cardiac cycle

what is the cardiac cycle

the 3 stages in which the myogenic cardiac muscle (in walls of the heart) contracts and relaxes to pump blood - one complete cycle creates a heart beat

what is diastole

relaxation

what is systole

contraction

what are the 2 types of systole

atrial systole

ventricular systole

what is AP

atrial pressure = blood pressure inside the atria

what is VP

ventricular pressure = blood pressure inside the ventricles

outline the 3 stages of the cardiac cycle

1.atrial systole

2.ventricular systole

3.diastole

what is the AoP

aortic pressure = blood pressure in the aorta, as blood leaves the heart from the ventricles

what occurs during atrial systole

1. atria contract causing AP increase (as atria contracts the space gets smaller but since there is still the same volume of blood so pressure incr.)

2. AV valves open causing blood to be pushed into ventricles (AP > VP, a pressure gradient is generated forcing AV valves open)

what occurs during ventricular systole

1. ventricles contract causing VP increase, while atria relax causing AP decrease

2. AV valves close (VP > AP blood tries to move backwards into atria therefore valves close to prevent backflow of blood)

3. SL valves open causing blood to be pushed into arteries (VP > arteries e.g. AoP, a pressure gradient is generated forcing SL valves open)

what occurs during diastole

1. ventricles and atria relax causing VP decrease

2. SL valves close (AoP > VP blood tries to move backwards into ventricles therefore valves close to prevent backflow of blood)

3. blood flows passively into atria (through vena cava and pulmonary artery) and ventricles so cycle restarts

How many seconds roughly does one cardiac cycle take

0.7 - 0.8s 

draw diagram for cardiac cycle + label

 What side of the heart does this graph apply to

left side of the heart 

» graphs will always present left side of heart because pressure changes are much greater

why is VP significantly bigger/ higher than AP

because the ventricle walls are much thicker than atria walls meaning they can contract more strongly

…

both ventricles and both atria contract together

why would there never be whole heart systole

-blood moves through the heart via pressure gradient:

1. atrial systole = atria > ventricles because ventricles are at lower pressure

2. ventricular systole = ventricles > arteries because arteries are at lower pressure

» if whole heart systole occurred the atria and ventricles would contract at the same meaning

…

why is there whole heart diastole

entire cardiac muscle is relaxed meaning pressure in all four chambers is lower than pressure of incoming veins = allows heart chambers to passively fill up with blood

what is cardiac output

volume of blood pumped by 1 ventricle in 1 minute/ per minute

how do you calculate cardiac output

Cardiac Output = Heart Rate X Stroke Volume

define what is Heart Rate and Stroke Volume

Heart Rate - number of beats per min

Stroke Volume - volume of blood pumped out the ventricles with each beat

why is cardiac output useful

to calculate how efficiently the heart is supplying body with oxygenated blood