Structure and function of lymph nodes

By Dr Ananya Mandal, MD

The lymphatic system is basically a channel that carries a clear or whitish fluid called the lymph. This lymph aids in clearing the tissues of infective organisms, toxins etc.

The basic structure and functions of the lymphatic system can be broken into the lymph channels. The lymph nodes, lymph and other organs. (1-4)

The lymph channels

These are a network of tubes or vessels much like the blood vessels that cover all the tissues of the body.

The lymphatic channels get progressively smaller as they pass in to distant organs and tissues.

For example, the vessel at the beginning of the arm is thicker. It branches into thinner tubes that progressively become thinner and thinner as they travel up to the fingers.

At the tips of the fingers the vessels may be the thinnest with places where they may be only a few cells thick. These are called lymphatic capillaries.

The walls of the capillaries are usually single cell thick. This helps in the movement of the immunity producing cells called lymphocytes (type of white blood cells), and the toxins, germs and chemicals to move in to the lymph capillaries freely.

The arteries also branch similarly at the tips of the organs. These capillaries give out a clear fluid called the plasma. This plasma bathes the tissues and enters the lymphatic channels as lymph.

The lymph channels eventually drain at a large lymphatic vessel called the thoracic duct at the chest that drains into a blood vessel.

All the filtered fluid, salts, and proteins as well as the debris thus ends up in the blood stream.

The lymph nodes

The lymph nodes are small bean shaped glands or bulbs that tend to occur in clusters much like grapes.

Along the lymph channels reside approximately 600 lymph nodes. These act as filters that sieve off the harmful substances brought by the lymphatic channels.

The lymphatic channels of the fingers, hand and arm for example comes to be filtered at the lymph nodes that lie at the elbow and the arm pit.

Similarly, those of the legs, toes and thighs drain and nodes behind the knees and the groin.

Lymph channels from the face, head and scalp drain at the nodes present at the back of the head, behind the ears and sides of the neck.

Some lymph nodes are located deeper within the body at the chest (between the two lobes of the lungs), around the coils of the intestines, in the pelvis etc.

The lymph nodes contain 2 regions within them – these include the cortex and the medulla.

The cortex contains collections of lymphocytes. These contain predominantly B-lymphocytes and some T-lymphocytes.

The B lymphocytes mature completely within the bone marrow while the T lymphocytes exit the bone marrow immature and attain maturity within the thymus.

The lymphatic vessels entering the lymph nodes are called afferent lymphatic vessels and those exiting are called efferent lymphatic vessels.

Lymph

This is a clear fluid that travels via the lymphatic channels. This contains fluid, debris, chemicals, toxins, bacteria, viruses and lymphocytes on its way back from the tissues.

Other organs and the lymphatic system

The lymphatic system also consists of other organs like the spleen that lies on the above left sided part of the abdomen.

It acts like a large filter to remove worn out and damaged red blood cells from the blood and recycle them.

The spleen also contains B lymphocytes and T lymphocytes. When blood passes through the organ these cells pick up the infections.

The lymphatic system also contains the thymus that lies behind the chest bone.

The thymus is a maturation site for T lymphocytes.

Tonsils and adenoids are also part of the lymphatic system. The lie at the back of the throat. These are sentinels that protect the digestive system and the lungs from bacteria and viruses.

Function of the lymphatic system

Functions of the lymphatic system include (3):

  • Drainage of fluid from blood stream into the tissues – The circulating blood through narrow vessels leads to leakage of fluid or plasma into the tissues carrying oxygen and nutrients to the tissues and carrying waste materials from the tissues into the lymph channels.

    The leaked fluid drains into the lymph vessels. This forms a circulatory system of fluids within the body.

  • Filtration of the lymph at the lymph nodes – The nodes contain white blood cells that can attack any bacteria or viruses they find in the lymph as it flows through the lymph nodes.

    The cancer cells may also get trapped similarly at the lymph nodes and thus lymph nodes act as indicators of how far the cancer has already spread.

  • Filtering blood – This is done by the spleen. The spleen filters out bacteria, viruses and other foreign particles.
  • Raise an immune reaction and fight infections – The lymphatic system especially the lymph nodes are over active in case of an infection the lymph nodes or glands often swell up in case of a local infection.

Edited by April Cashin-Garbutt, BA Hons (Cantab)

Further Reading

What are lymph nodes?
Swollen lymph nodes
Lymph nodes and disease
Lymph node removal

Sources

  1. http://www.cancerquest.org/anatomy-lymphatic-system.html?gclid=CK3t7qz26LACFUF76wodlVzedA
  2. http://www.cancer.org/Cancer/CancerBasics/lymph-nodes-and-cancer
  3. http://cancerhelp.cancerresearchuk.org/about-cancer/what-is-cancer/body/the-lymphatic-system
  4. http://emedicine.medscape.com/article/937855-overview
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