The blood is a liquid tissue that circulates in the cardiovascular system. Its volume in a healthy adult person averages 5 liters.
The blood picks up oxygen from the lungs, nutrients and water from the gastrointestinal tract, hormones from the endocrine glands and enzymes from some of the other organs of the body. These materials transport to all tissues of the body where they diffuse from the capillaries into the intercellular fluid. At the same time, cellular wastes pass from the intercellular fluid into the blood.
The two main components of blood:
2. Formed elements
This is the liquid intercellular material that imparts fluid properties to the blood. It is about 90% water. A group of proteins. called plasma proteins (Mainly albumin and globulin) comprise another 7 percent of plasma.
The remaining 3% consists of glucose. amino acids, nutrients, various hormones, enzymes. metabolic waste, and traces of many other organic and morganic materials.
2. Formed Elements
The formed elements are of three types:
1. Red blood cells
2. White blood cells
Red blood cells
The (RBCs) are the most numerous of the formed elements of blood and their count varies from 4 to 6 million per micro liter. The RBCs, also called erythrocytes, are non-nucleated cells, which are biconcave discs and measure about 8 micro meter in diameter and 2 Micro meter in maximum thickness. Their cytoplasm contains the iron-containing pigment hemoglobin, which has the capability to bind and carry oxygen well as carbon dioxide. A single erythrocyte has a pale yellow or tan color but in dense masses these cells exhibit red color which is characteristic of blood.
White blood cells
The (WBCs) are also called leukocytes. Their main function is to destroy micro-organisms at infection sites and, acting a scavenger, to remove debris that results from dead or injured tissue cells Unlike RBC. the WBC do contain nuclei, and are able to move about independently and pass through the vessel walls into the tissues.
In size they range from slightly larger to much larger than RBC. Their normal count varies from 4000 to 11000 cells per microliter. The leukocytes are divided into two main groups: agranulocytes and granulocytes.
The agranulocytes are those leukocytes whose cytoplasm does not contain any granules. The agranulocytes are further classified into two, types: (i) lymphocytes, and (ii) monocytes.
The granulocytes are those cells, which exhibit granules in the cytoplasm
Depending on the staining reaction of their granules, the granulocytes are classified into three categories (i) neutrophils, (ii) eosinophils, and basophils.
The platelets, also called thrombocytes, are small, flat cytoplasm: fragments; 2-4 micro meter in diameter. A cell membrane covers them but do not contain a nucleus. Their normal count is variable ranging from 150,000 to 400,000 per microliter of blood. Their principal function is to start the intricate process of blood clotting.