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Blood Circulation

Blood components, the double circulation, blood vessels, heart rate and circulatory health.

  • SEC G1 Science 2027
  • 4 lessons
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Before you begin

Blood links the lungs, digestive system and body cells by transport. Its components, vessels and pump are each suited to a different part of that job.

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.

  1. Blood componentsMatch plasma, red cells, white cells and platelets to their jobs in the blood.
  2. Blood pathways and vesselsTrace blood through the double circulation and compare arteries, veins and capillaries.
  3. Pulse, exercise and recoveryInterpret pulse and blood-pressure measurements, and explain why breathing, heart and pulse rates change during activity and recovery.
  4. 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

Recommended nextBlood Circulation topic check

Topic reference

Topic picture

One circulation, two exchange sitesA clockwise route follows the right side of the heart, pulmonary artery, lungs, pulmonary veins, left side of the heart, body arteries, body tissues and body veins. Oxygen enters blood at the lungs and reaches cells at body tissues; carbon dioxide moves the other way. Below, an artery cross-section has a thick wall, a view along a vein shows valves opening towards the heart, and a capillary has a one-cell-thick wall.Trace one complete journeyBlood passes through the heart twice during this route.Right side of heartPumps blood to lungsLungsOxygen enters bloodCarbon dioxide leavesLeft side of heartPumps blood to bodyBody tissuesOxygen reaches cellsCO₂ enters bloodPulmonary arteryOxygen-poor bloodPulmonary veinsOxygen-rich bloodBody arteriesOxygen-rich bloodBody veinsOxygen-poor blood“Oxygen-poor” means less oxygen, not no oxygen.Relate vessel structure to its jobArteryThick muscular, elastic wallWithstands higher pressureCarries blood away from heartVeinShown open towards heart →Flaps can close against backflowThinner wall; lower pressureCapillaryOne-cell-thick wallShort distance for exchangeLinks arteries and veins
Scroll diagram horizontally to read all labels.
Follow the arrowheads, not the colours. The two heart boxes are parts of the same organ. The artery is shown in cross-section; the vein and capillary are shown along their length. The open vein valves can close against backflow. The vessel drawings use different scales and do not compare actual vessel diameters.