January 22, 2022


5 min read




In this article, we shall study the lymphatic system in humans.                  



In animals there two systems, that take part in the transport of materials (Plasma, water, and other substances ) from one part of the body to another. i.e  (1) Blood circulatory system (2) Lymphatic system. Here we are discussing the lymphatic system.


Generally, capillaries are highly permeable allowing most of the substances to pass through the cell, while fencing others and consisting of a single cell, so different substances e.g. plasma, water, minerals some gases leak out from them and pass in tissues. Exchange of gases, as well as materials, takes place there. The lymphatic system plays its role to return the material from tissues to the heart. The lymphatic system consists of the following parts,

  • Lymph capillaries
  • Lymph vessels
  • Lymph nodes
  • Lymphoid masses(thymus gland in thoracic cavity and spleen)
  • Lymph

On the basis of these components, we called it a lymphatic system.


As we know that capillaries are highly permeable, water and dissolved substances enter intercellular spaces. Blood cells never leave the capillaries. The remaining fluid which in inter-cellular spaces is called “Lymph” returns to the heart via the lymphatic system. Lymph actually starts to collect in lymph capillaries from inter-cellular spaces, then it comes in lymph veins. The walls of the lymphatic system are porous, so they can uptake even larger molecules in them. Lymph capillaries join to form lymph vessels. All the lymph vessels collect to form the lymph duct which is present in the thoracic cavity. The lymph duct opens in a larger vein called the “subclavian” vein which is present in the shoulders. The lymph passes from lymph vessels to the lymph duct and ultimately it transfers to the subclavian vein. This vein discharges lymph into the superior vena cava and finally into the heart. The small intestine contains many vessels of the lymphatic system. These vessels are called “lacteals”. The flow of lymph is regulated by breathing movements and skeletal muscles. There are valves in the lymphatic system which regulate the unidirectional flow of lymph in the body. Lymph vessels contain lymph nodes. Basically, lymph nodes are the smaller structure that is composed of connective tissues. They are the sites where the maturation of lymphocytes takes place. Generally, lymphocytes are the type of immune cells produced in the bone marrow and lymph tissue. Lymphocytes B produces antibodies, while lymphocytes T kill tumor cells and help in immune responses. Many afferent vessels enter lymph nodes to discharge lymph in lymph nodes, but only one efferent vessel from which the lymph comes out. Lymph nodes are more concentrated in the following parts of the body;

  1. Neck region
  2. Axilla
  3. Groin

Besides these structures, they are present in different parts in small numbers. Several lymphoid masses are also part of the lymphatic system. They are present in the following parts of the body;

  • Thymus (In thorax)
  • Spleen
  • Tonsils
  • Walls of the digestive tract
  • Adenoids

The function of lymphoid masses

Lymph is a clear or colorless fluid; the word lymph derived from a Latin word called “lympha” which means “connected to water” according to the National Lymphedema Network.

Lymphoid masses, the collection of several organs play a vital role in the production of lymphocytes. As discussed before, lymphocytes are special immunes cells (B lymphocytes produce antibodies and T lymphocytes kill tumors or germs assisting immune response). The lymphatic system brings plasma back to the heart. About 3 liters of plasma reaches to heart by the lymphatic system every day.

Many branches of lymph vessels exist in the villi of the small intestine. Such lymph vessels are known as Lacteals. In our body fats are not soluble in blood. So after digestion in the small intestine, they are transported to the heart through the lacteals.

In lymph nodes, Lymphocytes kill all types of pathogens like viruses and bacteria.  Spleen, a lymphoid mass cleans up dead red blood cells and also kills disease-causing germs (bacteria and viruses). Thymus which is present in the chest just above the heart, stores immature immune cells (Lymphocytes) and converts them into active mass T cells that kill infected or cancerous cells. Tonsils are clusters of lymphatic cells to be found in the pharynx. According to the American Academy of Otolaryngology, they are the body’s first line of defense as a part of the immune system. Bacteria or viruses enter the body through the mouth or nose. Sometimes they cause infection and although tonsillectomies occur much less frequently today than they did in the 1950s. Plasma leaves the body’s cells once it has delivered its nutrients and removed debris. Most of this fluid returns to the venous circulation via tiny blood vessels called venules and continues as venous blood, the remaining becomes lymph.

Unlike blood, which travels in the body in a regular and continuous manner, the lymph flows in uni-direction up toward the neck region.  Lymphatic vessels connected to two subclavian veins, which are present on either side of the neck near collarbones and the fluid re-enters the circulatory system.

                                         DISORDERS OF LYMPHATIC SYSTEM

The most common disorders of the lymphatic system are (1) lymphadenopathy (2) lymphoma, both are briefly described below

  1. Lymphadenopathy

This disorder generally caused by infection, inflammation, or cancer. Bacterial infections causing lymphadenopathy are strep throat, locally infected skin wounds. Viral infection includes mononucleosis or HIV infection. The enlargement of the lymph nodes may be localized in the area of infection, as in strep throat, and is more general, as in HIV. In some parts of the body lymph nodes are palpable, while others to deep to feel and can be seen on a CT scan or MRI.

  1. Lymphoma

Lymphoma concerns the cancer of lymph nodes also lymphocytes.  It appears when the lymphocytes grow and divide uncontrollably. There are many types of lymphoma. The most common types of NHL (non-Hodgkin lymphoma) are follicular, which accounts for about 30 percent of all NHL cases, diffuse large B-cell lymphoma (DLBCL) which comprises 40 to 50 percent of NHL cases.

As mentioned before lymphoma is cancer that begins in immune system cells, the lymphocytes. These cells are present in lymph nodes, thymus, spleen, bone marrow, and other parts of the body.

Lymphoma can affect those areas as well as other body organs.

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