3. Cardiac Cycle

Question 1

The cardiac Cycle, AVN SAN

Answer 1

SAN acts as pacemaker, and sends a wave of electrical activity causing to atrria to contract

AVN delays the electrical activity allow the atria to empty before the ventricles contract

The wave of electrical activity goes through the Bundle of His and down the Purkyne fibres causing the ventricle to contract from the base upwards

Question 2

pulmonary vein and the vena cava to aorta/pulmonary artery

Answer 2

A. Blood returns to the atria through the pulmonary vein and the vena cava
D. as the atria fill up, the pressure in them rises, pushing open the atrioventricular valves, allowing blood to flow from atria to ventricles
B. Atria contract to force remaining blood into the ventricle
G. Ventricles then contract, which increases pressure within these chambers
C. When the pressure in the ventricles is greater than the pressure in the atria, the atrioventricular valves close, preventing back flow of blood into the atria
J. With the AV valves shut, the ventricular pressure rises
E. When the pressure in the ventricles is greater than the pressure in the aorta/pulmonary artery, the semi lunar valves open
K. Blood then flows into aorta/pulmonary artery
F. Ventricles relax, pressure decreases
I. Semi lunar valves close when pressure in aorta/pulmonary artery is greater than pressure in ventricles
H. Both atria and ventricles now relaxed

Question 3

Cardiac Output

Answer 3

cardiac output = stroke volume x heart rate

Heart rate- the number of heartbeats per minute. You can measure your heart rate by feeling your pulse, which is basically surges of blood forced through the arteries by the heart contracting.

Stroke volume — the volume of blood pumped during each heartbeat, measured in cm³.