NROSCI/BIOSC 1070 MSNBIO 2070 September 14, 2015

Functions of Hormones Hormones act on their target cells in one of three basic ways: 1. Control the rate of enzymatic reactions 2. Control transport of molecules across cell membranes 3. Control gene expression and synthesis

Types of Hormones Peptides Amino Acids Steroids

Divisions of Pituitary Anterior pituitary (also called adenohypophysis) True glandular tissue Posterior pituitary (also called neurohypophysis) Extension of brain

Hypothalamic-Hypophyseal Portal System

Tropic Hormones — Control the Release of Other Hormones Anterior Pituitary Hormones are Tropic Hormones End Products Regulate Tropic Hormone Secretion Short Loop Feedback Long Loop Feedback Ultra Short Loop Feedback

Anterior Pituitary Hormones No Known Tropic Role

Proopiomelanocortin (POMC) POMC is cleaved within a vesicle to form ACTH,  -Endorphin,  LPH, and 16K fragment

Hypophysiotropic Hormones: Control Anterior Pituitary Secretions Others likely exist, but have not been discovered because of their low concentrations in blood

What happens if feedback mechanisms are dysfunctional? Tumors can produce large amounts of hormones without feedback regulation Autoimmune diseases can damage receptors on hormone-secreting cells, so they no longer respond to tropic hormones Intracellular signal transduction pathways can become aberrantly altered, thereby affecting how hormone-producing cells respond to tropic hormones.

Posterior Pituitary Hormones Arginine Vasopressin Named as such because the first vasopressin discovered was from pig; this hormone has a lysine instead of arginine as residue 8 Produces vasoconstriction when present in high concentrations (hence the name) Affects water reabsorption in kidney at lower concentrations, hence the secondary name: antidiuretic hormone Oxytocin Triggers uterine contractions during birthing Triggers milk release from mammary glands during suckling May have roles in cardiovascular control and renal function (men and women who are not of child-bearing age also synthesize oxytocin)

Posterior Pituitary Hormones Posterior pituitary hormones are synthesized by neurons in the paraventricular and supraoptic nuclei of the hypothalamus These hormones are released like neurotransmitters when the neurons fire The release of the hormones is dependent on the number of neurons that fire and the rate and duration of their firing

Examples of Some Hormones Hormon e Where Produce d EffectStimu-lation Inhi- bition LH Anterior Pituitary Stimulates Leydig cells of testis to synthesize & release testosterone; stimulates estrogen & progesterone secretion by corpus luteum; stimulates ovulation GnRH from Hypo- thalamus Testos- terone, estrogen, proges- terone, Inhibin Testos- terone Leydig Cells of Testis (mainly) Production & maintenance of male sexual characteristics LH from anterior pituitary None Erythro- poietin Tubular epithelial cells of Kidney Stimulation of red blood cell production by bone marrow Hypoxia of tubular epithelial cells None Aldos- terone Adrenal cortex Promotes reabsorption of Na + and excretion of K + by tubular epithelial cells of kidney Increased K + in plasma, Angiotensin II Increased Na+ in plasma Gastrin G cells of stomach Stimulates acid secretion by stomach Peptides and amino acids in stomach; enteric nervous system Somato- statin and low pH in stomach Insulin Islets of Langer- hans Enhances glucose transport by many tissues; increases glucose metabolism and storage High plasma glucose levels, hormone GIP, parasym- pathetic activity Sympa- thetic activity Epin- ephrine Adrenal medulla Many effects mediated by binding to  - receptors Sympathetic nervous system influences on Adrenal medulla None