Lymphatic System Overview

Overview

This lecture explains the structure and function of the lymphatic system, highlighting its crucial roles in fluid balance and immune defense.

Maintains homeostasis by returning excess interstitial fluid to the bloodstream.
Prevents tissue swelling, low blood pressure, and fluid accumulation in organs.
Plays a key role in immune defense by monitoring and filtering lymph for pathogens.

Consists of lymph (watery fluid), lymphatic vessels, lymph nodes, and lymphoid organs.
Lymph originates as blood plasma forced out of capillaries during nutrient exchange.
Only 17 of the 20 liters of fluid filtered from capillaries are reabsorbed; 3 liters become lymph.
Lymph is collected by lymphatic capillaries with one-way valves and transported through vessels to two major ducts.
The right lymphatic duct drains the upper right body into the internal jugular vein; the thoracic duct drains the rest into the subclavian vein.
Vessels have valves and smooth muscle to ensure one-way, low-pressure flow.

Lymph nodes act as checkpoints where immune cells (lymphocytes, macrophages) inspect and respond to pathogens in lymph.
Special lymphoid organs include spleen, thymus, adenoids, tonsils, and other tissues.
Thymus and spleen support the maturation of lymphocytes.
Mucosa-associated lymphoid tissue (MALT) protects entry points in respiratory and digestive tracts (tonsils, Peyer’s patches, appendix).

Blockage in lymphatic vessels can cause edema (swelling) and disrupt blood flow.
Swollen lymph nodes indicate infection or disease.
Tonsils and appendix play important roles in defending against ingested or inhaled pathogens.

Lymph — Fluid derived from plasma that circulates in the lymphatic system.
Lymphatic vessels — Network of tubes transporting lymph back to the bloodstream.
Lymph nodes — Small structures that filter lymph and house immune cells.
Lymphocytes — Immune cells (B and T cells) found in lymphatic tissue.
MALT (Mucosa-associated lymphoid tissue) — Lymphoid tissue in mucous membranes guarding body entry points.
Edema — Swelling caused by excess fluid in tissues.