Chapter 20: The Lymphatic System and Immunity – Overview and Functions

Chapter 20: The Lymphatic System and Immunity

Overview of the Lymphatic System

The lymphatic system is a network of organs and tissues that works closely with the immune system to protect the body from disease-causing cells and pathogens. It is composed of lymphatic vessels, lymphatic tissue, and lymphoid organs.

• Lymphatic vessels are distributed throughout the body and are responsible for transporting lymph.

• Lymphatic tissue includes specialized connective tissue that supports immune cells.

• Lymphoid organs include structures such as lymph nodes, spleen, and thymus.

Example: The diagram shows the major lymphatic vessels and organs, including the heart, stomach, large intestine, and small intestine, highlighting their integration with the lymphatic system.

Functions of the Lymphatic System

The lymphatic system performs several essential functions that contribute to homeostasis and immunity.

• Regulation of Interstitial Fluid Volume: Lymphatic vessels pick up excess interstitial fluid from tissues and deliver it back to the cardiovascular system. When interstitial fluid enters the lymphatic vessels, it is called lymph.

• Absorption of Dietary Fats: Breakdown products of dietary fats enter small lymphatic vessels called lacteals in the small intestine and are delivered to the blood with lymph.

• Immune Functions: Lymphoid organs filter pathogens from the lymph and blood, and also house some leukocytes (white blood cells) that are essential for immune responses.

Example: Lacteals in the small intestine absorb fats and transport them as chyle, a milky fluid, to the bloodstream.

Lymphatic Vessels & Circulation

Lymphatic circulation is a specialized system for collecting and transporting lymph throughout the body.

• Lymphatic capillaries are blind-ended tubes that collect fluid from the interstitial spaces.

• Collecting vessels gather lymph from capillaries and transport it to lymph nodes for filtration.

• Lymph nodes filter the lymph, and lymph-collecting vessels then carry the filtered lymph away, merging to form lymph trunks.

• There are 9 lymph trunks that drain specific regions of the body:

  • Right & Left Lumbar Trunks: Drain the lower limbs and pelvic area into the cisterna chyli of the thoracic duct.

  • Intestinal Trunk: Drains fat-containing lymph from lacteals into the cisterna chyli of the thoracic duct.

  • Right and Left Jugular Trunks: Drain lymph from the head and neck.

  • Right and Left Bronchomediastinal Trunks: Drain the thoracic cavity.

  • Right and Left Subclavian Trunks: Drain the upper limbs.

• All trunks merge to drain into either the Right Lymphatic Duct or the Thoracic Duct.

Example: The thoracic duct is the largest lymphatic vessel and drains lymph from most of the body into the venous circulation.

Additional info: The lymphatic system is essential for maintaining fluid balance, absorbing dietary fats, and providing immune defense by filtering pathogens and supporting leukocyte function.