Introduction:-Blood is a connective tissue. It provides one of the means of the communication between the cells of different parts of the body and external environment.
Functions of blood:-
(1) Oxygen from the lungs to the tissues, & carbon dioxide from the tissue to the lungs for excretion.
(2) Nutrients from the alimentary tract to the tissues, and cell wastes to the excretory organs by kidney.
(3) Hormones secreted by endocrine glands to their target glands & tissues.
(4) Heat produced in active tissues to the other less active tissues.
(5) Protective substances e.g antibodies , to areas of infection
(6) Clotting factors that coagulate blood, minimising bleeding from ruptured blood vessels.
Blood makes up about 7% of body weight about 5.6 litre in a 70 kg man.
Composition of blood:-
Blood is composed of a straw – coloured transparent fluid, Plasma, in which different types of cells are suspended. Plasmaconstitutes about 55% and cells about 45% of blood volume.
Plasma:- The constituents of plasma are water 90- 92% and dissolved substances , including:
• Plasma proteins
• Inorganic salts
• Nutrients from digested foods
• Waste materials
(1) Plasma proteins:– It is make about 7% of plasma are normally retained within the blood, because they are too big to escape through the capillary pores into the tissues. Plasma viscosity is due to plasma proteins, mainly albumin and fibrinogen. Viscosity is used as a measure of the body’s response to the some diseases.
(2) Inorganic (minerals) salts:– These are involved in a wide variety of activities, including muscle contraction, transmission of nerve impulses, formation of secretion and maintenance of acid- base balance.
(3) Nutrients :- In the alimentary tract , food is broken down into small molecules, e.g monosaccharides, amino acids, fatty acids & glycerol are absorbed.
(4) Waste products:- Urea, creatinine & uric acid are the waste products of protein metabolism. They are formed in the liver and conveyed in blood to the kidneys for excretion.
(5) Hormones:– These are substances by endocrine glands .Hormones pass directly from the endocrine cells into the blood which, transports them to their targets tissues & organs in the body, where influence cellular activity.
(6) Gases:– oxygen ,carbon dioxide & nitrogen.