The cardiac cycle Flashcards
pathway of blood, how the heart pumps blood, systole, diastole
How does blood flow change and why?
- cell requirements change constantly (e.g., during exercise = skeletal muscle needs more oxygen = produce more CO2)
- happens in two ways:
- change output of blood from the heart
- change diameter of the vessels
what is the cardiac cycle?
Cardiac cycle = heartbeat
Sequence of events in one complete heat beat
what is diastole
Filling phase (when heart relaxes)
- There is a short period of time where both atria & ventricles are relaxed (diastole) - Both atria and ventricles receive blood
systole
Pumping phase (when heart contracts)
atrial systole (ventricles in diastole)
Contraction of atria pumps blood to ventricles
ventricular systole (atrial diastole)
ventricles contract
pump blood through the arteries
what happens to ventricles and atria when refilling starts again
- ventricles relax
- atria is still relaxed
what happens to AV valves when atria contract
AV valves must be open (semilunar valves still closed from last ventricular contraction)
what happens to AV valves when ventricles contract
AV valves must be closed, and semilunar valves open so that blood doesn’t flow back into atria and goes out through arteries (pulmonary and aorta)
what happens to semilunar valves when ventricles relax
semilunar valves must close to prevent blood flowing backwards from pulmonary arteries and aorta into ventricles
Heart rate
The number of times the heart beats per minute
Stroke volume
Volume of blood forced from ventricle every contraction
Cardiac Output + equation
The amount of blood leaving one of the ventricles every minute
Cardiac output (mL/minute) = stroke volume (mL) x heart rate (beats/minute).
how does arterial blood flow work?
Arteries carry blood AWAY from the heart.
Arteries contain smooth muscle & elastic fibres when ventricles contract and push blood into arteries, they stretch. When ventricles relax, the arteries recoil.
The stretching/recoiling of the arteries keep pressure up and blood moving
vasoconstriction of arteries
arteries contract to reduce their size and limit blood flow
vasodilation of arteries
arteries relax to increase blood flow
how does blood flow work in veins
Capillaries join into small veins (venules) then join to make larger veins.
Veins carry blood TOWARDS the heart Have low pressure because pressure dropped across capillary bed
Do not have highly muscular walls (less muscle than arteries) can’t change size
Contain many valves to stop blood flowing backwards or pooling
factors affecting heart rate (4)
autonomic innervation
hormones
fitness levels
age
factors affecting stroke volume (5)
heart size
fitness levels
gender
contractility
duration of contraction
