BLOOD

The Blood

Blood is classified as a connective tissue, since nearly half of it is made up of cells. However, it differ from other connective tissues in that its cells are not fixed in position, instead they move freely in the liquid portion of the blood, the plasma. Blood is a viscous (thick) fluid that varies in colour from bright to dark red, depending on how much oxygen it is carrying. Its quantity differs with the size of the person; the average adult male, weighing 70 kg has about 5-6 litres of blood. This volume accounts for about 8% of the total body weight. It is carried through a closed system of vessels pumped by the heart. The circulating blood is of fundamental importance in maintaining the internal environment in a constant state (homeaostasis).

Functions of the Blood Transportation

A. Oxygen- from inhaled air diffuses into the blood through the thin lung membranes and is carried to all the tissue of the body. Carbon dioxide, a waste product of cell metabolism, is carried from the tissues to the lungs, where it is breathed out.

B. The blood transports foods and other needed substances such as minerals and vitamins, to the cells. These materials may inter the blood from the digestive system or may be released into the blood from body stores.

C. The blood transports waste products from the cells to the sites from which they are released. The kidney removes excess water, minerals, and urea from protein metabolism and maintains the acid-base balance of the blood. The liver removes bile pigments and drugs.

D. The blood carries hormones from their sites of origin to the organs they affect.

Regulation

A. Buffers in the blood help keep the PH of body fluids at about 7.4

B. The blood serves to regulate the amount of fluid in the tissues by means of substances (mainly proteins) that maintain the proper osmotic pressure

C. The blood transports heat that is generated in the muscles to other parts of the body thus aiding in the regulation of body temperature by the blood, thus aiding in the regulation of body temperature.

Protection

A. The blood carries the cells that are among the body’s defenders against pathogens. It also contains substances (antibodies) that are concerned with immunity to disease.

B. The blood contains factors that protect against blood loss.

Composition of Blood

The blood is composed of four components:

1.      The liquid element is called plasma

2.      Erythrocytes, from erythro, meaning “red,” are the red blood cells, which transport oxygen.

3.      Leukocytes, from leuko, meaning “white,” are the several types of white blood cells, which protect against infection.

4.      Platelets, also called thrombocytes, are cell fragments that participate in blood clotting.

QUIZ