Anatomy of the endocrine system

The hypothalamus and pituitary glands are two endocrine glands that exclusively stimulate other endocrine glands, which is why they are responsible for hormonal regulation.

Other glands, such as the pancreas, testicles, ovaries, etc., produce hormones that act on other organs or tissues of the body.

The main endocrine glands are:

• Hypothalamus and pituitary.
• Thyroid and parathyroid.
• Pancreas.
• Adrenal glands.
• Ovaries and testicles.
• Pineal gland or cerebral epiphysis.
• Thymus.

Interactive activity: Organization of the endocrine system.

Interactive activity: Main glands of the endocrine system.

Thyroid and parathyroid

The thyroid and parathyroid glands are endocrine glands located in the front part of the neck, surrounding the trachea and larynx.

The thyroid is an endocrine gland regulated by the pituitary gland and secretes two types of hormones:

• The thyroxine, the most important hormone produced by the thyroid, contains iodine. Its effects on the body are:
  • It is responsible for regulating the  body's metabolism and the body's sensitivity to other hormones.
  • When the body is growing, growth hormone (GH) stimulates the increase in size, while thyroxine causes the tissues to take the appropriate shape as they grow. That is, thyroxine makes tissues develop in the proper shapes and proportions.
• The calcitonin, which promotes ossification because it reduces the level of calcium in the blood by stimulating their deposition in bones.

When an excess of thyroid secretion occurs, a disease called hyperthyroidism appears. The deficit produces hypothyroidism. Both diseases will be discussed later.

The  parathyroid glands are located behind the thyroid. It secretes the parathormone that produces the increase of calcium in the blood, releasing it from the bones. Its function is antagonistic to calcitonin.

By unknown for original image[1]Miguelferig for the Galician annotation (File:Illu thyroid parathyroid.jpg) [CC0 or Public domain], via Wikimedia Commons

Activity: Thyroid and parathyroid.

Pancreas

The pancreas is a mixed gland located in the abdomen that has dual functions:

• Exocrine secretion: it produces digestive enzymes that it discharges to the small intestine, forming the pancreatic juice that digests carbohydrates, lipids and proteins. Therefore, it is part of the digestive system.
• Endocrine secretion: it has cells, the islets of Langerhans, that produce hormones that are released into the blood, so the pancreas is also part of the endocrine system. The main hormones secreted are:
  • The insulin facilitates different tissues, mainly muscle, to absorb glucose from the blood. Glucose is a source of energy for cells. The pancreas releases insulin when the level of glucose in blood is high.
  • The glucagon has an antagonistic effect to insulin. It acts when the level of glucose in the blood is low, favoring the breakdown of glycogen stored in the tissues, releasing glucose into the blood.

If the amount of insulin produced by the pancreas is insufficient, the level of glucose in the blood rises and a disease called diabetes appears.

Tomado de https://en.wikipedia.org/wiki/File:Pancreatic-Model-of-Exocrine-and-Endocrine-Function-Locations.jpg#file

Activity: Crossword about the pancreas.

Adrenal glands

The adrenal glands or capsules are endocrine glands located above the kidneys. They are made up of two parts:

• The adrenal medulla, which produces catecholamines, of which the most important is adrenaline, which acts on the autonomic nervous system activating the body in emergency situations. Thus, increased levels of glucose in the blood, accelerates the heart rate, increases blood pressure, and lungs take more air, allowing rapid response to that risk.
• The adrenal cortex, which is regulated by the pituitary gland, produces three types of hormones:
  • Corticosteroids, which increase the level of glucose in the blood, suppress the immune system and help the metabolism of lipids, proteins and carbohydrates. They also help raise blood pressure.
  • Aldosterone, which acts in the blood and kidneys, controlling the amount of Na/K ions in the blood and urine, stimulating sodium absorption and renal potassium excretion.
  • Sex hormones: It is a secondary place of production of androgens, estrogens and progesterone.

The hormones secreted by the adrenal glands stimulate the heart and increase blood pressure. They also help control salt and water in the body.

By Basquetteur, arcadian, ortisa (derivative of File:Illu adrenal gland.png) [CC0], via Wikimedia Commons

Activity: Adrenal capsules.

Ovaries and testicles

The ovaries and testes are also mixed glands, since:

• They are part of the reproductive system. They discharge secretions to the outside through ducts. There are two types of sex glands or gonads they are:
  • The ovaries in the female sex.
  • The testicles in the male sex.
• They are part of the endocrine system. They produce hormones that leak into the blood. At puberty, sex hormones begin to be produced that cause sexual differentiation and the appearance of secondary sexual characteristics.
  • The ovaries produce two types of hormones:
    • The estrogen involved in the development of female secondary sex characteristics. It is also involved in the menstrual cycle.
    • The progesterone encourages the endometrium (uterine wall) is developed to prepare for pregnancy and inhibits the production of milk the breasts.
  • The testicles release testosterone, a hormone that favors the appearance of male secondary sexual characteristics.

Tomado de https://es.wikipedia.org/wiki/Archivo:Endocrine_Reproductive_system_es.svg

Activity: Gonads.

Activity: Action of the endocrine glands.

Pineal gland or cerebral epiphysis

The pineal gland or cerebral epiphysis is a small endocrine gland located in the brain. It produces melatonin, a hormone that regulates the sleep-wake pattern, as well as circadian and seasonal rhythms.

Thymus

The thymus is an endocrine gland that is involved in the manufacture of T lymphocytes, responsible for the cellular immune response, and secretes some hormone related to the immune system.