Blood

It is a fluid connective tissue flowing in its closed path called blood vessels. It is red in colour due to thepresence of the iron-rich pigment called haemoglobin in RBC.

Blood can further be classified into two major groups:

• Plasma: It is the nonliving portion of the blood, which consist 90% of water and 10% of minerals. It occupies 55% of total volume of blood and performs the following major functions:
• It transports digested food to different organs and tissues of the body.
• Waste substances from the tissues are removed and carried to the related excretory organs for their organs for their elimination.
• It removes the major portion of carbon dioxide from the tissue.
• The hormones secreted by various endocrine and exocrine glands are transported by circulatory system
• It regulates the body temperature.
• It contains fibrinogen (protein) and prothrombin hormone that helps in clotting of the blood after clots.

Blood cells

1. Red blood cells: They are also called erythrocytes. They are circular, biconcave, disc-shaped and non-nucleated cells. They are formed in red bone marrows and destroyed in the spleen. Their life span is very short that is 4 months. In one cubic millilitre of the blood of a healthy person 42-45 lakhs of RBC present. RBC contains an iron pigment called haemoglobin that carries oxygen from place to place in the form of oxyhemoglobin. When haemoglobin is exposed to oxygen, it turns red. So the blood is red in colour. If RBC is less in blood then, a person is suffering from anaemia, as there is not enough haemoglobin to transport oxygen.
2. White blood cells: They are also called leukocytes. They are irregular in shape. They form in bone marrow and mature in lymph node or bone marrow. Their life span is about of 15 days. In one cubic millilitre of the blood of a healthy person, there are 6000- 10000 WBC present. WBC maintain immunity of our body. They fight against germs and keep us safe from disease. If WBC count is less in our body then we tend to get diseases, as our capacity for fighting with diseases is compromised.

   

   

3. Platelets: It is also called thrombocytes. They are rod-shaped without a nucleus. They are formed in bone marrow and destroyed in the spleen. Their life span is about 9 days. In one cubic millilitre of the blood of a healthy person, there are 2 to 4 lakhs platelets present. They are responsible for clotting of blood.

Functions of blood

• Transportation: Blood transports oxygen from lungs to tissue and carries carbon dioxide from tissue to their excretory organs. It carries hormones to their target organs. It helps to transport minerals up to tissue and byproducts to their excretory organs.
• Regulation: Body temperature is regulated by blood.
• Protection: Blood maintains the immunity of the body, which fights against disease. Blood produces antibody in response to antigen and protects from germs.