Tissue fluid

Question 1

Some people produce a much higher ventricular blood pressure than normal. This can cause tissue fluid to build up outside the blood capillaries of these people.

Explain why.

Answer 1

More fluid forced/filtered out of capillary/blood (due to high pressure);

Accept: water for fluid.

Must convey idea of ‘more’.

Reject: more tissue fluid is forced out.

Do not credit ‘more plasma forced out’.

2. Less return of fluid (into capillary/blood) due to pressure

OR

Lymph(atic) (system) cannot drain away all excess fluid;

Question 2

Explain how tissue fluid is formed and how it may be returned to the circulatory system.

Answer 2

(hydrostatic) pressure of blood high at arterial end;

2. fluid / water / soluble molecules pass out (reject plasma);
3. proteins / large molecules remain;
4. this lowers the water potential / water potential becomes more negative;
5. water moves back into venous end of capillary (reject tissue fluid) by osmosis / diffusion;
6. lymph system collects any excess tissue fluid which returns to blood / circulatory system / link with vena cava / returns tissue fluid to vein;

Question 3

Explain how fluid leaves the capillary at the arterial end.

Answer 3

hydrostatic pressure / blood pressure / arterial pressure;
greater than osmotic effect which forces molecules / fluid out;

Question 4

he figure below represents a capillary surrounded by tissue fluid.
The values of the hydrostatic pressure are shown.

Arteriole
end

direction of blood flow

Venule
end

Hydrostatic pressure = 4.3 kPa Hydrostatic pressure = 1.6 kPa

Tissue fluid
Hydrostatic pressure = 1.1 kPa

(a) Use the information in the figure above to explain how tissue fluid is formed.

Answer 4

(Overall) outward pressure of 3.2 kPa;

2. Forces small molecules out of capillary.

Question 5

High blood pressure leads to an accumulation of tissue fluid. Explain how.

Answer 5

High blood pressure = high hydrostatic pressure;

2. Increases outward pressure from (arterial) end of capillary / reduces inward pressure at (venule) end of capillary;
3. (So) more tissue fluid formed / less tissue fluid is reabsorbed.

Question 6

The hydrostatic pressure falls from the arteriole end of the capillary to the venule end of the capillary. Explain why.

Answer 6

Loss of water / loss of fluid / friction (against capillary lining).

Question 7

The water potential of the blood plasma is more negative at the venule end of the capillary than at the arteriole end of the capillary. Explain why.

Answer 7

Water has left the capillary;

2. Proteins (in blood) too large to leave capillary;
3. Increasing / giving higher concentration of blood proteins (and thus wp).

Question 8

In children, some diets may result in a 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.

Answer 8

Water potential (in capillary) not as low / is higher / less negative / water potential gradient is reduced;

More tissue fluid formed (at arteriole end);

Less / no water absorbed (into blood capillary) by osmosis; (into blood capillary);

Question 9

In humans, substances move out of the capillaries to form tissue fluid. Describe how this tissue fluid is returned to the circulatory system.

Answer 9

(Hydrostatic) pressure lower in capillary / blood / higher in tissues / tissue fluid;

2. Water (returns);
3. By osmosis;
4. Water potential lower / more negative in blood / capillary / higher / less negative water potential in tissues / via water potential gradient;
5. Due to protein (in blood);
6. (Returns) via lymph (system / vessels);