The cardiovascular system · GCSE PE

Structure of the heart

The heart is a muscular pump with four chambers: the right and left atria at the top and the right and left ventricles below.
The septum divides the left side from the right side, so oxygenated and deoxygenated blood don't mix.
Valves (tricuspid, bicuspid and semilunar) stop blood flowing backwards.
Blood vessels: the vena cava brings deoxygenated blood to the right atrium; the pulmonary artery takes it to the lungs; the pulmonary vein brings oxygenated blood back to the left atrium; the aorta carries it to the body.

Pulmonary circulation: the right side of the heart pumps deoxygenated blood to the lungs to collect oxygen.
Systemic circulation: the left side pumps oxygenated blood around the body. Its wall is thicker because it pumps further.
Blood passes through the heart twice on each circuit of the body.

Arteries carry blood away from the heart at high pressure. They have thick, muscular, elastic walls.
Veins carry blood back to the heart at low pressure. They have thinner walls and valves to stop backflow.
Capillaries are one cell thick, so oxygen, carbon dioxide and nutrients can diffuse through them to the muscles.
Red blood cells carry oxygen using haemoglobin. White blood cells fight infection. Platelets help clotting. Plasma carries everything.
Vascular shunting: during exercise, blood vessels to the working muscles widen (vasodilation) and those to organs like the stomach narrow (vasoconstriction), so more blood goes where it's needed.

Heart rate: the number of times the heart beats per minute (bpm).
Stroke volume: the volume of blood pumped out of the left ventricle in one beat.
Cardiac output: the volume of blood pumped out of the heart per minute. Cardiac output = stroke volume × heart rate.
Example: a stroke volume of 70 ml and a heart rate of 70 bpm give a cardiac output of 4,900 ml (4.9 litres) a minute.

Atrium: An upper chamber of the heart that receives blood.
Ventricle: A lower chamber of the heart that pumps blood out.
Septum: The wall dividing the left and right sides of the heart.
Aorta: The artery carrying oxygenated blood from the heart to the body.
Stroke volume: The volume of blood pumped from the left ventricle in one beat.
Cardiac output: The volume of blood pumped by the heart per minute.
Vascular shunting: Redirecting blood to working muscles by widening and narrowing vessels.
Haemoglobin: The protein in red blood cells that carries oxygen.