5.2 Body Fluids and Circulation

Blood Composition

• Plasma (55%): Water, proteins (fibrinogen, globulins, albumins), minerals, nutrients.
• Formed Elements (45%):
  • Erythrocytes (RBCs): Oxygen transport (haemoglobin).
  • Leucocytes (WBCs): Immunity (neutrophils, eosinophils, basophils, lymphocytes, monocytes).
  • Platelets (Thrombocytes): Blood clotting.

Blood Groups

• ABO System: Based on antigens (A, B) on RBCs and antibodies in plasma.
  • Universal Donor: O
  • Universal Recipient: AB
• Rh Factor: Rh antigen on RBCs (Rh+ or Rh-).
  • Erythroblastosis Fetalis: Rh incompatibility between mother (Rh-) and foetus (Rh+).

Blood Coagulation

• A cascade process to prevent blood loss.
• Mechanism:
  1. Injury -> Platelets release factors.
  2. Prothrombin → Thrombin (catalyzed by thrombokinase).
  3. Fibrinogen → Fibrin (catalyzed by thrombin).
  4. Fibrin forms a clot.

Lymph (Tissue Fluid)

• Fluid that bathes the tissues, formed from blood plasma.
• Functions: Exchange of nutrients and gases, immune response.
• Lymphatic System: Collects lymph and returns it to the blood.

The Human Heart

• Four Chambers: Right Atrium, Right Ventricle, Left Atrium, Left Ventricle.
• Valves:
  • Tricuspid Valve: Between right atrium and ventricle.
  • Bicuspid (Mitral) Valve: Between left atrium and ventricle.
  • Semilunar Valves: In pulmonary artery and aorta.

Cardiac Cycle

• Systole: Contraction of heart chambers.
• Diastole: Relaxation of heart chambers.
• Heart Sounds:
  • 'Lub': Closure of tricuspid and bicuspid valves.
  • 'Dub': Closure of semilunar valves.

Electrocardiogram (ECG)

• A graphical representation of the heart's electrical activity.
• Waves:
  • P-wave: Atrial depolarization.
  • QRS complex: Ventricular depolarization.
  • T-wave: Ventricular repolarization.

Double Circulation

• Blood flows through the heart twice in one complete cycle.
• Pulmonary Circulation: Heart → Lungs → Heart.
• Systemic Circulation: Heart → Body → Heart.

Regulation of Cardiac Activity

• Myogenic Heart: Intrinsic regulation by nodal tissue (SA node, AV node).
• Neural Control (ANS):
  • Sympathetic: Increases heart rate.
  • Parasympathetic: Decreases heart rate.
• Hormonal Control: Adrenaline increases heart rate.

Circulatory Disorders

• Hypertension: High blood pressure (≥ 140/90).
• Coronary Artery Disease (CAD): Atherosclerosis (narrowing of arteries).
• Angina Pectoris: Chest pain due to insufficient oxygen to the heart.
• Heart Failure: The heart cannot pump blood effectively.