L7.2 Cardiac Output Flashcards
The heart responds to changes in demand (e.g. exercise, blood loss). How does the heart adapt to these changes?
By adjusting the cardiac output
What is cardiac output and what does it indicate?
- volume of blood pumped by each ventricle per minute
- indicates blood flow through peripheral tissues
What is the cardiac output formula?
cardiac output: heart rate (beats/min) x stroke volume (ml/beat)
what divisions of the nervous system controls the heart rate?
sympathetic and parasympathetic
can change the rate of depolarisation in the SA node- heart beat changes
what effect does the parasympathetic nervous system have on the heart?
- reduces the rate of action potential in SA node
- decreases heart rate: causes hyperpolarisation, so increases time to reach threshold; slower depolarisation
- PNS is dominant in resting individual: heart rate is normally slower than SA node speed
- parasympathetic stimulation releases ACh which extends repolarization and decreases the rate of spontaneous depolarization. the heart rate slows.
what effect does the sympathetic nervous system have on the heart?
- increases the rate of action potentials in SA node
- increases heart rate = causes depolarisation
- sympathetic stimulation releases NE, which shortens repolarization and accelerates the rate of spontaneous depolarization. As a result, the heart rate increases.
what is stroke volume?
- volume of blood pumped out of the ventricle during contraction. it is the difference between EDV and ESV (EDV-ESV)
- stroke volume is determined by sympathetic activity and venous return (increase in these increases strength of contraction)
- sympathetic stimulation enhances the contractile strength of the heart
define EDV and ESV
End Diastolic Volume (EDV): volume of blood in the ventricle during relaxation
End Systolic Volume (ESV): volume of blood in the ventricle after systole
what is venous return? and what will increase it?
- volume of blood returning back to the heart each minute
- increasing venous return will: increase EDV; causes heart muscle to stretch; as cardiac muscle stretches, the next contraction will be stronger
describe the frank-starling law of the heart
the greater the end diastolic volume, the greater the force of contraction during systole
increase EDV = increase force of contraction = more optimal overlap
describe the pressure in the vein circuit
as the blood flows through the vein circuit (starting at the left ventricle), the pressure in the veins decreases (high to low pressure)
what are the factors controlling venous return?
cardiac suction, skeletal muscle pump, venous valves, respiratory pump, sympathetic nervous system
what is cardiac suction? and describe the effect of the contraction and relaxation of the ventricles.
heart acting as a suction pump pulling blood through venous system back into the heart
contraction of ventricles:
- AV valves drawn downward
- increase volume in atria - decreased pressure in atria
- sucks blood from veins into atria
relaxation of ventricles:
- increased volume in ventricles -> decreased pressure in ventricles
- sucks blood from veins and atria into ventricles
what is skeletal muscle pump?
large veins lie between skeletal muscle; muscle action compresses the vein - push blood through vein; inactivity = swollen ankles
what is venous valves?
valves control the direction of blood flow = prevents back flow
