3.1.2d) The formation of tissue fluid from plasma

Question 1

Tissue fluid

Answer 1

Substances dissolved in plasma can pass through the capillary walls but large plasma proteins cannot
Same composition as plasma
Diffusion takes place between the blood & cells through the tissue fluid

Question 2

Plasma protein have an osmotic effect

Answer 2

Gives blood in the capillaries a high solute potential (low water potential) compared to surrounding fluid
Result: water moves into the blood in the capillaries from surrounding fluids by osmosis

Question 3

Oncotic pressure

Answer 3

Water moving into the blood capillaries
-3.3 kPa

Question 4

Hydrostatic pressure

Answer 4

Blood flows through the arterioles into the capillaries
Under pressure from heart contractions

Question 5

Arterial end

Answer 5

Hydrostatic pressure is high at 4.6 kPa
Higher than oncotic pressure attracting water by osmosis so fluid is forced out of the capillaries
Tissue fluid fills the space between the cells

Question 6

Tissue fluid movement process

Answer 6

Blood at the arterial end moves through the capillaries towards the venous end - balance of forces change
Hydrostatic pressure falls to 2.3 kPa until fluid has moved out & pulse is lost
Oncotic pressure stays the same & becomes stronger than the hydrostatic pressure - water moves back into capillaries by osmosis at the venous end
By the time the blood returns to the veins 90% of tissue fluid is back in the blood vessels