The cardiac cycle

function

circulates blood through the pulmonary and systemic circuits that make up the double circulatory system

occurs when the heart beats

why is a double circulatory system more efficient?

because the oxygenated and deoxygenated blood are kept separate

pulmonary circuit function

carries blood to the lungs to be oxygenated and then back to the heart

in the lungs, co2 is removed from the blood, and oxygen taken up by the haemoglobin in red blood cells

systemic circuit function

carries blood around the body to deliver the oxygen and returns deoxygenated blood to the heart

cardiac cycle

a broken down version of the systemic circuit

the sequence of mechanical and electrical events that are repeated every heartbeat

it includes 2 phases:

diastole - relaxation phase, blood pressure is at its lowest

systole - contraction phase, blood pressure rises

how is frequency of the cardiac cycle monitored?

heart rate

recorded by number of beats per minute

cardiac cycle in left side of the heart process

blood drains into the left atrium from lungs along the pulmonary vein

raising of the blood pressure in the left atrium forces the left tricuspid valve open

contraction of the left atrial muscles forces more blood through the valve

as soon as left atrial systole (muscle contraction) is over, the left ventricular muscles start to contract. This is called the left ventricular systole

this forces the left tricuspid valve to close and opens the valve in the mouth of the aorta (semilunar valve). Blood then leaves the left ventricle along the aorta

the same steps are repeated on the right side at the same time

cardiac diastole

when the heart refills with blood

ventricular diastole

when the ventricles are refilling and relaxed

baroreceptors

aka stretch receptors

detect changes in the pressure of blood filling the atria

send signals to the CNS which triggers vasodilation - this reduces pressure in the blood

heartbeat process

electrical signals trigger muscles to contract and relax. The pathway for this to happen is:

1. sinoatrial node - aka natural pacemaker. Causes an impulse to travel through the atria causing them to contract and force blood into the ventricles. This node also sets the heart’s rhythm and rate

2. atrioventricular node - detects the impulse travelling through the atria and redirects the impulse to the bundle of His. This causes a delay, slowing the spread of the electrical impulse across the heart and allowing the atria to contract before the ventricles

3. Bundle of His - aka atrioventricular bundle. A group of fibres in the septum which the impulse travels through to the base of the ventricles.

4. Purkinje fibres - act like neurons and are found in the walls of the ventricles. The impulse from the bundle of His reaches the Purkinje fibres which cause the ventricles to contract