HUMAN FUNCTION

TRANSPORT IN HUMAN

Like other higher animals, the task of the transport of different material human body is performed by two systems i.e. blood circulatory system and lymphatic system. The two systems are well-coordinated and associated with each other. Like other vertebrates, humans have a closed blood circulatory system (meaning that blood never leaves the network of arteries, veins and capillaries).

The main components of the human blood circulatory system are blood, heart and blood

vessels. 

 BLOOD

Blood is a specialized body fluid (a connective tissue) that is composed of a liquid called blood plasma and blood cells. The weight of blood in our body is about 1/12th of our body. The average adult body has about 5 litres of blood.

In a healthy person, plasma constitutes about 55% by volume of blood, and cells or cell-like bodies are about 45% by volume of the blood.

-BLOOD PLASMA

Plasma is primarily water in which proteins, salts, metabolites and wastes are dissolved. Water constitutes about 90-92% of plasma and 8-10% are dissolved substances. Salts make up 0.9% of plasma, by weight. Sodium chloride (the table salt) and salts of bicarbonate are present in considerable amounts, Ca, Mg, Cu, K and Zn are found in trace amounts. Changes in the concentration of any salt can change the pH of blood (normal is 7.4). Proteins make 7-9 % by weight of plasma. The important proteins present in plasma are antibodies, fibrinogen (blood clotting protein), albumin (maintains the water balance of blood) etc. Plasma also contains the digested food (absorbed from digestive system), nitrogenous wastes and hormones. Respiratory gases i.e. CO, and O₂ are present in the plasma.

Plasma is primarily water in which proteins, salts, metabolites and wastes are dissolved. Water constitutes about 90-92% of plasma and 8-10% are dissolved substances. 

Red Blood Cells (Erythrocytes)

These are the most numerous of blood cells. A cubic millimeter of blood contains 5 to 5.5 million of RBCs in blood cell matures, its nucleus is lost. After the loss of nucleus, RBC enters blood. About 95% of the cytoplasm of RBCs is filled with hemoglobin, which transports O, and small amounts of CO₂. The remaining 5% consists of enzymes, salts and other proteins. RBCs are biconcave and have an elastic cell membrane. In the embryonic and foetal life, they are formed in liver and spleen. In adults, they are formed in the red bohe marrow of short and flat bones, such as stemum, ribs and vertebrae. Average life span of RBC is about four months (120 days) after which
it breaks down in liver and spleen by phagocytosis.
In a normal person about 2-10 million red blood cells are males, and 4 to 4.5 million in females. When RBCs are formed and destroyed every formed, they have nucleus. In mammals, when a red second.

White Blood Cells (Leukocytes)

These are colourless, because they do not contain pigments. They are not confined to blood vessels and also migrate out into tissue fluid. One cubic millimeter of blood contains 7000 to 8000 WBCs. Their life span ranges from months to even years, depending on body's needs. WBCs function as the main agents in body's defence system. There two main types of WBCs. Granulocytes have granular cytoplasm. These include neutrophils (destroy small particles by phagocytosis), eosinophils (break inflammatory substances and kill parasites) and basophils (prevent blood clotting).
Agranulocytes have clear cytoplasm and include monocytes (produce macrophages which engulf germs) and B and T lymphocytes (produce antibodies and kill germs).