he pituitary gland is also called the pituitary . It is the directing gland of the endocrine system and together with the hypothalamus (which is a structure of the brain and which you can delve into here ) are the ones that direct the body’s response to changes in the external environment in order to achieve balance ( homeostasis) with the external medium at all times.
The pituitary is colored green and purple with its “testis-like” appearance.
Index [ close ]
- What is the pituitary?
- Location of the pituitary
- Structure of the pituitary gland
- The neurohypophysis
- The adenohypophysis
- Pituitary functions
- Hormones secreted by the pituitary
- Hormones of the adenohypophysis
- Growth hormone (GH) or somatotropin
- Thyrotropin or Thyroid Stimulating Hormone (TSH)
- Follicle-stimulating hormone (FSH)
- Luteinizing hormone (LH)
- Prolactin
- Adrenocorticotropic hormone (ACTH)
- Melanocyte-stimulating hormone (MSH)
- Other hormones in animals
- Neurohypophysis hormones
- Hormones of the adenohypophysis
What is the pituitary?
The pituitary is a gland with a unique characteristic, since although we consider it as a whole, it has two parts with different embryonic origins that we will see later.
Its size is very small, barely between 1 and 1.6 cm and weighs 6 grams with a shape similar to that of some testicles and is attached to the hypothalamus through the infundibulum.
Location of the pituitary
It is located below the hypothalamus at the base of the brain and above the bone structure called the sella turcica that protects it. In a more profane way, it would be behind where the nose begins, in an area attached to the brain, in this case the hypothalamus.
Structure of the pituitary gland
As we said before, the pituitary gland or pituitary has two different parts : on the one hand the neurohypophysis or posterior pituitary and on the other hand the adenohypophysis or anterior pituitary.
Both parts have two different embryonic origins. On the one hand, the neurohypophysis arises from a thickening of the brain floor and, on the other hand, the adenohypophysis arises from an ectodermal evacuation of the stomodeum , called the Rathke pouch.
Although we are not going to delve further, this allows us to understand why the neurohypophysis is the neural part of the pituitary (because it comes from the brain, in short, the brain) and the adenohypophysis is the most glandular part (because it comes from a different origin than the brain). ).
The neurohypophysis
The neurohypophysis is made up of three parts or portions:
- Pars nervosa: it is the nerve portion or posterior lobe that is the largest
- Infundibulum
- Middle eminence: it is the junction point between the hypothalamus and the pituitary.
The adenohypophysis
The adenohypophysis is made up of two parts that form between 75 and 80% of the total pituitary gland:
- Pars distalis: distal portion and is the largest
- Pars tuberalis: tuberal portion that is at the top and surrounds the infundibulum
The upper part of the pars tuberalis and the infundibulum make up what is called the pituitary stalk, which is the junction between the hypothalamus and the pituitary.
In some species the pars intermedia or intermediate lobe can be found which in the case of humans after birth has no functional importance and atrophies, ceasing to be a lobe.
In the adenohypophysis there are 5 types of cells, each one specialized in a certain type of hormones:
- somatotropics: are the cells that are responsible for secreting growth hormone, as the name suggests (soma-body)
- Thyrotropic: they are the ones in charge of secreting thyroid hormones such as TSH as indicated by the name thyroid – thyroid
- lactotropic: they are the ones in charge of secreting prolactin as its name lacto – milk indicates.
- gonadotropics: are those that are responsible for secreting hormones related to sexual cycles such as luteinizing hormone (LH) and follicle-stimulating (FSH)
- corticotropics: are those that are responsible for secreting hormones from the adrenal cortex such as ACTH.
Pituitary functions
The function of this gland is to regulate and secrete hormones that are necessary to regulate balance in the body. The two parts have slightly different functions.
The neurohypophysis is responsible for distributing to the rest of the target organs the hormones that the hypothalamus synthesizes, while the adenohypophysis synthesizes and secretes hormones depending on the regulation that the hypothalamus performs through hypothalamic factors.
The neurohypophysis distributes hormones and the adenohypophysis synthesizes and distributes hormones.
Hormones secreted by the pituitary
The pituitary secretes hormones properly synthesized in the pituitary itself, specifically in the cells of the adenohypophysis, and is responsible for distributing two hormones synthesized by the hypothalamus through the neurohypophysis: oxytocin and vasopressin that you can find in this post.
Hormones of the adenohypophysis
The hormones that the adenohypophysis secretes are:
- Growth hormone (GH) or somatotropin
- Thyrotropin or Thyroid Stimulating Hormone (TSH)
- Follicle-stimulating hormone (FSH)
- Luteinizing hormone (LH)
- Prolactin (PRL)
- Adrenocorticotropic hormone (ACTH)
- Melanocyte-stimulating hormone (MSH)
Growth hormone (GH) or somatotropin
It is secreted by somatotropic cells and is most abundantly secreted by the adenohypophysis.
Stimulates cell growth and replication by accelerating protein synthesis.
It acts on all cells but especially it does so in skeletal and muscular development. For this reason, when there is trauma, this hormone increases its secretion.
This hormone acts on the liver, where liver cells respond by synthesizing and secreting somatomedins (also called IGFs or insulin-like growth factors) . Somatomedins are peptide hormones that work by stimulating protein synthesis and cell replication in striated muscle fibers, cartilage, and other target cells. Cartilage and muscle tissue can also produce IGFs due to somatotropin, or GH.
In children, this hormone is responsible for increasing the growth rate of muscles and skeleton in children, and in adults, preventing the loss of muscle tissue.
This hormone also increases lipolysis in adipose tissue, avoiding the use of amino acids as an energy source.
It is released at periodic pulses every few hours especially during sleep. It is controlled by GHRH and GHIH which are both hypothalamic factors.
The hormone secretion of growth is enhanced by: lowering fatty acids and increased blood amino acid, physical exercise, stress, non – REM sleep and other hormones such as glucagon, estrogen, cortisol and insulin.
It is inhibited by a low concentration of amino acids in the blood, REM phase sleep, affective deficiency, obesity, low levels of thyroid hormones and growth hormone (GH) by negative feedback.
Thyrotropin or Thyroid Stimulating Hormone (TSH)
It is secreted by the thyrotropic cells and acts on the thyroid gland inducing the release of thyroid hormones (triiodothyroninia or T3 and thyroxine or T4) and stimulating the growth of the thyroid gland . It is regulated through TRH, which is a hypothalamic factor controlled by the concentration of T3 and T4.
Follicle-stimulating hormone (FSH)
It is one of the gonadotropin hormones (that is, they act on the gonads: ovaries and testicles). secreted by gonadotropic cells and its function is to stimulate the development of the ovules or oocytes in the ovaries of mature women and in men maintains sperm production in the testicles .
In addition, FSH also stimulates estrogen secretion that occurs in the follicles of the ovaries where the eggs mature. Estrogens are female sex hormones, the most important being estradiol.
The release of this hormone is induced by the hypothalamic factor GnRH (gonadotropic releasing hormone) and its inhibition is produced by the concentration of these hormones by negative feedback.
Luteinizing hormone (LH)
It is the second gonadotropin hormone secreted by gonadotropic cells, its function is to induce ovulation in women and stimulate the secretion of progestins (mainly progesterone) in the ovaries, which are responsible for repairing the body for possible pregnancy : they prepare the breasts for milk secretion and the uterus for implantation of a fertilized egg.
The function of this hormone in men is to stimulate the synthesis of male sex hormones (androgens, the most important being testosterone) in the testicles, specifically in Leydig cells.
It is also regulated by the hypothalamic factor GnRH.
Prolactin
Prolactin is secreted by lactotropic cells. This hormone is in charge of stimulating the development of the mammary glands and the production of milk. Although it has a dominant effect, the mammary glands are regulated by other hormones as well: estrogens, progesterone, growth hormone, glucocorticosteroids, and hormones produced by the placenta.
During the fetal period, it is also responsible for stimulating growth. In other animal and bird species it regulates sexual and reproductive behavior.
In men the role of prolactin is not very clear although its high secretion is known to cause erectile dysfunction.
Recall that prolactin acts on milk production not on milk expulsion that oxytocin (another hormone released by the neurohypophysis) does.
The prolactin is regulated by hormonal domapina or inhibiting prolactin (PIH) . Shortly before the start of menstruation (remember that the start of menstruation is the first day of bleeding), the decrease in estrogens causes a drop in the secretion of PIH so that prolactin is secreted at the start of menstruation, when the Estrogen level rises, PIH returns to its usual levels and prolactin returns to a low concentration. Since prolactin is short-lived, there is no time for milk to secrete during menstruation.
Adrenocorticotropic hormone (ACTH)
It is secreted by corticotropic cells and stimulates the release of steroid hormones by the adrenal gland. These hormones are called glucocorticoids and regulate cortisol metabolism .
Hypothalamic factor, corticotropin-releasing hormone, or CRH, stimulates ACTH secretion. It is stimulated by stress, low blood glucose, trauma, and interleukin (a substance produced by macrophages). Its inhibition is made by negative feedback according to the glucocorticoid concentration.
Melanocyte-stimulating hormone (MSH)
It is secreted by corticotropic cells and is the only hormone that releases the intermediate part of the adenohypophysis. Its function is to stimulate the melanocytes of the skin, increasing the rate of melanin production and distribution .
It is only secreted during fetal development, in young children, and in pregnant women. Otherwise, if it appears it can be associated with pathological processes.
In lower vertebrates, it acts by regulating the melanin distribution in the skin, such as amphibians.
You can see how hypothalamic factors work and are regulated in this Youtube video:
Other hormones in animals
There are other hormones secreted by the adenohypophysis that appear in other species such as lipotropin (LPH) and beta-endorphin. Lipotropin is responsible for mobilizing lipids in other vertebrates, but in humans its role is of little importance.
Neurohypophysis hormones
The neurohypophysis is responsible for distributing the two hormones that the hypothalamus synthesizes to the target organs: oxytocin and vasopressin or antidiuretic hormone (ADH).
