Question

Describe in brief the structure and functions of human blood.

Answer 1

Blood is a fluid connective tissue that circulates constantly around the body, allowing constant communication between tissues distant from each other. Blood is composed of a clear, straw-coloured, watery fluid called plasma in which several different types of blood cells are suspended.

Plasma contains water (90-92%) and other disolved and suspended substances like plasma proteins, inorganic salts, nutrients, waste materials, hormones and gases.

There are three types of formed elements (blood cells) in blood:

1) Erythrocytes (red cells)

2) Leukocytes (white cells)

3) Platelets (thrombocytes)

Erythrocytes(RBC) - Most abundant type of blood cells. Their main function is transport of respiratory gases, mainly oxygen, but they also carry some carbon dioxide. They also maintain the viscosity and pH of blood.

Leukocytes (WBC) - These cells have an importnat function in defence and immunity. They detect foreign or abnormal (antigenic) material and destroy it, through a range of defence mechanisms. There are two main types:

(a) Granulocytes (polymorphonuclear leukocytes)- neutrophils, eosinophils and basophils.

(b) Agranulocytes - monocytes and lymphocytes.

Platelets (Thrombocytes) - These are very small discs, 2-4 micrometer in diameter. They are responsible for coagulation or clotting of blood.

Functions of blood:

1) Transport of - gases, nutrients, waste products, processed molecules, regulatory molecules, blood cells, plasma proteins, hormones and enzymes

2) Regulation of pH and osmosis

3) Maintenance of body temperature

4) Protection against foreign substances

5) Clot formation