Pituitary gland is one of the most important endocrine glands. It secretes a number of hormones which control a wide range of body functions. Pituitary gland is situated just below the mid brain behind the optical chiasma and lies in the cavity of sphenoid bones called Sella turcica. It is about 10mm in diameter and average weight is 0.5-0.6g in males and 0.6-0.7g in females.
It has two lobes. The anterior lobe called adenohypophysis and the posterior lobe is called neurohypophysis.
Hormones secreted by the anterior lobe or adenohypophysis are:
- Somatotrophic hormone: It is also called as growth hormone. It stimulates the body growth by influencing protein synthesis. Mobilization of fat from the adipose tissue and the free acids in the blood is accelerated by this hormone.
It also increases the intestinal absorption of calcium as well as its excretion. As it stimulates the growth of long bones and also the soft tissues, maintains retention of other minerals such as potassium, phosphate, sodium, magnesium and chloride.
Deficiency of this hormone in childhood retards growth and leads to dwarfism and over secretion causes gigantism.
- Thyroid stimulating hormone: It mainly controls the activity of the thyroid gland. These hormones speedup oxidative energy releasing process, thus controlling the rate of metabolic activities and growth.
It also influences the release of thyroxine from the thyroid gland.
Hypersecretion of TSH shows that person has hypothyroidism and thyroid gland is underactive. Less amount of TSH in blood shows thyroid gland is producing too much thyroid hormone, and the condition is called hyperthyroidism.
- Adrenocorticotropic hormone: It regulates the normal functioning of adrenal cortex and release of glucocorticoids and mineralocorticoids. It helps in the increase of the total protein synthesis and also causes the synthesis of steroid hormone from cholesterol.
Increased secretion of this hormone results in Addison disease, Cushing syndrome etc.
- Follicle stimulating hormone: In females this hormone stimulates the growth and maturation of graafian follicles and prepares them for ovulation and the action of Luteinizing hormone and enhances the release of estrogen. Hence, we can say that this hormone is very active during menstrual cycle.
In males, it stimulates growth of seminal tubule and testicular growth and early stages of spermatogenesis, the process of generation of sperms.
High FSH level shows low chances of getting pregnant. In males shows damaged testicles. It may also indication of Klinefelter syndrome.
- Luteinizing hormone: This hormone continues the action of follicle stimulating hormone and helps in maturation of graafian follicle and ovulation. This also involves in the development of corpus luteum. This hormone also stimulates the secretion of estrogen and progesterone.
In males, this hormone stimulates the interstitial cells of the testes to secrete testosterone thereby maintains the spermatogenesis.
Increased LH secretion may cause irregularities in menstruation and troubles to get pregnant.
- Prolactin or Lactogenic hormone: This hormone promotes the growth of mammary glands during pregnancy. This hormone also helps in milk secretion after delivery of the baby. Prolactin is secreted in high amount if a female is pregnant or a new mother.
- Melanocyte stimulating hormone: It influences the melanin secretion and deposition on human skin by acting on melanocytes. Increased levels of the hormone mean increased melanin deposition.
Hormones secreted by posterior lobe or neurohypophysis are,
- Oxytocin: This hormone controls the contraction of muscles of the uterus during labor. It also helps in stimulation of lactation after child-birth. This is also a chemical messenger to the brain and controls the reproductive system.
- Vasopressin: this hormone has a major role in controlling the water balance of the body. This increases the reabsorption of water from the distal tubules of nephron. If there is failure in secretion of enough amount of this hormone, large amount of dilute urine which causes excess amount of thirst. This condition is called diabetes insipidus.