Hypophysis or Pituitary Gland

Transcription

1 Hypophysis or Pituitary Gland It is also called master gland because it not only secretes hormones for physiological effects, it also controls the development and functions of other endocrine glands whereas it is itself remains under the control of hypothalamus. Origin: - It is dual in origin, both components being derived from the ectoderm. Adenohypophysis arises from the roof of buccal cavity in the form of an outgrowth called Rathke s Pouch. The neurohypophysis originates as a downgrowth from the floor of diencephalon in the fore brain. Adenoypophysis soon loses its connection whereas neurohypophysis remain attached to the diencephalon as infundibula or, pituitary stalk. Location: - It is located in a depression, the sella-turcica or hypophyseal fossa of the sphenoid bone. Size & Weight: - The human pituitary is a reddish grey oval structure about 10 mm in diameter and 0.5 gm in weight. Structure: - The pituitary gland can be differentiated into two lobes on the basis of origin that are Adenohypophysis and Neurohypophysis.

2 Adenohypophysis:- It has following parts: - 1. Pars-tuberalis: - It is simply a supporting structure for the gland and its blood vessels. It doesn t secrete any hormones. 2. Pars-intermedia: - It is also taken as intermediate lobe. It becomes rudimentary in adult human being. 3. Pars-distalis: -

3 It forms about 75% of the hypophysis and main secretary part. It contains three types of cells that are acidophils (40%), basophils (10%) and chromophobes (50%). Neurohypophysis: - It has two sub-divisions i.e. pars-nervosa or, neural lobe and infundibulum or, pituitary stalk. It consists of non-myelinated nerve fibres and non-secretory supporting cells. Hormones of Adenohypophysis: - 1. Somatotropin or, Growth hormone or, human growth hormone (hgh) [soma body, trophe nourishment]: - It is a protein consists of 190 amino acids. It has a molecular weight of about 21,500. It acts on the liver to produced IGF-1 & IGF-2 (Insulin like growth factor). IGF-1 produces growth of bones, cartilages, muscles, viscera and the body as a whole in post-natal life whereas IGF-2 chiefly in foetus for foetal growth and differentiation. Major Functions: - Carbohydrate metabolism: - It increases blood and sugar level indeed, in past hgh was known as Growth and diabetogenic hormone. Fat metabolism: - Þ Rise of plasma FFA (free fatty acid) Þ It increases adipose tissue lipolysis. Protein metabolism: - It promotes protein metabolism. Calcium metabolism: - It increases absorption of calcium from the intestine. It also stimulates cell division.

4 2. Adrenocorticotrophic hormone (ACTH): - It is a polypeptide of molecular weight 4,500 containing 39 amino acids. It controls development and secretion of adrenal cortex. 3. Thyrotrophic hormone or, Thyroid Stimulating Hormone (TSH): - It is a glycoprotein with a molecular weight less than 10,000. It controls various aspects of the thyroid gland function including the development and maintenance. 4. Gonadotrophic Hormone (GTH): - There are three types of gonadotrophic hormones: - a) Follicle Stimulating Hormone (FSH): - It is a glycoprotein with molecular weight of about 30,000. In female it stimulates development and maturation of the ovarian follicle and one of the female sex hormone estrogens. In the male, it induces spermatogeneus in the testes. b) Luteinizing Hormone (LH) or, Interstitial Cell Stimulating Hormone (ICSH): - It is also glycoprotein with molecular weight about 30,000. In female, it helps in ovulation and development of corpus luteum that in turn secrete progesterone. In male, it stimulates interstitial cell to secrete androgens, male sex hormone. c) Lactogenic or, Luteotrophic or, Prelactin Hormone (LTH or PRL): - It is a polypeptide. In female, it stimulates growth of milk glands during pregnancy and the secretion of milk after delivery. Nicoll & Bern (1971) have found more than eight functions in other mammals except human being such as reproduction, osmoregulation, growth etc. In males & woman who aren t breast feeding, a prolactin inhibiting hormone produced in the hypothalamus suppresses

5 prolactin synthesis in the anterior pituitary. The inhibition is removed in nursing mothers by nerve impulses produced when the infant sucks on the nipples. 5. Intermedian or, Melanocyte Stimulating Hormone (MSH): - This hormone is secreted by pars-intermedia which was known by intermediate lobe. It controls or, spreads melanin in other mammals. But its function is not known in human beings whereas under certain conditions such as pregnancy, an increase in its secretion does cause some darkening of the skin. Hormone of Neurohypophysis: - Neurohypophysis doesn t secrete any hormone. It stores two types of hormones, secreted by Neurosecretory cells of hypothalamus, called pituitrin and releases it. 1. Oxytocin or Birth hormone or Milk ejecting hormone or Pitocin: - It is a polypeptide hormone contains 10 amino acids. It produces contraction of the uterine muscles. In late pregnancy, the uterus becomes very sensitive to oxytocin. It facilitates the flow of milk from mammary glands by contraction of the myoepithelial cells of lactating breast. Several observations suggest that it may play a role in the reabsorption of Na by kidney. 2. Vasopressin or, Antidiuretic hormone (ADH) or Pitressin: - It is a polypeptide. It increases reabsorption of water by kidney. As a result concentrated urine is secreted. (Dimosis Release of dilute urine). It also contracts the involuntary muscle of the intestine, gall bladder, urinary bladder and blood vessels. Contraction of the muscle layer in the blood vessel will raise the blood pressure.

6 Disorder of Pituitary Gland: - 1. Hyposecretion of Growth Hormone: - (i) Dwarfism: - It is caused by hyposecretion or deficiency of growth hormone in childhood. It is of two types: - A. Lorain Type: - In this disease mentally and sexually normal. But growth of long bones of the body stops prematurely making the patient dwarf. B. Frohlich s Type: - In this disease, obesity, mental deficiency and sexual development are also retarded. (ii) Simmond s Disease: - It is caused by deficiency of growth hormone in adult. This condition is very rare. The skin becomes dry & wrinkled, the hair grey & sparse & there is degeneration of the sexual organs with cessation of menstruation in female.

7 The image cannot be displayed. Your computer may not have enough memory to open the image, or the image may have been corrupted. Restart your computer, and then open the file again. If the red x still appears, you may have to delete the image and then insert it again. 2. Hypersecretion of Growth Hormone: - (i) Gigantism:- It is caused by excess of growth hormone from childhood. The patient gets excessive skeletal growth and the individual may become 8 or 9 feet tall. (ii) Acromegaly: - It is caused by hypersecretion in the adult or, after union of epiphyses of bones. There is excessive growth of the bones of the face, specially the frontal bone and the mandible. The hands and feet become large and spade like. There is also thickening of the skin on the face and hands.

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9 3. Hyposecretion of ADH:- (i) Diabetes Insipidus (inspidus tasteless):- Due to deficiency of ADH, reduces reabsorption of water and increases urine output, causing excessive thirst.