Plasma is the liquid in which blood cells and nutrients travel through the blood stream. It's a golden yellow colored substance and can be seen in the picture below. Plasma is made up mostly of water and salts. The kidneys analyze and maintain the salt concentration of a person's plasma. This is done because even the smallest changes in plasma salt concentration can force cells in the human body to function improperly. If the salt concentration is not maintained by the kidneys it can result in seizures, coma, or even death. There is about 2 - 3 litters of plasma in the average adult human body. Plasma also contains important proteins.
Two main types of proteins found in plasma are albumin and gamma globulin.
Albumin is the main protein that is found within blood. It works to regulate the water content of tissues and blood.
Gamma globulin is made up of many anti-body molecules. Anti-bodies are extremely important to the body because these are what neutralize or destroy infectious organisms.