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The Pituitary Gland or Pituitary: how does the Adenohypophysis System work?

The Pituitary Gland or Pituitary: how does the Adenohypophysis System work?

ThePituitary gland or pituitary gland is an endocrine gland the size of a pea and weighs 0.5 grams in humans. It is a bulge of the lower part of the hypothalamus at the base of the brain. The pituitary gland rests on the pituitary fossa of the sphenoid bone in the center of the middle cranial fossa and is surrounded by a small bone cavity (Turkish chair) covered by a dural fold.

Content

  • 1 The Pituitary or Pituitary Gland
  • 2 The adenohypophysis
  • 3 Pituitary Hypothalamus Porta System
  • 4 Hypothalamic corticoadrenal hypothalamus axis
  • 5 Axis hypophytic hypothalamus thyroid
  • 6 Hypothalamic gonadal hypothalamus axis
  • 7 Prolactin axis
  • 8 Axis of growth hormone

The Pituitary or Pituitary Gland

The pituitary gland is often called the master gland because it controls other hormonal glands in your body, including the thyroid and adrenal glands, ovaries and testicles.

It secretes hormones from both the front and the back of the gland. Hormones are chemicals that carry messages from one cell to another through your bloodstream.

The pineal gland is divided into three sections:

  • The anterior lobe: It is mainly involved in body development, sexual maturation and reproduction. They regulate growth and stimulate the adrenal and thyroid glands, as well as the ovaries and testicles. It also generates prolactin, which allows mothers to produce milk for their children.
  • The intermediate lobe releases a hormone that stimulates melanocytes, the cells that control pigmentation (skin color) through the production of melanin.
  • The posterior lobe: It produces the antidiuretic hormone, which recovers water from the kidneys and preserves it in the bloodstream to prevent dehydration. Oxytocin is also produced by the posterior lobe, aiding in uterine contractions during delivery and stimulation of milk production and release, among other things.

The hypothalamus

This organs serves as a communications center for the pituitary gland, by sending messages or signals to the pituitary gland in the form of hormones that travel through the bloodstream and nerves through the pituitary stalk. These signals, in turn, control the production and release of other hormones from the pituitary gland that are sent to other glands and organs in the body.

The hypothalamus influences the functions of temperature regulation, food intake, thirst and water intake, sleep and wake patterns, emotional behavior and memory.

The adenohypophysis

The anterior pituitary or adenohypophysis is the anterior part of the pituitary gland that forms in the embryonic phase and is mainly glandular in nature.

The anterior pituitary regulates various physiological processes that include stress, growth, reproduction and lactation. The correct functioning of the anterior pituitary gland can be determined through blood tests that measure hormone levels.

Pituitary Hypothalamus Porta System

Adenohypophysis It works like a true endocrine gland, since it is formed by neurosecretory cells. But, in addition, it is also under strict hormonal control by the hypothalamus.

Hypothalamus hormones are generally small peptides and are called releasing factors or releasing hormones, and inhibitory factors u inhibitory hormones, depending on whether they act by stimulating or inhibiting the hormonal secretion of the anterior pituitary gland.

How hormones are released

There are hypothalamic nuclei, of the periventricular zone (for example, the arch, the periventricular, the medial preoptic area) that synthesize and send the release or inhibition factors in the portal circulation (the capillaries of the middle eminence). From there they are transported to the adenohypophysis, where they stimulate or inhibit the cells that secrete pituitary hormones.

Adenohypophyseal hormones act on other glands in the body, and stimulate the release of hormones in the blood. Some of these glands are the adrenal glands, the thyroid, the gonads, the mammary glands.

Hormones secreted by the anterior pituitary gland

Of the hormones secreted by the adenohypophysis, four are tropic hormones, that is, they have as their target another gland on which they act to regulate their hormonal production. These are the following:

  • Adrenocorticotropic hormone or corticotropin (ACTH). The acronym with which hormones are commonly known corresponds to their name in English (ACTH, adrenocorticotropic hormone).
  • Thyroid stimulating hormone (TSH) or thyrotropin

They include follicle stimulating hormone (FSH) and luteinizing hormone (LH)

Apart from these tropic hormones, the adenohypophysis also secretes:

  • Prolactin
  • Growth hormone (GH) or somatotropin

Taking into account the target organ of pituitary hormones, we can distinguish different hormonal axes:

  • Corticoadrenal hypothalamohypophytic axis
  • Thyroid hypothalamohypophytic axis
  • Hypothalamohypophytic gonadal axis
  • Prolactin shaft
  • Growth hormone axis

Hypothalamic corticoadrenal hypothalamus axis

The basic scheme is as follows:

The main control of this axis is exercised by the ACTH hormone of the anterior pituitary gland; When ACTH reaches the adrenal gland, hormone release occurs. ACTH secretion is controlled by the hypothalamic hormone CRH and also by the level of adrenocortical (or corticosuprenal) hormones in the blood. If the level of adrenocortical hormones decreases, CRH and ACTH secretion occurs.

Functions of adrenocortical hormones

Glucocorticoids:

  • Increase blood glucose level, accelerate protein degradation.
  • In high concentrations, they have anti-inflammatory effects.

The mineralocorticoids:

  • They cause sodium ion retention and elimination of potassium ions in the urine.

Adrenocortical hormone deficit

Addison's disease, which consists of a hypofunction of the adrenal glands. It has the following consequences: tiredness, apathy, cognitive deficits, depression, etc.

Excess of adrenal corticosteroid hormones

In situations of chronic stress, a large amount of glucocorticoids is released and that means that in the medium-long term there is a depression in the immune system, an increase in blood pressure, damage to the nervous tissue (for example, in the hippocampus) and muscle, growth inhibition, infertility, etc.

Hypothalamic thyroid hypothalamus axis

The basic scheme is as follows:

The main control of this axis is exercised by the TSH hormone of the anterior pituitary gland; When TSH reaches the thyroid gland, the release of thyroid hormones occurs. TSH secretion is controlled by the hypothalamic hormone TRH and also by the level of thyroid hormones in the blood. If the level of thyroid hormones decreases, secretion of TRH and TSH occurs.

Functions of thyroid hormones

The main role is to regulate metabolic processes and especially the use of carbohydrates.

It also influences growth and development, both body and nervous system.

Hypothyroidism

Thyroxine is the only substance produced by the body that contains iodine; so that, The manufacture of this hormone depends critically on the supply of iodine. In areas where the iodine content in the diet is poor, many people develop hyperthyroidism. In these cases, the thyroid enlarges in an attempt to produce more hormone, a situation known as goiter. Iodized salts are currently used to prevent this alteration.

If it is during development, there is a stop of body growth, facial malformations and reduction of the size and cellular structure of the brain. This leads to a congenital deficiency called cretinism.

If it occurs later, behavioral disorders such as apathy, depression, delayed speech, etc. are observed.

Hyperthyroidism

Generally, physiological and behavioral changes: insomnia, irritability, nervousness, increased heart rate and blood pressure, temperature changes, weight loss, etc.

Hypothalamic gonadal hypothalamus axis

The basic scheme is as follows:

The control mechanisms are similar to those explained by the two previous axes.

Functions of sex hormones

Androgens

  • They promote the development, growth and maintenance of male reproductive organs.
  • They promote the development of male secondary sexual characteristics (body shape, tone of voice, beard, etc.).
  • Stimulate protein metabolism.

Estrogens

  • They promote the development, growth and maintenance of the female reproductive organs.
  • They promote the development of female secondary sexual characteristics (body shape, breasts, hair pattern, etc.).

Progestogens

  • Prepare the walls of the uterus for implantation of the fertilized egg.
  • Prepare the breasts to secrete milk.

Prolactin shaft

Prolactin stimulates milk production by the mammary glands. During breastfeeding, the hypothalamus reduces the secretion of dopamine so that a sufficient level of prolactin is produced and milk production does not stop.

Growth hormone axis

Growth hormone or somatotropin stimulates the body's growth by producing substances that regulate bone growth. It is controlled by GHRH that stimulates its production and somatostatin, which inhibits it.

The shortage of GH produces dwarfism, while the excess produces gigantism. However, if the excess is in adulthood it no longer produces gigantism because the bones cannot grow in length, but it does occur acromegaly, characterized by an increase in some tissues such as the jaw and the joints of the hands and feet.

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