Transport in animals and disease
The heart, blood vessels and blood, and how the body defends itself against pathogens.
📌 Key points
- Mammals have a double circulation: blood passes through the heart twice in one complete circuit – to the lungs (pulmonary) and to the body (systemic). Fish have a single circulation.
- The right side of the heart pumps deoxygenated blood to the lungs in the pulmonary artery; the left side pumps oxygenated blood to the body in the aorta. The left ventricle has a thicker muscle wall because it pumps blood at higher pressure around the whole body.
- Blood enters the right atrium from the vena cava and the left atrium from the pulmonary vein. Valves prevent backflow; the septum separates the two sides.
- Coronary heart disease is the blockage of coronary arteries. Risk factors: diet high in saturated fat, smoking, lack of exercise, stress, genetic factors, age and sex.
- Arteries have thick, muscular, elastic walls and carry blood away from the heart at high pressure; veins have thin walls, a wide lumen and valves, and carry blood to the heart at low pressure; capillaries have walls one cell thick for exchange.
- Blood: red blood cells carry oxygen using haemoglobin; white blood cells include phagocytes (phagocytosis) and lymphocytes (antibody production); platelets help clotting; plasma transports nutrients, CO2, urea, hormones, ions and blood cells.
- In blood clotting, soluble fibrinogen is converted to insoluble fibrin, forming a mesh that traps blood cells. Clots prevent blood loss and stop pathogens entering.
- A pathogen is a disease-causing organism. Transmissible diseases spread by direct contact (blood, body fluids) or indirectly (contaminated surfaces, food, animals, air). Defences include skin, nose hairs, mucus, stomach acid and white blood cells.
- Antibodies are proteins that bind to antigens on pathogens, leading to their destruction or marking them for phagocytes. Each antibody has a shape complementary to one antigen.
- Active immunity (after infection or vaccination) makes antibodies and memory cells, giving long-term protection. Passive immunity (antibodies from the mother through the placenta or breast milk) is short-term.
📖 Key terms
- Double circulation
- Blood passes through the heart twice for each complete circuit of the body.
- Artery
- A blood vessel that carries blood away from the heart at high pressure.
- Vein
- A blood vessel that carries blood back to the heart at low pressure, with valves.
- Pathogen
- A disease-causing organism.
- Antigen
- A molecule on the surface of a pathogen that triggers the production of antibodies.
- Antibody
- A protein that binds to a specific antigen.
- Active immunity
- Defence against a pathogen by making your own antibodies, with memory cells.
✏️ Worked example
A student counts 21 pulse beats in 15 seconds at rest and 33 beats in 15 seconds just after exercise. Calculate the increase in heart rate in beats per minute.
- There are four 15-second periods in one minute, so multiply each count by 4.
- Resting heart rate = 21 × 4 = 84 beats per minute.
- Heart rate after exercise = 33 × 4 = 132 beats per minute.
- Increase = 132 − 84 = 48 beats per minute.
Arteries carry blood away from the heart and veins carry it towards the heart – not "oxygenated" and "deoxygenated". The pulmonary artery carries deoxygenated blood.
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