PRELIMS

Human Blood: Composition and Groups

Blood is a fluid connective tissue, constituting ~7% of human body weight.

I. Composition of Blood

Plasma: Percentage: 60%. Composition: Water (90%), Protein (7%), Salt (0.9%), Glucose (0.1%).. Functions: Transportation of food, hormones, and waste.
RBC (Erythrocytes): Percentage: —. Composition: Biconcave; non-nucleated (except Camel/Llama). Formed in Bone Marrow.. Functions: Carries Oxygen (Haemoglobin/Iron).
WBC (Leucocytes): Percentage: —. Composition: Nucleated; Amoeba-like shape.. Functions: Immunity; ratio of 1 WBC to 600 RBC.
Platelets: Percentage: —. Composition: Non-nucleated; found only in mammals.. Functions: Blood Clotting.

I(a). Types of WBCs (Leucocytes)

Granulocytes: Neutrophils (most abundant, ~60-65%; first responders, phagocytosis of bacteria), Eosinophils (allergic reactions, parasitic infections), Basophils (release Histamine and Heparin; allergic/inflammatory response).
Agranulocytes: Lymphocytes (produce antibodies; B-cells and T-cells; key to immune memory), Monocytes (largest WBC; become macrophages, phagocytose debris/pathogens).

II. Blood Clotting Mechanism

Three major reactions involving Vitamin K and clotting factors:

III. Blood Groups and Transfusion

Discovered by Landsteiner (1900). Difference is due to Antigens (A, B) in RBCs.

A: Antigen (RBC): A. Antibody (Plasma): b. Recipient Status: Can receive from A and O.
B: Antigen (RBC): B. Antibody (Plasma): a. Recipient Status: Can receive from B and O.
AB: Antigen (RBC): Both A and B. Antibody (Plasma): Absent. Recipient Status: Universal Receptor (can receive from all groups).
O: Antigen (RBC): Absent. Antibody (Plasma): Both a and b. Recipient Status: Universal Donor (can donate to all groups); can only receive from O.

IV. Rh Factor and Rh Incompatibility

Discovered in Rhesus monkey (1940) by Landsteiner and Wiener.

Erythroblastosis Foetalis: If the father is Rh+ and mother is Rh-, the second child may die in pregnancy or shortly after birth due to agglutination.

UPSC Relevance

Hematology is the basis for public health and immunology studies.

Universal Status: Knowing that Group O has no antigens (Donor) and Group AB has no antibodies (Receptor).
Clotting Factors: The role of Vitamin K and the impact of diseases like Hemophilia (genetic) or Thrombocytopenia (low platelets).
Blood Conditions: Anaemia (low Hb), RBC increase at high altitudes (compensation), and the "Grave of RBC" (Spleen).

Human Blood: Composition and Groups ​