3.1 Circulatory System

Introduction

• Network of organs and vessels transporting nutrients, oxygen, CO₂, hormones, and blood cells.
• Maintains homeostasis, fights disease, stabilizes temperature and pH.
• Components: Cardiovascular system (heart, blood, vessels) and Lymphatic system.

Blood: Composition

• Plasma (55%): Liquid component; carries cells, nutrients, hormones, waste.
• Red Blood Cells (RBCs/Erythrocytes): Most numerous; transport oxygen (via hemoglobin) and CO₂.
  • Biconcave, anucleated (mammals) for efficient gas exchange.
• White Blood Cells (WBCs/Leukocytes): Crucial for immune system; fight infections.
• Platelets (Thrombocytes): Small fragments; vital for blood clotting.

Blood Coagulation

• Definition: Process of blood changing from liquid to gel, forming a clot.
• Purpose: Prevents excessive bleeding from damaged vessels.
• Mechanism: Cascade of enzymatic reactions involving clotting factors, leading to fibrin mesh formation that traps cells.

Tissue Fluid and Lymph

• Tissue Fluid (Interstitial Fluid): Surrounds cells; formed from blood plasma leaking from capillaries.
  • Delivers O₂/nutrients, removes waste.
• Lymph: Tissue fluid that enters lymphatic vessels.
  • Clear fluid with WBCs; circulates in lymphatic system; crucial for immune response.

The Heart: Structure

• Muscular organ pumping blood throughout the body.
• Four Chambers:
  • Two Atria: Upper chambers, receive blood.
  • Two Ventricles: Lower chambers, pump blood out.
• Valves: Ensure unidirectional blood flow (e.g., tricuspid, bicuspid/mitral, semilunar).

Working of the Heart and Circulation

• Cardiac Cycle: Sequential events of heart contraction (systole) and relaxation (diastole).
• Double Circulation (Mammals): Blood passes through heart twice per body circuit.
  1. Pulmonary Circulation: Right ventricle → Lungs (oxygenation) → Left atrium.
  2. Systemic Circulation: Left ventricle → Body (oxygen delivery) → Right atrium.

Main Blood Vessels (Entering/Leaving Heart)

• Entering Heart:
  • Vena Cava: Deoxygenated blood from body to right atrium.
  • Pulmonary Veins: Oxygenated blood from lungs to left atrium.
• Leaving Heart:
  • Pulmonary Artery: Deoxygenated blood from right ventricle to lungs.
  • Aorta: Oxygenated blood from left ventricle to body.

Blood Vessels: Types

• Arteries: Thick-walled, muscular; carry blood away from heart (high pressure).
• Veins: Thinner-walled; carry blood towards heart (low pressure); contain valves.
• Capillaries: Smallest, one-cell thick; site of exchange (gases, nutrients, waste) between blood and cells.

Lymphatic System

• Network of tissues and organs to remove toxins, waste, and unwanted materials.
• Transports lymph (fluid with WBCs) throughout the body.
• Lymphatic Organs: Spleen (filters blood, recycles RBCs), Tonsils (fight infections).

Blood Groups

• Determined by presence/absence of specific antigens on RBC surface.
• ABO System:
  • Type A: A antigen, anti-B antibody.
  • Type B: B antigen, anti-A antibody.
  • Type AB: A & B antigens, no antibodies (Universal Recipient).
  • Type O: No antigens, anti-A & anti-B antibodies (Universal Donor).
• Rh Factor: Rh antigen present (Rh+) or absent (Rh-).
  • Important in pregnancy (Rh- mother, Rh+ fetus).

Hepatic Portal System

• Unique venous system carrying blood from digestive organs (stomach, intestines, spleen, pancreas) to the liver.
• Allows liver to process absorbed nutrients and detoxify substances before blood reaches general circulation.