NROSCI/BIOSC 1070 MSNBIO 2070

September 14, 2015

Control 2

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

PeptidesAmino AcidsSteroids

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 FeedbackLong Loop FeedbackUltra Short Loop Feedback

Anterior Pituitary Hormones

No Known TropicRole

Proopiomelanocortin(POMC)

POMC is cleaved within a vesicle to form ACTH, β-Endorphin, γLPH, 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 regulationAutoimmune diseases can damage receptors on hormone-secreting cells, so they no longer respond to tropic hormonesIntracellular 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

Hormone

Where Produce

dEffect Stimu-

lationInhi-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

stomachInsulin

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 β-

receptors

Sympathetic nervous system

influences on Adrenal

medulla

None