Chapter 20: The Lymphatic System and Immunity Part 1

Module 20.1 Structure and Function of the Lymphatic System

Introduction to the Immune and Lymphatic Systems

The immune and lymphatic systems work together to provide immunity, which protects the body from cellular injury and disease-causing agents known as pathogens. These systems are essential for maintaining health and defending against infections.

• Lymphatic system: A group of organs and tissues that collaborate with the immune system and participate in functions such as fluid homeostasis.

• Main components:

  • Lymphatic vessels: A system of blind-ended tubes that transport lymph.

  • Lymphatic tissue and organs: Includes clusters of lymphoid follicles (e.g., tonsils), as well as lymph nodes, spleen, and thymus.

Functions of the Lymphatic System

The lymphatic system performs several basic functions vital to homeostasis and immunity:

• Regulation of interstitial fluid volume: Net filtration pressure in blood capillaries favors filtration, causing water to move from plasma to interstitial fluid. The lymphatic system returns excess interstitial fluid to the bloodstream, preventing edema.

• Absorption of dietary fats: Dietary fats are broken down into products too large to pass between endothelial cells of blood capillaries. Specialized lymphatic vessels called lacteals in the small intestine absorb these fats and transport them as chyle.

• Immune functions: Lymphoid organs filter pathogens from lymph and blood, house various types of leukocytes, and play a role in their maturation.

Overview of the Lymphatic System

The lymphatic system is distributed throughout the body and includes:

• Lymphatic vessels

• Lymphatic tissue and organs (tonsils, thymus, lymph nodes, spleen, mucosa-associated lymphatic tissue)

Example: Lymph nodes are found in clusters in regions such as the neck, armpits, and groin, where they filter lymph before it returns to the bloodstream.

Lymphatic Vessels and Lymph Circulation

Lymph is collected in lymph-collecting vessels, which merge to form larger lymph trunks. There are nine major lymph trunks, each draining lymph from specific body regions:

• Lumbar trunks: Lower limbs and pelvic area

• Jugular trunks: Head and neck

• Intestinal trunk: Fat-containing lymph from the small intestine

• Bronchomediastinal trunks: Thoracic cavity

• Subclavian trunks: Upper limbs

The intestinal trunk and lumbar trunks drain into a large, swollen vessel called the cisterna chyli. The cisterna chyli and other lymph trunks drain into one of two lymph ducts:

• Thoracic duct: Drains all of the lower body and the left side of the upper body.

• Right lymphatic duct: Drains the upper right side of the body (right head, neck, and upper limb) into the junction of the right internal jugular and right subclavian veins.

Additional info: The lymphatic system is a one-way system, ensuring that lymph flows toward the heart and is eventually returned to the venous circulation.