Circulation

Muscular organ enclosed in Pericardium.

• Chambers: 4 Chambers. 2 Atria (Receiving), 2 Ventricles (Pumping). Left Ventricle has thickest wall (pumps to body).
• Valves: Prevent backflow.
  • Tricuspid: Between Right Atrium/Ventricle.
  • Bicuspid (Mitral): Between Left Atrium/Ventricle.
  • Semilunar: At base of Pulmonary Artery and Aorta.

Sequence of events in one heartbeat (0.8s). 72 beats/min.

1. Atrial Systole (0.1s): Atria contract, blood pushed to ventricles.
2. Ventricular Systole (0.3s): Ventricles contract. AV valves close (Lub sound). Semilunar valves open. Blood pumped to lungs/body.
3. Diastole (0.4s): Relaxation. Semilunar valves close (Dub sound). Ventricles fill passively.

Myogenic heart (impulse generates from within).

• SA Node (Pacemaker): In Right Atrium. Initiates impulse.
• AV Node: At junction. Delays impulse (allows atrial emptying).
• Bundle of His & Purkinje Fibers: Transmit impulse to Ventricles for contraction.

• Arteries: Carry oxygenated blood away from heart (except Pulmonary). Thick, elastic walls. High pressure. No valves.
• Veins: Carry deoxygenated blood to heart (except Pulmonary). Thin walls. Low pressure. Valves present.
• Capillaries: Single cell thick. Site of material exchange between blood and tissues.

Network of vessels returning Interstitial Fluid to blood.

• Components: Lymph (Fluid), Lymph Vessels, Lymph Nodes (Filter, e.g., Neck/Axilla), Lymphoid organs (Spleen, Thymus).
• Functions: Returns excess fluid (prevents Edema). Absorbs Fats (via Lacteals). Defends body (Lymphocytes).

• Atherosclerosis: Deposition of hard yellow plaque (Cholesterol/Calcium) in arteries. Narrows lumen.
• Arteriosclerosis: Hardening of arteries (loss of elasticity) due to calcium precipitations. Associated with old age.
• Myocardial Infarction (Heart Attack): Death of heart muscle due to blockage of Coronary Artery. Symptoms: Chest pain (Angina), Left arm pain.