Blood 1, Plasma, constituents and functions

A lesson on the components of the plasma. Plasma is a yellowish fluid which is about 91% water. This keeps the blood fluid,

allowing it to circulate around the body. The rest of the plasma is made up of various substances in solution and suspension; these include plasma proteins, nutrients, dissolved gases and waste products.

Plasma proteins

Proteins are organic molecules made up of precise sequences of amino acids

which are chemically bound together. There are three main plasma proteins;

albumin, globulin and fibrinogen. Proteins are very large molecules and their

presence is vital to generate plasma osmotic potential. Without this osmotic

property the blood would be unable to reabsorb tissue fluid into the venous

ends of the capillaries. Albumin is the most common plasma protein and also

generates most of the osmotic potential of plasma. The globulin proteins include

the immunoglobulins, also called antibodies, which allow the body to fight off

infections. Without these immune proteins we would probably die from the

next viral or bacterial infection we pick up. Other globulin proteins act as carrier

molecules which transport some hormones and minerals around the body.

Fibrinogen is a plasma protein which is essential for the process of normal

blood clotting.

As fats are not soluble in water they are transported around the body bound

to plasma proteins. These combinations of fat and protein are termed

lipoproteins and are soluble in water.

Nutrients and waste products

Plasma carries absorbed nutrients from the gut to all of the tissues of the body

which need them. These include glucose, amino acids and vitamins. It also

transports waste substances such as ammonia from the tissues to the liver, where

this poisonous waste is converted into urea, which is much less toxic. Once

formed, the urea is transported in solution from the liver to the kidneys for

excretion.