Structure, Function, and Mechanisms Flashcards
endocrine function
circulate in body fluids and produce a specific effect on the activity of the cells, away from its point of origin
neurocrine function
transmit molecular signal from neuron to its axon and then into blood stream to distant target cells
paracrine function
secreted by endrocrine cells can also reach and act on target cells within the same locale simply by diffusing through the intersitial fluid separating the adjacent cells
autocrine function
act back on the cells of their origin to modulate their own secretion or other intracellular processes
preprohormone
peptide hormone right after translation before modification to final form
prohormone
after the signal peptide is removed from the preprohormone within the ER
then transferred to the golgi for final processing and packaged into secretory granules
peptide hormones characteristics
soluble in blood and thus circulates without being bound to anything
not soluble in the lipid environment therefore cannot enter the cells by simple diffusion
catecholamine hormones
epinephrine, NE, DA
made from tyrosine
stored in the secretory granules and secreted in a manner similar to that of peptide hormones
thyroid hormones
T3 and T4
made from tyrosine and iodide that occur with the amino acid already present in a large protein molecule
secretione of TH requires retrieval and enzymatic release form its protein storage form
steroid hormone
cortisol, aldosterone, androgen, estrogen, and progestins, vit D
made from cholesterol by a series of reactions
not stored to any appreciable amount within the gland of origin
activation of biosynthetic sequence from cholesterol increases secretion of these hormones
steps that lead to peptide hormone secretion
- require increase of Ca2+ and cAMP
- stimulates phosphorylation via cAMP and Ca+ dependent kinases
- phosphorylate tubulin and promote microtubule and microfilament formation, which promote granule movement to the plasma membrane - Ca2+ also activates myosin light chain kinase leading to phosphorylation of myosin which is located on the surface of secretory granules
initial determinant of the rate of hormone action
reaction between the hormone and receptor
receptor kinetics
?????
Scatchard Plot
represents ratio of bound hormone to free hormone
should be a straight line with a negative slope
slope = - Kd
intercept = Ro (receptor capacity)
**only small occupancy of receptors with hormone can yield max response
straight line = no cooperativity
exponential = negative cooperativity
spare receptors
amount of unbound receptors when maximum response is achieved
with peptide hormones, relatively high due to greater signal amplification (secondary messengers)
secondary messenger examples
cAMP cGMP Ca2+ IP3 DG
hormone dose response curve
sigmoidal like an enzyme curve
shift down = decrease maximum responsiveness
shift right = decrease sensitivity
how can amount of hormone secreted be determined from plasma and urine samples
radioimmuno assay (RIA)
ELISA
problem with RIA
measures antigenic amounts of hormone, which may not be biologically active amount of hormone
and thus may not always be important for receptor binding
ELISA
just as sensitive as RIA without the problem of radioactive waste
binding of hormones by plasma proteins greatly influences the (?) of hormonal turnover
rates of
metabolic clearance rate
expresses the sum of hormonal removal
equals the mass of hormone removed per unit of time divided by its plasma concentration
Atrial and brain natriuretic peptide (ANP and BNP)
released by heart in response to an elevation of atrial pressure or blood pressure
(+) increase excretion of salt and water by the kidneys
(+) relaxation of vascular SmM and thus lower bp
(+) guanylyl cyclase/natriuretic peptide receptor –> (+) cGMP –> cGMP dependent kinases
nitric oxide
paracrine mediator
made by NO synthase (Ca2+-calmodulin dependent enzyme that accelerates conversion of Arg –> citrulline and NO)
NO causes vasodilation in immediate viscinity
(+) cGMP
