Lymphatic System Overview

Definition

• Lymph: Means "clear water" in Latin.
• Refers to fluid that flows through lymphatic vessels and lymph nodes.

Major Roles of the Lymphatic System

1. Fluid Return: Returns fluid from tissues back to the heart.
2. Molecule Entry: Helps large molecules (hormones and lipids) enter the blood.
3. Immune Surveillance: Aids in preventing infections.

Lymph Formation and Flow

• Blood Pressure: Blood in arteries is under high pressure, leading to fluid seepage.
• Capillary Dynamics:
  • Arteries branch into arterioles, then capillaries (one cell thick, slightly porous).
  • 20 liters of fluid seep into interstitial fluid daily; 17 liters reabsorbed, leaving 3 liters.
• Lymphatic Vessels: Collect excess interstitial fluid (lymph).
  • Lymphatic capillaries: Small, permeable, with one-way minivalves.
  • Minivalves open with higher interstitial pressure and close with lower pressure.
• Flow Mechanism:
  • Lymph flows through larger vessels and trunks without a pump.
  • Smooth muscle and skeletal muscle contractions aid lymph movement.
  • Valves prevent backflow.

Lymphatic Trunks and Ducts

• Trunks:
  • Named after regions they drain:
    • 2 Lumbar trunks
    • 2 Bronchomediastinal trunks
    • 2 Subclavian trunks
    • 2 Jugular trunks
    • 1 Intestinal trunk
• Ducts:
  • Right lymphatic duct: Drains right arm and right side of head/chest.
  • Thoracic duct: Larger, drains the rest of the body.
  • Dumps lymph into venous blood at the junction of jugular and subclavian veins.

Functions of the Lymphatic System

• Larger Molecule Transport: Transports hormones, nutrients, and chylomicrons (fatty acids).
• Immune Function:
  • Lymphoid organs filter foreign material from lymph.
  • Lymphoid Organs:
    • Lymph Nodes: Clustered along lymph vessels; filter lymph and present antigens to B cells.
    • Spleen:
      • Contains white pulp (filters blood, generates antibodies) and red pulp (destroys old blood cells).
      • Acts as a reservoir for red blood cells and platelets.
    • Thymus:
      • Located in the upper chest; involved in T cell development.
    • Tonsils:
      • Form a ring of lymphoid tissue around the throat; trap pathogens.

Summary

• The lymphatic system is a one-way network of vessels that transport lymph for nutrient delivery and waste removal, cleansing lymph at nodes crucial for immune response.