Lymphatic System & Immunity: Structure, Function, and Clinical Relevance

Chapter 20. Lymphatic System & Immunity

Characteristics and Components of Lymph

The lymphatic system is a vital part of the circulatory and immune systems, responsible for fluid balance, fat absorption, and defense against pathogens.

• Formation of Lymph: Interstitial fluid leaves blood capillaries and enters lymphatic capillaries, where it is called lymph.

• Components of Lymph: Contains water, dissolved solutes, small amounts of protein, cell debris, pathogens, and cancer cells (metastasis).

Functions of the Lymphatic System

• Fluid Balance: Excess interstitial fluid enters lymphatic capillaries and becomes lymph.

• Fat Absorption: Absorption of fat and other substances from the digestive tract via lacteals. Lymph fluid containing fat is called chyle.

• Defense: Microorganisms and foreign substances are filtered from lymph by lymph nodes and from blood by the spleen.

Anatomy of the Lymphatic System

Primary Lymphatic Structures

Primary lymphatic organs are responsible for the production and maturation of lymphocytes.

• Bone Marrow: Site of all white blood cell (WBC) production and maturation of B-cells.

• Thymus: Site of T-cell maturation.

Secondary Lymphatic Structures

Secondary lymphatic organs house mature lymphocytes and are sites of immune responses.

• Lymph Nodes: Filter lymph and are distributed along lymphatic vessels.

• Spleen: Filters blood and removes old or defective blood cells.

• Tonsils: Protect against pathogens entering through the mouth and nose.

• MALT (Mucosa-associated lymphatic tissue): Aggregations of lymphatic nodules in mucous membranes throughout the body.

Lymphatic Vessels

Structure and Function

Lymphatic vessels transport lymph from tissues to lymph nodes and eventually to the circulatory system.

• Lymphatic Capillaries: Differ from blood capillaries by being closed-ended, having larger diameter, and thinner, more permeable walls. Overlapping endothelial cells act as one-way valves.

• Lymphatic Vessels: Carry lymph to lymph nodes for filtration.

• Lymphatic Trunks: Large lymphatic vessels such as jugular, subclavian, bronchomediastinal, intestinal, and lumbar trunks.

• Lymph Nodes: Small, bean-shaped structures that filter lymph and remove antigens.

• Edema: Blockage of lymph drainage from a limb can cause swelling and interfere with immune function.

Illustrative Example

• Lymphatic Capillaries: Surround blood capillaries and collect excess interstitial fluid.

• One-way Valve Mechanism: Prevents backflow, ensuring lymph moves toward lymph nodes.

Key Terms

• Lymph: Fluid collected from tissues, containing immune cells and debris.

• Lacteals: Specialized lymphatic capillaries in the small intestine for fat absorption.

• Chyle: Lymph fluid rich in absorbed fats.

• MALT: Mucosa-associated lymphatic tissue, important for immune defense in mucous membranes.

Additional info:

• Clinical Relevance: Lymphatic system disorders include lymphedema (swelling due to lymph blockage) and metastasis (spread of cancer cells via lymph).