Overview of the Lymphatic System

Definition and Function

• Lymph: Derived from Latin meaning "clear water"; the fluid in lymphatic vessels and nodes.
• Primary Roles:
  • Returns fluid from tissues back to the heart.
  • Helps large molecules, like hormones and lipids, enter the blood.
  • Provides immune surveillance to prevent infections.

Fluid Movement

• Blood Pressure: Arteries have high pressure, pushing blood throughout the body.
• Capillaries: Walls one cell thick, allow fluid and small proteins to pass.
• Fluid Movement:
  • 20 liters of fluid seep from capillaries daily, 17 liters reabsorbed.
  • Remaining 3 liters form lymph in tissues, returned by lymphatic vessels.

Lymphatic Vessels

• Lymphatic Capillaries:
  • Located in interstitial spaces, very permeable.
  • Made of loosely overlapping endothelial cells forming one-way valves.
  • Anchored by collagen filaments.
• Lymph Flow:
  • Moves through larger vessels, trunks, and ducts.
  • No pump; movement aided by muscle contractions and nearby artery pulsations.
  • Valves prevent backflow.

Lymphatic Trunks and Ducts

• Trunks: Lumbar, bronchomediastinal, subclavian, jugular, intestinal.
• Ducts:
  • Right Lymphatic Duct: Drains right arm, head, and chest.
  • Thoracic Duct: Larger, drains the rest of the body.
  • Lymph dumped into the junction of jugular and subclavian veins.

Additional Functions

• Hormones and Nutrients: Transfers large molecules like hormones and chylomicrons (from fatty acids) into the bloodstream.
• Lacteals: Specialized lymphatic vessels for chylomicrons, delivering them to the thoracic duct.

Immune Function

• Lymphoid Organs:
  • Diffuse Lymphoid Tissue: Loose arrangement in gastrointestinal and respiratory tracts.
  • Lymph Nodes: Filter pathogens; B cells produce antibodies; T cells patrol for infections.
  • Peyer's Patches: Located in the intestinal wall.
• Spleen: Filters blood, stores red blood cells and platelets, involved in recycling old blood cells.
• Thymus: Develops T cells, active during early life.
• Tonsils: Trap pathogens in food and air.

Summary

• Lymphatic System: A one-way network for transporting lymph, cleansing it, and supporting immune function.
• Support: Keeps fluid levels balanced, delivers nutrients, and protects against pathogens.