The formation of tissue fluid and its return to the circulatory system

Question 1

Where is tissue fluid found?

Answer 1

surrounds cells in tissues and is made from small molecules (such as oxygen, water and nutrients) that leave the blood plasma.

Question 2

Why does tissue fluid lack RBC or large proteins

Answer 2

They are big enough to be pushed out through the capillary walls

Question 3

How do substances move out of the capillary into the tissue fluid?

Answer 3

By pressure filtration in a capillary bed, substances move out of the capillaries into the tissue fluid

Question 4

Outline the 5 steps requires to form tissue fluid

Answer 4

1) The hydrostatic pressure inside the capillaries is greater than the hydrostatic pressure in the tissue fluid at the beginning of the capillary bed.
2) As a result an overall outward pressure forces fluid go out of the capillaries and enter into the spaces around the cells thus forming tissue fluid.
3) When fluid leaves, the hydrostatic pressure decreases in the capillaries and is very low at the venule end of the capillary bed.
4) The fluid loss and increase in concentration of plasma proteins leads to low water potential at the venule end of the capillary bed. This is lower than the water potential in the tissue fluid.
5) Thus some water re‑enters the capillaries from the tissue fluid at the venule end by osmosis.
6) Remaining excess tissue fluid is taken by the lymphatic system back into the circulatory system.