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 dissolved substances. These are circulated throughout the body and diffuse into tissues and cells where needed. Thes substances include proteins which are responsible for oncotic pressure within the blood vessels. The main proteins in plasma are albumin, globulins and clotting factorsparticularly fibrinogen.