⚡ Quick Revision: Blood & Its Components
🔹 Composition of Blood
- ✔ Plasma (55%): Liquid part containing water, proteins, and dissolved salts.
- ✔ RBCs (Erythrocytes): Biconcave, lack nucleus (in humans); carry oxygen via haemoglobin.
- ✔ WBCs (Leukocytes): Fight infections. Includes Phagocytes (engulf germs) and Lymphocytes (produce antibodies).
- ✔ Platelets (Thrombocytes): Essential for blood clotting (coagulation).
🔹 Blood Vessel Comparison
| Feature | Arteries | Veins |
|---|---|---|
| Direction | Away from Heart | Towards Heart |
| Wall | Thick and Muscular | Thin |
| Valves | Absent | Present |
Diapedesis: The process by which WBCs (specifically neutrophils) squeeze through the walls of capillaries to reach the site of infection.
Pulmonary Artery with regular arteries. Remember: While most arteries carry oxygenated blood, the Pulmonary Artery carries deoxygenated blood to the lungs.
⚡ Quick Revision: Heart Structure & Circulation
🔹 Anatomy of the Heart
- ✔ 4 Chambers: Right/Left Auricles (Atria) and Right/Left Ventricles.
- ✔ Ventricles: Have much thicker walls than auricles; the Left Ventricle is the thickest to pump blood to the whole body.
- ✔ Valves: Prevent backflow. Tricuspid (Right side), Bicuspid/Mitral (Left side), and Semilunar (at the base of Aorta/Pulmonary Artery).
🔹 Double Circulation
Blood passes through the heart twice for one complete body circuit.
- 1 Pulmonary Circulation: Heart → Lungs → Heart. (Oxygenates blood).
- 2 Systemic Circulation: Heart → Body Tissues → Heart. (Delivers oxygen).
Hepatic Portal System: A unique vein system that carries nutrient-rich blood from the digestive tract directly to the liver before it enters the main circulation.
Systole with Diastole. Remember: Systole is the phase of Contraction (pumping out), while Diastole is the phase of Relaxation (filling up).
⚡ Quick Revision: Blood Clotting & Lymph
🔹 The Blood Clotting Cascade
A series of chemical reactions to prevent excessive blood loss at an injury site.
- 1 Thromboplastin: Released by injured tissues and platelets.
- 2 Prothrombin to Thrombin: Occurs in the presence of Calcium ($Ca^{2+}$) ions.
- 3 Fibrinogen to Fibrin: Thrombin converts soluble fibrinogen into insoluble Fibrin threads that trap RBCs.
🔹 The Lymphatic System
- ✔ Lymph: Tissue fluid that has entered lymph vessels. It lacks RBCs and platelets but is rich in WBCs.
- ✔ Lymph Nodes: Filter lymph and produce Lymphocytes to destroy pathogens.
- ✔ Spleen: The largest lymphatic organ; acts as a reservoir for blood and destroys worn-out RBCs.
Serum: The straw-colored liquid that remains after blood has clotted (Plasma minus Fibrinogen).
Agglutination with Coagulation. Agglutination is the "clumping" of RBCs due to incompatible blood transfusion; Coagulation is the natural clotting of blood.