LEARNING OBJECTIVES
By the end of this chapter, you should be able to:
- compare single and double circulation
- explain heart action
- relate vessel structure to function
- describe blood and clotting
- evaluate coronary risk
THE BIG IDEA
How heart, vessels and blood maintain rapid exchange throughout the body.
This chapter builds each process from its structures, inputs and outputs. Follow the connections rather than memorising isolated facts, then use precise biological terms when explaining cause and effect.
SECTION 01
Circulation and heart
Fish have one circuit; mammals have separate pulmonary and systemic circuits. Double circulation restores pressure after the lungs and separates oxygenated from deoxygenated blood.
DETAILED EXPLANATION
- Body → vena cava → right atrium → right ventricle → pulmonary artery → lungs.
- Lungs → pulmonary vein → left atrium → left ventricle → aorta → body.
- The septum prevents mixing; atrioventricular and semilunar valves stop backflow.
- Atria contract before ventricles. The left ventricle is thickest because it supplies the whole body.
SECTION 02
Heart rate and coronary disease
Activity increases muscle respiration, so heart rate rises to deliver oxygen and glucose and remove carbon dioxide. Pulse, valve sounds and ECG monitor the heart.
DETAILED EXPLANATION
- Coronary arteries supply heart muscle; blockage may cause a heart attack.
- Risk factors include smoking, inactivity, diet, stress, genes, age and sex.
- Exercise and balanced diet reduce controllable risk.
SECTION 03
Vessels and blood
Arteries carry high-pressure blood in thick elastic walls; veins have wider lumens and valves; one-cell-thick capillaries provide a short exchange path.
DETAILED EXPLANATION
- Red cells carry oxygen using haemoglobin; white cells phagocytose or make antibodies.
- Platelets trigger fibrin formation, limiting blood loss and pathogen entry.
- Plasma transports cells, nutrients, hormones, carbon dioxide, urea and heat.
- Know aorta, vena cava, pulmonary, renal and hepatic vessels, including the hepatic portal vein.
QUICK CHAPTER SUMMARY
The ideas to carry forward
- Double circulation separates two circuits.
- Valves ensure one-way flow.
- Vessel structure matches pressure and exchange.
- Blood transports, defends and clots.