Trophic hormones – secreted by the anterior pituitary (the pars distalis of the adenohypophysis)

Trophic – “feed”

High concentrations = hypertrophy of target organ

Low concentrations= atrophy of target organ

PITUITARY HORMONES

1. Growth Hormone (GH or somatrotropin)-promotes movement of amino acids overall tissue and organ growth

2. Thyroid-stimulating hormone (TSH or thyrotropin)-stimulates thyroid gland to produce and secrete thryoxine and triiodothyronine

3. Adrenocoritcotropic hormone (ACTH or corticotropin)-stimulates adrenal cortex to secrete glucocorticoids such as hydrocortisone

Hormones of Anterior Pituitary Hormones:

4. Follicle-stimluating hormone (FSH or folliculotropin)-stimluates the growth of ovarian follicles in females-production of sperm cells in males

5. Luteinizing hormone (LH or luteotropin)-with FSH are collectively called gonadotropic hormones- in females: stimluates ovulation and conversion of ovulated ovarian follicle into a corpus luteum.-in males: sometimes called interstitial cell stimulating hormone (ICSH); stimulates secretion of male sex hormones from interstitial cells in the testes

6. Prolactin (PRL)- stimulation of milk production by mammary glands after birth of baby- regulation of male reproductive system by gonadotropins -help regulate water and electrolyte balance

*Pituitary dwarfism – inadequate growth hormone during childhood - pituitary cachexia (Simmonds’ disease) for adultsGigantism-oversecretion of growth hormone

Stores and releases 2 hormones:1. Antidiuretic hormone (ADH or arginine

vasopressin [AVP])-promotes retention of water by the kidneys- “pressor effect” – vasoconstriction in experimental animals

2. Oxytocin -females: stimulates contraction of uterus during labor; contraction of mammary glands-males: rise in oxytocin secretion at time of ejaculation

Posterior Pituitary (pars nervosa)

produced in neuron cell bodies of supraoptic nuclei and paraventricular nuclei of the hypothalamus

Hormones produced are transported along axons of the hypothalamo-hypophyseal tract to the posterior pituitary (stored and later released)

Release of ADH and oxytocin is controlled by neuroendocrine reflexes

injection of oxytocin to pregnant women to induce labor; severe pregnancy-induced hypertension or preeclampsia.

“master gland” Secretes hormones that regulate other

endocrine glandsHormone & Target Organ:Prolactin mammary glandGH bone, muscle, adipose tissueTSHThyroidACTHadrenal cortexFSH & LHovary and testis

Hypothalamic Control of the Anterior Pituitary

Produced by neurons in the hypothalamus; transported to axon endings in the basal portion of the hypothalamus (median eminence)

Deliver blood to second capillary bed in the anterior pituitary (link between the median eminence and anterior pituitary form a portal system)

Hypothalamo-hypophyseal portal system – vascular link between the hypothalamus and anterior pituitary

Releasing and Inhibiting Hormones

HYPOTHALAMIC HORMONE EFFECT ON ANTERIOR PITUITARY

Corticotropin-releasing hormone (CRH)

Stimulates the secretion of adrenocorticotropic hormone (ACTH)

Gonadotropin-releasing hormone (GnRH)

Stimulates the secretion of follicle-stimulating hormone (FSH) and luteinizing hormone (LH)

Prolactin-inhibiting hormone (PIH) Inhibits prolactin secretion

Somatostatin Inhibits secretion of growth hormone

Thyrotropin-releasing hormone (TRH)

Stimulates secretion of thyroid-stimulating hormone (TSH)

Growth hormone-releasing hormone (GHRH)

Stimulates growth hormone secretion

Releasing and Inhibiting Hormones

Hypothalamus

Thyrotropin-releasting hormone (TRH)

Anterior pituitary

Thyroid-stimulating hormone (TSH)

Thyroid

Thyroxine

The Hypothalamus-pituitary-thyroid axis (control system)