Short notes on the hormones of adenohypohysis

Short notes on hormones of adenohypohysis

1. Somatotrophic hormone (STH):

This is also known as Growth hor­mone and it influences growth in human beings by controlling the synthe­sis of proteins known as somatomedins by liver cells. The hormone is secreted by the acidophilic cells of adenohypophysis. Chemically the hormone is proteinaceous being made up of about 200 amino acids.

It has a molecular weight ranging between 21500 to 48000 and precipitates at pH 4.9. In children, the concentration of STH is about 300 micrograms per litre of plasma which drops to about 30% in adult human beings. STH does not have a target reaction instead it shows its influence on all most all tissues of the body by increasing the number and size of the cells. The growth hormone should be secreted at the 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.

Chemically the growth hormone increases the release of fatty acids from the adipose tissue and thereby increases the fatty acid concentration in the body fluids. STH decreases the utilisation of the carbohydrates for energy and promotes protein synthesis.

Adenocorticotropic hormone (ACTH):

Also known as Adenotropin or Corticotropin, this hormone promotes the production of steroid hormones from the adrenal cortex. Chemically the hormone is a polypeptide made up of 39 amino acids. Synthesised by the basophills of the adenohypo­physis it has a molecular weight of about 45000. The following are the functions of ACTH.

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 stressfull 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 corti- sol. 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.

Thyroid stimulating hormone (TSH):

Also known as Thyrotropin, this hormone is produced by the basophills of the adenohypophysis. This hor­mone stimulates the growth and activity of the thyroid gland. Chemically TSH is a glycoprotein with a molecular weight ranging be­tween 10,000 to 30,000. The concentration of TSH in blood is approxi­mately 25 mili units per ml of plasma. The daily secretion of TSH in normal individual is a little more than 2 international units per day. 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.

Prolactin (lactogenic hormone – LTH):

This hormone is also known as lactogen or galactin or mammotropic hormone.

Chemically prolactin is a polypeptide consisting of more than 205 amino acids. It has a molecular weight ranging between 25000 to 30000. This hormone has a variety of activities and according to Nicoll and Bern (1971), more than 75 different activities are ascribed to this hormone. The secretion of this hormone is under the control of hypothalamus which produces a prolactin realising factor and a prolactin inhibiting factor. 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

Or

Gonadotropic hormone (GTH):

Also called Gonadotropins, these hor­mones are secreted by the basophils of the adenohypophysis. There are two kinds of Gonadotropins in human beings. These are follicle stimulat­ing hormone (FSH) and luteinizing hormone (LH).

Follicle Stimulating hormone (FSH):

This hormone is found in both males and females influencing the activity of the reproductive structures. Chemically FSH is a water soluble glycoprotein having a molecular weight between 30000 and 67000. The main components of this hormone are Galactose, Glucosamine, Galactosamme, Mannose etc. The main function of FSH in females is to stimulate the development and maturation of ovarian follicles up to the stage of ovulation. In males FSH stimulates the process of spermatogenesis including sperm formation. FSH is also known as Gametokinetic factor as it has influence on both male and female gametes.

FSH is not found in childhood. It is secreted in little quantities only in sexually matured organisms.

Luteinizing Hormone (LH):

Also known as interstitial cell stimulating hormone (ICSH), this hormone is a conjugated protein having a molecular weight between 26000 to 30000. 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.

Hypothalamus controls the production of LH through a hormone called gonadotropin releasing hormone (GnRH). Many environmental factors like stimulation of the genitals, light, temperature etc. also have a regula­tory effect on the secretion of LH.