The Structure and Functions of the Lymphatic System


The lymphatic system functions similarly to the circulatory system. The structure extends into all the major regions of the body. It works together with the immune system because one of the functions of its function is to produce and release lymphocytes (Moore Jr & Bertram, 2018). The structure is made up of a large network of lymph, lymphatic vessels, lymph nodes, lymphatic organs, and lymphoid tissues. It is essential for the optimal functioning of our body because of the role it plays in certain immune responses. This paper will outline the structure and functions of the lymphatic system and describe its synergy with the immune system and circulatory system.

Structure of Lymphatic System
Figure 1: Structure of Lymphatic System

The lymphatic system organs can be grouped into primary lymphoid organs and secondary lymphoid organs. The primary lymphoid organs include the bone marrow and thymus. The development of B and T cells happens in the two organs. Once the cells mature, they are transported to the secondary lymphoid organs where they are used to fight foreign materials (Boes & Durham, 2017). The thymus consists of an outer cortex that is rich in lymphocytes and an inner medulla. The cortex of the thymus is crucial in the differentiation of T cells. The thymus is present early in fetal development and continues its development until puberty, where it begins to shrink. Scientists are of the view that this is one of the reasons why as people age T cell production reduces. Developing T cells or thymocytes discern between the ‘self’ and the foreign substances ‘nonself’ in the cortex of the thymus (Boes & Durham, 2017). This process is commonly referred to as positive selection which involves exposure to a group of genes that assist the immune system recognize foreign substances.

The thymocytes that are capable of recognizing the group of genes are preserved while those which cannot are destroyed. The cells move to the medulla of the thymus where more differentiation occurs in a process known as negative selection. Here, the cells which can attack the body tissues are destroyed. Studies on thymocytes show that the processes of negative and positive selection destroy a majority of thymocytes with about 5-10% remaining (Moore Jr & Bertram, 2018). The cells that survive move to the secondary lymphoid organs through the efferent lymphatic vessel. The development of B-lymphocytes occurs in the bone marrow of mammals. The bone marrow does not shrink in size when an individual reaches puberty.

The secondary lymphoid organs include the lymph nodes, spleen, and lymph tissues. Lymph nodes consist of lymphatic tissue and appear like bean-shaped structures. There are thousands of lymph nodes throughout the body along the lymphatic routes. The nodes are made up of lymphocytes that enter the bloodstream. The T cells converge in the inner cortex while the B cells assemble in the germinal centers in the inner cortex (Boes & Durham, 2017). The lymph fluid travels into the nodes through the afferent lymphatic vessels and penetrates through the lymph nodes where it activates the lymphocytes. The activated lymphocytes are transported out of the node using the efferent vessels and distributed throughout the body.

The spleen is by far the biggest organ of the lymphatic system. It consists of the red pulp and the white pulp. The red pulp removes bacteria, old blood cells, and debris using cells called macrophages. The white pulp contains both B and T lymphocytes which congregate in different regions of the spleen (Moore Jr & Bertram, 2018). The lymphoid tissues which are associated with mucosa are another secondary lymphoid organ. They are tissues found in different organs such as genitourinary, and respiratory tracts which are exposed to harmful microorganisms hence require antigens.

Functions of the Lymphatic System

One of the main functions of the lymphatic system is the removal of the interstitial fluid from tissues. The interstitial fluid functions as the primary exchange medium for most of the human tissues (Li et al., 2021). An average adult human body contains 11-12 liters in the interstitial spaces. The fluid is rich in oxygen, sugars, amino acids, lipids, electrolytes, hormones, and waste products such as urea and uric acid. This fluid accumulates in the tissues due to pressure from capillaries and protein leakage into the tissues. The lymphatic system works to drain the excess interstitial fluid that has accumulated. The removal of the surplus fluid prevents the formation of edema, which is any type of tissue swelling that results from a buildup of the interstitial fluid in the tissues (Li Z. et al., 2021). In some cases, edema can be harmful especially if it happens in the pulmonary areas.

Another important function of the lymphatic system is to transport fatty acids. Nutrient absorption occurs in the ilium through the villi that are composed of central blind-ended lymphatic vessels called lacteal (Li et al., 2021). The digestion of fatty acids occurs is different from carbohydrates and proteins. Fatty acids are digested, emulsified, and converted within the intestinal walls into a lipoprotein called chylomicrons (Li et al., 2021). The lacteals that line the intestine walls absorb the chylomicrons into the lymph fluid. The lymph vessels transport the lipoprotein into the blood circulation where they react High-Density Lipoprotein (HDL) and are further broken down in the liver (Li et al., 2021). HDLs are also referred to as good cholesterol because a high concentration of HDL can lower the risk for heart disease and stroke. The lymphatic system functions as a major route for transportation of fat digestion products but does not suffer from the effects of fat build-up which is common in arteries.

The other major function is the transportation of immune cells. The system serves as a conduit for the conveyance of the cells involved in immune system functions. The lymphatic system drains almost all tissues in the human body. This means that bacteria, viruses, and fungal cells circulate in the lymph fluid. Lymph nodes trap and process pathogens and activate immune responses to destroy the pathogens (Liet al., 2021). In an average adult, there are around 600 lymph nodes that vary in size. In the presence of an infection, the lymph nodes typically enlarge or become inflamed. The assessment of lymph nodes can provide information on the areas where there is an infection. The dendritic cells mediate the immune response in the lymph nodes (Li et al., 2021). For the lymphatic vessels cytokines positively regulate the uptake of antigens from the peripheral tissues. Even though the system helps in transporting immune cells, studies have shown that the lymphatic system can provide a pathway for the spread of cancer (Li et al., 2021). This is because lymph circulation is one of the main ways in which tumors can spread to other parts of the body which is hard to prevent.

Lymphatic System and Circulatory System

The circulatory system moves blood throughout the body while the lymphatic system transports the interstitial fluid from tissues to the circulatory system. The flow of lymph fluid towards the heart indicates synergy between the work of the circulatory system and the lymphatic system. The lymphatic system supports the circulatory system by draining excess fluids and proteins from tissues back into the bloodstream (Moore Jr & Bertram, 2018). This is essential because it prevents tissue swelling which can cause problems to the human body. Blood vessels may be made up of thick walls to prevent leakages. In some cases, blood vessels can leak due to various reasons.

The lymphatic system works to transport the leaked blood back to the bloodstream. The leaked fluid collects in the spaces between cells and tissues where it is collected by the lymph vessels. The collected fluid is known as lymph and is transported to the cardiovascular system. The movement of the fluid is slow because, unlike the circulatory system, the lymphatic structure does not have a pump (Moore Jr & Bertram, 2018). The lymph fluid also flows in the circulatory system and works to produce white blood cells and create antibodies. Therefore, the lymphatic system and the circulatory system function together to ensure the normal functioning of the human body.

Lymphatic System and Immune System

The immune system and the lymphatic system work together to destroy the unwanted pathogens in the body. The lymphatic system alerts the body to the infection and responds to the pathogens (Randolph et al., 2017). Lymphocytes make up 20-30% of the circulating leucocytes and consist of both B and T lymphocytes. The bone marrow is made up of 12% of the body’s lymphocytes while the spleen and lymph nodes consist of about 55% of lymphocytes (Randolph et al., 2017). The B-lymphocytes are created with the ability to determine the antigens which are harmful to the body and which are not. The T-lymphocytes locate compromised body cells and break them up into tiny molecules.

The T-lymphocytes can only act in this way only when they are activated by other cells. This indicates the synergy between the lymphatic system and the immune system. The lymph nodes are useful in monitoring the presence of pathogens in the lymph fluid and eliminating them. The red pulp that makes up 75% of the spleen also plays a part in maintaining the immunity of the human body (Randolph et al., 2017). The red pulp destroys the old red blood cells whereas the white pulp activates the immune response. The mucosa-associated lymphoid tissue also works to protect the entry points of sensitive tissues such as those in the respiratory and gastrointestinal tracts (Randolph et al., 2017). Therefore, the lymphatic system plays a significant part in the immune response. It works to defend the body against infections, bacteria, and viruses.


In summary, the lymphatic system is made up of primary and secondary lymphoid organs. The primary lymphoid organs include the bone marrow and the thymus gland while the secondary lymphoid organs include the spleen, lymph nodes, and mucosa-associated lymphoid tissues. The functions of the lymphatic system are to remove interstitial fluid from tissues, help in fatty acids absorption, and transport immune cells. The lymphatic system works together with the circulatory system to transport leaked fluids back to the circulation system. It also works together with the immune system to provide an immune response.


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Randolph, G. J., Ivanov, S., Zinselmeyer, B. H., & Scallan, J. P. (2017). The lymphatic system: Integral roles in immunity. Annual Review of Immunology, 35, 31-52. Web.

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