The endocrine system is a network of glands that secrete chemicals called hormones to help your body function properly.
Hormones are chemical signals that coordinate a variety of bodily functions.
The endocrine system works to regulate certain internal processes. The exocrine glands, such as sweat and salivary glands , secrete externally and internally through ducts. The endocrine glands secrete hormones internally, using the bloodstream.
The endocrine system helps control the following processes and systems:
- Growth and development.
- Homeostasis (the internal balance of the body’s systems).
- Metabolism (energy levels of the body).
- Response to stimuli (stress and / or injury).
The endocrine network
The endocrine system completes these tasks through its network of glands, which are small but very important organs that produce, store, and secrete hormones.
The glands of the endocrine system are:
- Pineal gland.
- Pituitary gland.
These glands produce different types of hormones that elicit a specific response in other cells, tissues, or organs located throughout the body. Hormones reach these distant targets using the bloodstream .
Like the nervous system, the endocrine system is one of your body’s main communicators. But instead of using nerves to transmit information, the endocrine system uses blood vessels to deliver hormones to cells.
To make sure everything runs smoothly, certain processes need to work properly:
- The endocrine glands must release the correct amount of hormones (if they release too much or too little, it is known as hormonal imbalance).
- Your body also needs a strong blood supply to carry hormones throughout your body.
- There must be enough receptors (which is where hormones bind and do their work) in the target tissue.
Endocrine diseases are common and occur even when a step in the process does not work as it should. If you have an endocrine disease or disorder, you can consult a specialist known as an endocrinologist who will effectively diagnose and help treat your condition.
The hypothalamus is located below the thalamus (a part of the brain that transmits sensory information) and above the pituitary gland and brain stem. This is as small as an almond.
The hypothalamus is the link between the endocrine and nervous systems. It also produces hormone release and inhibition, which stops and starts the production of other hormones throughout the body.
The hypothalamus helps stimulate or inhibit many of your body’s key processes, including:
- Heart rate and blood pressure.
- Body temperature.
- Fluid and electrolyte balance, including thirst.
- Appetite and body weight.
- Glandular secretions of the stomach and intestines.
- Production of substances that influence the pituitary gland to release hormones.
- Sleep cycles.
The hypothalamus is involved in many functions of the autonomic nervous system, receiving information from almost all parts of the nervous system.
Hormones of the hypothalamus
The hypothalamus is heavily involved in the function of the pituitary gland. When it receives a signal from the nervous system, the hypothalamus secretes neurohormones that control the secretion of pituitary hormones.
The primary hormones secreted by the hypothalamus include:
- Antidiuretic hormone: increases the absorption of water in the blood by the kidneys.
- Corticotropin-releasing hormone: sends a message to the anterior pituitary gland to stimulate the adrenal glands to release corticosteroids, which help regulate metabolism and immune response.
- Gonadotropin-releasing hormone: stimulates the anterior part of the pituitary to release follicle-stimulating hormone (FSH) and luteinizing hormone (LH), which work together to ensure normal function of the ovaries and testes.
- Growth Hormone Releasing Hormone (GHRH) or Growth Hormone Inhibiting Hormone (GHIH): GHRH prompts the anterior pituitary gland to release growth hormone (GH); GHIH has the opposite effect.
- Oxytocin – participates in a variety of processes, such as orgasm, confidence, body temperature, sleep cycles, and the release of breast milk.
- Prolactin Releasing Hormone (PRH) or Prolactin Inhibiting Hormone (PIH) : PRH drives the anterior pituitary gland to stimulate breast milk production by producing prolactin. On the contrary, PIH inhibits prolactin and therefore milk production.
- Thyrotropin-Releasing Hormone (TRH): TRH triggers the release of thyroid-stimulating hormone (TSH), which stimulates the release of thyroid hormones, which regulate metabolism, energy, and growth and development.
The pineal gland, also known as the “pineal body” is located at the back of the brain’s third ventricle, which is a fluid-filled space in the brain.
This gland is located between the two halves of the brain. In adults, it is approximately 5 to 9 mm long and 0.1 grams in weight. However, it is often larger before puberty.
The gland gets its name from its shape, which resembles a pineapple (Latin for ‘pinea’). It is made up of glial cells, portions of neurons, and cells known as ‘pinealocytes’. Pinealocytes are types of endocrine cells.
Hormone and function
The pineal gland secretes a single hormone, melatonin. This simple hormone is special because its secretion is dictated by light. Melatonin fulfills the function of controlling the circadian rhythm of humans and regulating some reproductive hormones.
Your circadian rhythm is a 24-hour biological cycle characterized by patterns of sleep and wakefulness.
Melatonin secretion is low during daylight hours and high during dark periods, which has some influence on your reaction to the photoperiod (the length of day versus night). Naturally, the photoperiod affects sleep patterns, but the degree of impact of melatonin on sleep patterns is controversial.
Relationship with the ovaries and testes
Melatonin blocks the secretion of gonadotropins (luteinizing hormone and follicle stimulating hormone) from the anterior pituitary gland. These hormones contribute to the growth and good function of the ovaries and testicles.
The full purpose of the pineal gland remains a mystery. But research suggests that we are getting closer to understanding the pineal gland, and more about the endocrine system in general.
Hormones from the pituitary gland help regulate the functions of other endocrine glands. This gland has two parts, the anterior lobe and the posterior lobe, which have two very separate functions.
The hypothalamus sends signals to the pituitary to release or inhibit the production of pituitary hormones. In some cases, the hypothalamus sends signals to the pituitary gland to stimulate or inhibit the production of hormones. Essentially, the pituitary gland acts after the hypothalamus drives it.
The pituitary gland is only 1/3 inch in diameter (about as big as a pea) and is located at the base of the brain.
Since their functions are so intertwined, it is not surprising that the hypothalamus and pituitary are close to each other. They are actually connected by the pituitary stalk, or more technically, the infundibulum.
The pituitary glands are made up of the anterior lobe and the posterior lobe. The anterior lobe makes and releases hormones. The posterior lobe does not produce hormones per se, this is done by the nerve cells of the hypothalamus, but it does release them into the circulation.
Hormones of the anterior lobe:
- Adrenocorticotropic hormone: stimulates the adrenal glands to produce hormones.
- Follicle Stimulating Hormone (FSH) – Works with LH to ensure normal function of the ovaries and testes.
- The growth hormone: it is essential in the first years to maintain a healthy body composition and for growth in children. In adults, it supports healthy bone and muscle mass and affects fat distribution.
- Luteinizing Hormone (LH) – Works with FSH to ensure normal function of the ovaries and testes.
- Prolactin : hormone responsible for the production of milk in the breasts.
- Thyroid stimulating hormone: stimulates the thyroid gland to produce hormones.
The posterior lobe contains the ends of the nerve cells that come from the hypothalamus. The hypothalamus sends hormones directly to the posterior lobe through these nerves, and then the pituitary gland releases them.
Hormones of the posterior lobe:
- Antidiuretic Hormone (ADH): This hormone prompts the kidneys to increase the absorption of water in the blood.
- Oxytocin: participates in a variety of processes, such as contracting the uterus during childbirth and stimulating the production of breast milk.
The thyroid is a gland that is characterized by having a shape similar to that of a butterfly silhouette, which is located just below the larynx. It is composed of two like lobes joined by a band called the isthmus. The thyroid gland covers the windpipe from three sides.
Two hormones in the thyroid gland, T4 (thyroxine) and T3 (triiodothyronine), help the body make and regulate the hormones adrenaline (also called epinephrine) and dopamine.
Adrenaline and dopamine are active in many physical and emotional responses, including fear, excitement, and pleasure. Other hormones in this gland also help regulate metabolism, which is the process by which calories and oxygen are converted into energy.
Without a working thyroid, the body could not break down protein and could not process carbohydrates and vitamins. For this reason, problems with this gland can lead to uncontrollable weight gain.
For many people, these irregularities can be controlled through medication, as well as a modification of their diet. However, there is another controlling factor. The gland cannot produce hormones on its own. You need the help of the pituitary gland, which creates the thyroid stimulating hormone (TSH).
As a result, a non-functional pituitary gland will eventually lead to thyroid-related problems. TSH will activate the production of thyroxine or triiodothyronine. If TSH is not present at the correct levels, too much or too little of any of the hormones will be made.
The parathyroid glands are four small glands (shape and size of a grain of rice) located at the back of the thyroid that have the sole purpose of secreting parathyroid hormone to regulate the level of calcium in our bodies.
The parathyroid essentially helps the nervous and muscular systems function properly. Calcium is the primary element that causes muscles to contract, and calcium levels are very important for the normal conduction of electrical currents along the nerves.
Parathyroid hormone (PTH) has a very powerful influence on your bone cells by causing them to release their calcium into the bloodstream.
- PTH regulates the amount of calcium that is absorbed from your diet, the amount of calcium that is excreted by the kidneys, and the amount of calcium that is stored in the bones.
- We store many pounds of calcium in our bones, and it is available to the rest of the body at the request of the parathyroid glands.
- PTH increases the formation of active vitamin D, and it is active vitamin D that increases the intestinal absorption of calcium and phosphorus.
Before birth and throughout childhood, the thymus is instrumental in the production and maturation of T lymphocytes or T cells, a specific type of white blood cell that protects the body from certain threats, including viruses and infections.
The thymus produces and secretes thymosin, a hormone necessary for the development and production of T cells.
The thymus is special in that, unlike most organs, it is larger in children. Once you reach puberty, the thymus reaches its maximum weight and begins to slowly shrink and be replaced by fat. At age 75, the thymus is little more than fatty tissue.
The thymus is located in the upper anterior (front) part of your chest directly behind your breastbone and between your lungs. The pinkish-gray organ has two thymic lobes.
Thymosin, the thymus hormone
Thymosine stimulates the development of T cells. During your childhood years, white blood cells called lymphocytes pass through the thymus, where they transform into T cells.
Once T cells have fully matured in the thymus, they migrate to lymph nodes (groups of immune system cells) throughout the body, where they help the immune system fight disease.
However, some lymphocytes, regardless of whether they reside in the lymph nodes or the thymus, can develop into cancers (known as Hodgkin’s disease and non-Hodgkin’s lymphomas).
Although the thymus gland is only active until puberty, its dual role as an endocrine and lymphatic gland plays an important role in your long-term health.
The adrenal gland (adrenal gland) is located at the top of each kidney; therefore, each person has two adrenal glands. The adrenal glands are divided into two parts.
Hormones and function
The outer portion of the gland is called the adrenal cortex. The adrenal cortex is responsible for creating three different types of hormones: mineralocorticoids that conserve sodium in the body, glucocorticoids that increase blood glucose levels, and gonadocorticoids that regulate sex hormones like estrogen.
The adrenal medulla is the inner portion of the adrenal gland (adrenal gland). This portion secretes epinephrine and norepinephrine in times of stress.
There are several diseases that can affect the functionality of the adrenal gland (adrenal gland).
Two notable examples are Cushing’s disease, which is the creation of too much cortisol, and Addison’s disease, which occurs when not enough cortisol is created. Both can be treated with medication.
The pancreas is unique in that it is an endocrine and exocrine gland. In other words, the pancreas has the dual role of secreting hormones into the blood (endocrine) and secreting enzymes through ducts (exocrine).
The pancreas belongs to the endocrine and digestive systems, with most of its cells (over 90%) working on the digestive side. However, the pancreas has a vital duty to produce hormones, especially insulin, to maintain the balance of blood glucose (sugar) and salt in the body.
Without this balance, your body is susceptible to serious complications, such as diabetes.
The pancreas is a 6-inch-long flattened gland found deep in the abdomen, between the stomach and the spine. It is connected to the duodenum, which is part of the small intestine.
Only about 5% of the pancreas is made up of endocrine cells. These cells clump together within the pancreas and look like small islands of cells when examined under a microscope. These groups of pancreatic endocrine cells are known as pancreatic islets or more specifically, islets of Langerhans.
Hormones of the pancreas
The production of pancreatic hormones, including insulin, somatostatin, gastrin, and glucagon, play an important role in maintaining the balance of sugar and salt in our bodies. The primary hormones secreted by the pancreas include:
- Gastrin: aids digestion by stimulating certain cells in the stomach to produce acid.
- Glucagon – Helps insulin maintain normal blood glucose by working in the opposite way from insulin. It stimulates your cells to release glucose, and this increases your blood glucose levels.
- Insulin – regulates glucose in the blood by allowing many of the cells in your body to absorb and use glucose. In turn, this lowers blood glucose levels.
- Somatostatin: When the levels of other pancreatic hormones, such as insulin and glucagon, become too high, somatostatin is secreted to maintain a balance of glucose and / or salt in the blood.
- Vasoactive Intestinal Peptide – Helps control the secretion and absorption of water from the intestines by stimulating intestinal cells to release water and salts in the intestines.
The ovaries are a pair of egg-producing organs (that is, they produce eggs) that maintain the health of the female reproductive system. The ovaries, like their male counterpart, the testes, are known as gonads. This simply means that they are the main reproductive organs.
In addition to its role in egg production, the ovaries also have the distinction of being an endocrine gland because they secrete hormones, primarily estrogen and progesterone, which are vital for normal reproductive development and fertility.
The ovaries are oval in shape and about the size of a large grape. They are located at opposite ends of the pelvic wall, on either side of the uterus. The ovaries are attached to the fimbria (tissue that connects the ovaries to the fallopian tube).
Hormones of the ovaries
The ovaries make and release two groups of sex hormones: progesterone and estrogen. There are actually three main estrogens, known as estradiol, estrone, and estriol. These substances work together to promote the healthy development of female sexual characteristics during puberty and to ensure fertility.
Estrogen (specifically estradiol) is instrumental in breast development, the distribution of fats in the hips, legs, and breasts, and in the development of the reproductive organs.
To a lesser extent, the ovaries release the hormone relaxin before delivery. Another minor hormone is inhibin, which is important in signaling the pituitary gland to inhibit the secretion of follicle-stimulating hormone.
Production and function of progesterone and estrogen
Progesterone and estrogen are necessary to prepare the uterus for menstruation, and their release is triggered by the hypothalamus.
Once you reach puberty, the ovaries release only one egg each month (the ovaries typically alternate releasing one egg); This is called ovulation.
The hypothalamus sends a signal to the pituitary gland to release gonadotrophic substances (follicle stimulating hormone and luteinizing hormone). These hormones are essential for normal reproductive function, including regulation of the menstrual cycle.
As the egg migrates into the fallopian tube, progesterone is released. It is secreted by a temporary gland formed within the ovary after ovulation called the corpus luteum.
Progesterone prepares the body for pregnancy by making the lining of the uterus thicken. If a woman is not pregnant, the corpus luteum disappears.
If a woman is pregnant, pregnancy will trigger high levels of estrogen and progesterone, preventing more eggs from maturing. Progesterone is secreted to prevent uterine contractions that can disrupt the growth of the embryo. The hormone also prepares the breasts for lactation.
Rising estrogen levels near the end of pregnancy alerts the pituitary gland to release oxytocin, which causes uterine contractions. Before delivery, the ovaries release relaxin, which, as the name suggests, loosens the pelvic ligaments in preparation for delivery.
More hormones are released during pregnancy than at any other time in a woman’s life, but during menopause, which marks the end of fertility, estrogen levels drop rapidly. This can lead to a variety of complications.
The testes are a pair of sperm-producing organs that maintain the health of the male reproductive system. The testes are known as gonads. Its female counterpart is the ovaries.
In addition to its role in the male reproductive system, the testes also have the distinction of being an endocrine gland because they secrete testosterone, a hormone that is vital for the normal development of male physical characteristics.
The testes are twin oval-shaped organs the size of a large grape. They are found inside the scrotum, which is the loose bag of skin that hangs outside the body behind the penis.
While this location makes the testicles vulnerable to injury (they don’t have muscles or bones to protect them), it provides a cooler temperature for the organs. A cooler environment is necessary for healthy sperm production.
Testosterone, the hormone of the testicles
Testosterone is necessary for proper physical development in children. It is the primary androgen, which is the term for any substance that stimulates and / or maintains male development.
During puberty, testosterone is involved in many of the processes that make a boy’s transition to adulthood, including:
- Healthy development of the male sexual organs.
- Growth of facial and body hair.
- Height increase.
- Increase in muscle mass.
- Adam’s apple growth.
The importance of testosterone is not limited to puberty. During adulthood, the hormone is integral in a variety of functions, such as:
- Maintain libido.
- Sperm production.
- Maintain strength and muscle mass.
- Promote healthy bone density.
The hypothalamus and pituitary gland control how much testosterone the testicles make and secrete. The hypothalamus sends a signal to the pituitary gland to release gonadotrophic substances (follicle stimulating hormone and luteinizing hormone).
Luteinizing hormone (LH) stimulates the production of testosterone. If too much testosterone is produced, the hypothalamus alerts the pituitary gland to produce less LH, signaling the testes to drop testosterone levels.