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Endocrine system. The human endocrine system in general and the thyroid gland in particular

The endocrine system is the most important regulatory-integrating, guiding system of the internal organs of each of us.

Organs with endocrine function

These include:

and hypothalamus. These endocrine glands are located in the brain. The most important centralized signals come from them.
Thyroid. This is a small organ that is located on the front of the neck in the shape of a butterfly.
Thymus. Here, at a certain point, people's immune cells undergo training.
The pancreas is located under and behind the stomach. Its endocrine function is the production of the hormones insulin and glucagon.
Adrenal glands. These are two cone-shaped glands on the kidneys.
Sex glands are male and female.

There is a relationship between all these glands:

If commands are received from the hypothalamus and pituitary gland, which function in the endocrine system, then feedback signals are received from all other organs of this structure.
All endocrine glands will suffer if the function of any of these organs is impaired.
For example, with increased or impaired functioning of other internal secretion organs.
human being is very complex. It regulates all structures of the human body.

Importance of the endocrine system

Endocrine glands produce hormones. These are proteins containing various amino acids. If the diet has enough of these nutrients, the required amount of hormones will be produced. If they are deficient, the body produces insufficient substances that regulate the functioning of the body.

Pituitary gland and hypothalamus:

These endocrine glands direct the work of all organs that synthesize biologically active substances.
Thyroid-stimulating hormone of the pituitary gland regulates the synthesis of biologically active substances of the thyroid gland.
If this organ is active, the level of thyroid hormone in the body is reduced.
When the thyroid gland is not working well, the level.

The adrenal glands are a paired gland that helps a person cope with stress.

Thyroid:

It uses tyrosine, a non-essential amino acid. Based on this substance and iodine, the thyroid gland produces hormones:,.
Its main function is energy metabolism. It stimulates synthesis, energy production, and its absorption by cells.
If the function of the thyroid gland is increased, then there will be too much of its hormones in the body.
If the thyroid gland works in a reduced mode, it develops, and there are not enough hormones in the body.
The thyroid gland is responsible for metabolism - proper energy exchange in the body. Therefore, all processes that occur in the thyroid gland affect metabolic processes.

The nature of the reaction to stress is determined by the work of the adrenal glands

This paired gland produces hormones.

Adrenalin:

It provides a reaction to sudden severe stress and causes fear.
This hormone constricts peripheral blood vessels, expanding deep tube-like formations inside the muscles. This improves blood circulation.
The body is ready for active action in a stressful situation in order to escape.
This reaction manifests itself in the appearance of heavy sweating, tears, urination, and the desire to escape.

Norepinephrine:

It evokes courage and rage.
Its level increases with injury, fear, shock.

Cortisol:

It regulates people's experiences of chronic stress.
The hormone provokes cravings for unhealthy foods.
Proteins in the body are broken down under its influence.

If a person is under chronic stress:

Adrenal exhaustion occurs. This manifests itself as asthenic syndrome.
A person wants to do something, but cannot.
Mental activity decreases.
The person is distracted and finds it difficult to concentrate.
Allergies to cold, sun, and other allergens occur.
Sleep is disturbed.

To restore adrenal function:

You need to actively relax, go fishing, go to the gym.
Vitamin C in a dosage of 1000 mg helps restore the activity of the gland.
Taking bee pollen, which contains all amino acids, eliminates loss of strength.

Pancreas

Produces beta cells that synthesize the hormones glucagon and insulin:

This is a protein whose structure contains zinc and chromium. If there is a deficiency of these microelements, diseases occur.
Human energy is provided by the presence of glucose and oxygen in tissue cells.
If there is enough insulin in the body, then glucose from the blood enters the cells. Ensures normal metabolism in the body. It will perform all its functions.
If there is a lot of glucose in the blood and the cells are starving, this is a sign of a disorder in the pancreas.
When insulin production is impaired, type 1 diabetes develops. If this hormone is not absorbed, type 2 diabetes occurs.

Conditions necessary for the normal functioning of the endocrine glands:

No chronic intoxication.
Adequate blood circulation in the body. Good blood circulation in the cerebral vascular system is especially important.
Balanced diet, essential vitamins and microelements.

Factors that adversely affect the condition of the endocrine glands

Toxins. The human endocrine system is most sensitive to the effects of various toxins on the body.
State of chronic stress. Endocrine organs are very sensitive to such situations.
Poor nutrition. Junk food with synthetic preservatives, trans fats, dangerous food additives. Deficiency of basic vitamins and microelements.
Harmful drinks. Taking tonic drinks, as they contain a lot of caffeine and toxic substances. They have a very negative effect on the adrenal glands, deplete the central nervous system, and shorten its life.
Aggression of viruses, fungi, protozoa. They provide a total toxic load. The greatest harm to the body is caused by staphylococci, streptococci, herpes virus, cytomegalovirus, and candida.
Lack of physical activity. This is fraught with circulatory problems.
Medicines. Antibiotics, non-steroidal anti-inflammatory drugs: Indomethacin, Nise and others. Children overfed with antibiotics in childhood have problems with the thyroid gland.
Bad habits.

This diagram shows the influence of the proper functioning of the human endocrine system on the functions of various organs

Thyroid

Kidneys and adrenal glands

Pancreas

Testicles

Foot office

The endocrine system plays a very important role in the human body. It is responsible for the growth and development of mental abilities and controls the functioning of organs. Endocrine glands produce various chemicals called hormones. Hormones have a huge impact on mental and physical development, growth, changes in the structure of the body and its functions, and determine gender differences.

The main organs of the endocrine system are:

thyroid and thymus glands;
pineal gland and pituitary gland;
adrenal glands; pancreas;
testes in men and ovaries in women.

Age-related features of the endocrine system

The hormonal system in adults and children does not work the same. The formation of glands and their functioning begins during intrauterine development. The endocrine system is responsible for the growth of the embryo and fetus. During the formation of the body, connections are formed between the glands. After the birth of a child, they become stronger.

From the moment of birth until the onset of puberty, the thyroid gland, pituitary gland, and adrenal glands are of greatest importance. During puberty, the role of sex hormones increases. During the period from 10-12 to 15-17 years, many glands are activated. In the future, their work will stabilize. If you follow a correct lifestyle and are free from illness, there are no significant disruptions in the functioning of the endocrine system. The only exception is sex hormones.

Pituitary

The pituitary gland plays the most important role in human development. It is responsible for the functioning of the thyroid gland, adrenal glands and other peripheral parts of the system.

The main function of the pituitary gland is considered to control body growth. It is performed through the production of growth hormone (somatotropic). The gland significantly influences the functions and role of the endocrine system, therefore, if it does not work properly, the production of hormones by the thyroid gland and adrenal glands is carried out incorrectly.

Pineal gland

The pineal gland is a gland that functions most actively until primary school age (7 years). The gland produces hormones that inhibit sexual development. By the age of 3-7 years, the activity of the pineal gland decreases. During puberty, the number of hormones produced decreases significantly.

Thyroid

Another important gland in the human body is the thyroid. It begins to develop one of the first in the endocrine system. The greatest activity of this part of the endocrine system is observed at 5-7 and 13-14 years of age.

Parathyroid glands

The parathyroid glands begin to form at 2 months of pregnancy (5-6 weeks). The greatest activity of the parathyroid gland is observed in the first 2 years of life. Then, until the age of 7, it is maintained at a fairly high level.

Thymus

The thymus gland or thymus is most active during puberty (13-15 years). Her absolute weight begins to increase from the moment of birth, and the relative weight decreases; from the moment the growth of the iron stops, it does not function. It is also important during the development of immune bodies. And to this day it has not been determined whether the thymus gland can produce any hormone. The correct size of this gland can vary in all children, even those of the same age. During exhaustion and illness, the mass of the thymus gland rapidly decreases. With increased demands on the body and during increased secretion of sugar hormone from the adrenal cortex, the volume of the gland decreases.

Adrenal glands

Adrenal glands. The formation of glands occurs up to 25-30 years. The greatest activity and growth of the adrenal glands is observed in 1-3 years, as well as during puberty. Thanks to the hormones that the gland produces, a person can control stress. They also affect the process of cell restoration, regulate metabolism, sexual and other functions.

Pancreas

Pancreas. The development of the pancreas occurs before age 12. This gland, together with the gonads, belongs to the mixed glands, which are organs of both external and internal secretion. In the pancreas, hormones are produced in the so-called islets of Langerhans.

Female and male gonads

Female and male gonads are formed during intrauterine development. However, after the birth of a child, their activity is restrained until 10-12 years, that is, until the onset of the puberty crisis.

The male gonads are the testes. From the age of 12-13, the gland begins to work more actively under the influence of gonadoliberin. In boys, growth accelerates and secondary sexual characteristics appear. At the age of 15, spermatogenesis is activated. By the age of 16-17, the process of development of the male gonads is completed, and they begin to work in the same way as in an adult.

The female reproductive glands are the ovaries. The development of the gonads occurs in 3 stages. From birth to 6-7 years, a neutral stage is observed.

During this period, the female-type hypothalamus is formed. The pre-pubertal period lasts from 8 years to the onset of adolescence. From the first menstruation, puberty is observed. At this stage, active growth occurs, the development of secondary sexual characteristics, and the formation of the menstrual cycle.

The endocrine system in children is more active compared to adults. The main changes in the glands occur at an early age, junior and senior school age.

Functions of the endocrine system

takes part in the humoral (chemical) regulation of body functions and coordinates the activities of all organs and systems.
ensures the preservation of homeostasis of the body under changing environmental conditions.
together with the nervous and immune systems, it regulates the growth, development of the body, its sexual differentiation and reproductive function.
takes part in the processes of formation, use and conservation of energy.

Together with the nervous system, hormones take part in providing emotional reactions to human mental activity.

Endocrine diseases

Endocrine diseases are a class of diseases that result from a disorder of one or more endocrine glands. Endocrine diseases are based on hyperfunction, hypofunction or dysfunction of the endocrine glands.

Why do you need a pediatric endocrinologist?

The specificity of a pediatric endocrinologist is to monitor the correct formation of a growing organism. This direction has its own subtleties, which is why it was isolated.

Parathyroid glands

Parathyroid glands. Responsible for the distribution of calcium in the body. It is necessary for bone formation, muscle contraction, heart function and transmission of nerve impulses. Both deficiency and excess lead to serious consequences. You should consult a doctor if you experience:

Muscle cramps;
Tingling in the limbs or spasms;
Bone fracture from a slight fall;
Poor dental condition, hair loss, split nails;
Frequent urination;
Weakness and fatigue.

Long-term lack of hormones in children leads to delayed development, both physical and mental. The child does not remember what he has learned well, is irritable, prone to apathy, and complains.

Thyroid

The thyroid gland produces hormones that are responsible for metabolism in the cells of the body. Disruption of its functioning affects all organ systems. You should consult a doctor if:

There are clear signs of obesity or extreme thinness;
Weight gain even with a small amount of food consumed (and vice versa);
The child refuses to wear clothes with a high neck, complaining of a feeling of pressure;
Swelling of the eyelids, bulging eyes;
Frequent coughing and swelling in the goiter area;
Hyperactivity gives way to severe fatigue;
Drowsiness, weakness.

Adrenal glands

The adrenal glands produce three types of hormones. The former are responsible for the water-salt balance in the body, the latter for the metabolism of fats, proteins and carbohydrates, and the third for the formation and functioning of muscles. You should consult a doctor if your child has:

Craving for salty foods;
Poor appetite is accompanied by weight loss;
Frequent nausea, vomiting, abdominal pain;
Low blood pressure;
Pulse is below normal;
Complaints of dizziness, fainting;

The baby's skin is golden brown, especially in places that are almost always white (elbows, knee joints, scrotum and penis, around the nipples).

Pancreas

The pancreas is an important organ primarily responsible for digestive processes. It also regulates carbohydrate metabolism with the help of insulin. Diseases of this organ are called pancreatitis and diabetes mellitus. Signs of acute inflammation of the pancreas and reasons for calling an ambulance:

Sharp pain in the abdomen (sometimes girdling);
The attack lasts several hours;
Vomit;
Sitting and bending forward, the pain subsides.

You need to recognize the onset of diabetes and visit a doctor when your child has:

Constant thirst;
He often wants to eat, but in a short time he has lost a lot of weight;
Urinary incontinence appeared during sleep;
The child is often irritated and begins to study poorly;
Skin lesions (boils, styes, severe diaper rash) appeared frequently and did not go away for a long time.

Thymus

The thymus gland is a very important organ of the immune system, which protects the body from infections of various etiologies. If your child is often sick, visit a pediatric endocrinologist; the cause may be an enlarged thymus gland. The doctor will prescribe maintenance therapy and the frequency of diseases can be reduced.

Testicles and ovaries

Testicles and ovaries are glands that produce sex hormones according to the gender of the child. They are responsible for the formation of the genital organs and the appearance of secondary symptoms. It is necessary to visit a doctor if you experience:

Absence of testicles (even one) in the scrotum at any age;
The appearance of secondary sexual characteristics before 8 years of age and their absence by 13 years of age;
After a year, the menstrual cycle had not improved;
Hair growth in girls on the face, chest, and midline of the abdomen and its absence in boys;
The boy's mammary glands swell, his voice does not change;
Abundance of acne.

Hypothalamic-pituitary system

The hypothalamic-pituitary system regulates the secretion of all glands in the body, so a malfunction in its functioning can cause any of the above symptoms. But in addition to this, the pituitary gland produces a hormone responsible for growth. You should consult a doctor if:

The child’s height is significantly lower or higher than that of his peers;
Late change of primary teeth;
Children under 4 years old do not grow more than 5 cm, after 4 years - more than 3 cm per year;
In children over 9 years of age, there is a sharp jump in growth, and further growth is accompanied by pain in the bones and joints.

If you are short in stature, you need to carefully monitor its dynamics, and visit an endocrinologist if all relatives are above average height. Hormone deficiency at an early age leads to dwarfism, excess leads to gigantism.

The work of the endocrine glands is very closely related, and the appearance of pathologies in one leads to the malfunction of another or several. Therefore, it is important to promptly recognize diseases associated with the endocrine system, especially in children. Improper functioning of the glands will have an impact on the formation of the body, which can have irreversible consequences if treatment is delayed. If children have no symptoms, there is no need to visit an endocrinologist.

High-quality prevention

To maintain the health of the endocrine glands, and even better, regularly take preventive measures, first of all, you need to pay attention to your daily diet. The lack of vitamin and mineral components directly affects the well-being and functioning of all body systems.

Iodine value

The thyroid gland is the storage center for such an important element as iodine. Preventive measures include sufficient iodine in the body. Since in many populated areas there is a clear deficiency of this element, it should be used as a preventive measure against disorders of the endocrine glands.

For quite a long time, iodine deficiency has been compensated for by iodized salt. Today it is successfully added to bread and milk, which helps eliminate iodine deficiency. These may also be special medications with iodine or food supplements. Many products contain a large amount of useful substances, including seaweed and various seafood, tomatoes, spinach, kiwi, persimmon, and dried fruits. By eating a little healthy food every day, iodine reserves are gradually replenished.

Activity and exercise

In order for the body to receive minimal stress during the day, you only need to spend 15 minutes in motion. Regular morning exercises will give a person a boost of vigor and positive emotions. If it is not possible to do sports or fitness in the gym, you can organize walking walks from work to home. Walking in the fresh air will help strengthen your immune system and prevent many diseases.

Nutrition for disease prevention

Too fatty, spicy foods and baked goods have never made anyone healthier, so it’s worth reducing their consumption to a minimum. All foods that increase cholesterol levels in human blood should be excluded to prevent diseases of the endocrine and other systems. It is better to cook dishes by steaming or baking; you need to avoid smoked and salty dishes and semi-finished products. Excessive consumption of chips, sauces, fast food, and sweet carbonated drinks is hazardous to health. It is better to replace them with various nuts and berries, for example, gooseberries, which contain essential manganese, cobalt and other elements. To prevent many diseases, it is better to add porridge, more fresh fruits and vegetables, fish, and poultry to your daily diet. Also, do not forget about the drinking regime and drink about two liters of clean water, not counting juices and other liquids.

Hormones are substances produced by the endocrine glands and released into the blood, their mechanism of action. The endocrine system is a collection of endocrine glands that produce hormones. Sex hormones.

For normal life, a person needs many substances that come from the external environment (food, air, water) or are synthesized inside the body. With a lack of these substances in the body, various disorders occur that can lead to serious diseases. These substances synthesized by endocrine glands inside the body include hormones .

First of all, it should be noted that humans and animals have two types of glands. Glands of one type - lacrimal, salivary, sweat and others - secrete the secret outward and are called exocrine (from the Greek exo- out, outside, krino– highlight). The glands of the second type release the substances synthesized in them into the blood that washes them. These glands were called endocrine (from the Greek endon- inside), and substances released into the blood are hormones.

Thus, hormones (from the Greek hormaino– set in motion, induce) – biologically active substances produced by endocrine glands (see Figure 1.5.15) or special cells in tissues. Such cells can be found in the heart, stomach, intestines, salivary glands, kidneys, liver and other organs. Hormones are released into the bloodstream and have an effect on cells of target organs located at a distance or directly at the site of their formation (local hormones).

Hormones are produced in small quantities, but remain active for a long time and are distributed throughout the body through the bloodstream. The main functions of hormones are:

– maintaining the internal environment of the body;

– participation in metabolic processes;

– regulation of growth and development of the body.

A complete list of hormones and their functions are presented in Table 1.5.2.

Table 1.5.2. Basic hormones

Hormone	Which gland produces	Function
Adrenocorticotropic hormone	Pituitary	Controls the secretion of hormones from the adrenal cortex
Aldosterone	Adrenal glands	Participates in the regulation of water-salt metabolism: retains sodium and water, removes potassium
Vasopressin (antidiuretic hormone)	Pituitary	Regulates the amount of urine excreted and, together with aldosterone, controls blood pressure
Glucagon	Pancreas	Increases blood glucose levels
A growth hormone	Pituitary	Manages the processes of growth and development; stimulates protein synthesis
Insulin	Pancreas	Lowers blood glucose levels; affects the metabolism of carbohydrates, proteins and fats in the body
Corticosteroids	Adrenal glands	Have an effect on the entire body; have pronounced anti-inflammatory properties; maintain blood sugar levels, blood pressure and muscle tone; participate in the regulation of water-salt metabolism
Luteinizing hormone and follicle stimulating hormone	Pituitary	Control reproductive functions, including sperm production in men, egg maturation and the menstrual cycle in women; responsible for the formation of male and female secondary sexual characteristics (distribution of areas of hair growth, volume of muscle mass, structure and thickness of skin, timbre of voice and, possibly, even personality traits)
Oxytocin	Pituitary	Causes contraction of the muscles of the uterus and mammary ducts
Parathyroid hormone	Parathyroid glands	Controls bone formation and regulates the excretion of calcium and phosphorus in urine
Progesterone	Ovaries	Prepares the inner lining of the uterus for the implantation of a fertilized egg, and the mammary glands for milk production
Prolactin	Pituitary	Induces and maintains milk production in the mammary glands
Renin and angiotensin	Kidneys	Control blood pressure
Thyroid hormones	Thyroid	Regulate the processes of growth and maturation, the speed of metabolic processes in the body
Thyroid-stimulating hormone	Pituitary	Stimulates the production and secretion of thyroid hormones
Erythropoietin	Kidneys	Stimulates the formation of red blood cells
Estrogens	Ovaries	Control the development of female genital organs and secondary sexual characteristics

The structure of the endocrine system. Figure 1.5.15 shows the glands that produce hormones: hypothalamus, pituitary gland, thyroid gland, parathyroid glands, adrenal glands, pancreas, ovaries (in women) and testes (in men). All glands and cells that secrete hormones are combined into the endocrine system.

The link between the endocrine and nervous systems is the hypothalamus, which is both a nerve formation and an endocrine gland.

It controls and combines endocrine regulatory mechanisms with nervous ones, being also the brain center autonomic nervous system . The hypothalamus contains neurons capable of producing special substances - neurohormones regulating the release of hormones by other endocrine glands. The central organ of the endocrine system is also the pituitary gland. The remaining endocrine glands are classified as peripheral organs of the endocrine system.

Follicle-stimulating And luteinizing Hormones stimulate sexual function and the production of hormones by the gonads. The ovaries of women produce estrogens, progesterone, and androgens, and the testes of men produce androgens.

The endocrine system includes all the glands of the body and the hormones produced by these glands. The glands are controlled directly by stimulation of the nervous system, as well as by chemical receptors in the blood and hormones produced by other glands.
By regulating the functions of organs in the body, these glands help maintain homeostasis in the body. Cellular metabolism, reproduction, sexual development, sugar and mineral levels, heart rate and digestion are some...[Read below]

Head and neck
Upper body
Lower body (M)
Lower body (W)

[Start at the top] ... of the many processes regulated by the actions of hormones.

Hypothalamus

It is the part of the brain located above and in front of the brain stem, inferior to the thalamus. It performs many different functions in the nervous system and is also responsible for direct control of the endocrine system through the pituitary gland. The hypothalamus contains special cells called neurosecretory cells-neurons, which secrete endocrine hormones: thyrotropin-releasing hormone (TRH), growth-releasing hormone (GRHR), growth inhibitory hormone (GRIG), gonadotropin-releasing hormone (GRH), corticotropin-releasing hormone (CRH) , oxytocin, antidiuretic (ADH).

All releasing and inhibiting hormones affect the function of the anterior pituitary gland. TRH stimulates the anterior pituitary gland to release thyroid-stimulating hormone. GHRH as well as GRIH regulate the release of growth hormone, GHRH stimulates the release of growth hormone, and GRIH inhibits its release. GnH stimulates the release of follicle-stimulating hormone and luteinizing hormone, while CRH stimulates the release of adrenocorticotropic hormone. The last two endocrine hormones, oxytocin and antidiuretic, are produced by the hypothalamus, then transferred to the posterior lobe of the pituitary gland, where they are located, and then released.

Pituitary

The pituitary gland is a small, pea-sized piece of tissue connected to the lower part of the hypothalamus in the brain. Many blood vessels surround the pituitary gland, carrying hormones throughout the body. Located in a small depression of the sphenoid bone, the sella turcica, the pituitary gland actually consists of 2 completely different structures: the posterior and anterior lobes of the pituitary glands.

Posterior pituitary gland.
The posterior pituitary gland is not actually glandular tissue, but more nervous tissue. The posterior lobe of the pituitary gland is a small extension of the hypothalamus through which the axons of some of the neurosecretory cells of the hypothalamus pass. These cells create 2 types of endocrine hormones of the hypothalamus, which are stored and then released by the posterior pituitary gland: oxytocin, antidiuretic.
Oxytocin activates uterine contractions during labor and stimulates milk production during breastfeeding.
Antidiuretic (ADH) in the endocrine system prevents loss of body water by increasing the reabsorption of water by the kidneys and decreasing blood flow to the sweat glands.

Adenohypophysis.
The anterior lobe of the pituitary gland is the true glandular part of the pituitary gland. The function of the anterior pituitary gland controls the releasing and inhibitory functions of the hypothalamus. The anterior lobe of the pituitary gland produces 6 important hormones of the endocrine system: thyroid stimulating hormone (TSH), responsible for stimulating the thyroid gland; adrenocorticotropic - stimulates the outer part of the adrenal gland - the adrenal cortex - to produce its hormones. Follicle-stimulating (FSH) - stimulates the gonad cell bulb to produce gametes in females and sperm in males. Luteinizing hormone (LH) - stimulates the gonads to produce sex hormones - estrogens in women and testosterone in men. Human growth hormone (HGH) affects many target cells throughout the body, stimulating their growth, repair, and reproduction. Prolactin (PRL) has many effects on the body, the main one being that it stimulates the mammary glands to produce milk.

Pineal gland

It is a small knob-shaped mass of endocrine glandular tissue found just behind the thalamus of the brain. It produces melatonin, which helps regulate the sleep-wake cycle. The activity of the pineal gland is inhibited by stimulation from the photoreceptors of the retina. This sensitivity to light means that melatonin will only be produced in low light or dark conditions. Increased melatonin production causes people to feel sleepy at night when the pineal gland is active.

Thyroid

The thyroid gland is a butterfly-shaped gland, its location is at the base of the neck and wraps around the sides of the trachea. It produces 3 main hormones of the endocrine system: calcitonin, thyroxine and triiodothyronine.
Calcitonin is released into the blood when calcium levels rise above a set point. It serves to reduce the concentration of calcium in the blood, promoting the absorption of calcium into the bones. T3, T4 work together to regulate the body's metabolic rate. Increasing the concentration of T3, T4 increases energy consumption as well as cellular activity.

Parathyroid glands

The parathyroid glands are 4 small masses of glandular tissue found on the posterior side of the thyroid gland. The parathyroid glands produce the endocrine hormone parathyroid hormone (PTH), which is involved in the homeostasis of calcium ions. PTH is released from the parathyroid glands when calcium ion levels are below a set point. PTH stimulates osteoclasts to break down the calcium contained in the bone matrix to release free calcium ions into the blood. PTH also stimulates the kidneys to return filtered calcium ions from the blood back into the bloodstream so that they are stored.

Adrenal glands

The adrenal glands are a pair of roughly triangular glands of the endocrine system located just above the kidneys. They are made up of 2 separate layers, each with their own unique functions: the outer adrenal cortex, and the inner one, the adrenal medulla.

Adrenal cortex:
produces many cortical endocrine hormones of 3 classes: glucocorticoids, mineralocorticoids, androgens.

Glucocorticoids have many different functions, including breaking down proteins and lipids to produce glucose. Glucocorticoids also function in the endocrine system to reduce inflammation and enhance the immune response.

Mineralocorticoids, as their name suggests, are a group of endocrine hormones that help regulate the concentration of mineral ions in the body.

Androgens, such as testosterone, are produced at low levels in the adrenal cortex to regulate the growth and activity of cells that are receptive to male hormones. In adult males, the amount of androgens produced by the testes is many times greater than the amount produced by the adrenal cortex, which leads to the appearance of male secondary sexual characteristics, such as facial hair, body hair, and others.

Adrenal medulla:
it produces adrenaline and norepinephrine when the sympathetic division of the ANS is stimulated. Both of these endocrine hormones help increase blood flow to the brain and muscles to improve the response to stress. They also work to increase heart rate, breathing rate, and blood pressure, decreasing blood flow to organs that are not involved in emergency response.

Pancreas

This is a large gland located in the abdominal cavity with the lower rear part closer to the abdomen. The pancreas is considered a heterocrine gland because it contains both endocrine and exocrine tissues. Endocrine cells of the pancreas make up only about 1% of the mass of the pancreas and are found in small groups throughout the pancreas called the islets of Langerhans. Within these islets there are 2 types of cells - alpha and beta cells. Alpha cells produce glucagon, which is responsible for increasing glucose levels. Glucagon stimulates muscle contractions of liver cells to break down the polysaccharide glycogen and release glucose into the blood. Beta cells produce insulin, which is responsible for lowering blood glucose after meals. Insulin causes glucose to be absorbed from the blood into cells, where it is added to glycogen molecules for storage.

Gonads

Gonads - organs of the endocrine and reproductive system - ovaries in females, testes in males - are responsible for the production of sex hormones of the body. They determine the secondary sexual characteristics of adult females and adult males.

Testes
are a pair of ellipsoidal organs found in the male scrotum that produce the androgen testosterone in males after the onset of puberty. Testosterone affects many parts of the body, including muscles, bones, genitals, and hair follicles. It causes growth and increased strength of bones and muscles, including accelerated growth of long bones in adolescence. During puberty, testosterone controls the growth and development of male reproductive organs and body hair, including pubic, chest and facial hair. In men who have inherited the genes for hair loss, testosterone causes the onset of androgenetic alopecia, commonly known as male pattern baldness.

Ovaries.
The ovaries are a pair of tonsil-shaped glands of the endocrine and reproductive system, located in the pelvic cavity of the body, superior to the uterus in women. The ovaries produce the female sex hormones progesterone and estrogens. Progesterone is most active in women during ovulation and pregnancy, where it provides the appropriate conditions in the human body to support the developing fetus. Estrogens are a group of related hormones that function as primary female sex hormones. The release of estrogen during puberty causes the development of female sexual characteristics (secondary) - the growth of pubic hair, the development of the uterus and mammary glands. Estrogen also causes increased bone growth during adolescence.

Thymus

The thymus is a soft, triangular organ of the endocrine system located in the chest. The thymus synthesizes thymosins, which train and develop T-lymphocytes during fetal development. T-lymphocytes obtained in the thymus protect the body from pathogenic microbes. The thymus is gradually replaced by adipose tissue.

Other hormone-producing organs of the endocrine system
In addition to the endocrine system glands, many other non-glandular organs and tissues in the body also produce endocrine system hormones.

Heart:
The muscle tissue of the heart is capable of producing the important endocrine hormone atrial natriuretic peptide (ANP) in response to high blood pressure levels. ANP works to lower blood pressure by causing vasodilation to allow more room for blood to pass through. ANP also reduces blood volume and pressure, causing water and salt to be removed from the blood through the kidneys.

Kidneys:
produce the endocrine hormone erythropoietin (EPO) in response to low levels of oxygen in the blood. EPO, once released by the kidneys, travels to the red bone marrow, where it stimulates increased production of red blood cells. The number of red blood cells increases the oxygen carrying capacity of the blood, eventually stopping the production of EPO.

Digestive system

The hormones cholecystokinin (CCK), secretin and gastrin, are all produced by the gastrointestinal tract. CCK, secretin and gastrin help regulate the secretion of pancreatic juice, bile, and gastric juice in response to the presence of food in the stomach. CCK also plays a key role in the feeling of satiety or “fullness” after eating.

Adipose tissue:
produces the endocrine hormone leptin, which is involved in controlling appetite and energy expenditure in the body. Leptin is produced at levels relative to the existing amount of fat tissue in the body, which allows the brain to monitor the state of energy storage in the body. When the body contains sufficient levels of fat tissue to store energy, leptin levels in the blood tell the brain that the body is not starving and can function normally. If body fat or leptin levels drop below a certain threshold, the body goes into starvation mode and attempts to conserve energy by increasing hunger and food intake and decreasing energy intake. Adipose tissue also produces very low levels of estrogen in both men and women. In obese people, large amounts of fat tissue can lead to abnormal estrogen levels.

Placenta:
In pregnant women, the placenta produces several endocrine hormones that help maintain pregnancy. Progesterone is produced to relax the uterus, protect the fetus from the mother's immune system, and also prevent premature birth of the fetus. Human chorionic gonadotropin (HCT) helps progesterone by signaling the ovaries to maintain estrogen and progesterone production throughout pregnancy.

Local endocrine hormones:
Prostaglandins and leukotrienes are produced by every tissue in the body (except blood tissue) in response to harmful stimuli. These two hormones of the endocrine system affect cells that are local to the source of damage, leaving the rest of the body free to function normally.

Prostaglandins cause swelling, inflammation, increased sensitivity to pain, and increased local organ temperature to help block damaged areas of the body from infection or further damage. They act as the body's natural bandages, keeping pathogens at bay and swelling around injured joints like a natural bandage to restrict movement.

Leukotrienes help the body heal after prostaglandins have taken effect by reducing inflammation while helping white blood cells move into the area to clear it of pathogens and damaged tissue.

Endocrine system, interaction with the nervous system. Functions

The endocrine system works together with the nervous system to form the body's control system. The nervous system provides very fast and highly targeted control systems to regulate specific glands and muscles throughout the body. The endocrine system, on the other hand, is much slower in action but has very widespread, long-lasting and powerful effects. Endocrine hormones are distributed by glands through the blood throughout the body, affecting any cell with a receptor for a particular type. Most affect cells in multiple organs or throughout the body, resulting in many varied and powerful responses.

Hormones of the endocrine system. Properties

Once the hormones have been produced by the glands, they are distributed throughout the body through the bloodstream. They travel through the body, through cells or along the plasma membrane of cells until they encounter a receptor for that particular endocrine hormone. They can only affect target cells that have the appropriate receptors. This property is known as specificity. Specificity explains how each hormone can have specific effects in common parts of the body.

Many hormones produced by the endocrine system are classified as tropic. Tropics can cause the release of another hormone in another gland. These provide a control pathway for the production of hormones, and also provide a way for glands to control production in distant areas of the body. Many of those produced by the pituitary gland, such as TSH, ACTH and FSH, are tropic.

Hormonal regulation in the endocrine system

Levels of endocrine hormones in the body can be regulated by several factors. The nervous system can control hormone levels through the action of the hypothalamus and its releasers and inhibitors. For example, TRH produced by the hypothalamus stimulates the anterior pituitary gland to produce TSH. Tropics provide an additional level of control for hormone release. For example, TSH is a tropic, stimulating the thyroid gland to produce T3 and T4. Diet can also control their levels in the body. For example, T3 and T4 require 3 or 4 iodine atoms respectively, then they will be produced. In people who do not have iodine in their diet, they will not be able to produce enough thyroid hormones to support healthy metabolism in the endocrine system.
Finally, the number of receptors present in cells can be changed by cells in response to hormones. Cells that are exposed to high levels of hormones for long periods of time can reduce the number of receptors they produce, causing the cell to become less sensitive.

Classes of endocrine hormones

They are divided into 2 categories depending on their chemical composition and solubility: water-soluble and fat-soluble. Each of these classes has specific mechanisms and functions that dictate how they affect target cells.

Water-soluble hormones.
Water-soluble ones include peptide and amino acid ones, such as insulin, adrenaline, growth hormone (somatotropin) and oxytocin. As their name suggests, they are water soluble. Water-soluble cannot pass through the phospholipid bilayer of the plasma membrane and therefore depends on receptor molecules on the cell surface. When a water-soluble endocrine hormone binds to a receptor molecule on the surface of a cell, it triggers a reaction inside the cell. This reaction can change factors within the cell, such as membrane permeability or the activation of another molecule. The usual reaction causes the formation of cyclic adenosine monophosphate (cAMP) molecules to synthesize it from adenosine triphosphate (ATP) present in the cell. cAMP acts as a second messenger inside the cell, where it binds to a second receptor to alter the physiological functions of the cell.

Lipid-containing endocrine hormones.
Fat-soluble include steroid hormones such as testosterone, estrogen, glucocorticoids and mineralocorticoids. Because they are fat soluble, they can pass directly through the phospholipid bilayer of the plasma membrane and bind directly to receptors inside the cell nucleus. Lipids are able to directly control cell function from hormone receptors, often causing the transcription of certain genes in DNA to produce “messenger RNA (mRNA),” which is used to produce proteins that influence cell growth and function.