LEARNING OBJECTIVES
What you will be able to do
- compare single and double circulation
- explain heart action
- relate vessel structure to function
- describe blood and clotting
- evaluate coronary risk
AT A GLANCE
INTRODUCTION · THE BIG IDEA
How heart, vessels and blood maintain rapid exchange throughout the body.
Large active organisms need a mass-transport system because diffusion alone is too slow over long distances. The heart maintains pressure while vessels control flow and exchange.
Learn the circulation as one connected route, then relate the structure of each chamber, vessel and blood component to its function.
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
- 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
- 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
- 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.
STEP-BY-STEP EXAM EXAMPLE
Tracing one red blood cell
- Begin in the vena cava and enter the right atrium.
- Move through the right ventricle and pulmonary artery to the lungs.
- After oxygen uptake, return in the pulmonary vein to the left atrium.
- Pass through the left ventricle and leave through the aorta.
Answer: Vena cava → right heart → pulmonary artery → lungs → pulmonary vein → left heart → aorta.
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.
QUICK REVISION CHECKLIST
Can you do each of these without your notes?
- compare single and double circulation
- explain heart action
- relate vessel structure to function
- describe blood and clotting
- evaluate coronary risk