Pituitary: Characteristics, Functions, Pathologies

The pituitary gland or pituitary gland is an endocrine gland that secretes hormones responsible for regulating the body’s homeostasis. It is responsible for regulating the function of other glands of the endocrine system and its operation is conditioned by the hypothalamus, a region of the brain.

It is a complex gland located in a bony space known as the sella turcica of the ephenoid bone. This space is located at the base of the skull, specifically in the medial cerebral fossa, which connects the hypothalamus with the pituitary stalk or pituitary stalk.

illustration of the pituitary

The pituitary gland is an endocrine gland that allows the body’s hormonal responses to be well coordinated with each other. That is, it is a gland that is responsible for maintaining a state of harmony between the body and the environment of the person.

Functions and characteristics of the pituitary

The pituitary gland is one of the regions through which orders to produce certain hormones are rapidly transmitted when certain stimuli are detected in the environment. For example, when a person visually detects the presence of a dangerous animal, the perceived visual stimulus generates an immediate response in the pituitary.

This fact allows a rapid response of the organism, produced before the perceived information reaches the upper regions of the brain area, which are in charge of analyzing and converting the signal into abstract thoughts.

This function performed by the pituitary is carried out through the intervention of a specific region of the brain known as the hypothalamus. This brain structure processes visual information and, upon detecting data related to danger, transmits a signal that quickly passes to the pituitary.

Image result for hypothalamus lifeder

In this way, the response carried out by the pituitary makes it possible to adapt the body’s functioning quickly and efficiently. On some occasions, such a response may be unnecessary, for example when a person plays a joke on someone and scares them.

In this type of situation, the pituitary gland acts before the cerebral cortex in detecting the perceived stimulus. For this reason, the fear response appears before the person can realize that the situation is not dangerous, but is a simple joke from a partner.

However, the pituitary gland is not limited to releasing hormones in response to specific emotional states, but is also responsible for releasing a large number of hormones that are vital for the proper functioning and development of the body.

Location

The pituitary gland is a complex gland that is housed in a bony space called the sella turcica of the sphenoid bone. This region is located at the base of the skull, occupying an area known as the middle cerebral fossa.

The middle cerebral fossa is the region of the body that connects the hypothalamus with the pituitary stalk. It has an oval shape, and an antero-posterior diameter of 8 millimeters, a transverse diameter of 12 millimeters and a vertical diameter of 6 millimeters.

Anatomy

Generally, the pituitary gland of an adult person weighs about 500 milligrams. This weight may be slightly higher in women, especially those who have given birth several times.

Anatomically, the pituitary can be divided into three large regions: the anterior or adenohypophysis lobe, the middle or intermediate pituitary, and the posterior or neurohypophysis lobe.

Adenohypophysis

The adenohypophysis is the anterior lobe of the hypophysis, that is, the most superficial region of this structure; It has an ectodermal origin since it comes from the Rathke bag.

The adenohypophysis is formed by anastomosed epithelial cords, which are surrounded by a network of sinusoities.

This region of the pituitary gland is responsible for secreting six different types of hormones: adrenocotricotropic hormone, betaenforfin, thyroid-stimulating hormone, follicle-stimulating hormone, luteinizing hormone, and growth hormone.

Hyposecretion (excessively low secretion) of hormones from the anterior pituitary gland usually causes dwarfism due to atrophy of the gonads and other growth-related glands. On the other hand, hypersecretion (excessively high secretion) of hormones from the adenohypophysis usually causes gigantism in children and acormegaly in adults.

Regarding its cellular activity, the pituitary has five different cell types: somatotropic cells, maotropic cells, corticotropic cells, gonadotropic cells, and thyroid cells.

  • Somatotropic : these are cells that contain large acidophilic granules, have an intense orange color and are located mainly in the distal part of the adenohypophysis. These cells are responsible for secreting growth hormone.
  • Mamotropes : they are cells that are found in clusters and appear individually separated. They are small in size with prolactin granules. The release of these granules is regulated by vasoactive intestinal peptide and thyrotropin-releasing hormone.
  • Corticotropes : they are round, basophilic cells that contain rough endoplasmic reticulum and abundant mitochondria. They are responsible for secreting the gonodotropins LH and FSH.
  • Thyropes : they are basophilic cells that are found near the cords. They are distinguished from the rest of the cells of the adenohypophysis by presenting small thyrotropin granules. Its activity is responsible for stimulating the release of prolactin.
  • Chromophobes : these cells do not stain as they contain little cytoplasm. They are found in the middle of the cords that form chromophilic cells and have large amounts of polyribosomes.
  • Stellate follicles : these cells constitute a large population located in the distal part, they present long processes with which tight junctions are formed and they are characterized by not containing granules.

Middle pituitary

The median pituitary is a narrow region of the pituitary that acts as a boundary between its anterior lobe and its posterior lobe. It is small in size (approximately 2% of the total size of the pituitary gland) and comes from the rathke bag.

The median pituitary is characterized by presenting a different function to that of the rest of the pituitary regions. It is made up of both reticular cells and stellate cells, a colloid, and a surrounding cubic cell epithelium.

Likewise, the median pituitary contains other cells with oval shapes, which have granules in their upper part. These cells are responsible for secreting the melanocyte-stimulating hormone.

The median pituitary is located above the capillaries, thus allowing a faster and more effective transit of the hormone into the bloodstream.

Neurohypophysis

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Finally, the neurohypophysis constitutes the posterior lobe of the pituitary. Unlike the other two parts of the pituitary, it does not have an ectodermal origin, since it is formed through a downward growth of the hypothalamus.

The neurohypophysis can be divided into three parts: the median eminence, the infundibulum, and the pars nervosa. The latter is the most functional region of the neurohypophysis.

The cells of the neurohypophysis are glial support cells. For this reason, the neurohypophysis does not constitute a secretory gland, since its function is limited to storing secretion products of the hypothalamus.

Hormones of the pituitary

The main function of the pituitary is to release different hormones, which modify the functioning of the body. In this sense, the pituitary gland releases a large number of different hormones.

The most important are: growth hormone, prolactin, thyroid-stimulating hormone, adrenal cortex-stimulating hormone, luteinizing hormone, and follicle-stimulating hormone.

Growth hormone

Growth hormone, also known as somatrotropin hormone, is a peptide hormone. Its main function is to stimulate growth, cell reproduction and regeneration.

The effects of this hormone on the body can be generally described as anabolic. The main functions of this hormone are:

  1. Increase calcium retention and bone mineralization.
  2. Increase muscle mass.
  3. Promote lipolysis
  4. Increase protein biosynthesis.
  5. Stimulate the growth of organs (except the brain).
  6. Regulate homeostasis of the body.
  7. Reduce the glucose consumption of the liver.
  8. Promote gluconeogenesis in the liver.
  9. Contribute to the maintenance and function of the pancreatic islets.
  10. Stimulate the immune system.

Prolactin

Prolactin is a peptide hormone that is secreted by the lactotropic cells of the pituitary. Its main function is to stimulate milk production in the mammary glands and to synthesize progesterone in the corpus luteum.

Thyroid stimulating hormone

Thyroid stimulating hormone, also known as thyrotropin, is a hormone that is responsible for regulating thyroid hormones. The main effects of this hormone are:

  1. It increases the secretion of thyroxine and triiodothyronine by the thyroid glands.
  2. Increases proteolysis of intrafollicular thyroglobulin.
  3. Increases the activity of the iodine pump.
  4. Increases the iodination of tyrosine.
  5. Increases the size and secretory function of thyroid cells.
  6. Increases the number of cells in the glands.

Stimulating hormone of the adrenal cortex

Adrenal Cortex Stimulating Hormone is a polypeptide hormone that stimulates the adrenal glands. It exerts its action on the adrenal cortex and stimulates steroidogenesis, the growth of the adrenal cortex and the secretion of cortico-steroids.

Luteinizing hormone

Luteinizing hormone, also known as luteostimulating hormone or iutropin, is a gonadotropic hormone produced by the anterior lobe of the pituitary.

This hormone is responsible for stimulating female ovulation and male testosterone production, which is why it is an element of vital importance for the development and sexual functioning of people.

Follicle Stimulating Hormone

Finally, follicle-stimulating hormone or follicle-stimulating hormone is a gonadotropin hormone synthesized by gonadotropic cells in the inner part of the pituitary.

This hormone is responsible for regulating the development, growth, pubertal maturation and reproductive processes of the body. Likewise, in women it generates the maturation of oocytes and in men the production of sperm.

Diseases related to the pituitary

Alterations in the adrenal gland can cause a large number of pathologies. Of all of them, the best known of all is Cushing’s syndrome. This pathology was detected at the beginning of the 20th century, when the neurosurgeon Harvey Cushing detected the effects of the malfunctioning of the pituitary gland.

In this sense, it was shown that an excessive excretion of adrenocotricotropin alters the metabolism and growth of people through a series of symptoms that are included within Cushing’s syndrome.

This syndrome is characterized by causing weakness in the limbs and fragility in the bones; It affects different systems and organs of the body, and is characterized mainly by hypersecretion of cortisol. The main symptoms of the syndrome are:

  1. Round and congestive face (face in full moon).
  2. Fat accumulation in the neck and nape (buffalo neck).
  3. Central obesity (obese abdomen and thin limbs).
  4. Stretch marks on the abdomen, thighs and breasts.
  5. Frequent back pain
  6. Increased pubic hair in women.

Other pathologies

Apart from Cushing’s syndrome, abnormalities in the functioning of the pituitary can cause other important conditions in the body. Those that have been detected today are:

  1. Acromegaly, produced by an overproduction of growth hormone.
  2. Gigantism, produced by an overproduction of growth hormone.
  3. Growth hormone deficiency, due to low production of growth hormone.
  4. Syndrome of inappropriate antidiuretic hormone secretion caused by low vasopressin production.
  5. Diabetes insipidus caused by a low production of vasopressin.
  6. Sheehan syndrome due to a low production of any hormone from the pituitary gland.

References

  1. Afifi, AK (2006). Functional neuroanatomy. Mexico: McGraw-Hill / Interamericana.
  2. Bear, MF; Connors, BW i Paradiso, MA (2008). Neuroscience Brain scan. Barcelona: Wolters Kluwer / Lippincott Williams and Wilkins Spain.
  3. Bear, MF; Connors, BW i Paradiso, MA (2016). Neuroscience. Exploring the brain. (Fourth edition). Philadelphia: Wolters Kluwer.
  4. Carlson, NR (2014). Physiology of Behavior (11 Edition). Madrid: Pearson Education.
  5. Bartholomew, Edwin F .; Martini, Frederic; Judi Lindsley Nath (2009). Fundamentals of anatomy & physiology . Upper Saddle River, NJ: Pearson Education Inc. pp. 616-617.
  6. Knepel W, Homolka L, Vlaskovska M, Nutto D. (1984). Stimulation of adrenocorticotropin / beta-endorphin release by synthetic ovine corticotropin-releasing factor in vitro. Enhancement by various vasopressin analogs. Neuroendocrinology. 38 (5): 344-50.
  7. Mancall, Elliott L .; Brock, David G., eds. (2011). “Cranial Fossae”. Gray’s Clinical Anatomy . Elsevier Health Sciences. p. 154.

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