Which are the hormones secreted by the adenolypophysis; list briefly their functions?
Hormones of the adenohypophysis:
Six hormones are produced by the adenohypophysis. These are:
1 .Somatotrophic hormone (STH) or Growth hormone (GH)
2. Adenocarticotrophic hormone (ACTH)
3. Thyroid stimulating hormone (TSH)
4. Prolactin or Lactogenic hormone (LTH)
5. Gonadotropic hormone (GTH)
a. Follicle stimulating hormone (FSH)
b. Luteinizing hormone (LH)
STH brings about normal growth when secreted in normal rate. It should neither be high nor low. Oversecretion of STH in childhood leads to excessive growth in length of the bones and results in a condition known as gigantism. In adults hypersecretion of STH results in a condition known as acromegali.
In this condition there is enlargement of bone and soft tissues resulting in hands and feet getting grossly enlarged, jaws growing abnormally long and broad. In some cases there is less secretion of pituitary during the growth period. As a result of this there is undergrowth resulting in a small sized body. And this is known as midget. Over secretion of growth hormone in midget adults will result in an unproportionate growth of the body and it is known as acromicria.
1. ACTH stimulates the adrenal cortex and causes the secretion glucocorticoids.
2. Gluco-corticoid is a very essential hormone for an individual to meet the stressful conditions. When an animal is faced with a stressful situation, impulses from the sense organs pass to the brain and then to the hypothalamus.
The hypothalamus inturn influences adenohypophysis to secrete more quantity of ACTH. ACTH will stimulate the secretion of gluco-corticoid from the adrenal cortex. Thus the pituitary – adrenal coordination acts in a homeostatic manner to meet the needs of the situation.
3. Melanocyte pigmentation is also under the control of ACTH and patients in whom there is insufficiency of adrenal secretion are abnormally pigmented as a result of the loss of negative feedback provided by Cortisol. This condition is known as Addison’s disease.
4. There is a diurnal variation in the secretion of ACTH. As a result of this, the Cortisol levels in the plasma will be at its peak in the morning (about 6 am) and will reach their lowest level around midnight. In an abnormality known as Cushing’s disease there is hypersecretion of Cortisol and the diurnal variation is lost. TSH has the following functions.
1. It controls the various aspects of the functioning of the thyroid gland.
2. Promotes accumulation of iodine and increases the quantity of intracellular colloids in the epithelial cells of the thyroid gland. This induces the liberation of the hormone thyroxin.
There is a negative feed back between the level of thyroxin and TSH. If the secretion is decreased the level of thyroxin is also decreased resulting in hypothyroidism. This results in reduced growth. On the other hand increased TSH secretion resulting in increased thyroxin production causes hyperthyroidism. This is characterised by irritability, increased rate of metabolism, bulging of the eye balls etc.
The production of TSH is controlled by thyrotrophin releasing hormone
(TRH) produced from the hypothalamus.
The general functions assigned to LTH hormone are
1. It stimulates the production of milk in the mammary glands.
2. It stimulates the production of Corpus-luteum
3. During pregnancy prolactin helps in maintaining the functional state of corpus-leutem which is necessary for continued pregnancy.
4. This hormone stimulates the maternal instinct and behavior in women which is very essential for the maintenance of the offspring. It is also believed that this hormone induces in the mother and the child a strong emotional attachment.
The following are the functions of LH.
1. It causes ovulation(release of mature ovum from the ovary) and helps in the formation of corpus lutem working along with FSH. The corpus lutem inturn secrets progesterone in women which is essential for the continuation of the pregnancy.
2. In males LH is generally known as ICSH. This stimulates the interstitial cells(cells of Leydig)of testis to secrete the male sex hormone – testosterone. Testosterone is also necessary for the maintenance of secondary sexual characters.