Exchange of materials

 Arteries become narrower towards a capillary network causing pressure filtration to occur

 Pressure filtration causes plasma to pass through capillary walls into the tissue fluid surrounding the cells

o Tissue fluid and blood plasma are similar in composition, except for plasma proteins, which are too large to be filtered through the capillary walls

 Tissue fluid supplies cells with glucose, oxygen and other substances

 Carbon dioxide and other metabolic wastes diffuse out of the cells and into the tissue fluid to be excreted

 Much of the tissue fluid returns to the blood

 Lymphatic vessels absorb excess tissue fluid and return it as lymph to the circulatory system