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8.2.1. Endocrine glands

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 pancreastesticlesovaries, etc., produce hormones that act on other organs or tissues of the body.

The main endocrine glands are:


Interactive activity: Organization of the endocrine system.

Interactive activity: Main glands of the endocrine system.

Hypothalamus - Pituitary

The hypothalamus and pituitary can be considered as a functional unit located within the skull, at the base of the encephalon.

The hypothalamus is a part of the encephalon, made up of neurons, which receives nerve signals, but whose neurons have the ability to secrete hormones. These neurons are called neurosecretory.

The hypothalamus has a double function:

  • Nervous function: regulates sleep and wakefulness, as well as hunger and satiety, and body temperature.
  • Endocrine function: coordinates all hormonal function, since it controls the production of hormones secreted by the pituitary.

The pituitary gland (or pituitary gland) is a small endocrine gland that hangs from the hypothalamus, located at the base of the skull. The pituitary gland controls the rest of the endocrine glands in the body and acts on certain target organs.

The tropic hormones are hormones secreted by the pituitary gland that control secretion of other endocrine glands, such as the thyroid, the adrenals, the ovaries or testicles.

Not all hormones secreted by the pituitary gland are tropic hormones, such as growth hormone (GH).

The pituitary gland is divided into several lobes. Those that are related to the endocrine system are:

  • The adenohypophysis or anterior pituitary.
  • The neurohypophysis or posterior pituitary.

Hipotálamo e hipófisis

By Catalinagh (Own work) [CC BY-SA 4.0], via Wikimedia Commons

The table below shows a summary of the different hormones produced by the pituitary and their corresponding effects:

Activity: Hypothalamus and pituitary (1).

Activity: Hypothalamus and pituitary (2).

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 appearsThe deficit produces hypothyroidismBoth 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.

Glándula tiroides y paratiroides

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.

El páncreas en una glándula mixta

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

Activity: Crossword about the pancreas.

Answer in your notebook

8.3.- What consequences can a person have had to remove the pancreas?

Answer in your notebook

8.2.- What are the main characteristics of hormones?

Answer in your notebook

8.4.- How does the pancreas act when the level of glucose in the blood is too low? And when is it too high?

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 lipidsproteins 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.

Glándulas suprarrenales

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:
  • They are part of the endocrine systemThey 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.

Ovarios y testículos

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.

Imagen con la glándula pineral y la hipófisis

Tomado de https://commons.wikimedia.org/wiki/File:Illu_pituitary_pineal_glands.jpg

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.

Timo, situado en la parte central delantera del pecho

Tomado de https://sco.wikipedia.org/wiki/File:Illu_thymus.jpg

Answer in your notebook

8.5.- Make a diagram with the name of the main endocrine glands indicating their function.


         

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Biology and Geology teaching materials for Compulsory Secondary Education (ESO) and Baccalaureate students.