Lec 06 Flashcards
Cell can adjust their sensitivity to hormone
Adjust sensitivity of receptor (min/hour FASTER)
Adjust number of receptors (days/week)
Up-regulation
Try to maintain response despite low hormone conc.
Increase number of receptors in response to sustained low hormone conc.
Down-regulation
Decrease receptor number in response to sustained high hormone conc.
Usually Endocytosis of membrane receptors
Up/down regulation are long-term effects
Time required for endo/exocytosis, proteins synthesis
Faster changes may be achieved by ——
Sensitization—desensitization
Modification of existing receptors to change their activity
**total number of receptors does not change
Tropic hormones
-Many neurohormone of the hypothalamus
-hormone of the anterior pituitary
— target another endocrine gland to control hormone release
Synergism
Influence of multiple hormones
— there is functional overlap of hormones
— combination of any chemical signal
Permissiveness
B is permissive for A if:
— if hormone A can’t produce its full effect without the presence of hormone B
-B does not need to have same effect like A
Hormones as functional antagonists
-opposite action
-insulin vs glucagon
-don’t need to share receptors or signaling pathways
Insulin cycle
1-STIMULUS: Blood glucose level rises 2- Pancreas betta cells produce insulin
3- liver takes up glucose and store as glycogen
3- body cells takes up more glucose
4- Blood glucose level declines
5-homeostasis
Glucagon cycle
1-STIMULUS: Blood glucose level decreases
2- Pancreas alpha cells produce glucagon
3- liver breaks down glycogen and release into blood
4- Blood glucose level rises
5-homeostasis
Ligand
Chemical molecule that bind to the receptor
**Primary ligand usually
Agonist
Ligand that binds to a receptor and enhances its activity
Antagonist
Ligand binds to a receptor and inhibits its activity
Target cell response determined by receptor and intracellular signal pathways not the ligand
Agonist for this receptor can be antagonist for the other
Specificity
Receptors may show preference for particular ligand
-very specific—bind very few ligands
-non-specific—bind many different ligands(not at same time)
**ligands can have specificity for receptor as well
Competition
Multiple ligand may compete for same receptor
-usually one has higher affinity
-overall effect of each ligand decrease compared if they were the only one
Competitive antagonist
Same binding site on receptor as agonist
—can be overcome by increasing agonist conc.
Non-competitive antagonist
Different binding site on receptor(allosteric site)
-or same active site but cannot unbind (irreversible antagonist)
-cannot overcome by increasing agonist concentration
Dose-response curve
%response depends on agonist conc.
-increases with %of receptors bound to agonist
-if agonist conc. Is high enough, receptor will be saturated and response is maximal
EC50
Agonist concentration producing 50% of the max response
Competitive antagonist and dose-response curve
Make it mire difficult for agonist to bind
-max response can still be achieved with increasing agonist concentration
**EC50 INCREASES BY ANTAGONIST CONCENTRATION INCREASE
Non-competitive antagonist and dose-response curve
Change availability of binding site or irreversibly block it
**DECREASE IN MAX POSSIBLE RESPONSE BY INCREASE IN ANTAGONIST CONCENTRATIONS
