Blood circulation
Blood components, the double circulation, blood vessels, heart rate and circulatory health.
Offline pages
Saved on this device only. Connect at least once every 30 days to confirm Premium. Sign-out or a change of account removes saved copies.
Before you begin
Blood carries oxygen, food and waste between the lungs, the gut and every cell in the body. This topic covers what blood is made of, the route blood takes through the heart, lungs and body and the vessels it travels in, how pulse rate responds to exercise, and how blocked arteries lead to heart attacks and strokes.
Be comfortable with: gas exchange in the lungs, and absorption of digested food in the small intestine.
Learning goals
- Components of blood
- Plasma
- Platelets
- Red blood cells
- White blood cells
- Heart–lung blood pathway
- Vessel structure and function
- Circulatory measurements
- Response to physical activity
- Plaque, heart attack and stroke
- Circulatory risk factors
Syllabus statements covered
- state the following components of blood: plasma, platelets, red blood cells and white blood cells
- state the role of blood and its following components in transport and defence: — plasma – transport of digested food substances and waste substances (carbon dioxide)
- state the role of blood and its following components in transport and defence: — platelets – clotting of blood
- state the role of blood and its following components in transport and defence: — red blood cells – transport of oxygen
- state the role of blood and its following components in transport and defence: — white blood cells – antibody formation, destruction of bacteria and viruses, and tissue rejection
- outline the pathway of blood through the heart and the lungs in relation to the transport of oxygen and carbon dioxide
- state the structure of arteries, veins and capillaries, and relate it to their functions
- state that blood pressure, heart rate and pulse rate can be used to monitor the condition of the circulatory system
- explain why breathing rate, heart rate and pulse rate increase during physical activities
- describe how the formation of plaque leads to heart attack and stroke
- state how diet, level of physical activity and smoking can affect the risk of developing heart diseases, high blood pressure and stroke
Lessons
Work through them in order.
- Blood componentsMatch plasma, red cells, white cells and platelets to their jobs in the blood.
- Blood pathways and vesselsTrace blood through the double circulation and compare arteries, veins and capillaries.
- Pulse, exercise and recoveryInterpret pulse and blood-pressure measurements, and explain why breathing, heart and pulse rates change during activity and recovery.
- Blocked arteries and circulatory healthExplain how plaque and clots can interrupt blood supply, distinguish heart attacks from strokes caused by blockage, and connect diet, activity and smoking to risk.
Practise and check
Or choose
Topic reference
Quick reference
| Part of blood | Job |
|---|---|
| plasma | carries dissolved substances |
| red blood cells | carry oxygen |
| white blood cells | defend against pathogens |
| platelets | help blood clot |
| Vessel | Carries blood | Key feature |
|---|---|---|
| artery | away from the heart | thick, elastic wall |
| vein | towards the heart | valves |
| capillary | through the tissues | wall one cell thick |
Route: right side of heart → lungs → left side of heart → body → right side of heart
Core knowledge to remember
- Blood passes through the heart twice on each complete trip round the body: double circulation.
- Arteries and veins are named by the direction of flow, not by how much oxygen the blood carries.
- During exercise, muscles respire faster, so heart rate, pulse rate and breathing rate rise; they fall again during recovery.
- Plaque narrows arteries; a clot can then block one. A blocked supply to heart muscle can cause a heart attack, and to part of the brain, a stroke.
- Diet, physical activity and smoking affect the risk of heart disease, high blood pressure and stroke.
Common mistakes
- Saying arteries always carry oxygen-rich blood.
- Saying red blood cells stop bleeding; platelets help blood clot.
- Giving a 15-second pulse count as a rate per minute.
- Calling every blocked artery a heart attack.
- Saying a risk factor makes a disease certain.