Watery liquid containing glucose, amino acids, fatty acids, salts and O₂

Exchange between blood and cells - bathes all cells in it (their immeediate environment)

Formed from blood plasma so maintains a mostly constant environment

Hydrostatic pressure from blood flow from arteries to capillaries at arteriole end

Tissue fluid forced out

Opposed by:

Hydrostatic pressure of tissue fluid outside capillary preventing outward movement of tissue fluid

Lower water potential of blood from plasma proteins pulls water back into blood

This creates overall pressure that pushes tissue fluid out of capillaries

Only small molecules

ULTRAFILTRATION

Loss of tissue fluid from capillaries reduces their hydrostatic pressure

Blood reaches the venous end of the capillary network - hydrostatic pressure of tissue fluid is higher outside the capillaries

Tissue fluid forced back into capillaries as a result

Tissue fluid has lost lots of O₂ and nutrients by diffusion

Gained CO₂ and wate products

Sysytem of vessels initially look like capillaries but merge into vessels

Network throughout body starting at tissue

Larger vessels drain contents back into blood stream

Via two ducts that join veins close to the heart

Moved by:

Hydrostatic pressure of tissue fluid that has left the capillaries

Muscle contractions that squeeze the lymph vessels (contain valves to ensure movement away from tissues to heart)