systole
ventricles contract, blood ejects
diastole
ventricles relax, refill
2 periods of systole
1. isovolumetric ventricular contraction
2. ventricular ejection
isovolumetric ventricular contraction
ventricular walls develop tension; volume constant; ventricular pressure increasing; muscle fibers can't shorten
ventricular ejection
happens once intraventricular pressure exceeds that in aorta and pulmonary trunk, aortic and pulmonary semilunar values open, blood forced into aorta/trunk as muscle fibers shorten
volume of blood ejected from each ventricle during systole is called
stroke volume
2 periods of diastole
1. isovolumetric ventricular relaxation
2. ventricular filling
isovolumetric ventricular relaxation
ventricles relax, valves close, pressure in aorta and pulmonary trunk exceed intraventricular pressure, AV valves closed ; no blood entering or leaving
ventricular filling
AV valves open because pressure in atria comes to exceed that in ventricles and ventricular filling occurs; atrial contraction comes at end of ventricular diastole
Cardiac Output
the volume of blood that each ventricle pumps ; volume of blood flowing through the pulmonary or systemic circuit per minute
Cardiac Output dependent on...
heart rate & stroke volume (CO = HRxSV)
Sympathetic stimulation causes heart rate to:
increase; increases slope of pacemaker potential by increasing permeability of Na+ channels
Parasympathetic stimulation causes heart rate to:
decrease; decreases slope of pacemaker potential and hyper polarizes plasma membranes of SA cells by increasing permeability to K+
End-diastolic volume
volume of blood in ventricles just before contraction
Changes in stroke volume are produced by.....
1. Changes in preload (end-diastolic volume)
2. Changes in magnitude of sympathetic nervous system input into ventricles
3. Changes in afterload (arterial pressure against which ventricles pump)
what is the Frank Starling Mechanism?
as end-diastolic volume increases, stroke volume increases, stretch in sarcomeres increases; greater the stretch in sarcomeres, the greater the force of contraction
an important consequence of the Frank Starling mechanism is that it...
helps maintain equality of flow between the systemic and pulmonary circuit
if the right side of the heart begins to pump more blood than the left: venous return from pulmonary circulation to left atrium will _________, end-diastolic volume in left ventricle will ___________, left ventricular output(SV) will ___________
increase
increase
increase
ventricular contractility
strength of contraction at given end-diastolic volume (EDV)
neurotransmitter norepinephrine acts on B1 adrenergic receptors of myocardial cells to:
increase ventricular contractility
Ejection fraction equation
EF = SV/EDV