Session 5.1 Flashcards
What does the ANS control in the cardiovascular system?
- heart rate
- inotropy
- peripheral resistance
How does parasympathetic input into the heart work?
Preganglionic fibres synapse with post ganglionic cells on epicardial surface
Post ganglionic cells release ACh
Acts on m2 receptors (GPCR) which increase k+ conductance and decrease cAMP
- decrease Heart rate
- decrease AV node conduction velocity
How does sympathetic input in the heart work?
Post ganglionic fibres from sympathetic trunk innervate SA node, AV node and myocardium = release noradrenaline
Acts mainly on B1 adrenoreceptors to increase heart rate and have a positive inotropic effect
GPCR increases cAMP and speeds up pacemaker potential
How does noradrenaline increase force of contraction?
NA acting on B1 receptors in myocardium causes an increase in cAMP which activates PKA.
1) phosphorylation of Ca2+ channels increase Ca2+ entry during the plateau of the AP
2) increased uptake of Ca2+ in sacroplasmic reticulum
Leads to increased force of contraction
What receptors are in arteries and how does vasoconstriction occur?
A1 adrenoreceptors in arteries and veins
Decreased sympathetic output = vasodilation
Increased = vasoconstriction
Which blood vessels have b2 adrenoreceptors as well as a1 and how will this effect adrenaline binding?
Skeletal muscle
Myocardium
Liver
Adrenaline has a higher affinity for b2 than a1, so will preferentially bind to b2. At higher conch it will also activate a1 receptors
What does activation of b2 adrenoreceptors do?
Causes vasodilation
Increases cAMP to PKA opens potassium channels and inhibits MLCK relaxation of smooth muscle
What does activation of a1 adrenoreceptors do?
Vasoconstriction
Stimulates IP3 production
Increases in ca2+ in from stores and via influx of extracellular ca2+ contraction of smooth muscle
What are baroreceptors?
Nerve endings in the carotid sinus and aortic arch that are sensitive to stretch.
Increased arterial pressure stretches these receptors
What is the baroreceptor reflex when mean arterial pressure increases?
1) mean arterial pressure increases
2) detected by baroreceptors
3) via afferent pathways goes to medulla
4) via efferent pathways bradycardia and vasodilation counteract increased mean arterial pressure.
What are sympathomimetics?
A1 adrenoreceptors agonist and B2 adrenoreceptors agonist
- restore function in cardiac arrest
- adrenaline administered for anaphylactic shock (for vasodilation)
- B2 agonist acts on receptors on bronchioles smooth muscle for vasodilation e.g salbutamol
Why would you want a heart drug antagonist to be selective for b1 instead of b2?
B2 is also in the lungs = antagonist causes bronchoconstriction
B1 is more cardio selective
What is glucoma?
Build up of pressure in space above lense
