Pituitary Gland • Is also known as Hypophysis • Sits in the small bony cavity Sella Turcica at the base of the brain. • Secretes hormones regulating homeostasis including trophic hormones that stimulate other endocrine glands. • 3 lobes-Adenohypophysis also known as the anterior pituitary and the neurohypophysis also known as the Posterior hypophysis.
Pituitary Gland • Also an intermediate lobe that secretes MSH.Rudimentary. • Anterior pituitary synthesize and secretes ACTH, LH,FSH,GH,TSH,prolactin. • Posterior pituitary secretes oxytocin and ADH. • Posterior lobe is connected to the hypothalamus through the pituitary stalk • Hormones are actually made in the nerve cell bodies of the hypothalamus and then transported down the posterior pituitary
ACTH • Is a polypeptide • Acts on the adrenal cortex • Secreted in response to the corticotropin-releasing hormone (CRH) from the hypothalamus. • Consists of 39 amino acids and 13 may be cleaved to (MSH). • Hypocortisolism and Addison’s disease have tanned skin. • Stimulates the cortex of the adrenal gland to produce corticosteroids, mainly glucocorticoids. • Excess ACTH-Addison’s disease Small cell carcinoma Congenital Adrenal hyperplasia Cushing’s syndrome.
TSH • Is a glycoprotein • Also known as Thyrotropin • 2 subunits • α and β • α is identical to HCG,LH,FSH • β subunit is unique to TSH therefore determines its function. • Stimulates thyroid gland to secrete T3, T4 • Controlled by Thyrotropin-releasing hormone (TRH)
TSH (ctd) • Stimulating antibodies to this receptor mimic TSH action and found in grave’s disease.
Luteinising Hormone • A glycoprotein • Also known as Lutropin • Acts in concert with Follicular stimulating hormone • Play a part in normal reproductive function. • In females, an acute rise triggers ovulation. • In males, stimulates leydig cells to produce testosterone. • Controlled by Gonadotropin-releasing hormone.
Follicle Stimulating Hormones. • A glycoprotein. • Acts in synergy with LH. • In women, stimulates the growth of immature Graafian follicles to maturation. • In men, enhances production of sperm cells. • Half life of 3-4 hrs. • Controlled by Gonadotrophin-releasing hormones . • High in menopause and low in childhood. • High levels is indicative of defective feed-back from the gonads.
FSH (ctd) • High levels is typical in menopause, but abnormal in reproductive years and may be a sign of------- Premature menopause Gonadal dysgenesis, Castration. Testicular failure. Low levels is seen in.. Kallman syndrome Hypopituitarism Hypothalamic causes Drugs-GnRH antagonists.
Prolactin • A peptide hormone • Associated with lactation. • In breast feeding, suckling reflex—prolactin production—Fills breast with milk (lactogenesis) • Production is regulated by neuroendocrine neurons of the hypothalamus.
Growth Hormone • Also known as Somatotropin. • A protein hormone. • Stimulates growth and cell production. • Excess GH leads to acromegaly and Gigantism. • Highest amount of GH is secreted during puberty. • Regulated by GHrH and somatostatin. • Other stimulators are.. Sleep, exercise, Reduced blood sugar, dietary protein, estradiol. • Inhibitors are ..somatostatin, circulating GH, Dietary carbohydrates, glucocorticoids.
Regulation of GH • GH release is stimulated by the GHrH • Which act on somatomedins(IGF-1 somatomedinC) • Act to increase growth of cells, cartilage and protein metabolism. • GH release is inhibited by Somatostatins which are produced in the hypothalamus. • Secretion of somatostatins is stimulated by increased circulating levels of GH. • Other sites where we find somatostatins are the GIT and pancreas.
Dwarfism • Can be due to GHrH deficiency, GH deficiency or other cause. • Extreme shortness • But proportional body parts. • Other causes not due to pituitary GH are osteodystrophy, achondroplasia.
Oxytocin • In females, released in large amounts after distension of the cervix and vagina during labor. • Actions. let-down reflex and uterine contraction in lactating mothers. • Acts on the mammary glands causing milk let-down into collecting chamber where it is extracted by suckling the nipple. • Suckling produces stimulation of the neurons that make oxytocin to fire action potential which results in pulses of oxytocin from the pituitary.
Oxytocin • Also important for uterine contraction—important for cervical dilatation before birth at the 2nd and 3rd stages of labor. • During breastfeeding, causes mild but painful contractions of the uterus during the first few weeks of lactation. • Other actions.. sexual arousal and bonding-monogamous pair bond.
Antidiuretic Hormone • A peptide hormone. • Also known as vasopressin. • Released during dehydration. • Regulates retention of water within the body. • Act by increasing the permeability of the collecting duct to water and allows water reabsorbtion and excretion of small volume of concentrated urine. • Also induces moderate vasoconstriction. • Regulation—Reduced plasma volume---increased production. • Other influences are caffeine and ethanol which reduces secretion. • Angiotensin II stimulates secretion.
Pituitary insufficiency • The changes that develop in pituitary insufficiency are predictable in terms of the known hormonal functions of the gland • In hypopituitarism, the adrenal cortex atrophies. • They develop reduced glucocorticoids and sex hormones. • Initially,no mineralocorticoid deficiency • Growth is inhibited, • Thyroid function is depressed • The gonads atrophy • Sexual cycles stop • Some secondary sexual characteristics disappear.
Pituitary Hyper function • Usually due to tumors of the pituitary • Cause symptoms of hyper secretion of the hormones.