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.