Plasma

Introduction

Plasma is the fluid portion of the blood in which the blood cells are suspended. Plasma in combination with the interstitial fluid makes up the extracellular body fluid compartment. Blood plasma can be prepared following centrifugation of a fresh sample that has been placed in a sample pot containing anti-coagulant. Whilst in the centrifuge the red blood cells separate and fall to the bottom leaving a layer of yellow plasma on top. The plasma can consequently be drawn off.

Blood plasma is to be distinguihed from serum which is plasma without fibrinogen which is separated following the clotting process.

Composition

Plasma is mostly water (90%) but it also contains the following substances:

• Plasma Proteins
• Nutrients
• Minerals
• Gases
• Waste products
• Hormones and enzymes.

These substances are circulated throughout the body by plasma and diffuse into tissues and cells where needed.

Plasma proteins are large molecules of which there are four main types, albumin, Globulin, fibrinogen and prothrombin. Albumin maintains oncotic pressure within the blood vessels and hence blood volume and blood pressure. Globulins which are produced by lymphocytes act in immune reactions and fibrinogen and prothrombin are required in order for clotting to occur.