14.1: Structures of the Endocrine System

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The endocrine system consists of cells, tissues, and organs that secrete hormones as a primary or secondary function. The endocrine gland is the major player in this system. The primary function of these ductless glands is to secrete their hormones directly into the surrounding fluid. The interstitial fluid and the blood vessels then transport the hormones throughout the body. The endocrine system includes the pituitary, thyroid, parathyroid, adrenal, and pineal glands (Figure \(\PageIndex{1}\)). Some of these glands have both endocrine and non-endocrine functions. For example, the pancreas contains cells that function in digestion as well as cells that secrete the hormones insulin and glucagon, which regulate blood glucose levels. The hypothalamus, thymus, heart, kidneys, stomach, small intestine, liver, skin, female ovaries, and male testes are other organs that contain cells with endocrine function. Moreover, adipose tissue has long been known to produce hormones, and recent research has revealed that even bone tissue has endocrine functions.

Figure \(\PageIndex{1}\): Endocrine System Endocrine glands and cells are located throughout the body and play an important role in homeostasis

The ductless endocrine glands are not to be confused with the body’s exocrine system, whose glands release their secretions through ducts. Examples of exocrine glands include the sebaceous and sweat glands of the skin. As just noted, the pancreas also has an exocrine function: most of its cells secrete pancreatic juice through the pancreatic and accessory ducts to the lumen of the small intestine

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Endocrine System – Definition, Function & Parts

Definition

The endocrine system is a collection of ductless glands that produce hormones and secrete them into the circulatory system. Endocrine glands work without ducts for carrying secretions towards target organs. Instead, hormones can act as chemical messengers for a large number of cells and tissues simultaneously.

Overview

The endocrine system consists of many glands, which work by secreting hormones into the bloodstream to be carried to a target cell. Endocrine system hormones work even if the target cells are distant from the endocrine glands. Through these actions, the endocrine system regulates nearly every metabolic activity of the body to produce an integrated response. The endocrine system can release hormones to induce the stress response, regulate the heartbeat or blood pressure, and generally directs how your cells grow and develop.

Endocrine glands are usually heavily vascularized, containing a dense network of blood vessels. Cells within these organs produce and contain hormones in intracellular granules or vesicles that fuse with the plasma membrane in response to the appropriate signal. This action releases the hormones into the extracellular space, or into the bloodstream. The endocrine system can be activated by many different inputs, allowing for responses to many different internal and external stimuli.

Endocrine System Function

The endocrine system, along with the nervous system, integrates the signals from different parts of the body and the environment. In addition, the endocrine system produces effector molecules in the form of hormones that can elicit an appropriate response from the body in order to maintain homeostasis. The nervous system produces immediate effects. The endocrine system is designed to be relatively slow to initiate, but it has a prolonged effect.

As an example, the long-term secretion of growth hormone in the body influences the development of bones and muscles to increase height and also induces the growth of every internal organ. This happens over the course of many years. Hormones like cortisol, produced during times of stress, can change appetite, and metabolic pathways in skeletal and smooth muscle for hours or weeks.

The endocrine system is involved in every process of the human body. Starting from the motility of the digestive system, to the absorption and metabolism of glucose and other minerals, hormones can affect a variety of organs in different ways. Some hormones affect the retention of calcium in bones or their usage to power muscle contraction. In addition, they are involved in the development and maturation of the adaptive immune system, and the reproductive system. Crucially, they can affect overall growth and metabolism, changing the way every cell assimilates and utilizes key nutrients.

Endocrine System Parts

The endocrine system consists of a number of organs – some of which have hormone production as their primary function, while others play important roles in other organ systems as well. These include the pituitary and pineal glands in the brain, the thyroid and parathyroid glands in the neck, the thymus in the thoracic region, the adrenals and pancreas in the abdominal region and the gonads in the reproductive system.

Endocrine System Diagram

Endocrine System in the Brain

Starting from the brain, the hypothalamus, pituitary and pineal glands are involved in the regulation of other endocrine organs and in the regulation of circadian rhythms, changing the metabolic state of the body. The pineal gland is located near the center of the brain, in a region called the epithalamus. The pituitary gland is seen very near the hypothalamus and has some direct interactions and feedback loops with the organ for the production of hormones.

Together, the hypothalamus and pituitary can regulate a number of endocrine organs, particularly the gonads, and the adrenals. In fact, the hypothalamus can be considered as the nodal point that integrates two major pathways for regulation – the nervous and endocrine systems. It is made of a collection of neurons that collect information from the body through the nervous system and integrate it into a response through the endocrine system, especially the anterior and posterior parts of the pituitary gland.

Endocrine System within the Neck

The neck contains the thyroid and parathyroid glands. The thyroid gland consists of two symmetric lobes connected by a narrow strip of tissue called the isthmus glandularis, forming a butterfly-like structure. Each lobe is about 5cm in height, and the isthmus is approximately 1.25 cm in length. The gland is situated in the front of the neck, behind the thyroid cartilage. Each lobe of the thyroid gland is usually positioned in front of a pair of parathyroid glands. Each of the four parathyroid glands is approximately 6x3x1 mm in size, and weighs between 30 and 35 gms. There can be some variation in the number of parathyroid glands among individuals, with some people having more than 2 pairs of glands.

Endocrine System within the Body

The thymus is an endocrine organ situated behind the sternum (also known as the breastbone), between the two lungs. It is pinkish-gray in color and consists of two lobes. Its endocrine function complements its role in the immune system, being used for the development and maturation of thymus-derived lymphocytes (T-cells). This organ is unusual because of its activity peaks during childhood. After adolescence, it slowly shrinks and gets replaced by fat. At its largest, before the onset of puberty, it can weigh nearly 30 gms.

The adrenals are placed above the kidney and therefore also known as suprarenal glands. They are yellowish in color and surrounded by a capsule of fat. They can be seen just under the diaphragm and are connected to that muscular organ by a layer of connective tissue. The adrenal glands consist of an outer medulla and an inner cortex, having distinct secretions and roles within the body.

The pancreas plays a dual role, being an integral and important part of both the digestive and endocrine systems. The glandular organ located close to the C-shaped bend of the duodenum, and it can be seen behind the stomach. It contains cells with an exocrine function that produce digestive enzymes as well as endocrine cells in the islets of Langerhans that produce insulin and glucagon. The hormones play a role in the metabolism and storage of blood glucose and thus the two different functions of the organ are integrated at a certain level.

The gonads also have important endocrine functions that influence the proper development of reproductive organs, the onset of puberty, and maintenance of fertility. Other organs such as the heart, kidney, and liver also act as secondary endocrine organs, secreting hormones like erythropoietin that can affect red blood cell production.

Endocrine System Structure

Unlike some body systems, the endocrine system is widely distributed within the body. Further, unlike some systems, the parts of the endocrine system can function independently from one another to regulate and coordinate the body. For example, the pineal gland in the brain responds to light received in the eyes, which causes it to release the hormone melatonin. This action can be completely separate from the actions of the reproductive endocrine glands, which are responding to a different set of signals to enable a different outcome.

However, some glands like the thyroid and hypothalamus also control other glands and their functions. These glands can help to coordinate the overall actions of the system and the body as a whole. A release of hormones from these glands can create a cascade of effects from the release of a single hormone. This makes the endocrine system one of the most complexly structured body systems.

Diseases of the Endocrine System

Endocrine system diseases primarily arise from two causes – either a change in the level of hormone secreted by a gland, or a change in the sensitivity of the receptors in various cells of the body. Therefore, the body fails to respond in an appropriate manner to messenger signals. Among the most common endocrine diseases is diabetes, which hampers the metabolism of glucose. This has an enormous impact on the quality of life since adequate glucose is not only important for fueling the body, but it is also important in maintaining glucose at an appropriate level to discourages the growth of microorganisms or cancerous cells.

Imbalances of hormones from the reproductive system are also significant since they can influence fertility, mood, and wellbeing. Another important endocrine gland is the thyroid, with both high and low levels of secretion affecting a person’s capacity to function optimally, even affecting fertility in women. The thyroid also needs a crucial micronutrient, iodine, in order to produce its hormone. Dietary deficiency of this mineral can lead to an enlargement of the thyroid gland as the body tries to compensate for low levels of thyroid hormones.

Diabetes

Diabetes, or diabetes mellitus, refers to a metabolic disease where the blood consistently carries a high concentration of glucose. This is traced back to the lack of effective insulin hormone, produced by the pancreas, or a lack of functioning hormone receptors. Diabetes mellitus could either arise from a low level of insulin production from the pancreas or an insensitivity of insulin receptors among the cells of the body. Occasionally, pregnant women with no previous history of diabetes develop high blood sugar levels. This can threaten the health of the mother and fetus, as well as increase all the risks associated with childbirth.

Insulin is an anabolic hormone that encourages the transport of glucose from the blood into muscle cells or adipose tissue. Here, it can be stored as long chains of glycogen, or be converted into fat. Concurrently it also inhibits the process of glucose synthesis within cells, by interrupting gluconeogenesis, as well as the breakdown of glycogen. A spike in blood sugar levels causes the release of insulin. Its release protects cells from the long-term damage of excess glucose, while also allowing the precious nutrient to be stored and utilized later. Glucagon, another hormone secreted by the pancreas (alpha cells), acts in an antagonistic manner to insulin and is secreted when blood sugar levels drop.

Hypothyroidism

Hypothyroidism is a condition where the body has an insufficient supply of thyroid hormones – thyroxine (T4) and triiodothyronine (T3). Both these hormones contain iodine and are derived from a single amino acid – tyrosine. Iodine deficiency is a common cause for hypothyroidism since the gland is unable to synthesize adequate amounts of hormone. This can arise due to damage to the cells of the thyroid gland through infection or inflammation, or medical interventions for excessive thyroid activity. It can also arise from a deficiency in the pituitary hormone that stimulates the thyroid. Alternatively, it could be due to defects in the receptors for the hormone. Thyroxine is the more common hormone in the blood and has a longer half-life than T3.

Hypogonadism

Hypogonadism refers to a spectrum of disorders where there is an insufficiency of sex hormones. These are usually secreted by the primary gonads (testes and ovaries) and affect the development, maturation, and functioning of sex organs and the appearance of secondary sexual characteristics. It can arise due to a low level of sex hormone production by the gonads itself, or the insensitivity of these organs to cues from the brain for hormone production. The first condition is called primary hypogonadism and the latter is called central hypogonadism.

Depending on the period of onset, hypogonadism can result in different characteristics. Hypogonadism during development can cause ambiguous genitalia. During puberty, it can affect the onset of menstruation, breast development and ovulation in females, delay the growth of the penis and testicles, and affect the development of secondary sexual characteristics. It can also impact self-esteem and confidence. In adulthood, hypogonadism leads to reduced sex drive, infertility, fatigue or even loss in bone and muscle mass.

Quiz

1. Which of these organs secretes glucagon?

A.Pancreas

B.Pituitary

C.Hypothalamus

D.Adrenal Glands

2. Which of these endocrine glands situated in the brain interacts closely with the hypothalamus?

A. Pineal

B.Thyroid

C.Pituitary

D.Thymus

3. Which of these endocrine disorders can specifically affect women during the course of pregnancy?

A.Hypogonadism

B.Diabetes

C.Thymus gland development

D.None of the Above

4. Which area of the body DOES NOT have an endocrine gland?

A.The brain

B.The neck

C.The gonads

D.None of the above.

5. What is the role of the pancreas within the endocrine system?

A.To produce digestive enzymes.

B.To produce hormones like insulin and glucagon.

C.Neither of these functions

Endocrine glands – structure, functions, pathologies

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4. Endocrine glands

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Endocrine glands or endocrine glands do not have excretory ducts and release synthesized hormones into the blood that washes them. They play an important role in:

• maintaining the internal environment of the body;
• participation in exchange processes;
• regulation of growth, mental and physical development.

The endocrine system closely interacts with the central nervous system and together with it regulates body functions.

The connecting link between the endocrine and nervous systems is the hypothalamus – both a nerve formation and an endocrine gland. He is the highest center of the endocrine system, the head of the endocrine glands, and he weighs only 4 g.

Endocrine glands also include 0007 Pituitary gland

I. Pituitary – the cerebral appendage, along with the hypothalamus, is the central endocrine organ, the rest of the glands are peripheral. The pituitary gland weighs only 0.5 – 0.7 g, but its role in the body is extremely important and diverse. It consists of three parts – anterior, middle, posterior, has a rounded shape, is located at the base of the brain.

II. The thyroid gland has an interesting butterfly shape, it secretes 2 types of hormones into the blood:

• Thyroid (tetraiodothyronine and triiodothyronine), necessary to ensure all types of metabolism and for the functioning of all organs and tissues without exception.
• Calcitonin – regulates calcium metabolism in the body.

III. Parathyroid glands (parathyroid) – located on the back surface of the thyroid gland. Their number can vary up to 12, but on average a person has 2 pairs.

These glands synthesize parathyroid hormone into the blood. Its role is to maintain calcium metabolism, along with calcitonin, but their effect on this type of metabolism is opposite.

IV. Thymus is very important in maintaining human immunity. Its size, and, accordingly, activity is highest in childhood. After the onset of puberty, it gradually atrophies. This may explain the fact that older people have reduced immunity.

V. Adrenal glands located above the upper pole of the kidneys, consist of two parts, different in function.

VI. Pancreas has cells that secrete very important hormones – insulin and glucagon. They regulate carbohydrate metabolism.

Sex glands The ovaries and testes produce sex hormones – male (androgens) and female (estrogens). In men, the former predominate, in women the latter.

They are responsible for the formation of sex, sexual characteristics, provide puberty and also sexual behavior of a person.

In women, they ensure the normal course of the menstrual cycle, pregnancy, preparation for breastfeeding.

As you have already seen, the endocrine glands are the most important regulatory organs that guard your body, your excellent mood!

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Endocrine ⭐️ system and glands of internal, external secretion: their functions and structure

What is the endocrine system

There are three types of glands in the human body :

1. Endocrine glands: hypothalamus, pituitary, epiphysis, thyroid and parathyroid glands, adrenal glands, thymus. These glands do not have outward ducts. They secrete hormones that circulate throughout the body.
2. Exocrine glands: sweat, lacrimal, salivary and milk. They secrete the secret out and make up the exocrine system.
3. Glands of mixed secretion. These include the pancreas and thymus, as well as the testes and ovaries. Their difference is that part of the cells secrete hormones, and part is a secret that enters the organs or the external environment.

The endocrine system consists of glands of internal and mixed secretion.

Definition 1

Hormones – are physiologically active substances that are produced by the endocrine glands.

In addition, hormones are found in special cells of the heart, intestines, stomach, kidneys and other organs.

How the human endocrine system works

The main role in the regulation of the endocrine glands in the hypothalamus.

Definition 2

Hypothalamus is the lower part of the diencephalon responsible for the neuroendocrine regulation of the body’s activity. It determines the overall work of the endocrine glands and the nervous system.

First, external or internal stimuli act on the receptors. The impulses are then sent to the hypothalamus. It produces releasing hormones that stimulate or suppress the work of another part of the brain – pituitary gland .

Such interaction of two parts of the brain form the hypothalamic-pituitary system .

Next, the pituitary gland synthesizes hormones, which are delivered to other GIs with the bloodstream. There specific hormones are produced. They go to target organs.

Endocrine system: structure and functions

The endocrine system is a glandular and diffuse apparatus.

1. Glandular system are formed glands that have a clear localization and structure. These organs produce thyroid, steroid, and some peptide hormones.
2. Diffuse system – a collection of individual endocrine cells that are distributed throughout the body. They synthesize the so-called glandular hormones.

The endocrine system consists of a central and a peripheral section.

Source: Kemerovograd.rf

Central Department

Hypothalamus. Produces liberins and statins. Regulates the pituitary gland, and also controls the cycles of sleep and wakefulness, appetite, body temperature.

Pituitary gland. Synthesizes tropic hormones, vasopressin, growth hormone. Regulates the work of the ZhVS, the processes of growth and reproduction, is responsible for metabolism.

Pineal gland or pineal gland. Releases serotonin and melatonin. It is also called the “third eye”. The functional significance of this part of the brain is not well understood. It is known that the pineal gland controls the biological rhythm, including the frequency of sleep and fluctuations in body temperature.

Peripheral

Thyroid. Produces thyroxine and triiodothyronine, calcitonin. Regulates metabolism, growth and development of the body.

Parathyroid glands. These are four small glands that produce parathyroid hormone and are responsible for the calcium status of the body, that is, they directly provide for the full development of the body, regulate the activity of the nervous and motor systems.

Adrenal glands. They secrete adrenaline and norepinephrine, cortisone, aldosterone. A pair of glands influence the growth and development of the body, are a reactor for stress, metabolism, and blood pressure.

Pancreas. With the help of insulin and glucagon controls blood sugar levels, regulates carbohydrate metabolism.

Thymus (thymus). Synthesizes thymulin, thymopoietin. Affects carbohydrate and calcium metabolism. Regulates the growth of the skeleton, is involved in the work of the immune system.

Testes. The male gonads secrete androgens and are responsible for spermatogenesis and the development of the body according to the male type.

Ovaries. With the help of estrogens, they influence the primary and secondary female sexual characteristics, regulate the menstrual cycle.

Placenta. A temporary organ that forms during pregnancy. Placental lactogen determines the course of pregnancy and fetal development.

The endocrine glands and the hormones they synthesize are one. Violation of the endocrine system seriously affects the functioning of the whole organism. Hyperfunction 9 is said to increase in the secretion of fatty acids0023 , in case of weakening – about hypofunction .

Example : with insufficient work of the pituitary gland, dwarfism develops, and with its hyperfunction, gigantism. With hypofunction of the pancreas, diabetes mellitus develops. And with hyperfunction, the general condition of the body is disturbed, dizziness, weakness appear. Possible loss of consciousness. To avoid such problems, you need to minimize sweet and starchy foods in your diet, remove simple carbohydrates.

Functions of the endocrine system

Humoral regulation . ZhVS regulate the processes of vital activity with the help of hormones through the liquid media of the body: blood, lymph, tissue fluid.

Humoral function is closely related to nervous regulation, which, in turn, is performed by the nervous system. The activity of the latter is affected by chemicals that come with the blood. Here, the reverse reaction occurs – under the control of the nervous system, chemicals are released and transported through the blood. This mutual process is called neurohumoral regulation of organisms.

Humoral regulation also helps to carry out other functions:

• maintenance of homeostasis (constancy) and adaptation of the body to changing environmental conditions;
• regulation of body growth and development;
• sexual differentiation and reproductive activity;
• regulation of metabolism and energy;
• participation in emotional reactions and mental activity of a person.