10. Cardiac Output Flashcards
Cardiac Output=
Heart Rate x Stroke Volume
What do the sympathetic nerves innervate?
SA node, AV node, atria and ventricles
Stimulate at beta-1-adrenoceptors
What is the role of the parasympathetic nervous system on the heart?
Vagal nerve endings release ACh
aInhibit heart by action at M2 Muscarinic Receptors
Act on SA node, AV node, atria
Action of noradrenaline on cardiac mucle
Bind to beta receptors
Activation of adenylate cyclase
Increase production of cAMP
Action of noradrenaline on the SAN
cAMP binds to Na+/K+ channel Increased entry of Na Reaches threshold action potential Opens slow L-type Ca channels Increase HR
Action of noradrenaline on the atria and ventricles
cAMP increases permeability to Ca
Increased Ca= increased force contraction
Effect of acetylcholine
Binds to muscarinic receptors
Decreases cAMP and Na/K channel
Decrease HR
What is the effect of beta blockers on heart rate?
Slow heart rate by 10+ bpm
Prevent noradrenaline binding
How does the vagus stimulate the heart?
Action on SA node to decrease HR
Strong stimulation can stop heart for few seconds
At rest heart is under vagal control
What increases resting HR?
Atropine, prevents acetylcholine binding
Sympathetic control of stroke volume
Increase ventricle contractibility
Describe neural reflexes in relation to cardiac output
Tissue demands increase blood, vasodilate to increase tissue blood flow, decrease total peripheral resistance, reflex increase CO to maintain BP
Describe the Frank-Starling Mechanism
More blood enters the ventricle in diastole
Ventricular muscle is stretched more (increased preload)
Actin and myosin are at a more optimal sarcomere length
Increase force ventricular contraction
Increase stroke volume
What is preload?
End diastolic value
What is afterload?
Resistance ventricle must pump against to eject blood
