tissue fluid

Question 1

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.

Answer 1

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

Accept: ‘blood or plasma’ instead of ‘capillary’

2. Less / no water removed (into capillary);

Accept converse: water remains in the tissue

3. By osmosis (into capillary);

Question 2

Explain the role of the heart in the formation of tissue fluid.

Answer 2

Contraction of ventricle(s) produces high blood / hydrostatic pressure;

2. (This) forces water (and some dissolved substances) out (of blood capillaries);

Question 3

Lymphoedema is a swelling in the legs which may be caused by a blockage in the lymphatic system.

Suggest how a blockage in the lymphatic system could cause lymphoedema.

Answer 3

Excess tissue fluid cannot be (re)absorbed / builds up;

Question 4

The hydrostatic pressure of the blood at the arteriole end of the capillary helps to form tissue fluid. Explain how.

Answer 4

Hydrostatic pressure higher than osmotic “effect”;
Forces / squeezes / pushes out / water / small molecules / ions / examples

Question 5

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

Answer 5

(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 6

Explain why there is a net loss of water from a capillary at the arterial end.

Answer 6

(at arterial end) hydrostatic pressure / blood pressure;
greater than pressure of water potential gradient / greater than
osmotic uptake;

Question 7

Tissue fluid accumulates in the tissues of people who do not eat enough protein. Explain why.

Answer 7

less protein in blood;
water potential gradient is lower

Question 8

Describe and explain how water is exchanged between the blood and tissue fluid as blood flows along the capillary.

Answer 8

HP forces water out;

idea that HP is “higher” than WP;

proteins remain in blood (increases WP);

idea that WP is now “higher” than HP;

water returns by osmosis / along WP gradient;

water moves out at arteriole end and back in (at venule end);