AHL Content Statements

• B3.2.11

  Release and reuptake of tissue fluid in capillaries
  

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  Tissue fluid is formed by pressure filtration of plasma in capillaries. This is promoted by the higher pressure of blood from arterioles. Lower pressure in venules allows tissue fluid to drain back into capillaries.

• B3.2.12

  Exchange of substances between tissue fluid and cells in tissues
  

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  Discuss the composition of plasma and tissue fluid.
  

• B3.2.13

  Drainage of excess tissue fluid into lymph ducts

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  Limit to the presence of valves and thin walls with gaps in lymph ducts and return of lymph to the blood circulation.

• B3.2.14

  Differences between the single circulation of bony fish and the double circulation of mammals

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  Simple circuit diagrams are sufficient to show the sequence of organs through which blood passes.

• B3.2.15

  Adaptations of the mammalian heart for delivering pressurized blood to the arteries

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  Include form–function adaptations of these structures: cardiac muscle, pacemaker, atria, ventricles, atrioventricular and semilunar valves, septum and coronary vessels. Students should be able to identify these features on a diagram of the heart in the frontal plane and trace the unidirectional flow of blood from named veins to arteries.

• B3.2.16

  Stages in the cardiac cycle

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  AOS: Students should understand the sequence of events in the left side of the heart that follow the initiation of the heartbeat by the sinoatrial node (the “pacemaker”). Students should be able to interpret systolic and diastolic blood pressure measurements from data and graphs.

• B2.3.7

  Adaptations to increase surface area-to-volume ratios of cells
  

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  Include flattening of cells, microvilli and invagination. Use erythrocytes and proximal convoluted tubule cells in the nephron as examples.
  

• B2.3.9

  Adaptations of cardiac muscle cells and striated muscle fibres

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  Include the presence of contractile myofibrils in both muscle types and hypotheses for these differences: branching (branched or unbranched), and length and numbers of nuclei. Also include a discussion of whether a striated muscle fibre is a cell.

• D3.3.11

  Changes in blood supply to organs in response to changes in activity

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  As examples, use the pattern of blood supply to the skeletal muscles, gut, brain and kidneys during sleep, vigorous physical activity and wakeful rest.