Endocrine System (for Parents) – Nemours KidsHealth

What Is the Endocrine System?

The endocrine system is made up of glands that make hormones. Hormones are the body’s chemical messengers. They carry information and instructions from one set of cells to another.

The endocrine (EN-duh-krin) system influences almost every cell, organ, and function of our bodies.

What Does the Endocrine System Do?

• Endocrine glands release
  hormonesinto the bloodstream. This lets the hormones travel to cells in other parts of the body.
• The endocrine hormones help control mood, growth and development, the way our organs work,
  metabolism, and reproduction.
• The endocrine system regulates how much of each hormone is released. This can depend on levels of hormones already in the blood, or on levels of other substances in the blood, like calcium. Many things affect hormone levels, such as stress, infection, and changes in the balance of fluid and minerals in blood.

Too much or too little of any hormone can harm the body. Medicines can treat many of these problems.

What Are the Parts of the Endocrine System?

While many parts of the body make hormones, the major glands that make up the endocrine system are the:

• hypothalamus
• pituitary
• thyroid
• parathyroids
• adrenals
• pineal body
• the ovaries
• the testes

The pancreas is part of the endocrine system and the digestive system. That’s because it secretes hormones into the bloodstream, and makes and secretes enzymes into the digestive tract.

Hypothalamus: The hypothalamus (hi-po-THAL-uh-mus) is in the lower central part of the brain. It links the endocrine system and nervous system. Nerve cells in the hypothalamus make chemicals that control the release of hormones secreted from the pituitary gland. The hypothalamus gathers information sensed by the brain (such as the surrounding temperature, light exposure, and feelings) and sends it to the pituitary. This information influences the hormones that the pituitary makes and releases.

Pituitary: The pituitary (puh-TOO-uh-ter-ee) gland is at the base of the brain, and is no bigger than a pea. Despite its small size, the pituitary is often called the “master gland.” The hormones it makes control many other endocrine glands.

The pituitary gland makes many hormones, such as:

• growth hormone, which stimulates the growth of bone and other body tissues and plays a role in the body’s handling of nutrients and minerals
• prolactin (pro-LAK-tin), which activates milk production in women who are breastfeeding
• thyrotropin (thy-ruh-TRO-pin), which stimulates the thyroid gland to make thyroid hormones
• corticotropin (kor-tih-ko-TRO-pin), which stimulates the adrenal gland to make certain hormones
• antidiuretic (an-ty-dy-uh-REH-tik) hormone, which helps control body water balance through its effect on the kidneys
• oxytocin (ahk-see-TOE-sin), which triggers the contractions of the uterus that happen during labor

The pituitary also secretes endorphins (en-DOR-fins), chemicals that act on the nervous system and reduce feelings of pain. The pituitary also secretes hormones that signal the reproductive organs to make sex hormones. The pituitary gland also controls
ovulationand the menstrual cycle in women.

Thyroid: The thyroid (THY-royd) is in the front part of the lower neck. It’s shaped like a bow tie or butterfly. It makes the thyroid hormones thyroxine (thy-RAHK-sin) and triiodothyronine (try-eye-oh-doe-THY-ruh-neen). These hormones control the rate at which cells burn fuels from food to make energy. The more thyroid hormone there is in the bloodstream, the faster chemical reactions happen in the body.

Thyroid hormones are important because they help kids’ and teens’ bones grow and develop, and they also play a role in the development of the brain and nervous system.

Parathyroids: Attached to the thyroid are four tiny glands that work together called the parathyroids (par-uh-THY-roydz). They release parathyroid hormone, which controls the level of calcium in the blood with the help of calcitonin (kal-suh-TOE-nin), which the thyroid makes.

Adrenal Glands: These two triangular adrenal (uh-DREE-nul) glands sit on top of each kidney. The adrenal glands have two parts, each of which makes a set of hormones and has a different function:

1. The outer part is the adrenal cortex. It makes hormones called corticosteroids (kor-tih-ko-STER-oydz) that help control salt and water balance in the body, the body’s response to stress, metabolism, the immune system, and sexual development and function.
2. The inner part is the adrenal medulla (muh-DUH-luh). It makes catecholamines (kah-tuh-KO-luh-meenz), such as epinephrine (eh-puh-NEH-frun). Also called adrenaline, epinephrine increases blood pressure and heart rate when the body is under stress.

Pineal: The pineal (pih-NEE-ul) body, also called the pineal gland, is in the middle of the brain. It secretes melatonin (meh-luh-TOE-nin), a hormone that may help regulate when we sleep at night and wake in the morning.

Reproductive Glands: The gonads are the main source of sex hormones. In boys the male gonads, or testes (TES-teez), are in the scrotum. They secrete hormones called androgens (AN-druh-junz), the most important of which is
testosterone(tess-TOSS-tuh-rone). These hormones tell a boy’s body when it’s time to make the changes associated with puberty, like penis and height growth, deepening voice, and growth in facial and pubic hair. Working with hormones from the pituitary gland, testosterone also tells a boy’s body when it’s time to make sperm in the testes.

A girl’s gonads, the ovaries (OH-vuh-reez), are in her pelvis. They make eggs and secrete the female hormones
estrogen(ESS-truh-jen) and
progesterone(pro-JESS-tuh-rone). Estrogen is involved when a girl starts puberty. During puberty, a girl will have breast growth, start to accumulate body fat around the hips and thighs, and have a growth spurt. Estrogen and progesterone are also involved in the regulation of a girl’s menstrual cycle. These hormones also play a role in pregnancy.

Pancreas: The pancreas (PAN-kree-us) makes insulin (IN-suh-lin) and glucagon (GLOO-kuh-gawn), which are hormones that control the level of glucose, or sugar, in the blood. Insulin helps keep the body supplied with stores of energy. The body uses this stored energy for exercise and activity, and it also helps organs work as they should.

What Can Help Keep the Endocrine System Healthy?

To help keep your child’s endocrine system healthy:

• Get plenty of exercise.
• Eat a nutritious diet.
• Go for regular medical checkups.
• Talk to the doctor before taking any supplements or herbal treatments.
• Let the doctor know about any family history of endocrine problems, such as diabetes or thyroid problems.

When Should I Call the Doctor?

Let the doctor know if your child:

• drinks a lot of water but is still thirsty
• has to pee often
• has frequent belly pain or nausea
• is very tired or weak
• is gaining or losing a lot of weight
• has tremors or sweats a lot
• is constipated
• isn’t growing or developing as expected

Reviewed by: Larissa Hirsch, MD

Date reviewed: October 2018

Table: Major Hormones – MSD Manual Consumer Version

Major Hormones

Thyroid hormones

• Total T3
• T4 common
• T3 free
• T4 free
• TSH (thyrotropic)
• Anti-thyroglobulin (AT-TG)
• Thyroid peroxidase antibodies (AT-TPO)

Thyroid gland and its hormones , together with the nervous and immune systems, takes part in the regulation of the work of all human organs (heart, brain, kidneys, etc. ). Unlike most hormones, which act only on certain cells of individual organs (for example, for estradiol, these are the genital organs), thyroid hormones are necessary for the normal functioning of all tissues and all organs, without exception. Penetrating into the cell, the hormone is directed to the nucleus, where, by binding to certain sites on the chromosomes, it activates a complex of reactions responsible for the processes of oxidation and reduction. Thyroid hormones are the main regulators of energy consumption in the body, and maintaining their concentration at the required level is extremely important for the normal functioning of all organs and systems. For the synthesis of thyroid hormones, two essential components are required – iodine and the amino acid tyrosine. Without iodine, the synthesis of hormones stops completely, so it is extremely important to ensure that you get enough iodine from food. Tyrosine also enters the body with food; it is the basis of not only thyroid hormones, but also adrenaline, melanin, and dopamine.

T3 and T4 . The main two hormones produced by the thyroid gland are triiodothyronine and tetraiodothyronine (thyroxine). Triiodothyronine contains 3 iodine molecules, and thyroxine contains 4 molecules. These hormones are abbreviated as T3 and T4, respectively. In the cells and tissues of our body, T4 gradually turns into T3, which is the main biologically active hormone that directly affects metabolism. However, thyroxine (T4) is about 90% of total thyroid hormones.

Free T3 and T4 . Before entering the bloodstream, thyroid hormones must be bound to transport proteins-globulins (in order not to be “washed out” by the kidneys), but in order to enter the cells and tissues, they must be freed from this “transport”. That. in the blood, T3 and T4 are either free or bound. The level of free hormones is less than 0.1% of their total amount, but it is the free fraction of hormones that is the most biologically active, and it is they that provide all the effects of thyroid hormones.

Analysis of the level of the main hormones T3, T4 and their free variants is the first and most important step in determining the quality of the thyroid gland in case of any suspicion of its disease.

Thyroid stimulating hormone (TSH) is the main regulator of thyroid function. Produced by the pituitary gland, a small gland located on the lower surface of the brain. TSH controls the production of thyroid hormones (thyroxine and triiodothyronine), which, in turn, regulate the processes of energy production in the body. The feedback mechanism allows you to maintain a stable level of these hormones – when their blood levels decrease, the hypothalamus detects this fact and gives a signal to the pituitary gland to synthesize TSH. An increase in TSH concentration, in turn, stimulates the production of thyroid hormones by the thyroid gland. The reverse process is similar. Pituitary dysfunction can cause an uncontrolled increase or decrease in the level of thyroid-stimulating hormone, thereby provoking the thyroid gland to produce thyroxine and triiodothyronine in abnormal amounts. An increase in their concentration causes hyperthyroidism, and a decrease, respectively, hypothyroidism. Diseases of the hypothalamus, the regulator of TSH secretion by the pituitary gland, can also cause malfunctions in this system. In addition, diseases of the thyroid gland, accompanied by a violation of the production of thyroid hormones, can indirectly (by a feedback mechanism) affect the synthesis of thyroid-stimulating hormone, causing a decrease or increase in its concentration.

Anti-thyroglobulin (AT-TG) and thyroid peroxidase (AT-TPO) antibodies In general, antibodies are proteins synthesized by cells of the immune system. Their main function is to detect and destroy foreign objects (bacteria, viruses, etc.). However, it happens that as a result of a failure, the body begins to produce antibodies against its own healthy tissues. In the thyroid gland, most often, the enzyme thyroperoxidase (TPO) and the basis for the synthesis of hormones – thyroglobulin (TG) become objects for the production of antibodies.

Thyroglobulin is a preparation for thyroid hormones, from which thyroid cells “make” hormones T3 and T4. Initially, the cells produce thyroglobulin (thus creating iodine reserves), which is “stored for the future” in special containers – follicles. Then, as needed, T3 and T4 are synthesized from thyroglobulin.

Thyroid peroxidase is an enzyme of the thyroid gland involved in the formation of the active form of iodine and thus plays a key role in the production of thyroid hormones.

The damaging effect of antibodies can lead to a disruption in the normal production of thyroid hormones and negatively affect the regulation of its function, which ultimately causes chronic pathologies associated with hypo- or hyperthyroidism. Nevertheless, it is important to emphasize that antibodies to TPO and TG are not a key link in the pathogenesis of autoimmune thyroid diseases and begin to be produced already in response to its damage. Therefore, attempts to reduce the level of antibodies are devoid of any practical meaning.

AT-TG and AT-TPO tests are used to confirm or exclude the autoimmune nature of a particular thyroid disease (enlargement of the thyroid gland without disturbing its function, primary hypo- or hyperthyroidism, ophthalmopathy, etc.), as this allows you to prescribe the most effective therapy. Tests are also prescribed for children born to mothers with pathology of the endocrine organs to determine risk groups for the development of thyroid diseases. Quantitative analysis of blood serum for Ab-TPO is the most sensitive method for diagnosing autoimmune thyroid diseases. Analysis of AT-TG is valuable in differential diagnosis.

Prices for examinations can be found in the “Price List” section of the Clinical Laboratory. Blood for research is taken daily (except Sunday) from 7 a.m. to 11 a.m. Strictly on an empty stomach.

Read also about Adrenal hormones and Sex hormones

All processes related to procreation: maturation of spermatozoa and eggs, ovulation, preparation of the uterus for reception fetus, maintenance of pregnancy and childbirth are subject to strict control. How is it carried out?

Signals from the external and internal environment enter the brain, in the hypothalamus is the highest center of regulation of the organs of blood circulation, respiration, digestion, excretion and reproduction. In the hypothalamus, the information received is processed and, depending on the result of the analysis, a command follows to the nearby endocrine gland – pituitary gland , which is the immediate “chief” of all endocrine glands in the body (adrenal glands, thyroid, parathyroid, thymus and gonads). The hypothalamus transmits its commands to the pituitary gland with the help of special hormones, which, depending on the direction of their action, are called releasing hormones (from English release – “to release”) or inhibitory hormones (from Latin inhibeo – “to restrain, stop”).

To regulate the function of the gonads in the pituitary gland, 3 hormones are produced, which are called gonadotropins (Greek tropos – “direction”). These are: luteinizing hormone (abbreviated as LH ), follicle stimulating hormone (FSH ) and prolactin . Moreover, FSH and LH are produced under the stimulating effect of gonadotropin-releasing hormone (GnRH), and the release of prolactin is determined by an increase or decrease in the concentration of the inhibitory factor. Despite the fact that these hormones are the same in structure in men and women, they work differently in the two sexes.

Regulation of reproductive function in men

FSH in men is necessary for the normal formation, development and function of the seminiferous tubules. FSH actively influences spermatogenesis. LH stimulates the production of androgens by the testicles – male sex hormones. Prolactin in men potentiates the action of FSH and LH , affects the metabolic processes in the testicles.

The most important of the androgens is the hormone testosterone . Without this hormone, a normal spermatogenesis . In addition, testosterone is responsible for the normal formation of male genital organs, the appearance of secondary male characteristics (hair growth, a characteristic male physique), and also affects sexual behavior.

Secretion of testosterone is carried out according to the principle of direct and feedback: the hypothalamus stimulates the production of gonadotropins by the pituitary gland, under the influence of gonadotropins, the secretion of testosterone by the testicles increases – this is an example of a direct positive relationship. When the upper limit of testosterone concentration in the blood is reached, the so-called negative feedback begins to act, i.e. testosterone begins to inhibit the secretory activity of the hypothalamus and pituitary gland. When the concentration of testosterone in the blood falls to the lower limit, the hypothalamus again stimulates the production of testosterone through the pituitary gland. Thanks to such connections, the hypothalamus controls and regulates all processes occurring in the genital area.

Regulation of reproductive function in women

Hormonal regulation in the female body is more complicated than in the male. In a woman’s body, unlike a man’s, monthly cyclical changes occur, which are combined into one concept – menstrual cycle . These changes also affect the ovaries, in which the eggs mature, and the uterus , in which conditions are created for the onset of pregnancy, and the cervix , fallopian tubes and mammary glands , and even the skin and subcutaneous adipose tissue, in general, all the so-called “target organs”.

The duration of the menstrual cycle normally ranges from 21 to 32-34 days. Its beginning (1st day) is the beginning of bleeding ( menstruation ), which is due to the rejection of the mucous layer of the uterus ( endometrium ). The duration of menstruation (monthly) is 3-4 days. A normal menstrual cycle should be regular.

Already during menstruation, the level of follicle-stimulating hormone begins to rise. FSH stimulates several follicles to grow at once. However, as a rule, only one follicle reaches full maturity – the dominant follicle. Before ovulation, its diameter increases to 18-23 mm. The rest, the follicles that have begun to grow, degenerate, that is, they undergo reverse development. From the first days of the menstrual cycle, the production of LH by the pituitary gland gradually increases. In the middle of the menstrual cycle, there is a short release – a peak in the secretion of this hormone into the blood. Under the influence of peak LH over the next 34-36 hours, the final maturation of the egg occurs, which ends with the rupture of the follicle and the release of the egg into the abdominal cavity, that is, ovulation. By the level of LH in the blood or urine of a woman, one can quite accurately predict the time of ovulation. After ovulation, under the influence of gonadotropins, the corpus luteum is formed from the follicle.

Prolactin supports the function of corpus luteum and is responsible for the secretion of milk in the mammary glands. With an increase in its concentration in the ovaries, the development of follicles is inhibited, it may stop ovulation .

FSH and LH control the secretion of sex hormones in the ovary. The cells of the growing follicle produce hormones called estrogen (from the Greek oistrus – estrus, a state of sexual arousal in animals + genes – birth, origin), the main of which are estradiol, estriol and estrone. Estrogens determine the female image, influence the development of secondary sexual characteristics. Under their influence, the mammary glands develop, hair grows according to the female type, a female physique and voice timbre are formed.

In a woman of reproductive age, estrogens prepare the body every month for a possible pregnancy. During menstruation , the endometrium , the mucosa lining the uterine cavity, sharply becomes thinner. Under the influence of ever-increasing production of estrogen by the ovary, the endometrium begins to proliferate, i.e. grow, thicken, glands appear in it, vessels develop. At the same time, estrogens cause changes in fallopian tubes . The fallopian tubes and the cilia of the epithelium of the inner layer of the tubes begin to move in a certain way, facilitating the flow of the secret in them from the uterus to the ampullar section of the fallopian tube, thereby contributing to the advancement of spermatozoa in the lumen of the tube. Estrogens reduce muscle tone cervical , resulting in an increase in the diameter of the cervical canal. His external pharynx begins to gape. Under the influence of estrogens, the mucus in the lumen of the canal liquefies and hangs in long threads into the vagina. These changes are most pronounced before ovulation, when estrogen levels are at their highest. Thus, by the time of ovulation, the most favorable conditions are created for spermatozoa on the way to the cherished egg.

The main hormone of the corpus luteum is progesterone . It is also known as the pregnancy hormone. The duration of the existence of the corpus luteum will depend on whether pregnancy has occurred or not. Under the influence of progesterone, the endometrial glands begin to actively produce and accumulate a secret containing the nutrients necessary for the development of the ovum and embryo. After ovulation, under the influence of progesterone, the direction of contractions of the muscles of the fallopian tubes and the wave-like movements of the ciliated epithelium changes to the opposite direction, namely, to the uterus. This ensures the transport of the embryo into the uterine cavity.

If fertilization does not occur, then the corpus luteum , having existed for about 2 weeks, degenerates, and progesterone secretion decreases to a minimum. 2-3 days after the fall in the level of ovarian hormones, endometrial rejection occurs, i.e. menstruation, and a new menstrual cycle begins.

If pregnancy occurs, the corpus luteum continues to function, they say – it “blooms”. This is because the fertilized egg releases a special hormone called chorionic (from the Greek chorion – the outer shell of the fetal egg) gonadotropin, which stimulates the functional activity of the corpus luteum. Thus, the fetus itself affects the maternal organism, stimulates processes in it that ensure the preservation and development of pregnancy.

From the above it is easy and correct to conclude that ovary is a powerful hormonal laboratory. Of course, the subtle mechanism of regulation of reproductive processes can be disturbed, and then ovarian failure develops. It can manifest itself in weakness, insufficient hormonal activity of the follicles or the corpus luteum, which leads to menstrual irregularities and infertility.