Lymphatic System

Anatomy of the lymphatic system, showing the lymph vessels and lymph organs including lymph nodes, tonsils, thymus, spleen, and bone marrow. Lymph (clear fluid) and lymphocytes travel through the lymph vessels and into the lymph nodes where the lymphocytes destroy harmful substances. The lymph enters the blood through a large vein near the heart. Source: National Cancer Institute.

Other Names

• Lymph system

Description

The lymphatic system is made up of the following:

• Lymph: Colorless, watery fluid that travels through the lymph system and carries white blood cells called lymphocytes. Lymphocytes protect the body against infections and the growth of tumors.
• Lymph vessels: A network of thin tubes that collect lymph from different parts of the body and return it to the bloodstream.
• Lymph nodes: Small, bean-shaped structures that filter lymph and store white blood cells that help fight infection and disease. Lymph nodes are located along the network of lymph vessels found throughout the body. Clusters of lymph nodes are found in the underarm, pelvis, neck, abdomen, and groin.
• Spleen: An organ that makes lymphocytes, filters the blood, stores blood cells, and destroys old blood cells. The spleen is on the left side of the abdomen near the stomach.
• Thymus: An organ in which lymphocytes grow and multiply. The thymus is in the chest behind the breastbone. The thymus is much larger in children than in adults.
• Tonsils: Two small masses of lymph tissue at the back of the throat. The tonsils make lymphocytes.
• Bone marrow: The soft, spongy tissue in the center of large bones. Bone marrow makes white blood cells, red blood cells, and platelets.

Role of the Lymphatic System in the Body

The lymphatic system has three primary functions.

1. It returns excess interstitial fluid to the blood. Of the fluid that leaves the capillary, about 90% is returned. The 10% that does not return becomes part of the interstitial fluid that surrounds the tissue cells. Small protein molecules may "leak" through the capillary wall and increase the osmotic pressure of the interstitial fluid. This further inhibits the return of fluid into the capillaries, and fluid tends to accumulate in the tissue spaces. If this continues, blood volume and blood pressure decrease and the volume of tissue fluid increases, which results in edema (swelling). Lymph capillaries pick up the excess interstitial fluid and proteins and return them to the venous blood. After the fluid enters the lymph capillaries, it is called lymph.

1. The second function of the lymphatic system is the absorption of fats and fat-soluble vitamins from the digestive system and the subsequent transport of these substances to the venous circulation. The mucosa that lines the small intestine is covered with fingerlike projections called villi. There are blood capillaries and special lymph capillaries, called lacteals, in the center of each villus. The blood capillaries absorb most nutrients, but the fats and fat-soluble vitamins are absorbed by the lacteals. The lymph in the lacteals has a milky appearance due to its high fat content and is called chyle.

1. The third and probably most well known function of the lymphatic system is defense against invading microorganisms and disease. Lymph nodes and other lymphatic organs filter the lymph to remove microorganisms and other foreign particles. Lymphatic organs contain lymphocytes that destroy invading organisms.

How the Lymphatic System Works

Lymphatic vessels, unlike blood vessels, only carry fluid away from the tissues. The smallest lymphatic vessels are the lymph capillaries, which begin in the tissue spaces as blind-ended sacs. Lymph capillaries are found in all regions of the body except the bone marrow, central nervous system, and tissues, such as the epidermis, that lack blood vessels. The wall of the lymph capillary is composed of endothelium in which the squamous cells overlap to form a simple one-way valve. This arrangement permits fluid to enter the capillary but prevents lymph from leaving the vessel.

The microscopic lymph capillaries merge to form lymphatic vessels. Small lymphatic vessels join to form larger tributaries, called lymphatic trunks, which drain large regions. Lymphatic trunks merge until the lymph enters the two lymphatic ducts. The right lymphatic duct drains lymph from the upper right quadrant of the body. The thoracic duct drains all the rest.

Like veins, the lymphatic tributaries have thin walls and have valves to prevent backflow of blood. There is no pump in the lymphatic system like the heart in the cardiovascular system. The pressure gradients to move lymph through the vessels come from skeletal muscle action, respiratory movement, and contraction of smooth muscle in vessel walls.

When the body is exposed to microorganisms and other foreign substances, lymphocytes proliferate within the lymphatic organs and are sent in the blood to the site of the invasion. This is part of the immune response that attempts to destroy the invading agent.

Diseases of the Lymphatic System

Diseases of the lymphatic system include the following:

• Benign diseases, such as Lymphadenitis
• Malignant diseases, such as Lymphoma and Leukemia

Symptoms

Symptoms of disease of the lymphatic system include:

• Lymphedema
• Swollen lymph nodes

Procedures

The lymphatic system can be studied using the following procedures:

• CT scan
• Lymph node biopsy
• Lymphoscintigraphy
• MRI
• PET scan

Surgery

Types of surgery done to treat diseases of the lymphatic system include the following:

• Tonsillectomy
• Splenectomy

Related Professions

• Diseases of the lymphatic system are commonly treated by a hematologist.

History

How the Lymphatic System Was Discovered

Swedish physician Olaus Rudbeck (1630-1702) is credited with the first discovery and description of the lymphatic system.^[1]

Etymology

The word lymph originates from Latin lympha, meaning water goddess, and has been in use since around 1673.^[2]

Research

The Lymphatic Research Foundation is working to establish a National Patient Registry Tissue/Cell Bank for Lymphatic Diseases in order to accumulate tissue, blood, and data from patients with lymphatic diseases.^[3]

References

1. ↑ Eriksson G. Olaus Rudbeck as scientist and professor of medicine. Sven Med Tidskr. 2004;8(1):39-44. Abstract
2. ↑ Merriam-Webster Online. Lymph.
3. ↑ Lymphatic Research Foundation Web site. National Patient Registry and Tissue/Cell Bank.

External Links

American Society of Lymphology

Lymphatic Research Foundation

National Heart, Lung, and Blood Institute