Body Fluids and Circulation

1. Blood & Lymph (The Fluids)

  • Composition:
    • Plasma (55%): Liquid matrix with proteins (Fibrinogen for clotting, Globulins for immunity, Albumins for osmotic balance).
    • Formed Elements (45%): RBCs (Gas transport), WBCs (Immunity), Platelets (Coagulation).
  • Blood Groups:
    • ABO: Based on Antigens A & B. O- is Universal Donor; AB+ is Universal Recipient.
    • Rh: Rh incompatibility leads to Erythroblastosis Foetalis.
  • Lymph: Colourless fluid (Blood minus RBCs & large proteins). Important for immune response and fat transport.

2. The Heart (The Engine)

  • Structure: 4 Chambers (2 Atria, 2 Ventricles). Left Ventricle has the thickest wall.
  • Valves: Ensure one-way flow.
    • Tricuspid: Right side.
    • Bicuspid (Mitral): Left side.
    • Semilunar: Exit to arteries.
  • Conducting System: Auto-excitable (Myogenic). Path: SAN (Pacemaker) →\rightarrow AVN →\rightarrow Bundle of His →\rightarrow Purkinje Fibres.

3. Cardiac Cycle (The Action)

  • Duration: 0.8 seconds.
  • Sequence: Joint Diastole →\rightarrow Atrial Systole (0.1s) →\rightarrow Ventricular Systole (0.3s).
  • Output: Stroke Volume (70 mL) ×\times Heart Rate (72) ≈\approx 5000 mL (5L)/min.
  • Sounds: "Lub" (AV valves close) and "Dub" (Semilunar valves close).

4. ECG (The Graph)

  • P-Wave: Atrial Depolarisation (Contraction).
  • QRS Complex: Ventricular Depolarisation (Contraction).
  • T-Wave: Ventricular Repolarisation (Relaxation).

5. Disorders

  • Hypertension: BP > 140/90 mm Hg.
  • CAD (Atherosclerosis): Lumen narrowing due to fat/calcium deposits.
  • Angina: Acute chest pain due to low O2O_2.
  • Heart Failure: Weak pumping (Congestion).

Exam Tips & Critical Distinctions

1. Don't Confuse These Pairs!

Term A Term B Distinction
Heart Attack Cardiac Arrest Attack = Muscle death (Blockage). Arrest = Heart stops beating (Electrical failure).
Tricuspid Bicuspid Tri is on the Right. Bi (Mitral) is on the Left.
Stroke Volume Cardiac Output SV = Per beat (70ml). CO = Per minute (5L).
Antigen Antibody Antigen is on RBC surface. Antibody is in Plasma.

2. The "Clotting" Cascade

Remember: It's a chain reaction. Injury →\rightarrow Thrombokinase (Enzyme) →\rightarrow Prothrombin to Thrombin →\rightarrow Fibrinogen to Fibrin (Threads) →\rightarrow Clot. (Note: Calcium (Ca++) is the essential ion for this).

3. ECG Hacks for Questions

  • Heart Rate: Count the number of QRS complexes.
  • Ischemia: Identified by a flat or inverted T-wave.
  • Atrial Enlargement: Identified by an enlarged P-wave.

4. Vital Numbers to Memorize

  • BP: 120/80 mmHg.
  • RBCs: 5 - 5.5 million/mm3mm^3.
  • WBCs: 6000 - 8000/mm3mm^3 (Neutrophils are most abundant).
  • Platelets: 1.5 - 3.5 lakh/mm3mm^3.
  • Cardiac Cycle: 0.8 seconds.