physiology: endorcine #1: structure/function/mechanisms

hormones are generally chemicals that are SECRETED INTO THE BLOOD ('cept paracraine). generally are used to keep the body in homeostasis, but can also be important for growth, reproduction, etc.

four categories:

endocrine: secreted and have effect far away

neurocrine: signal is processed through nerves which release factors which are carried through the blood to distant sites of action

paracrine: chemical diffuses into the interstitial fluid and affects only its neighbors.

autocrine: substance feeds back directly on the cell of origin.

the pituitaries:

anterior does: ACTH (adrenocordicotropic hormone), growth hormone, prolactin, thyroid stimulating hormone (TSH), lutenizing hormone (LH), follicle stimulating hormine (FHS).

Posterior Pituitary: ADH/oxytocin

Thyroid (T4 and T3, triodothyroxine)

parathyroid: parathyroid hormone (PTH)

testis: testosterone

ovary: estradiol

pancreas: insulin, gulcagon, somatostatin.

hypothalmus (these are the "releasing" hormones: GHRH, LHRH, TRH, CRH

heart: ANP

kidney: erythropotein, renin

Liver: insulin-like growth factor (IGF-1)

platelets (PDGF = platelet derived growth factor, transforming growth factor (tgf-b)

macrophages: cytokines

GI: gastrin, secretin, VIP.

1. peptide hormones.

2. catecholamines;

3. thyroid hormones:

4. steroid hormones.


1. Peptide hormones: pre-pro-hormone is longest and has a signal-sequence with it (= pre section), which is cleaved in the ER.

the "pro-hormone" goes to the golgi and is modified to become a 'hormone' and packaged in its secretory granules.

note that peptide hormones are water soluble, so they can float around the blood without a carrier: but they generally don't cross the cell membrane of the target. they general react with a receptor on the cell's surface.

catecholamines: made from tyrosine, stored in granules (like peptide hormones) and released like peptide hormones.

thyroid hormones:

also made from tyrosine! involve adding iodines to it.

steroids: made from CHOLESTEROL. not stored really...signals to up expression turn on the pathway that converts cholesterol to the hormone of interest.

includes: cortisol, aldosterone, androgen, estrogens, progesterone, vitamin

in peptide hormones, disease is either in the hormone itself or in the receptor (insulin is an example)

if steroid, mutation is usually in a gene that helps process cholesterol into the hormone of interest.

a GTP-binding protein helps get the granule put on the cell surface.

upping intracellular Ca++ (from ER stores, usually) is required.

cAMP levels go up, which stims protein phospho. cAMP and Ca++ protein kinases help get TUBULIN going and make microtubules.

Myosine gets phosphoed (it's sitting on the vessicle membrane), which helps interaction with microfilaments and gets the granule moving to the surface.

negative feedback:

hormone-plasma protein binding affects turnover.


turnover = mg/min (cleared) / concentration.

this also equals mL of plasma cleared/minute

different for steroid and peptide hormones.

steroid hormone effects limited by NUMBER OF RECEPTORS, so effects are limited by the percentage occupied (receptors are the limiting factor). there are no spare receptors when experiencing a maximum effect.

for peptide hormones, full expression happens at comparatively low 'occupancy' - there are tons of "spare receptors" which go unused, even when effect is maximum.

the effect of having lots of left over receptors even at maximal effect may be due to "signal amplification"