Blood: components, functions and blood groups
Blood is a fluid connective tissue: plasma plus red cells, white cells and platelets. The ABO blood groups depend on antigens on red cells and antibodies in plasma.
Components of blood
| Component | Features | Job |
|---|---|---|
| Plasma (about 55%) | Pale yellow fluid, about 90% water, with proteins (albumin, globulin, fibrinogen), glucose, salts, hormones and wastes | Carries dissolved food, hormones, CO₂ and wastes; fibrinogen helps clotting |
| Red blood cells (erythrocytes) | Round, biconcave, no nucleus; contain haemoglobin; about 5 million per mm³; live about 120 days; made in red bone marrow | Carry oxygen (and some CO₂) |
| White blood cells (leucocytes) | Have a nucleus; no haemoglobin; far fewer than red cells | Defend the body against germs |
| Platelets (thrombocytes) | Small cell fragments without a nucleus | Help blood clotting |
Kinds of white blood cells
| Group | Type | Job |
|---|---|---|
| Granulocytes (granules in the cytoplasm) | Neutrophils, the most common | Engulf and destroy germs: phagocytosis |
| Granulocytes | Eosinophils | Fight allergies and some infections, such as worms |
| Granulocytes | Basophils | Release heparin, which stops clotting inside vessels, and histamine |
| Agranulocytes (no granules) | Lymphocytes | Make antibodies |
| Agranulocytes | Monocytes, the largest | Phagocytic: engulf germs and dead cells |
Functions of blood
- Transport: oxygen from the lungs to the tissues, CO₂ from the tissues to the lungs, digested food from the intestine, hormones from glands, and wastes to the kidneys.
- Defence: white blood cells and antibodies fight germs.
- Clotting: platelets and fibrinogen seal cuts and stop bleeding.
- Temperature control: blood spreads heat evenly through the body.
- It keeps the body's water balance and pH steady.
ABO blood groups
| Blood group | Antigen on red cells | Antibody in plasma | Can give blood to | Can receive blood from |
|---|---|---|---|---|
| A | A | Anti-B | A, AB | A, O |
| B | B | Anti-A | B, AB | B, O |
| AB | A and B | None | AB only | A, B, AB, O (universal recipient) |
| O | None | Anti-A and anti-B | A, B, AB, O (universal donor) | O only |
Why matching matters, and the Rh factor
Karl Landsteiner discovered the ABO blood groups in 1900. If the wrong blood is given, antibodies in the patient's plasma make the donor's red cells clump together (agglutination), which can kill. Another antigen, the Rh factor, was first found in Rhesus monkeys. People who have it are Rh positive; those without it are Rh negative. Hospitals always test and match blood for both ABO and Rh before a transfusion.
Red cells need iron to make haemoglobin, and too little iron causes anaemia, which is common among Indian teenagers. Green leafy vegetables, pulses and dates help, and after the age of 18 you can donate blood at a blood bank to save lives.
1 marks: “Which blood group is the universal donor?” Group O.
2 marks: “Why are people with blood group AB called universal recipients?” Their plasma has neither anti-A nor anti-B antibodies, so donor red cells of any ABO group do not clump.
4 marks: “Explain the ABO blood groups with a table.” Landsteiner; antigens on red cells and antibodies in plasma for A, B, AB and O; who can give to whom; O universal donor, AB universal recipient; agglutination on mismatch.
Your blood group is the antigen you have; your plasma carries the antibody you lack. O gives to all (an Open hand); AB takes from all (Accepts Both).