Circulatory System

• Arteries have a smooth inner lining called the endothelium, which helps reduce friction and promote smooth blood flow.
• Blood is a fluid connective tissue.
• The human body of an average has 4 to 6 litres of blood.
• The liquid part of blood is called plasma. It is pale yellow in color.
• Blood cells are of three types:
• Red Blood Cells (RBCs) or erythrocytes
• White Blood Cells (WBCs) or leucocytes.
• Blood Platelets or thrombocytes.
• RBCs are biconcave, disc-shaped cells, as if pressed from the sides.
• Unlike other cells, a mature RBC does not contain any nucleus.
• RBCs are the most abundant components of blood.
• RBCs are red in color because of the presence of a red-coloured iron-containing protein called haemoglobin.
• Haemoglobin is responsible for carrying oxygen to all parts of the body.
• The average life span of an RBC is about 120 days.
• Plasma is the liquid component of blood that carries nutrients, hormones, gases, waste products, etc., throughout the body.
• There are about 5-6 million RBCs in each mm3 of blood.
• WBCs do not contain any haemoglobin.
• WBCs are colourless cells with no haemoglobin.
• These cells are larger than RBCs and do not contain haemoglobin.
• WBCs are colourless as they do not contain haemoglobin.
• WBCs contain nuclei.
• They do not have a definite shape.
• WBCs are produced in the bone marrow and lymph nodes.
• WBCs have a life span ranging from 12 hours to 12 days.
• WBCs' number is much less than RBCs, that is about 4000-13000 per mm3 of blood.
• An abnormal increase in WBCs count, that is above 50,000 per mm3, indicates infection in the body.
• WBCs play a vital role in protecting the body from infection, by destroying germs and foreign bodies such bacteria and viruses.
• Because of their ability to change shape, WBCs easily reach the site of infection and destroy germs by engulfing them.
• Blood platelets are colourless disc-shaped cells without nuclei.
• Platelets are smaller than RBCs and WBCs.
• Platelets number is 200000-400000 per mm3 of blood.
• Platelets are produced in the bone marrow.
• Platelets have a life span of about 3-7 days.
• Platelets prevent blood loss by forming clots over wounds and cuts.
• There are functions of blood.
• Transportation of nutrients
• Transportation of respiratory gases
• Transportation of waste products
• Distribution of hormones
• Protection of body