protein vs peptide hormones

protein=50+ aa

peptide=<50 aa

glycoprotein hormone

protein componenet and covalently linked carb component

steroid hormone

synthesized from cholesterol

amine hormone

derived from tyrosine

transport of protein/peptide hormones

water soluble, carried in plasma as simple solutes

steroid hormone transport

steroid and thyroid hormones are made of lipids--very low solubility in water

carried in blood by plasma protein transporters(production of which can be altered by metabolic and endocrine factors)

determinants of free, active hormone conc. (4)

rate of secretion, binding to plasma (transport) proteins--if applicable, metabolism (degradation) and elimination, and binding to receptor proteins

negative feedback

when hormone inhibits production/secretion of more hormone

almost always a determinant in rate of secretion

fixed hormone receptors

located on cell memb

bind protein/pep, dopamine, and catecholamine hormones

binding activates second messengers which alter intracellular enz activity

mobile receptors

present within cell (usually nucleus, sometimes in cytosol)

bind steroid and thyroid hormones

binding alters gene expression/production of enz/proteins

now there is evidence that some steroids have extranuclear effects as well, "dual mechanism"

dose-response relationship

magnitude of response to a certain concentration of hormone

sensitivity

hormone conc required to produce 1/2 maximum response

How can maximum response and sensitivity be altered?

max response: dec. in # of functional target cells or receptors, intracellular enz changes

sensitivity: dec in # or affinity of receptors, inc. in hormone breakdown

causes of hypo/hypersecretion

hyper: endocrine tumor

hypo: damage to endocrine gland

adenophypophysis

anterior lobe of pituitary

derived from oral cavity ectoderm

endocrine tissue

pars distalis, pars tuberalis, pars intermedia

downstream from hypothalamus, endocrine effects

neurohypophysis

posterior lobe of pituitary

derived from neuroectoderm

infundibulum (axons of hypothalamic neurons)

pars nervosa (axon terminal endings)

has own arterial blood supply

doesn't produce hormones, stores/releases hypothalamic hormones in response to neuronal impulses

paraventricular and supraoptic nuclei

nuclei of neurons originating in hypothalamus whose axons extend into neurohypophysis (post pit)

hypothalamus functions

pathway for "visceral" expression of CNS activity

coordinates activities of autonomic nervous system and endocrine system

produces endocrine response to neural stimuli

hypothalamus and blood-brain barrier

blood-brain barrier is weak

hormones can get into cerebrospinal fluid to act on hypothalamic neurons

hormones easily move into capillaries

hypothalamus feedback

1. from neurons

2. from anterior pituitary (ultra-short loop)

3. from trophic hormones (short loop)

4. from peripheral endocrine glands (long loop)

positive feedback in hormones

estrogen during menstrual cycle

hormones of anterior pituitary--3 classes

ProOpioMelanoCortin (POMC)--basophiles

glycoproteins--basophiles, alpha chains identical, specificity conferred by beta chains

somatomammotrophins--single chain polypeptides w 2 or 3 S-S bridges, acidophiles