PRELIMS

Human Circulatory and Lymphatic Systems

The circulatory system distributes oxygen, nutrients, and hormones while removing waste. William Harvey discovered blood circulation in 1628.

I. Heart Anatomy and Function

• Weight: ~300 g; enclosed in Pericardial membrane.
• Chambers: 4 chambers (Left/Right Auricle & Left/Right Ventricle).
• Valves: Tricuspid (Right side) and Bicuspid/Mitral (Left side).
• Double Circulation: Blood passes through the heart twice (Lungs Heart Body).
• Pulmonary Circulation: Right Ventricle → Pulmonary Artery → Lungs (gas exchange) → Pulmonary Vein → Left Auricle. Carries deoxygenated blood to lungs, oxygenated blood back.
• Systemic Circulation: Left Ventricle → Aorta → Body tissues → Vena Cava → Right Auricle. Carries oxygenated blood to the body, deoxygenated blood back.

II. Blood Vessels: Arteries vs. Veins

• Artery: Direction: Heart Body. Blood Type: Pure (Oxygenated). Exception: Pulmonary Artery (Impure)
• Vein: Direction: Body Heart. Blood Type: Impure (Deoxygenated). Exception: Pulmonary Vein (Pure)

• Coronary Arteries: Supply blood to the heart muscles. Blockage causes Heart Attack.

III. Electrical Conduction and Heart Beat

1. SA Node (Sino-auricular): The Pace maker; generates cardiac impulses.
2. AV Node (Auriculo-ventricular): Picks up the impulse and spreads it to the ventricles.
3. Heart Beat: Normally 72 times/minute. Each beat pumps ~70 ml of blood.

• Hormones: Thyroxin and Adrenaline control the heart beat independently.

IV. Blood Pressure (BP)

• Normal BP: 120/80 mmHg (Systolic/Diastolic).
• Measurement: Using a Sphygmomanometer.
• Factors: increase in blood reduces pH and accelerates the heart beat.

V. Lymph Circulatory System

• Lymph: Light yellow fluid found in inter-cellular spaces. Flows only in one direction (Tissue Heart).
• Lymphocytes: WBCs present in lymph that provide immunity.
• Lymph Nodes: Small bean-shaped structures that filter lymph, trap pathogens, and are sites of lymphocyte production/activation (act as the body's filtration checkpoints, e.g., swollen nodes during infection).
• Function: Drains excess tissue fluid back into blood, transports absorbed fats (via lacteals in intestinal villi), and defends against infection.

UPSC Relevance

Circulatory health is a major focus for GS-III Biology and Public Health.

• Cardiovascular Physiology: Understanding the path of blood (Double Circulation) and the role of the Pacemaker (SA Node).
• Pathology: Linking coronary artery blockages to heart attacks and understanding the importance of BP readings (120/80).
• Evolutionary Biology: The one-way flow of lymph and its significance in immune defense (Lymphocytes).