# 72 Blood composition and Plasma
If blood is allowed to stand without clotting, it separates out into 4 components: plasma, red blood cells, white blood cells and platelets.
The plasma and red blood cells play an important role in the transportation of substances, around the body.
White blood cells and platelets are part of the body's immune system.
55% of the blood is plasma. This straw-coloured liquid contain water with many important dissolved substances which must be carried around the body. Most materials are carried by the blood plasma, except for oxygen.
- blood cells
- soluble nutrients e.g. glucose (products of digestion) from the small intestine to the organs
- amino acids (plasma acts as a pool for amino acids for these cannot be stored in the body)
- plasma proteins that are important in blood clotting (e.g. fibrinogen).
- CO2 (waste gas produced by respiration in cells) from the organs to lungs
- Other wastes of digestion (e.g. urea) from the liver to the kidneys.
- Antibodies and antitoxins
- Heat from the liver and muscles to all parts of the body.