The Circulatory System

Strucute of the Human Heart

Left side gets blood from the lungs and sends to rest of body Right Side gets blood from the body and sends it to the lungs

Blood enters the 2 atria (through the Vena Cava (r) and Pulmonary Vein (l)) which contract, forcing blood into the the ventricles The ventricles then contract and pump blood out into the arteries (Pulmonary Artery (r), and Aorta (l))

Remember that blood from the right side is not deoxygenated! It is Oxygen Depleted!

Remember to learn the structures of the diagrams! They're important!

The Cardiac Cycle

is one complete cycle of events beginning with diastole followed by atrial asystole and finally ventricular systole.

Name Event Outcome Valves Pressure Diastole Heart muscle is relaxed The atria fill with blood opening the atrioventricular (AV) valves and blood enters ventricles Semilunar valves close AV valves open Low but slowly rises as blood enters Low in arteries (diastolic pressure Atrial Systole Atrial muscle contracts Blood pushed into ventricles Atria are emptied AV valves pushed fully open Rises in both atria and ventricles as blood enters Ventricular systole Ventricular muscle contracts Blood forced into the arteries AV valves snap shut Heart tendons hold valves into place Semilunar valves pushed open as blood enters arteries Valves pushed open when ventricular pressure is greater than arterial pressure Atrial pressure falls Ventricular Pressure rises steeply as muscle contracts Continues to rise for 0.1 second but falls as empties Artery pressure if high (systolic pressure)

The Valves

The atrioventricular valves (AV) link the atria to the ventricles The semi-lunar valves (SL) link the ventricles to the pulmonary artery and aorta

Remember that the valves only open one way and it is the pressure changes that open and close them!

The Heart Muscles

The heart if mainly cardiac muscle - when it contracts it creates high pressure The more work the heart chamber has to do the thicker its wall is - the left ventricle is thicker than the right becuase it needs to pump blood all the way around the body where are the right only needs to get blood to the lungs which are nearby

It is myogenic and needs no stimulation to contract!

The Sinoatrial Node (SAN) in the right atrial wall generates an electrical impulse that traces across the atria and triggers atrial systole The Atrioventricular Node detects this and, after a short delay, relays it onto the ventricles via Purkyne fibres in the septum. The pulse then spreads across the ventricles to trigger ventricle systole The Bundle of His is a group of muscle fibres that conducts the waves of electrical activity (from the Artioventricular Node) to the right and left ventricle walls (the Purkyne fibres)

Controlling the Heart Beat

An ECG

(electrocardiograph) monitors the electrical impulse as a trace (the muscle depolarises {loses electrical charge} when it contracts and repolarises when it relaxes), differences in the trace indicate heart problems.

Cadriac Output is the volume of blood pumped out of the left ventricle per minuteThis is calculated by multiplying the stroke volume (volume pupmed with each beat) by the heart rate

Heart Rate is 60 divided by the time taken for one heart beat (s)

The heart rate formula only works if the time taken for one heartbeat is in seconds so always check your units!

The normal heart rate range for an adult at rest if 60 to 100 beats per minute so if your calculation is way outside this range (~5bpm) you need to do it again!

The Heart