Pituitary gland.

The pituitary.

The pituitary Gland.

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.

Gigantism

Acromegaly

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.