Write an explanatory note on blood.

ANS :



Blood is a living, red coloured, liquid connective tissue which circulates constantly throughout the body.

The two main components of blood are : (1) Blood Plasma (2) Blood Corpuscles.

BLOOD PLASMA :



It is pale yellow, nonliving, intercellular matrix with basic properties.

It consists of 90% of water and 10% of various constituents like plasma proteins, nutrients, metabolic waste, enzymes, hormones, vitamins, etc.





BLOOD CORPUSCLES :



Three main types of blood corpuscles in blood plasma are : (1) erythrocytes or red blood corpuscles (2) leucocytes or white blood corpuscles (3) thrombocytes (blood platelets).

They are formed from the undifferentiated stem cells found in the bone marrow of long bones.

ERYTHROCYTES (RBC) :



They are round, biconcave and light red in colour.

They do not possess nucleus and mitochondria.

The cell membrane is thin and elastic.

The cytoplasm contains haemoglobin which is a conjugated protein containing iron. Iron gives red colour to haemoglobin.

Haemoglobin absorbs oxygen from the walls of the lungs and forms oxyhaemoglobin. It takes this oxygen to every cell of the body.

Similarly haemoglobin collects carbon dioxide from each cell and brings it to lungs.

Since haemoglobin transports respiratory gases, it is known as respiratory pigment.

Every day about 30 lakh (3 million) erythrocytes die and as much of them are formed in the bone marrow.

The average life span of an erythrocyte is of 120 days.



LEUCOCYTES (WBC) :



The leucocytes vary in size, shape, appearance of the nuclei and the cytoplasmic constituents.

They do not contain any respiratory pigment.

They destroy pathogenic microorganisms and harmful toxic substances.

As they can pass through very thin membranes of capillaries, they are capable of reaching any part of the body.

Thus leucocytes provide protection to the body.

Lymphocytes (a type of WBC) produce immunoglobulins.



BLOOD PLATELETS :



They are very small, spindle-shaped fragments of cells in blood plasma.

They do not have any nucleus.

Their cell membrane is very thin and sensitive.

They rupture when they come in contact with air and release chemicals which initiate the process of blood clotting.