Functions of the Lymphatic System

Key Functions

• Drainage of Interstitial Fluid

  • Prevents edema by constantly draining interstitial fluid
  • Helps maintain hydrostatic pressure of interstitial fluid near zero mm Hg

• Filtration and Immunity

  • Lymph nodes & spleen filter debris and pathogens from lymph
  • The spleen recycles old/damaged red blood cells, stores iron (with the liver), and acts as a storage for red and white blood cells
  • White pulp (stores leukocytes) and Red pulp (recycles RBCs)

• Surveillance and Activation

  • Lymph nodes and lymphoid tissues act as surveillance points for lymphocytes and macrophages
  • Allows housing and proliferation of lymphocytes
  • Absorption of Lipids - Lipids absorbed via lymphatic system before entering circulatory system

Lymphatic Circulation

• Carries lymph in one direction; lymph is constantly renewed
• Lymphatic capillaries are more permeable than blood capillaries (loose endothelial overlap creates minivalves)
• Risks: potential entry of pathogens or cancer cells into lymph

Structures of the Lymphatic System

• Lacteals: specialized lymphatic capillaries in the small intestine for lipid absorption
• Lymphatic Vessels: Contain valves to prevent backflow, rely on muscular movement and respiratory pumps to move lymph
• Lymphatic Ducts: Two largest vessels, return cleansed lymph to circulatory system

Lymphoid Tissues and Organs

• Primary Lymphoid Organs: Thymus and red bone marrow; sites of lymphocyte maturation
• Secondary Lymphoid Organs: Lymph nodes, spleen, tonsils, Peyer’s patches, appendix, and MALT; sites of lymphocyte activation

Lymph Nodes

• Chief secondary lymphoid organs scattered throughout the body
• Filter lymph, allowing macrophages and lymphocytes to remove debris/pathogens
• Superficial lymph nodes in neck, armpits, and groin are more noticeable when swollen

Spleen

• High in the abdomen, near the diaphragm
• Functions: immune surveillance, storage of blood cells and iron, recycling of RBCs and platelets

Mucosa-associated Lymphoid Tissue (MALT)

• Found throughout mucous membranes
• Includes tonsils, Peyer's patches, and appendix

Tonsils

• Four tonsils: Pharyngeal (single), Palatine (paired), Lingual (single)
• Offer small surveillance sites for lymphocytes

Thymus

• Main site for T-cell maturation
• Atrophies with age

Study Advice

• Understand primary vs. secondary lymphoid organs
• Familiarize with locations and functions of lymphatic components
• Utilize diagrams and tables for memorization and visualization