receptors are present

4. Which of the following functions is NOT controlled by the endocrine system?

A.The release of saliva in the mouth

B.Hormonal control of the metabolism

C.Hormonal control of the heart rate

D.All of the above are endocrine functions

5. Which of the following is a true statement?

A.The endocrine system works alone

B. The endocrine system only responds to the nervous system

C.The endocrine system is highly associated with many different body systems

The Endocrine System — PT Direct

To ensure your clients adapt to exercise in the way they desire you must understand how hormones govern those adaptations. Here it is then; the endocrine system explained.

Endocrine system new terms

When it comes to the endocrine system there are some commonly used terms that may be new to you.  To help you some of these new terms and their definitions are shown in the following table.

What is the endocrine system?

The endocrine system is a control system of the human body much like the nervous system.   The endocrine system produces chemical messages in the form of hormones, whereas the nervous system produces electrical messages.

The endocrine system is made up of lots of specialised endocrine glands that secrete hormones into the bloodstream.

Some of the major endocrine glands are shown on this diagram. 

What does the endocrine system do?

The hormones that are secreted by the endocrine glands are chemical messengers which are carried by the bloodstream to other tissues or organs in the body.  The messages they deliver tell these tissues or organs to either increase or decrease their activity.

Hormones act only on target tissues or organs that have the appropriate receptor sites for that given hormone.  In this way hormonal messages are delivered to, and act on, only the areas of the body they are intended for.

The endocrine system is linked to the nervous system by effects of the hypothalamus on the pituitary gland, as seen in the adjacent image.  

The pituitary gland is known as the ‘master gland’ because its secretions control the activity of other endocrine glands.  The activity of the pituitary gland is however controlled by the hypothalamus which as well as being an endocrine gland, is also part of the nervous system.

Along with the nervous system, the endocrine system coordinates the body’s functions to maintain homeostasis during rest and exercise.  The nervous and endocrine systems also work together to initiate and control movement, and all the physiological processes movement involves. 

Where the nervous system acts quickly (virtually instantly) delivering messages by nerve impulses, the endocrine system has a slower but longer lasting response which compliments the nervous system.  The endocrine system regulates growth, development and reproduction and augments the body’s capacity for handling physical and psychological stress.

Why is the endocrine system important?

The endocrine system and the hormones it releases influence almost every cell, organ and function of our body. In general these hormones are in charge of body processes that occur slowly such as mood regulation, growth and development, tissue function, metabolism, sexual function and reproductive processes.  Other body processes that require a faster response such as breathing and body movements are controlled by the nervous system.

When training clients you are essentially trying to elicit the best possible hormone response in order to help them achieve their goals.  For example if a client wants to increase muscle mass it is important that they undertake the correct type of training to release more growth hormone.  This will help them repair and grow more muscle after the training session.

It’s therefore critically important to have a good understanding of the endocrine system and some of the key hormones, as this will help to ensure your training doesn’t over stress your clients endocrine system and instead provides the ideal training stimulus to achieve the desired hormonal response.

The endocrine system and fitness

The endocrine system and fitness go hand in hand.  Whether you are eating your last big meal before running a marathon, playing a game of football or recovering after a training session in the gym the endocrine system is constantly working.

An accompanying page in this folder summarises the major endocrine glands, the hormones they release, the tissues and organs they target and the effects they have with exercise.  We will briefly cover some of these hormones now as they relate to exercise.

Key hormones and the regulation of hormone activity

During exercise several hormones (adrenaline, nor adrenaline, growth hormone and cortisol) function together to mobilise fuel for the production of ATP (energy) for the exercise

These hormones affect the cells on three primary target tissues during exercise, these are:

1.      Fat

2.      Liver

3.       Skeletal muscle

When they bind to receptors on fat cells, fat storage is inhibited and fat mobilisation is enhanced for energy.  When they bind to receptors on the liver, glycogen is broken down into glucose for readily available energy.  When they bind to receptors on skeletal muscle, stored glycogen is broken down into glucose and the uptake and utilisation of fatty acids for energy is increased.

Hormones – glucagon and insulin

Glucagon and insulin are both secreted by the pancreas and act antagonistically to each other in order to maintain blood glucose levels, as shown in the adjacent diagram.

With exercise there is a greater demand from muscle tissue for blood glucose for fuel, causing blood glucose levels to drop.  Glucagon levels consequently increase with exercise and insulin levels are simultaneously suppressed.

This is vital as it ensures that blood glucose levels do not drop too low as the brain (neural tissue) can only use glucose to produce energy.   If there wasn’t any glucose in the blood the brain would be starved of fuel…which in case you’re wondering is definitely NOT a good thing – in fact it can be downright fatal!

Hormones  – adrenaline and nor adrenaline

Adrenaline and nor adrenaline also help to enhance cardiac (heart) function by increasing heart rate, constricting blood vessels and increasing blood pressure.  This in turn helps to distribute blood flow to active tissues, providing these tissues with the energy and oxygen they need. 

How is activity at the ‘target tissues’ regulated?

As we previously mentioned hormones are designed to affect specific target tissues that have the correct receptors.  Think of the receptors as a lock and the hormone as a key, if the key fits the lock then the hormone can affect the target tissue.

However there are three things that influence the activity of hormones on the target tissue, these are:

1.      Number of receptors:  The number of receptors for a specific hormone can be altered to meet the demands placed upon the body over time.   Up regulation means more receptors have developed.  Down regulation means there are less receptors.  Up and down regulation changes the cells sensitivity to hormones.

This is one reason exercise is beneficial for people with type II diabetes or at risk of developing type II diabetes. 

This is because it can help to increase the sensitivity of the tissues receptor cells to the hormone insulin, this in turn helps to control blood glucose (sugar) levels and even increase the total number of receptor cells on the target tissue.

Up regulation of receptor cells can also be seen when we look at growth hormone and the effect of exercise.  Completing a well structured resistance training programme aimed at muscle growth stimulates an increase in the number of receptor cells within muscle tissue.

2.      Chemical bond:  The chemical bonding between a hormone and its receptor can be weak or strong.  A strong bond will result in a greater reaction in the target tissues than a weak bond.

For example, with exercise greater demand is placed on the body for fuel for the working muscles.  Glucagon is one hormone that ensures that there is a regular supply of glucose in the blood for use by working muscles.  With exercise over time the bonds between glucagon and its receptors strengthen to meet the increased demands for glucose from the working muscle.

Completing a well structured resistance training programme aimed at muscle growth will also increase the sensitivity of the receptor cells to growth hormone and result in a stronger bond.

3.     Blood hormone levels:  Lastly the level of the hormone in the blood at any one moment will affect the response of the tissues.

The greater the stress that is put on the body the greater the hormonal response will be in order to meet the demands of the body and to maintain homeostasis. 

We see this with growth hormone in the adjacent diagram, which is released by the pituitary gland under the control of the hypothalamus.

Growth hormone acts on most tissues in the body, with two of its key roles being to stimulate cell growth and mobilise fat for energy.

Intense resistance training (heavy weights) stimulates the release of greater quantities of growth hormone than less intense forms of exercise.  Consequently intense resistance training has a greater response (growth in skeletal muscle) than other less intense forms of exercise.  This is due to the larger quantities of growth hormone that are released into the bloodstream.

How is the level of hormones in the blood regulated?

Hormones are released into the blood in brief spurts.  Having the correct amount of hormones in the blood when needed is vital in order for them to effectively carryout their functions.  Too much or not enough of certain hormones can put stress on systems and have negative effects like weight gain or depression.

For this reason it is important that the amount of hormones circulating in the blood at any given time is regulated and controlled, this is achieved through the following three methods:

1.       Neural stimulation:  Neural stimulation of hormones occurs when a stress is present.  The hypothalamus and sympathetic nervous system activate the adrenalin gland to release adrenalin and noradrenalin. 

This in turn increases heart rate and metabolic rate to allow enough blood sugars to be circulating to provide adequate fuelling of muscle and nerve tissue.  An example of this response, which is rapid and can be significant, is the ‘fight or flight’ reaction.

2.      Hormonal secretions (hormones that affect other hormones):  Hormones also influence the release of other hormones.  The hypothalamus makes and secretes hormones that act on the pituitary gland to promote or inhibit its secretion of other hormones. 

Regulation of hormone release in this form is usually achieved through a ‘negative feedback loop’.  An example would be that high levels of hormone ‘A’ causes hormone ‘B’ to be secreted.  Hormone ‘B’ acts on the gland that secretes hormone ‘A’, inhibiting further secretion of ‘A’.   Once hormone ‘B’ levels begin to drop the gland begins to secrete ‘A’ again. 

3.      Blood conditions (what is in the blood at any time):  Blood conditions refers to the levels of ions, nutrients, bile and other body compounds circulating in the blood.    

For example, high blood glucose levels signal the pancreas to release the hormone insulin.  The higher the levels of blood sugar the greater the amount of insulin released by the pancreas.  Insulin helps glucose to enter muscle and liver cells, thereby lowering blood glucose levels and removing the stimulus for further insulin release from the pancreas.

How negative feedback loops work – a closer look at the hormone cortisol

Out of the three hormonal control systems previously mentioned, the most predominant is the negative feedback loop (hormones that affect hormones).  It works in a similar way to how a thermostat in a heat pump works.

The thermostat detects the temperature is too low and turns the hot air on.   As the hot air raises the temperature to the set optimal level the thermostat turns the heat pump off.  

In the endocrine system, receptors in the body register that the amount of hormone or compounds in the blood are not optimal and cause a release or inhibition of hormones to manage the situation.

A good example of this concerns the hormone cortisol.  Cortisol is known as the ‘stress’ hormone as it is secreted in higher levels when higher levels of stress (physical and psychological) are present. 

Cortisol works on target tissues to increase blood glucose levels.  It does this by aiding the metabolism of carbohydrate reserves from the liver as well as breaking down fat and protein to help provide quick bursts of energy.

As protein is primarily used in the body to build and repair tissue, cortisol is known as a ‘catabolic’ or breakdown hormone, as it interferes with the ‘anabolic’ or building functions of protein.

Cortisol is very much a ‘fight or flight’ hormone, akin to the sympathetic division of the nervous system.   Small increases have positive effects such as providing a quick burst of energy and lowering sensitivity to pain via an anti-inflammatory action.  It is important that the levels of cortisol are regulated as prolonged elevated levels have negative effects. 

We see how cortisol is regulated via a negative feedback loop in the adjacent diagram. 

A physical or psychological stressor causes the hypothalamus to secrete corticotrophin releasing hormone (CRH) which causes the anterior pituitary gland to secrete adrenocorticotropin (ACTH) which in turn tells the adrenal glands to release cortisol. 

As well as acting on its target tissues (liver, fat, muscle etc) cortisol also sends ‘negative feedback’ to the hypothalamus and anterior pituitary telling them to stop secreting CRH and ACTH, and by virtue of this limiting the further release of cortisol.

Unfortunately this regulatory response is not as effective if the stressors that caused cortisol to be released in the first place remain.  

Intense exercise, financial stress, business stress, relationship stress, work stress etc are increasingly prevalent in today’s society.  If the stressors remain then so do the stimulants for elevated cortisol levels, irrespective of the negative feedback loop.

If cortisol remains elevated for a prolonged period of time the positive effects it can have become negative.  As the body stays in a catabolic ‘breakdown’ state there is a loss in muscle tissue, immunity is lowered, people become more vulnerable to illness, there is an increase in the storage of abdominal fat and imbalances in blood sugar levels develop. 

It is important to understand that cortisol is not responsible for this; rather the stressors that have caused cortisol to remain elevated are responsible.  As a trainer you need to be able to recognise when clients are highly stressed and make sure you don’t add to their stress levels by destroying them in the gym with long hard workouts.  The stressors must be removed or minimised through various means of relaxation if positive results are to occur.  

Biology Endocrine glands and their functions

Human organ systems perform strictly defined functions, and in order for the body to exist as a whole, it is necessary to regulate and coordinate this complex work. This regulation is carried out by the nervous and humoral systems. Humoral regulation is carried out due to the release of hormones into the internal environment of the body, which are produced by the endocrine glands.

Endocrine glands, or endocrine glands, do not have excretory ducts. The products of their vital activity – hormones – they secrete into the internal environment of the body: into the blood, lymph or tissue fluid. it is formed by endocrine glands. While the glands of external secretion – sweat, salivary, sebaceous, gastric – secrete the products of their vital activity into the external environment or body cavities.

Entering the bloodstream, the hormone is distributed throughout the body and carries out humoral regulation of the functions of organs and tissues, changing their activity, stimulating or inhibiting their work.

The most important endocrine glands are the thyroid, parathyroid, thymus, adrenal and pituitary glands.

There are also glands of mixed secretion in the body, which produce several waste products. Some of them enter the bloodstream, and some go through the ducts into the cavity of the internal organs. This type of gland includes the pancreas and gonads.

The product of the vital activity of the endocrine glands is a hormone. The term “hormone” (from the Greek “I excite”, “I induce”) was introduced into practice by W. Bayliss and E. Starling. In January 1902, they conducted an experiment that convincingly proved the participation of the humoral factor in the regulation of the secretory activity of the pancreas. According to Bayliss and Starling, a hormone is any substance normally produced by the cells of any part of the body and carried by the blood to the distant parts on which it acts.

Currently, hormones are defined as highly active substances formed in the endocrine glands, entering the bloodstream and exerting a regulatory influence on the functions of organs and body systems remote from their place of secretion.

According to the chemical structure, hormones are divided into:

– hormones – derivatives of amino acids;

– protein and polypeptide hormones;

– steroid hormones.

According to the physiological effect – on launchers and performers. Trigger hormones (activators of the activity of other endocrine glands) include neurohormones of the hypothalamus and tropic hormones of the pituitary gland. Hormones-performers have a direct effect on the functions of the body.

Hormones are distinguished by a strict specificity of action – the reactions of organs, tissues and cells to them are strictly selective. Hormones act even in negligible amounts, but they are quickly destroyed, and therefore must be synthesized by the glands as needed and enter the bloodstream.

The thyroid gland is the largest of the endocrine glands, its mass is 16-23 g. It is located on both sides of the trachea just below the thyroid cartilage of the larynx. Thyroid hormones (thyroxine and triiodothyronine) contain iodine. Its intake with water and food is a necessary condition for the normal functioning of the gland.

Thyroid hormones regulate metabolism, enhance oxidative processes in cells and the breakdown of glycogen in the liver, affect the growth, development and differentiation of tissues, as well as the activity of the nervous system.

The adrenal glands are paired glands adjacent to the upper poles of the kidneys. Like the kidneys, the adrenal glands have two layers: the outer one is the cortical layer, and the inner one is the medulla, which are independent secretory organs. They produce different hormones with different patterns of action.

The cells of the cortical layer synthesize cortisol and corticosterone, which regulate mineral, carbohydrate, protein and fat metabolism. So, with their participation, the level of sodium and potassium in the blood is regulated, a certain concentration of glucose is maintained, the formation and deposition of glycogen in the liver and muscles increases. The last two functions of the adrenal glands are performed in conjunction with pancreatic hormones.

The adrenal medulla produces adrenaline and norepinephrine, which are released during strong emotions – anger, fear, pain, danger. The entry of these hormones into the blood causes a rapid heartbeat, narrowing of blood vessels, increased blood pressure, increased breakdown of glycogen in liver cells and muscles to glucose, inhibition of intestinal motility, relaxation of bronchial muscles, increased excitability of retinal receptors, auditory and vestibular apparatus. As a result, the functions of the body are rebuilt, forces are mobilized to endure stressful situations.

The pancreas is a mixed secretion gland. It has special islet cells that produce insulin and glucagon, which regulate carbohydrate metabolism in the body. So, insulin increases the consumption of glucose by cells, promotes the conversion of glucose into glycogen, thus reducing the amount of sugar in the blood. Due to the action of insulin, the blood glucose content is maintained at a constant level, favorable for the flow of vital processes.

Another pancreatic hormone – glucagon – is an insulin antagonist, has the opposite effect, that is, it enhances the breakdown of glycogen to glucose, increasing its content in the blood.

The gonads, the testes, or testicles in men and the ovaries in women, are glands of mixed secretion. The testicles produce androgens and the ovaries produce estrogens. They stimulate the development of reproductive organs, the maturation of germ cells and the formation of secondary sexual characteristics, that is, the structural features of the skeleton, the development of muscles, the distribution of hairline and subcutaneous fat, the structure of the larynx, the timbre of the voice in men and women.

The most important gland of the human endocrine system is the pituitary gland, or the lower appendage of the brain weighing only 0.5 g. It is located at the base of the brain – in the so-called “Turkish saddle”. The pituitary gland produces hormones that stimulate the functions of other endocrine glands.

In the pituitary gland, there are two main sections: the anterior lobe – adenohypophysis and the posterior – neurohypophysis, each of them produces certain hormones. So, in the anterior pituitary gland, hormones are produced that stimulate the synthesis and secretion of thyroid hormones (thyrotropin), adrenal glands (adrenocorticotropin), gonads (gonadotropin), as well as growth hormone (somatotropin).

Vasopressin and oxytocin are synthesized in the posterior pituitary gland. Vasopressin, or antidiuretic hormone, regulates water metabolism and vascular tone. Oxytocin increases the tone of the smooth muscles of the uterus, regulates the birth act and the secretion of milk by the mammary glands.

The pituitary gland is located directly below the hypothalamus and is connected to it by a funnel and a stalk. The hypothalamus is a part of the brain that has properties of the nervous and endocrine systems. The hypothalamus receives an extensive flow of information from the senses and internal organs. The composition of the neurosecretory nuclei of the hypothalamus includes the so-called large and small cell nuclei. The former secrete oxytocin and vasopressin, which are transported along the nerve trunks to the posterior pituitary gland, accumulate there and are used as needed. Other functions are performed by the small cell nuclei of the hypothalamus. They are able to develop the so-called releasing factors (allowing factors). Releasing factors through the venous system reach the pituitary gland and regulate the release of hormones of the latter.

All endocrine glands are interconnected. Hormones produced by some glands affect the activity of other glands. This provides a unified system of coordination, which is carried out according to the feedback principle: a decrease in the level of a peripheral hormone in the blood leads to an increase in the secretion of the corresponding tropic hormone, and an increase in the level of a peripheral hormone causes inhibition of the secretion of the tropic hormone.

Thus, the endocrine regulation of the body’s vital activity is complex and strictly balanced. Changes in physiological and biochemical reactions under the action of hormones contribute to the adaptation of the body to constantly changing environmental conditions.

For many years, scientists believed that hormones could only be produced by specialized endocrine glands or groups of cells whose sole function was to produce hormones. Currently, scientists believe that almost all organs and tissues of a living organism secrete hormones and biologically active compounds into the intercellular space and blood, through which interactions are carried out that unite cells and tissues into a single whole. So, the synthesis of hormones is found in the cells of the blood and the immune system, in the retina of the eye, in the cells lining the intestines and blood vessels, in the heart muscles. Most likely, this list will expand in the future.

Endocrine glands Children’s Encyclopedia (first edition)

Sunburn and sunburn

Skeleton

There are two types of glands in the human body. Some have ducts through which the substances produced in them – secrets – are brought out or into the body cavity (in the cavity of the stomach, intestines, etc.). Such glands are called glands of external secretion (“secretion” – in Latin branch). These include, for example, sweat and salivary glands.

Scheme of the location of the endocrine glands.

But there are glands that do not have excretory ducts. Their secrets are not displayed either in the cavity of the body or on its surface. They are absorbed directly into the blood. Therefore, glands that do not have excretory ducts are called endocrine glands. The figure shows how they are located in the body.

Substances produced by the endocrine glands are called hormones, from the Greek word “hormao” which means “to excite”. They were named so because they most often excite, enhance the work of various organs. Each gland produces a specific hormone, and each hormone has its own name, such as the hormone insulin, the hormone adrenaline, the hormone thyroxine. They are in the blood in negligible quantities, but their action is very strong.

In order for the action of a hormone to manifest itself, an insignificant amount of it is needed, and the endocrine glands produce hormones in fractions of milligrams.

Many hormones are found in the blood in concentrations equal to ten millionths and even one hundred millionths of a percent. Therefore, it is not easy to detect any hormone in the blood, and it is not easy to determine its amount. Scientists have spent a lot of work to invent the most subtle methods of analysis that would allow us to detect the hormone in the blood, isolate it in its pure form, study the chemical structure and find out in detail its action.

Dwarfs and giants

Human growth depends on the activity of the pituitary gland. Compare dwarf stature (left) and giant stature (center) with normal stature (right).

Lilliputians performed in the circus. The audience watched with interest their cheerful dances and acrobatic exercises. My neighbor asked in bewilderment: “Who are the Lilliputians? Is this the kind of people?

No, such a nation does not exist. People of dwarf growth are found in any country. A person becomes a dwarf because of the underdevelopment of a small, with peas, glands – the pituitary gland. It is located in the cranial cavity, at its base, and is directly connected with important brain metabolic centers. Human growth depends on the development of the pituitary gland. With the correct activity of the pituitary gland, a person grows normally. If the pituitary gland secretes insufficient growth hormones from childhood, a person grows up as a dwarf, a midget.

But the pituitary gland can also secrete a lot of growth hormones, then a person grows very quickly and grows into a giant, a giant. There are people much taller than 2 m. The tallest person in the world described in the literature was 3 m 20 cm. The long parts of the tubular bones cannot grow further, but the growth of cartilage and soft tissues can continue. In such a person, the fingers and toes grow, the nose and tongue increase, and there is a sharp increase in some internal organs. In this case, the human body becomes disproportionate, ugly. This is what distinguishes such a disease from gigantism.

Lilliputians and giants performed in the circus.

THICK AND THIN

This man became obese from a lack of pituitary hormones that affect fat metabolism.

They say that there are three degrees of fullness: the first causes envy, the second – ridicule, and the third – sympathy. Fullness, at which body weight reaches 200, 300 and even 500 kg, can only cause sympathy and condolences. Such fullness does not come from gluttony, it is a consequence of the disease. The reason is the same pituitary gland. Not only the length of the body, but also the thickness depends on its condition, since the pituitary hormones affect not only growth, but also fat metabolism. If these hormones are not enough, then the fats in the body are not oxidized in a timely manner and accumulate in unlimited quantities, morbid obesity occurs.

It is also bad if the hormones that enhance fat oxidation are produced in excess. Then the fats are not retained in the body, and the person loses weight dramatically.

The normal activity of the pituitary gland is usually somewhat disturbed in old age. Therefore, excessive fullness or excessive weight loss is more common in older people.

It is bad if the hormones that enhance fat oxidation are produced in excess. Then the fats are not retained in the body, and the person loses weight dramatically.

Fat metabolism is also disturbed for other reasons: due to poor metabolism of proteins and carbohydrates in the body and poor water-salt metabolism. So, for example, excessive fullness is often associated with tissue swelling due to the fact that the body retains too much water. On the contrary, with a strong weight loss, the tissues dry up: the body does not retain water well.

MORE ABOUT Dwarfs

Dwarf growth occurs not only because the pituitary gland secretes insufficient growth hormones, but also because of the weak activity of another gland – the thyroid. It is located on the gley and consists of two lobes lying on the sides of the thyroid cartilage of the larynx and connected by an isthmus.

Insufficient activity of the thyroid gland from early childhood retards human growth. At the same time, the thyroid gland grows very strongly, and a goiter forms on the neck, sometimes very large, and people with such a

iron are called goiter dwarfs. The main reason for their appearance is very simple. Goiter dwarfs usually grew up in mountainous areas, where rivers originating from melting glaciers do not contain iodine, which is part of thyroxine, a thyroid hormone. Therefore, the thyroid gland cannot produce enough of this hormone, which affects the growth of the body and enhances metabolism. If there is no thyroxine in the body, then growth stops, metabolism is disturbed and conditions for the development of the nervous system worsen.

Crooked dwarfs are now rare. Scientists have found a simple remedy that prevents this disease. They suggested adding iodine to food.

It is bad when the thyroid gland is underdeveloped, but not better if it is too developed. In this case, a person’s metabolism is increased, the heart beats more often than usual, the movements are jerky. One of the signs of excessive activity of the thyroid gland is the so-called bulging eyes. Such a disease is called “Bazedov’s”, by the name of the scientist Bazedov who studied it.

CHILDREN’S GLAND

Not far from the thyroid gland is the thymus gland. Its properties are amazing. It is especially well developed in childhood. With age, the further development of this gland decreases, and in an adult it is replaced by fatty tissue. Its hormones, as it were, inhibit the development of other glands, on which the transition to the adult state depends, for example, the gonads, the thyroid gland, and some others. It seems to protect the child from premature aging, from too early transition to adulthood. Therefore, the thymus gland is considered the gland of childhood, the child’s gland.

THE SMALLEST GLANDS

In some cases, in case of thyroid diseases, it has to be partially removed. Sometimes the removal caused a serious complication – convulsions. This happened if, along with the thyroid gland, other small glands located near it were removed. They were called parathyroid. Scientists are convinced that these glands are very important for the body. The content of calcium salts in the blood depends on them. If they are removed, then calcium is not retained in the body, and with a lack of it, severe muscle cramps occur.

TOO MUCH SUGAR

After examining the patient, the doctor gave a referral to the polyclinic laboratory. In the direction it was indicated: to do an analysis for sugar. There was too much sugar in the blood of the studied patient. And since the analysis was performed on an empty stomach, blood sugar arose for some internal reason.

Insulin regulates the formation of glycogen stores in the liver from dietary carbohydrates. In the liver, glycogen is converted to sugar, which is carried in the blood to all cells in the body.

Sugar in the blood comes from the liver, where it is in the form of a complex carbohydrate – glycogen, or animal starch. Glycogen is deposited in the liver “in reserve” from carbohydrates (sugar, starchy substances – bread or potatoes) that enter the body with food. From the liver, sugar gradually enters the blood, and from the blood to the muscles and other organs.

Glycogen is deposited in the liver under the influence of insulin, a hormone of the pancreas. The pancreas plays a dual role in the human body. On the one hand, it is an external secretion gland. It produces digestive juices that pass through the excretory duct into the duodenum. Here they digest the food slurry coming from the stomach.

On the other hand, the pancreas is an endocrine gland. It has a cluster of special cells that produce the hormone insulin, which is absorbed directly into the blood.

If the pancreas produces enough insulin, the glycogen in the liver is produced satisfactorily. If the pancreas produces little insulin, then the liver is not able to form glycogen, retain sugar, and it enters the blood in excess. Therefore, if the analysis showed that blood sugar is more than normal, then the pancreas does not produce enough insulin. This disease is called diabetes or diabetes. She is treated with insulin.

FAN’S HORMONE

The stadium was noisy…

The stadium was noisy… Only one goal decided the fate of the championship. One of the “fans” was especially excited. The young man shouted, waved his arms, jumped up, sat down again. After the first half, a citizen approached him and said: “I am a scientist, a physiologist, I am interested in what happens in the blood during the emotional states of a person. Please come with me to the infirmary and let me take a few drops of blood from you.” The “fan” agreed, but asked to be informed later about the results of the analysis and left his address.

A few days later he received a letter saying that his blood contained an increased amount of the hormone adrenaline. This hormone is secreted by small glands. They are located above the kidneys and are called adrenal. Adrenaline enters the bloodstream intensely when a person is emotionally aroused. When the nervous system is excited, the excitement is transferred to the adrenal glands and causes increased production of this hormone.

Adrenaline has a variety of effects on the body. It enhances and speeds up the work of the heart; expands the thin airways inside the lungs, which contributes to increased breathing; causes compression of the vessels of the spleen and liver, which is why the blood accumulated in them enters the general circulation; from its action, the blood is enriched with sugar, which intensively enters the muscles; muscle fatigue is reduced and the central nervous system is excited.

Adrenaline is strongly released during muscular work. It enhances those physiological processes that should ensure the smooth functioning of the muscles. The Cheerleader didn’t do much physical work, but he was emotionally aroused and his adrenal glands were pumping adrenaline.

Adrenaline is intensely formed in athletes even before the start of the competition. Therefore, by the time of the start, blood circulation, respiration and other functions necessary for enhanced muscle work already increase their activity in advance.

Lack of strength

“I have a breakdown,” the patient says to the doctor. – I get very tired from the slightest physical exertion. I can’t do anything, I can’t work, I’m weak.”

The patient was admitted to the clinic and various studies were carried out, which showed a rather rare disease – damage to the outer, cortical layer of the adrenal glands. This disease was also evidenced by the beginning of a change in the color of the patient’s skin: it acquired a bronze hue. This disease is even called “bronze disease”.

The breakdown occurs because the adrenal cortex does not produce enough of the hormone cortin. The hormone got its name from the word “cortex”, which means bark. It has now been found that the adrenal cortex secretes many different types of cortin. This hormone regulates muscle metabolism, maintains performance and muscle strength.

COCK OR HEN?

It would seem that this is an idle question. Who does not distinguish a rooster from a chicken by a bright large crest, spurs, and lush tail plumage? But if he does not have external signs that distinguish him from a chicken, and at the same time you see that this is not a chicken, then who is it? Answering the question posed, it would be most correct to say that this is a former rooster. Why did he become like this? It turns out that his appearance has changed so dramatically because the gonads were surgically removed from the rooster. This caused the loss of secondary sexual characteristics – the crest and spurs. Even the behavior of the rooster after such an operation has changed a lot: he no longer began to crow and get into a fight. If, on the other hand, a rooster, from which the sex glands were removed, is transplanted with the sex glands of a chicken, it can no longer be distinguished from it at all. The same thing will happen to a chicken when the gonads of a rooster are transplanted into it. She not only becomes outwardly similar to him, but also acquires the cockiness characteristic of a rooster.

Scientists have performed such experiments more than once. This allowed us to draw an important conclusion that the gonads produce hormones that are absorbed into the bloodstream and affect the formation of secondary sexual characteristics. In humans, secondary sexual characteristics develop mainly during adolescence. Under the influence of hormones in boys, the voice “breaks” and becomes more bass, mustaches and beards begin to grow, muscles develop, he turns from a child into a young man. In girls at this time, the physique changes, the mammary glands develop.

Sex hormones also play an important role in the female body during pregnancy. Under the influence of sex hormones, the mammary glands intensively produce milk after the birth of a child.

Therefore, sex hormones influence the development of puberty and the important function of motherhood.

ALL TOGETHER

Everyone, everyone, everyone! So you can designate the addressee to which the action of the hormone is directed. The gland that produces the hormone does not produce it for any particular organ, but for the whole organism. However, some organs are more sensitive to the action of the hormone, while others are less. Therefore, some hormones predominantly act on some organs, while others – on others. But still, the main purpose of hormones is to influence the entire body, on various aspects of its activity: on growth, sexual activity, carbohydrate or fat metabolism, and muscle work.

If hormones can affect the functioning of various organs, then the endocrine glands themselves can also fall under their influence. Some endocrine glands can affect others. For example, the pituitary affects the gonads, the underdevelopment of the pituitary gland entails the underdevelopment of the gonads. Therefore, pituitary dwarfs, even in adulthood, are devoid of mustaches and beards and speak in a high-pitched childish voice.

The endocrine glands work together. Sugar metabolism is affected, for example, by the pancreas and adrenal glands, insulin promotes the accumulation of glycogen in the liver, and adrenaline, on the contrary, causes the breakdown of glycogen. Their joint activity carefully regulates the content of glycogen in the liver and the amount of sugar in the blood.

If the activity of any gland of internal secretion is disturbed, this will immediately affect the other glands. The normal life of the body is possible only if all the glands act together, in an organized manner.

The organizing principle, the regulator of the joint activity of all glands is the nervous system. Each gland has nerves. They are sent to the glands from the nerve centers of the brain and spinal cord.