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DrX Whiz Niraj
Body Fluids & Blood
Comprehensive notes on Blood Composition, Hemopoiesis, Coagulation Mechanism, Blood Grouping, and Reticuloendothelial System.
Water is the most abundant component in the human body (approx. 60% of body weight in adults). Body fluids are distributed into two main compartments:
- Intracellular Fluid (ICF): Fluid inside the cells. Makes up about 2/3rd of total body fluid.
- Extracellular Fluid (ECF): Fluid outside the cells. Makes up about 1/3rd of total body fluid. It is further divided into Interstitial fluid (between cells) and Blood Plasma.
What is Blood?
Blood is a specialized liquid connective tissue. It consists of cells surrounded by a liquid extracellular matrix called blood plasma.
Properties: Temperature: 38°C | pH: 7.35–7.45 (slightly alkaline) | Volume: 5-6 Liters in males, 4-5 Liters in females.
Hemopoiesis (Hematopoiesis): The process by which the formed elements of blood (RBCs, WBCs, Platelets) develop. After birth, it occurs primarily in the Red Bone Marrow from pluripotent stem cells.
Erythropoiesis (RBC Formation)
Stimulated by the hormone Erythropoietin (EPO), which is produced by the kidneys when oxygen levels are low (Hypoxia). Reticulocytes mature into Erythrocytes (RBCs).
Hemoglobin Formation
Hemoglobin (Hb) is the oxygen-carrying protein. It consists of:
- Globin: A protein made of 4 polypeptide chains.
- Heme: A ring-like non-protein pigment attached to each chain, containing an Iron (Fe²⁺) ion at its center to bind oxygen.
Hemostasis is a sequence of responses that stops bleeding. It involves 3 main steps:
- 1. Vascular Spasm: Smooth muscle in blood vessel walls contracts immediately to reduce blood loss.
- 2. Platelet Plug Formation: Platelets stick to damaged blood vessels, become activated, and release chemicals to form a plug.
- 3. Blood Coagulation (Clotting): A complex cascade of enzymatic reactions leading to the formation of fibrin threads.
The surfaces of red blood cells contain genetically determined assortment of antigens. Based on the presence or absence of these antigens, blood is categorized into different groups.
| Blood Group | Antigen on RBC | Antibody in Plasma | Can Donate To |
|---|---|---|---|
| A | Antigen A | Anti-B | A, AB |
| B | Antigen B | Anti-A | B, AB |
| AB (Universal Recipient) | Both A and B | Neither | AB only |
| O (Universal Donor) | Neither | Both Anti-A and Anti-B | A, B, AB, O |
Rh Factor & Erythroblastosis Fetalis:
People whose RBCs have Rh antigens are designated Rh+; those who lack them are Rh-.
HDN (Hemolytic Disease of the Newborn): If an Rh- mother carries an Rh+ fetus, maternal anti-Rh antibodies can cross the placenta and destroy the fetal RBCs. It is prevented by administering anti-Rh antibodies (RhoGAM) to the mother.
The Reticuloendothelial System (Mononuclear Phagocyte System) is a network of highly phagocytic cells widely distributed throughout the body (e.g., Kupffer cells in the liver, Alveolar macrophages in lungs). They help in destroying microbes and old RBCs.
Clinical Correlation: Blood Disorders
- Anemia: A condition in which the oxygen-carrying capacity of blood is reduced (due to low RBC count or low hemoglobin). Common types include Iron-deficiency anemia, Pernicious anemia (B12 deficiency), and Sickle cell disease.
- Leukemia: A group of red bone marrow cancers in which abnormal white blood cells multiply uncontrollably.
- Hemophilia: An inherited deficiency of clotting in which bleeding may occur spontaneously or after only minor trauma.