Introduction and locationThe pituitary gland has the regulatory influence on almost all the endocrine gland of the body, hence pituitary gland is regarded as master gland. The pituitary gland also forms a link between the nervous and endocrine system and maintains functional coordination between the two. Name pituitary was given by Vesalius. Pituitary develops from ectoderm of the embryo.
(Note: Image curtsey: https://en.wikipedia.org)
The pituitary gland is located on the ventral side of the brain in the region of diencephalon just behind the optic chiasma where the optic nerves cross each other. Pituitary gland lies in the cavity of the sphenoid bone, called sella turcica on the floor of the cranial cavity. The pituitary gland is a small, reddish-grey, rounded unpaired body, about the size of large pea weighing about 0.5 gm in man and usually becomes much larger in the pregnant woman. The pituitary gland hangs below the hypothalamus by a stalk called infundibulum> Hypothalamus is a part of the brain.
Structure of Pituitary gland The pituitary gland has three different parts:
The anterior lobe is a compact and highly vascular part. The anterior lobe is connected to the hypothalamus by hypophysial portal vessels. The anterior lobe and intermediate lobe are together known as adenohypophysis while the posterior one is known as neurohypophysis.
AdenohypophysisAdenohypophysis is the largest compact and vascular part of the pituitary in all vertebrates. Adenohypophysis develops as an outgrowth of the pharynx, called Rathke's pouch and is made up of three parts: Pars distalis, pars tuberalis, and Pars intermedia. Pars distalis is the largest part of the adenohypophysis. Pars distalis forms about 75 percent of the gland.
Neurohypophysis Neurohypophysis is the posterior part of the pituitary gland which forms the 1/4th portion of it. Neurohypophysis is connected to the brain with the help of infundibular stalk. The hormone of the posterior lobe is synthesized in the hypothalamus, they are carried along nerves to the posterior lobe which stores and secretes them into the blood.
Hormones of Adenohypophysis
The adenohypophysis releases six hormones which control the activities of various other endocrine glands also.
Somatotrophic hormone (STH) or Growth Hormone (GH)
GH acts directly on almost all tissues of the body to regulate general body growth. GH also controls protein, fat and carbohydrate metabolism to a great extent.
Hyposecretion of GH The hyposecretion of growth hormone causes following diseases:
Hypersecretion of GH The hypersecretion of growth hormone causes following diseases:
Lactogenic Luteotrophic Hormone (LTH)
It is also known as the Luteotrophic hormone or Mammotrophic hormone. Nicol and Bern called this hormone as "Jack of all trades" because of more than seventy-five different hormonal activities performed by it. this hormone has the following main functions:
Hyposecretion of LTH: Size of mammary glands is reduced. Milk is also not produced.
Hypersecretion of LTH: More milk is produced in mammary glands. The glands also become large sized. Lactation may occur ever without childbirth.
Adrenocorticotropic Hormone (ACTH)
The functions of ACTHare as follows:
Thyrotrophic or Thyroid Stimulating Hormone (TSH)
The primary function of TSH is to regulate the growth of the thyroid gland and its secretory activity. Thyrotrophin promotes accumulation of iodine and increases the quantity of intracellular colloid in the thyroid epithelial cells and induces the liberation of thyroxine hormone.
Gonadotrophins or Gonadotrophic Hormone (GTH)
These are two gonadotrophins secreted by basophils of adenohypophysis which control various activities of gonads:
Hypoactivity of GTH: In females, if Gonadotrophic Hormones are secreted in insufficient quantity, size of the ovary is reduced. Follicles are destroyed. Uterus and vagina are also deformed. In males also the condition leads to the collapse of the sexual reproductive system. Testes are diminished in size. The testes remain inside the abdomen if the deficiency of the hormone occurs in fetus stage. Suc males are called cryptorchid.
Hypersecretion of GTH : Over secretion gonadotrophic hormones leads to sexual prematurity.
melanocyte stimulating hormone (MSH)
MSH is secreted by the intermediate lobe of the pituitary. MSH influences chromatophore system in fishes, amphibians, etc. The role of MSH in mammals is not yet very clear. In man, MSH hormone controls the changes in the colour of skin.
Hormones of Posterior Lobe Neurohypophysis
The Neurohypophysis or posterior lobe of pituitary releases the following two peptide hormones. Both of these hormones are synthesized in the hypothalamus and are carried to the neurohypophysis along with nerve fibers where they are stored and then released into the blood.
Antidiuretic (ADH) or Vasopressin Hormone
ADH plays an important role in osmoregulation. ADH is released in response to stress and dehydration. When the body fluids become highly concentrated, the impulses are transmitted to the posterior lobe and ADH is released by way of blood. ADH reaches kidneys where it increases the permeability of the distal tubules and collecting tubules to water, as a result, most of the water is reabsorbed from the urine. ADH is inactivated primarily in the kidney and liver and then excreted along with urine. ADH also controls blood pressure. Alcohol inhibits the ADH secretion.
Oxytocin is an important uterus contracting hormone at the time of childbirth. Oxytocin also increases the motility of uterus during coitus thereby promoting fertilization. Pitocin also acts on mammary glands and helps in the milk ejection by initiating the contraction of smooth muscles and the myoepithelial cells which encircle the alveoli and cause expulsion of milk.
So it is clear that Pituitary gland controls all other endocrine glands of our body, hence Pituitary gland is called master gland of our body. The pituitary gland is also referred as Piyush gland. The removal of the pituitary gland is called hypophysectomy.
Hakimuddin Kuwakhedawala is based in India with over 15 years experience as a teacher. Teaching and writing are his passion. Most of the articles of Hakimuddin are related to education, exam, environmental problems, etc.
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