Tissue Fluid

• 1 (a) (i) An arteriole is described as an organ. Explain why.

  (1 mark)

  Made of different tissues.
• (ii) An arteriole contains muscle fibres. Explain how these muscle fibres reduce blood flow to capillaries.

  (2 marks)

  As muscle contracts, arteriole narrows, reducing size of lumen.See an expert-written answer!We have an expert-written solution to this problem!
• (b) (i) A capillary has a thin wall. This leads to rapid exchange of substances between the blood and tissue fluid. Explain why.

  (1 mark)

  Short diffusion pathway.
• (b) (ii) Blood flow in capillaries is slow. Give the advantage of this.

  (1 mark)

  More time for exchange of substances.
• (c) Kwashiorkor is a disease caused by a lack of protein in the blood. This leads to a swollen abdomen due to a build up of tissue fluid. Explain why a lack of protein in the blood causes a build up of tissue fluid.

  (3 marks)

  Water potential in capillary not as low as there is less water removed by osmosis into capillary.
• 2) Describe how tissue fluid is formed and how it is returned to the circulatory system.

  (6 marks)

  High hydrostatic pressure forced fluid out. Large proteins remain in capillary. Low water potential in capillary due to plasma proteins. Water re-enters capillary by osmosis. Lymphatic system return excess fluid to circulatory system.See an expert-written answer!We have an expert-written solution to this problem!
• 3) The diagram shows a tissue and cells surrounding a capillary

  [Diagram shows labelled tissue fluid, body cells, red blood cells and label F which points to substance surrounding red blood cells]

  (a) Name fluid F.

  (1 mark)

  Blood plasma
• (b) Give one way in which fluid F is different to tissue fluid.

  (1 mark)

  More proteins
• (c) (i) The blood pressure is high at the start of the capillary. Explain how the left ventricle causes the blood to be a high pressure.

  (1 mark)


  Contracts
• (ii) The blood pressure decreases along the length of the capillary. What causes this decrease in pressure?

  (1 mark)

  Loss of fluid
• (d) In children, some diets may result in low concentration of protein in fluid F. This can cause the accumulation of tissue fluid. Explain the link between a low concentration of protein in fluid F and the accumulation of tissue fluid.

  (3 marks)

  Water potential in capillary not as low. More tissue fluid is formed at arteriole end. Less water absorbed into capillary by osmosis.
• 4) Describe and explain how tissue fluid is formed and how it is returned to the blood.

  (6 marks)

  High hydrostatic pressure at arteriole end of capillary, forces fluid out, leaving the proteins behind. Water potential becomes more negative, low friction, reducing hydrostatic pressure. Water moved in by osmosis and excess water is taken up by lymphatic system and returned to blood stream via blood vessels.
• 5) Figure 3 shows a blood capillary and some surrounding cells. [Diagram shows X labelled as area around cells and Y as area surrounding red blood cells]

  (a) (i) Give one way in which the composition of fluid X is different from the composition of plasma at Y. Give a reason for your answer.

  (2 marks)

  Lower oxygen because oxygen used in respiration by cells.
• (a) (ii) Explain how fluid is returned to the blood at the venous end of the capillary.

  (4 marks)

  Low hydrostatic pressure at venule end, higher concentration of blood proteins so water potential of blood lower than tissue fluid. Meaning, water returned by osmosis.
• 6) Explain how the tissue fluid is formed and how it is returned to the circulatory system.

  (6 marks)

  Higher hydrostatic pressure at arterial end of capillary forcing fluid out of capillary into tissues. Proteins stay in capillary so water potential of blood plasma falls. Hydrostatic pressure falls due to loss of fluid. Water moves back into blood in venule end of capillary by osmosis. Lymphatic system collects excess tissue fluid.
• 7) (a) Tissue fluid returns to the blood in the capillaries. Describe how.

  (3 marks)

  Hydrostatic pressure is lower at venule end of capillary. Water potential is lower in capillary due to plasma proteins. Tissue fluid returned by osmosis and returns to blood via lymph vessels.
• (b) In some cases, lymph vessels in the legs may become blocked. Explain how this leads to swelling of the tissues in the feet and ankles.

  (2 marks)

  Swelling caused by fluid build up because fluid cannot be drained into lymphatic system.
• 8) The diagram shows a site of exchange of substances in a tissue. [Diagram shows X labelled as (fluid leaves) and Y as (fluid enters) pointing in (X) and out (Y) capillary]

  (i) What causes fluid to leave the blood capillary at point X?

  (1 mark)

  Hydrostatic pressure
• (ii) Fluid returns to the blood capillary at point Y. Explain how.

  (1 mark)

  Osmosis/lower water potential in capillary
• (iii) The lymph capillary empties into a larger lymph vessel which has valves. Explain how these valves assist the return of lymph to the blood plasma.

  (2 marks)

  Stop backflow, pressure of surrounding tissues force lymph along.
• 9) Describe and explain how water is exchanged between the blood and tissue fluid as blood flows along the capillary.

  (4 marks)

  Hydrostatic pressure forces water out as hydrostatic pressure is greater than water potential. Proteins remain increasing water potential (higher than hydrostatic pressure). Water returns via osmosis. Water moves out at arteriole end and back in at venule end.
• Explain how fluid leaves the capillary at the arterial end

  • There is a high hydrostatic pressure
  • Which is greater than the osmotic effect
  • So molecules/fluid is forced out