Blood is a living organ that flows. It carries oxygen, fights infection, seals wounds, and moves heat and nutrients everywhere in your body, about 5 litres of it in an average adult, roughly 7,8% of body weight. Understanding what it is made of explains everything else on this site: why donations are separated into components, why intervals exist, and why certain patients need certain donors. ## The four parts Plasma, about 55%. A pale yellow liquid that is 90% water. The rest: proteins (clotting factors, antibodies, albumin), salts, hormones and nutrients. Plasma is the delivery system, and on its own, a lifesaver for burn victims, patients with liver disease and clotting disorders. Red cells, about 45%. The workhorses. Each red cell is packed with haemoglobin, an iron-containing protein that grabs oxygen in your lungs and releases it everywhere else. Red cells live about 120 days, then your spleen recycles them, which is why your body needs a steady supply of iron, and why donated red cells are useful for about 35,42 days in storage. White cells, under 1%. Your immune defence: they hunt bacteria, viruses and abnormal cells. Donated blood is filtered of most white cells during processing, because donor white cells can cause reactions in patients. Platelets, a tiny fraction. Cell fragments that plug leaks. When you bleed, platelets clump and trigger clotting. They live only 8,10 days in your body, and about 5 days in storage, which is why platelet shortages appear suddenly (dengue season is the classic Assam example) and why platelet donors are asked for again and again. ## Where blood comes from Your bone marrow is the factory, spongy tissue inside bones (breastbone, hips, ribs, spine) producing billions of new cells daily. It needs raw materials: iron, protein, folate, vitamin B12. Eat well and the factory keeps up; donate and the factory simply ramps up, red cells are fully replaced within weeks, which is exactly why the donation interval (3 months for men, 4 for women) guarantees complete recovery before the next donation. ## What blood does, in four lines 1. Delivers oxygen from lungs to every cell (haemoglobin). 2. Delivers nutrients and hormones; carries wastes to kidneys and liver. 3. Clots when you bleed (platelets + plasma proteins). 4. Defends against infection (white cells + antibodies). ## Where groups come from Your red cells carry inherited markers (antigens) on their surface. The ABO system (A, B, AB, O) and the Rh factor (+/−) are the two that matter for transfusion; together they make the eight common groups. Compatibility is your immune system reacting to markers it doesn’t recognise, which is why matching matters and why the centre runs a crossmatch before every transfusion. How blood groups are inherited → ## Why this biology matters for donors - You regenerate. Donation is not depletion, the interval rules are designed around your biology.
- Your single unit reaches up to three patients once separated into red cells, platelets and plasma.
- Your group decides who you can help, and negative-group donors (O− above all) are needed most.
- Haemoglobin is the gate: 12.5 g/dL minimum at the health check, because low-Hb blood helps nobody and hurts you. How to keep haemoglobin up → ## The takeaway Blood is not mysterious, it is a factory product with a supply chain. Assam’s hospitals run short not because bodies fail, but because the supply chain has always depended on emergency appeals. A register of healthy, informed, regular donors fixes that. Join it →