Plasma is a clear, yellowish fluid and can sometimes appear milky after a very fatty meal or when people have a high level of lipids in their blood. Plasma is 90-percent water. The other 10 percent dissolved in plasma is essential for life. These dissolved substances are circulated throughout the body and diffuse into tissues and cells where they are needed.

Proteins make up a large part of the 10 percent of material dissolved in plasma and tend to attract water to keep their relative concentration in blood vessels more in line with fluid outside the blood vessels. This is one of the ways the body maintains a constant volume of blood.

Plasma contains 6.5 to 8 grams of protein per deciliter of blood. The main proteins in plasma are albumin (60 percent), globulins (alpha-1, alpha-2, beta, and gamma globulins (immunoglobulins), and clotting proteins (especially fibrinogen). These proteins function to maintain oncotic pressure (especially albumin) and transport substances such as lipids, hormones, medications, vitamins, and other nutrients. These proteins are also part of the immune system (immunoglobulins), help blood to clot (clotting factors), maintain pH balance, and are enzymes involved in chemical reactions throughout the body.

Electrolytes are another large category of substances dissolved in plasma. They include: Sodium (Na+), Potassium (K+), Chloride (Cl-), Bicarbonate (HCO3-), Calcium (Ca+2), Magnesium (Mg+2). These chemicals are absolutely essential in many bodily functions including fluid balance, nerve conduction, muscle contraction (including the heart), blood clotting and pH balance. 

Other materials dissolved in plasma are carbohydrates (glucose), cholesterol, hormones and vitamins. Cholesterol is normally transported attached to lipoproteins such as low-density lipoproteins (LDLs) and high-density lipoproteins (HDLs).