The Heart, Blood Vessels & Coronary Heart Disease
Humans have a double circulatory system in which blood passes through the heart twice for every complete circuit of the body: the right side pumps deoxygenated blood to the lungs, and the left side pumps oxygenated blood at high pressure to the rest of the body. Blood flows through three specialised vessels (arteries, capillaries, and veins) containing red blood cells, white blood cells, platelets, and plasma. Examiners regularly ask students to trace the pathway of blood through the four chambers and major vessels of the heart, compare blood vessel structures, and evaluate stents, statins, and replacement heart valves.
- Double Circulatory System
- Consists of two circuits: the pulmonary circuit (right ventricle pumps deoxygenated blood via the pulmonary artery to the lungs, returning oxygenated via the pulmonary vein to the left atrium) and the systemic circuit (left ventricle pumps oxygenated blood via the aorta to the body, returning deoxygenated via the vena cava to the right atrium).
- Arteries, Veins & Capillaries
- Arteries carry high-pressure blood away from the heart (thick muscular and elastic walls, narrow lumen). Veins carry low-pressure blood back to the heart (thinner walls, wide lumen, and valves to prevent backflow). Capillaries link arteries to veins at tissues (walls are one cell thick to allow rapid diffusion of oxygen and glucose).
- Four Components of Blood
- 1. Plasma: straw-coloured liquid transporting dissolved glucose, amino acids, urea, CO₂, hormones, and proteins. 2. Red blood cells: transport oxygen bound to haemoglobin. 3. White blood cells: defend against pathogens via phagocytosis, antibodies, and antitoxins. 4. Platelets: cell fragments that trigger blood clotting at wounds.
Interactive Human Body & Cell Structure Explorer
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Heart (Double Circulatory Pump)
Structure & Function:
Pumps blood in a double circulatory system: the right ventricle pumps deoxygenated blood to the lungs, and the thick muscular left ventricle pumps oxygenated blood at high pressure around the whole body.
Key Exam Mark-Scheme Point:
Exam tip: The left ventricle has a much thicker muscular wall than the right ventricle because it must pump blood at high pressure all the way around the entire body, not just to the lungs.
What happens if this organ fails or is removed?
Without pressure from the heart, blood flow stops immediately. Oxygen and glucose cannot reach tissues, and waste carbon dioxide cannot be removed.
Tip: Use the “Simulate Organ Failure” button above to see how each organ system depends on the others to maintain homeostasis and cellular respiration.
Key Concepts & Exam Definitions (6)
- Double Circulatory System
- Consists of two circuits: the pulmonary circuit (right ventricle pumps deoxygenated blood via the pulmonary artery to the lungs, returning oxygenated via the pulmonary vein to the left atrium) and the systemic circuit (left ventricle pumps oxygenated blood via the aorta to the body, returning deoxygenated via the vena cava to the right atrium).
- Arteries, Veins & Capillaries
- Arteries carry high-pressure blood away from the heart (thick muscular and elastic walls, narrow lumen). Veins carry low-pressure blood back to the heart (thinner walls, wide lumen, and valves to prevent backflow). Capillaries link arteries to veins at tissues (walls are one cell thick to allow rapid diffusion of oxygen and glucose).
- Four Components of Blood
- 1. Plasma: straw-coloured liquid transporting dissolved glucose, amino acids, urea, CO₂, hormones, and proteins. 2. Red blood cells: transport oxygen bound to haemoglobin. 3. White blood cells: defend against pathogens via phagocytosis, antibodies, and antitoxins. 4. Platelets: cell fragments that trigger blood clotting at wounds.
- Red blood cell adaptations
- Biconcave disc shape increases the surface area to volume ratio for rapid oxygen diffusion; packed with haemoglobin (which binds oxygen to form oxyhaemoglobin in the lungs); and has no nucleus, freeing up more internal volume to carry haemoglobin.
- Coronary Heart Disease (CHD)
- Layers of fatty material (cholesterol/atheroma) build up inside the coronary arteries (which supply the heart muscle itself with blood), narrowing the lumen. This restricts blood flow and oxygen supply to cardiac muscle, leading to anaerobic respiration, chest pain (angina), or a heart attack (myocardial infarction).
- Cardiac Output Equation
- Cardiac Output (cm³/min) = Heart Rate (beats/min) x Stroke Volume (cm³/beat). During exercise, both heart rate and stroke volume increase to deliver more oxygen and glucose to respiring muscles.
Quick-Fire Flashcards (6)
Click any card to check the answer, then mark it as Known to track your progress.
Which blood vessel is the only artery in the body that carries deoxygenated blood?
State three adaptations of red blood cells for oxygen transport.
How are arteries adapted to carry blood at high pressure?
Why do veins contain valves whereas arteries do not?
Compare biological and mechanical replacement heart valves.
What happens if a person has a low platelet count?
Exam-Style Questions & Mark Schemes (4)
Write or think through your answer first, then click Check Mark Scheme to see the exact points examiners award marks for.
- Q1
Explain how a build-up of fatty material in the coronary arteries can lead to a heart attack. [4 marks]
Click “Check Mark Scheme” to compare your answer, 1. Fatty deposits (cholesterol) build up inside the lining of the coronary arteries, narrowing the lumen [1 mark]. 2. This reduces blood flow to the cardiac muscle cells of the heart wall [1 mark]. 3. Less oxygen and glucose reach the heart muscle cells for aerobic respiration [1 mark]. 4. If a blood clot completely blocks the narrowed artery, the heart muscle cells are starved of oxygen, cannot respire, and die, causing a heart attack [1 mark].
- Q2
Evaluate the use of stents and statins to treat a patient with coronary heart disease. [6 marks]
Click “Check Mark Scheme” to compare your answer, 1. Stents physically widen the narrowed coronary artery immediately, restoring blood flow and oxygen supply to the heart muscle [1 mark]. 2. Stents remain in place for a long time and recovery time from keyhole surgery is fast [1 mark]. 3. However, stents require surgery, which carries risks of infection, bleeding, or a blood clot (thrombosis) forming near the stent, and they do not prevent other arteries from narrowing [1 mark]. 4. Statins are tablets that lower LDL ('bad') cholesterol in the blood, slowing fatty deposit build-up across all arteries without needing surgery [1 mark]. 5. However, statins must be taken long-term every day (patients may forget) and do not immediately unblock an already blocked artery [1 mark]. 6. Statins can also cause side effects such as muscle pain, headaches, or liver/kidney damage. A combined approach is often best [1 mark].
- Q3
Compare the structure and function of arteries and capillaries. [4 marks]
Click “Check Mark Scheme” to compare your answer, 1. Arteries carry blood away from the heart at high pressure, whereas capillaries exchange substances directly with body tissues at low pressure [1 mark]. 2. Arteries have thick walls containing thick muscle and elastic tissue layers, whereas capillary walls are only a single cell thick (endothelium) [1 mark]. 3. The thin, permeable capillary wall provides a very short diffusion pathway for oxygen and glucose to enter cells [1 mark]. 4. Capillaries have a microscopic lumen (just wide enough for red blood cells to pass in single file), whereas arteries have a wider lumen than capillaries (though narrower than veins) [1 mark].
- Q4
An athlete has a resting heart rate of 50 beats per minute and a resting stroke volume of 100 cm³/beat. During a race, their cardiac output rises to 24,000 cm³/min and their stroke volume increases to 150 cm³/beat. Calculate their resting cardiac output and their heart rate during the race. [3 marks]
Click “Check Mark Scheme” to compare your answer, 1. Resting cardiac output = Heart rate x Stroke volume = 50 x 100 = 5,000 cm³/min (or 5.0 dm³/min) [1 mark]. 2. Rearranging for race heart rate: Heart rate = Cardiac output / Stroke volume = 24,000 / 150 [1 mark]. 3. Race heart rate = 160 beats per minute (bpm) [1 mark].
Common Exam Questions (4)
Why is the wall of the left ventricle thicker than the right ventricle?
The left ventricle has a much thicker muscular wall because it must generate high pressure to pump oxygenated blood all the way around the entire body, whereas the right ventricle only pumps blood a short distance to the lungs.
What is the pathway of blood through the heart?
Deoxygenated blood enters from the body via the vena cava into the right atrium, passes through a valve into the right ventricle, and is pumped out via the pulmonary artery to the lungs. Oxygenated blood returns from the lungs via the pulmonary vein into the left atrium, passes into the left ventricle, and is pumped out via the aorta to the body.
What is the difference between stents and statins for treating coronary heart disease?
A stent is a metal mesh tube surgically inserted into a narrowed coronary artery to physically hold it open so blood can reach heart muscle. Statins are daily drugs taken to reduce blood cholesterol levels, slowing down the rate at which fatty deposits build up in the arteries.
Where is the natural pacemaker of the heart located?
The natural pacemaker is a group of specialised cells located in the wall of the right atrium (the sinoatrial node). It produces regular electrical impulses that spread across the heart muscle to control resting heart rate.
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