How does the heart pump blood around the body, and what goes wrong in cardiovascular disease?
Structure of the heart and the cardiac cycle, control of the heartbeat, the structure and roles of arteries, veins and capillaries, the composition of blood, and the causes, risk factors and treatment of coronary heart disease.
A CCEA Life and Health Sciences answer on the cardiovascular system: heart structure and the cardiac cycle, control of the heartbeat by the SAN and AVN, arteries, veins and capillaries, the composition of blood, and the risk factors and treatment of coronary heart disease.
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What this dot point is asking
CCEA wants you to describe the structure of the mammalian heart, explain the cardiac cycle and how the heartbeat is controlled, compare the structure and function of arteries, veins and capillaries, state the composition and roles of blood, and explain the causes, risk factors and treatment of coronary heart disease. This is core human physiology that underpins the nutrition, exercise and homeostasis content in the rest of the unit.
Heart structure and the cardiac cycle
The heart has four chambers: two thin-walled atria that receive blood, and two thicker-walled ventricles that pump it out. The left ventricle has the thickest muscular wall because it generates the high pressure needed to pump blood around the whole body, while the right ventricle pumps only to the nearby lungs. The atrioventricular valves (bicuspid on the left, tricuspid on the right) lie between atria and ventricles, and the semilunar valves guard the exits into the aorta and pulmonary artery. The cycle runs: atrial systole pushes the last blood into the ventricles; ventricular systole raises ventricular pressure, closing the atrioventricular valves and opening the semilunar valves to eject blood; diastole follows as pressures fall, the semilunar valves close, and the heart refills. Each valve opens only when the pressure behind it exceeds the pressure in front, which is what keeps blood moving in one direction.
Control of the heartbeat
The short delay at the AVN ensures the atria finish emptying before the ventricles contract, and conducting the impulse to the apex first means the ventricles squeeze blood upwards towards the arteries. An electrocardiogram (ECG) records this electrical activity: the P wave is atrial depolarisation, the QRS complex is ventricular depolarisation, and the T wave is ventricular repolarisation. Abnormal ECG traces can reveal conditions such as tachycardia (fast heart rate) and fibrillation (uncoordinated contraction).
Blood vessels and blood
Arteries have thick, muscular and elastic walls to withstand and smooth out the high pressure of blood leaving the heart; they have a narrow lumen and carry blood away from the heart. Capillaries are one cell thick with a very narrow lumen, giving a short diffusion distance and large surface area for the exchange of oxygen, glucose, carbon dioxide and wastes between blood and tissues. Veins have thinner walls, a wide lumen and valves to prevent backflow, returning blood at low pressure helped by the squeezing of skeletal muscles. Blood consists of plasma (carrying dissolved glucose, ions, carbon dioxide, hormones and proteins), red blood cells (carrying oxygen as oxyhaemoglobin), white blood cells (defence) and platelets (clotting).
Examples in context
Example 1. Exercise and cardiac output. During exercise the muscles need more oxygen and glucose and produce more carbon dioxide. The cardiovascular centre increases heart rate and the heart fills more strongly, so stroke volume rises. Cardiac output can rise from about 5 litres per minute at rest to over 20 litres per minute in a trained athlete, illustrating how the heart matches blood delivery to demand.
Example 2. Stents and statins for coronary heart disease. When a coronary artery narrows with atheroma, a stent (a small mesh tube) can be inserted to hold the artery open and restore blood flow to the heart muscle. Statins are drugs that lower blood cholesterol, slowing further atheroma formation. Together with lifestyle change (stopping smoking, a low-fat diet, exercise) these treatments reduce the risk of a myocardial infarction, linking the physiology to real clinical practice.
Try this
Q1. Explain why the wall of the left ventricle is thicker than the wall of the right ventricle. [2 marks]
- Cue. The left ventricle pumps blood at high pressure to the whole body; the right ventricle only pumps to the nearby lungs.
Q2. State two structural features of a capillary that suit it for exchange. [2 marks]
- Cue. One cell thick (short diffusion distance) and a large total surface area; narrow lumen slows flow for exchange.
Q3. Name the node that acts as the pacemaker of the heart. [1 mark]
- Cue. The sinoatrial node (SAN).
Exam-style practice questions
Practice questions written in the style of CCEA exam questions on this dot point, with worked answer explainers. The year tag is the paper they imitate, not the source.
CCEA AS 26 marksDescribe the events of the cardiac cycle, explaining how the heart valves ensure blood flows in one direction only.Show worked answer →
A 6-mark describe answer needs the three stages in order, plus the pressure-driven valve action.
Atrial systole: both atria contract, raising atrial pressure above ventricular pressure, so the atrioventricular valves are pushed open and the remaining blood is forced into the ventricles.
Ventricular systole: the ventricles contract, raising ventricular pressure above atrial pressure, which snaps the atrioventricular valves shut (preventing backflow into the atria). When ventricular pressure exceeds the pressure in the aorta and pulmonary artery, the semilunar valves open and blood is forced out.
Diastole: the heart relaxes; ventricular pressure falls below arterial pressure, so the semilunar valves close (preventing backflow from the arteries), and as atrial pressure exceeds ventricular pressure the atrioventricular valves open again and the heart refills.
Valves and one-way flow: each valve opens only when the pressure behind it is greater than the pressure in front, and the tendons (chordae tendineae) stop the atrioventricular valves turning inside out, so blood cannot flow backwards.
Markers reward the three stages named and in order, the pressure changes that open and close each valve, and the statement that valves prevent backflow.
CCEA AS 25 marksExplain how atheroma formation in a coronary artery can lead to a myocardial infarction, and state three risk factors for coronary heart disease.Show worked answer →
The answer must trace atheroma to a heart attack and then list modifiable or non-modifiable risk factors.
Atheroma to infarction: fatty deposits (atheroma, mainly cholesterol) build up in the wall of a coronary artery, narrowing the lumen and reducing blood flow to the heart muscle. The roughened surface can trigger a blood clot (thrombosis). If a clot blocks the coronary artery, the heart muscle beyond it is starved of oxygen and glucose, so respiration stops, the muscle cells die, and this is a myocardial infarction (heart attack).
Three risk factors: a diet high in saturated fat or salt, smoking, high blood pressure (hypertension), lack of exercise, obesity, excessive alcohol, genetic predisposition, or increasing age and being male (any three).
Markers reward narrowing of the lumen and reduced blood flow, the role of a clot, death of oxygen-starved heart muscle, and three valid risk factors.
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Sources & how we know this
- CCEA GCE Life and Health Sciences specification — CCEA (2016)