9.2 Heart
- Syllabus
- 0610–2026–2027
- Topic
- 9.2
- Level
- —
Learning objectives
9.2.1Structures of the mammalian heart• Identify in diagrams and images the structures of the mammalian heart, limited to: muscular wall, septum, left and right ventricles, left and right atria, one-way valves and coronary arteries9.2.2Blood is pumped away from the heart• State that blood is pumped away from the heart in arteries and returns to the heart in veins9.2.3Activity of the heart may be monitored• State that the activity of the heart may be monitored by: ECG, pulse rate and listening to sounds of valves closing9.2.4Effect of physical activity on• Investigate and describe the effect of physical activity on the heart rate9.2.5Coronary heart disease in terms• Describe coronary heart disease in terms of the blockage of coronary arteries and state the possible risk factors including: diet, lack of exercise, stress, smoking, genetic predisposition, age and sex9.2.6Roles of diet and exercise in reducing• Discuss the roles of diet and exercise in reducing the risk of coronary heart disease9.2.7Atrioventricular and semilunar valves• Identify in diagrams and images the atrioventricular and semilunar valves in the mammalian heart9.2.8Relative thickness of: (a) the muscle• Explain the relative thickness of: (a) the muscle walls of the left and right ventricles (b) the muscle walls of the atria compared to those of the ventricles9.2.9Importance of the septum in separating• Explain the importance of the septum in separating oxygenated and deoxygenated blood9.2.10Heart function• Describe the functioning of the heart in terms of the contraction of muscles of the atria and ventricles and the action of the valves9.2.11Effect of physical activity on• Explain the effect of physical activity on the heart rate
Identify the structures of the mammalian heart
In a standard front-view heart diagram, the anatomical left side usually appears on the viewer's right. Use structure and connections, not page position alone.
| Structure | Recognition cue |
|---|---|
| left and right atria | two upper, thinner-walled chambers |
| left and right ventricles | two lower chambers; the left ventricle has the thickest wall |
| septum | muscular partition between the left and right sides |
| one-way valves | flaps between chambers or at ventricular outlets |
| muscular wall | tissue surrounding the chambers, thickest around the left ventricle |
| coronary arteries | branching vessels visible on the outer surface of the heart |
First locate the atria and ventricles, then use wall thickness to orient left and right; finally identify the septum, valves and surface coronary arteries.
Do not identify left and right from the viewer's left and right alone; diagrams are commonly shown as if the heart faces the learner.
Distinguish arteries from veins by direction
Arteries carry blood away from the heart; veins return blood to the heart.
| Vessel type | Direction relative to heart |
|---|---|
| artery | heart → organ |
| vein | organ → heart |
Apply the direction rule before considering oxygen concentration: a vessel leaving a ventricle is an artery, and a vessel entering an atrium is a vein.
Artery does not mean oxygenated and vein does not mean deoxygenated; pulmonary vessels are the key exceptions to that shortcut.
Monitor the activity of the heart
Heart activity may be monitored using an ECG, pulse rate, or the sounds of valves closing.
| Method | What is detected |
|---|---|
| ECG (electrocardiogram) | electrical activity of the heart over time |
| pulse rate | pressure pulses in an artery, counted as beats per minute |
| listening with a stethoscope | sounds produced when heart valves close |
Each method provides a different observable signal of repeated heart activity; pulse rate is convenient for simple investigations.
An ECG records electrical activity; it is not a direct graph of blood pressure or heart sound.
Investigate and describe exercise effects on heart rate
Physical activity increases heart rate above the resting rate; after activity stops, heart rate gradually returns towards the resting value.
| Stage | Fair-test action |
|---|---|
| baseline | sit quietly, then measure resting pulse for a fixed time |
| activity | use the same exercise, duration and intensity for each comparison |
| response | measure pulse immediately after exercise and at fixed recovery intervals |
| reliability | repeat, calculate means and keep measurement method constant |
Describe the pattern with direction and data where available: starting value, peak or post-exercise value, and recovery over time.
A fair investigation controls exercise dose and timing; comparing pulses measured after different delays is not valid.
Describe coronary heart disease and its risk factors
Coronary heart disease (CHD) results when coronary arteries become narrowed or blocked, reducing blood supply to heart muscle.
| Change | Consequence |
|---|---|
| coronary artery narrows or blocks | less blood reaches cardiac muscle |
| oxygen and glucose supply falls | aerobic respiration releases less energy |
| severe or prolonged shortage | heart muscle may fail to contract normally or cells may die |
Possible risk factors include diet, lack of exercise, stress, smoking, genetic predisposition, increasing age and sex.
A risk factor changes probability; it does not guarantee that a person will develop CHD. Coronary arteries supply the heart muscle itself.
Discuss diet and exercise in reducing CHD risk
Diet and exercise can reduce modifiable CHD risk, but they do not remove non-modifiable risks such as age, sex or genetic predisposition.
| Change | How it may reduce risk |
|---|---|
| reduce saturated fat and excess dietary cholesterol | lowers the tendency for fatty deposits to narrow coronary arteries |
| reduce excess salt and maintain a balanced energy intake | helps control blood pressure and body mass |
| exercise regularly | helps control body mass and blood pressure and strengthens cardiac muscle |
The strongest conclusion is conditional: sustained healthy diet and regular exercise reduce risk, while individual risk also depends on smoking, stress and inherited or demographic factors.
Diet and exercise reduce risk rather than cure an existing blockage, and one lifestyle change cannot cancel every other risk factor.
Identify atrioventricular and semilunar valves
Atrioventricular valves lie between atria and ventricles; semilunar valves lie at the exits from ventricles into arteries.
| Valve type | Diagram location | Prevents backflow from |
|---|---|---|
| atrioventricular (AV) | between each atrium and ventricle | ventricle to atrium |
| semilunar | at each ventricular outlet | artery to ventricle |
Trace blood from atrium → ventricle → artery: it crosses an AV valve first and a semilunar valve second.
Both types are one-way valves, but their positions and the backflow they prevent are different.
Explain differences in heart-wall thickness
More muscular walls contract with greater force and generate higher pressure.
| Comparison | Explanation |
|---|---|
| left ventricle thicker than right ventricle | it pumps through the systemic circuit to the whole body at higher pressure; the right pumps only to the nearby lungs |
| ventricles thicker than atria | ventricles pump blood out of the heart; atria push blood only a short distance into ventricles |
For every comparison link destination and resistance to the pressure required, then link pressure to muscular-wall thickness.
The left ventricle is not thicker because it contains more blood; its thicker muscle is needed to generate greater pressure.
Explain the importance of the septum
The septum separates the right and left sides of the heart, preventing oxygenated and deoxygenated blood from mixing.
| With an intact septum | Why it matters |
|---|---|
| deoxygenated blood remains on the right before going to the lungs | it can be reoxygenated without mixing into systemic output |
| oxygenated blood remains on the left before going to the body | body tissues receive blood with a high oxygen concentration |
Separation supports efficient oxygen delivery and therefore aerobic respiration in body tissues.
The septum separates blood; it does not act as a valve and does not itself pump blood.
Describe how the heart functions
The cardiac cycle coordinates atrial and ventricular contraction with pressure-operated valves to produce one-way blood flow.
| Phase | Muscle action | Valve action and flow |
|---|---|---|
| filling | atria and ventricles relax | AV valves open; blood enters atria and flows into ventricles |
| atrial contraction | atria contract | AV valves stay open; blood is pushed into ventricles |
| ventricular contraction | ventricles contract | AV valves close; semilunar valves open; blood enters arteries |
| ventricular relaxation | ventricles relax | semilunar valves close, preventing arterial backflow; filling begins again |
Valves open or close because pressure differs on their two sides; they do not contract actively.
Atrial contraction precedes ventricular contraction. During ventricular contraction the AV valves are closed and the semilunar valves are open.
Explain why physical activity increases heart rate
During physical activity, contracting muscles respire faster and need faster transport of substances, so heart rate increases.
| Increased muscle demand | Transport response |
|---|---|
| more oxygen and glucose needed for aerobic respiration | faster blood flow delivers them more rapidly |
| more carbon dioxide and heat produced | faster blood flow removes them more rapidly |
| more energy needed for contraction | increased heart rate raises cardiac output |
Nervous signals and adrenaline can increase the rate of heart contraction. After exercise, heart rate stays elevated briefly while transport demand returns towards resting level.
The heart does not create energy for muscles; it increases blood flow so respiration can release energy where it is needed.