Week 1: Vasoconstrictors and Direct Vasodilators Flashcards
SNS
Thoracolumbar origin (T1-L2)
Preganglia near spinal cord
Post ganglia secrete ______ -adrenergic fibers
Norepinephrine
Norepinephrine:
_______ converts dopamine to NE
Dopamaine beta hydroxylase
An action potential releases NE for synaptic vessel
NE signal termination:
- reuptake
- dilution by diffusion
NE is metabolized by:
Monamine Oxidase (MAO) and Catechol-o-methyltranserase (COMT)
Adrenergic Receptors: SNS
Alpha 1 receptors stimulates:
Periphery
Post synaptic receptor:
- activation increases intracellular Ca
- smooth muscle contraction (vessel constriction)
- Peripheral vasoconstriction
- Bronchoconstriction (Beta 2 overrides)
- inhibits insulin secretion (beta 2 overrides)
- stimulates glycogenolysis and gluconeogenesis (SNS)
- Mydriasis (dilated pupils)
- GI relaxation (stops parastalsis)
Adrenergic Receptors: SNS
Alpha-2 receptors stimulates:
Negative feedback loop
Presynaptic in PNS
- decreases entry of Ca into the cell
- limits the release of NE
Post synaptic in CNS
- sedation
- decreased sympathetic outflow
- decreased BP
- platelet aggregation
Adrenergic Receptors: SNS
Beta-1 receptors stimulates:
Postsynaptic Receptor:
- increases HR
- increases conduction velocity
- increases myocardial
Adrenergic Recptors: SNS
Beta-2 receptors stimulates:
Postsynaptic receptor:
- stimulation leads to smooth muscle relaxation
- perpherial vasodilation
- decreases BP
- BRONCHODILATION
- increases insulin secretion
- increases glycogenolysis and gluconeogenesis
- decreases GI mobility
Parasympathetic NS: Cholinergic
Craniosacral (Brain & Butt) origin:
Postganglia secrete______
Cranial Nerves: III, V, VII, X
Sacral nerves 2,3,4
Preganglia near organs of innervation
ACETYLCHOLINE (ACH)
______ activates BOTH arms of the SNS
Acetylcholine (ACH)
Choleine+AetylCoA –> acetylcholine
(Choline acetyltranserase)
Calcium medicated action potential
Acetylcholine is deactivted/broken down by:
Acetylcholinesterase–> Choline and acetate
Cholinergic receptors (PNS):
Nicotinic
Muscarinic
Up-Regulation:
Chronic depletion of catecholamines or use of antagonists increases the number of receptors, but not their sensitivity.
May account for withdrawal syndrome with beta blockers
Down-Regulation:
Extended exposure to agonists reduces the number of receptors, but not their sensitivity.
Results in tachyphylaxis.
Receptor desensitization/ Down-regulation:
Receptor uncoupling:
Desensitization is the reduction in a physiologic response over time to a stimulus that remains constant.
Un-coupling:
- occurs rapidly (takes seconds to minutes)
- inability to the receptor to bind G protein (alter function of the receptor)
Uncouples the receptor from the signal transduction system. Caused by the phosphorylation of the receptor and possibly the G protein.
Receptor desensitization/ Down-regulation:
Sequesteration:
- occurs more slowly (minutes to hours)
- movement of receptors from the cell surface to intracellular compartments
Receptors moved from cells membrane to intracellular compartments are not accessible to hydrophilic ligands
Receptor desensitization/ Down-regulation:
Down-regulation:
- prolonged process (hours to days)
- Movement of receptors from the cell surface to intracellurlar compartments, but then destroyed.
Receptors are not available for recycling to the cell surface. New receptor protein must be made from RNA to replace lost receptors.
