Medical Physiology/Blood


A three-dimensional ultrastructural image analysis of a T-lymphocyte (right), a platelet (center) and a red blood cell (left), using a Hitachi S-570 scanning electron microscope (SEM) equipped with a GW Backscatter Detector.

Blood is a connective tissue Blood consists of two parts, plasma and blood cells. Plasma makes up 55% of total blood, while cells and cell like bodies make up 45% of total blood. Plasma is the medium in which various substances are dissolved. These include plasma proteins, various electrolytes, and enzymes. Blood cells are move in plasma. Almost 90% of plasma is water. Plasma proteins make up 7-9% of plasma. The other 1% consists of electrolytes, of which the most important is NaCl(about 0.9%). Cells present in blood are red blood cells(RBCs) and white blood cells(WBCs), while platelets are the cell like bodies.

Blood performs various functions. Some of these are:

1) Transport of nutrients and waste products of cells. Nutrients are transported from gastrointestinal tract to cells while waste products are transported from cells to kidneys.

2) Transport of gases like oxygen and carbon dioxide to and from cells.

3) Maintenance of homeostasis

4) Maintenance of body temperature

5) Protection from invading microbes by WBCs

6) Blood coagulation.