The pituitary gland lies in a bony hollow at the base of the brain. It is approximately 15 mm long and 5 mm across. It is attached to the brain by a stalk or nerve fibers, which is continuous with the hypothalamus above, behind the optic chiasm.
The pituitary gland is reddish-grey in colour and roughly oval in shape. It is regarded as the master gland of the body, since through its hormones it controls the activities of many of the other endocrine organs. Basically, it consists of two distinct parts- the anterior and posterior lobes, which have several modes of development and entirely different functions.
The Anterior lobe:
This part of the pituitary gland is the larger one and produces a number of hormones which controls the production of the secretions of all the other endocrine organs.
1. The Growth hormone or Somatotrophic hormone (GH):
This hormone promotes protein anabolism, absorption of calcium and conversion of glycogen to glucose, thus influencing growth and so regulates growth in height.
Over secretion of this hormone in childhood leads to excessive growth called as gigantism and under secretion results dwarfism. In adults, over activity results in acromegaly where the hands, feet and face enlarge progressively.
Secretions of the hormone are controlled by the hypothalamus.
2. Thyrotrophic Hormone (TSH):
This hormone controls the growth and activity of the thyroid gland. It influences the uptake of iodine, synthesis of the hormone, thyroxin, by the thyroid gland and the release of stored hormones into the blood stream.
3. Adrenocorticotrophic hormone (ACTH):
This hormone stimulates the cortex of the adrenal gland to secrete its own hormone.
4. Lactogenic hormone (Prolactin):
This hormone helps to control the secretion of milk from the breast.
5. Gonadotrophic hormones:
These hormones are essential for normal development of the sex organs and stimulate the production of various sex gland hormones. They are:
(a) The follicle-stimulating hormone (FSH): In the female, this stimulates the ovarian follicles to produce Oestrogen. In the male it stimulates the production of spermatozoa in the testes.
(b) The Luteinizing hormone (LH): In the female, this stimulates the corpus-luteum of the ovary to produce progesterone and in the male it stimulates the testes to produce testosterone.
The Posterior lobe
The posterior lobe of the pituitary gland is composed of secretary cells which produces two hormones:
(a) Anti diuretic hormone (ADH) or Vasopressin: It helps to regulate the output of water from the kidney by increasing the absorption of water in the distal renal tubules and collecting ducts. It also raises blood pressure, by contracting the in-voluntary muscles of the intestine and bladder.
(b) Oxytocin: This stimulates the plain muscles of the uterus during and immediately after labour. It also stimulates the lactating breast to reject milk.