Cardiac cycle and output

systole =

ventricular contraction and ejection

diastole =

ventricular relaxation and filling

7 steps in cardiac cycle

atrial systole - isovolumetric contraction-rapid ejection - reduced ejection - isovolumetric relaxation - rapid filling - reduced filling

atrial systole

atria contract - squeeze blood into ventricles - AV valves open. SL closed. slight increase in atrial pressures

end diastolic volume =

ventricular volume + atrial contribution

isovolumetric contraction

all valves close, beginning of systole, increase in intraventricular pressure from contraction but no blood ejected

rapid ejection

AV closed, SL open, valves open when intraventricular pressure is higher than aortic/pulmonary. atria continue filling

reduced ejection

SL valves open. AV closed, no blood moves. ventricle muscles relax and pressure decreases slightly, atria continue filling

isovolumetric relaxation

valves close, ventricle volume stays the same, atrial pressure and volume increase from venous return

rapid filling

AV valves open. SL close, ventricles fill, atrial pressure falls

reduced filling

hard to distinguish, ventricles at full stretch when filling is nearly finished, pressure increases

cardiac output

how much blood the heart ejects: CO = stroke vol x heart rate

stroke vol formula

SV = end diastolic vol - end systolic vol

3 factors regulating cardiac output

neural control, ion levels, heart rate

frank starling's law

bigger stroke volume ejected if there is a larger degree of filling at the end of diastole

preload

how stretchy the heart is at max fill

afterload

the pressure against which the heart needs to pump to expel blood

contractility

ability of the muscle to produce a force

how does exercise increase venous return

rapid breathing forcing reoxygenated blood into heart quicker, skeletal muscle pump forcing venous return

how does contraction of skeletal muscle in tissue surrounding veins compress them

compression closes upstream valves and opens downstream valves, compressed veins = increased pressure

blood pressure formula

bp = cardiac output x total peripheral resistance

peripheral resistance

degree of friction encountered by blood - resistance to flow

other measurements for blood pressure

pulse pressure (systolic BP - diastolic BP) - increases as arteries become less stretchy

mean arterial pressure (diastolic pressure + PP/3) - pressure at which blood is delivered to tissues

how do pressure changes control BP

baroreceptors in arterial carotids and aortic arch, each receptor is sensitive to a different pressure, small changes increase firing frequencies

how do chemoreceptors control BP

peripheral chemoreceptors - carotid bodies in carotid artery, detect changes in PO2, PCO2, pH

vasoconstriction

contraction of smooth muscle in vessel walls and precapillary sphincters in arterioles, narrowing of blood vessel - increases resistance and BP

vasodilation

relaxation of smooth muscle in vessel walls and precapillary sphincters in arterioles, widening of blood vessel caused by withdrawal of sympathetic nerve activity, decreases resistance and BP