4.4 Lymphatic and Immune Systems

Overview

The lymphatic system consists of a network of lymphatic vessels, lymph nodes, and ducts. One of the major functions of the lymphatic system is to drain free fluid in the body and return it to the bloodstream. Blood pressure can cause leakage of fluid from the capillaries, resulting in the accumulation of fluid in the spaces between individual cells in the tissues, called edema. The lymphatic system collects this excess fluid, now called lymph, from tissues in the body and returns it to the bloodstream. The lymphatic system is also associated with the immune system. The lymph passes through lymph nodes on the way back to the heart in order to “clean” it (remove potential pathogens) before it is pumped through the body.

The immune system is the complex collection of cells and organs that destroy and/or neutralize pathogens that could cause disease or death. Cells in the immune system use lymphatic vessels to make their way from the body back into the circulatory system, and they also use lymph nodes as areas for pathogen clearance and immune response. For example, lymph nodes swell during an infection.

Figure 4.18 Circulation of lymph and major lymph nodes

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Structures

Lymph: The fluid contained within the lymphatic system

Lymph nodes: Bean-shaped organs that can be found throughout the body. Their function is to remove debris and pathogens from the lymph. Bacteria that infect interstitial fluid are taken up by the lymphatic capillaries and transported to a regional lymph node to be cleared before being brought back to the heart.

Lymphatic vessels: These vessels begin as capillaries, which feed into larger and larger lymphatic vessels, and eventually empty through a series of ducts into the bloodstream.

Lymphoid nodules: Patches of lymphoid tissue found throughout the body. They are simpler than the lymph nodes and spleen and are located in the respiratory system and digestive tract, which are areas routinely exposed to environmental pathogens.

Lymphocytes: The primary cells of adaptive immune responses. The two basic types are B cells and T cells. Both types of cells initially develop in the bone marrow.

Bone marrow: Soft, fatty tissue within the bones. It is a primary lymphoid organ and is where B cells undergo nearly all of their development. It is also where immature T cells develop until they move to the thymus gland.

Spleen: Considered to be a major secondary lymphoid organ, the spleen is sometimes called the “filter of the blood” because of its extensive vascularization and the fact that it removes microbes and other materials from the blood. It also stores red blood cells that can be released in times of need; for example, when further oxygen transportation is required.

Thymus gland: This primary lymphoid organ is found in the space between the sternum and the aorta. It regresses as an animal ages.

Common Lymphatic & Immune Pathologies & Associated Terms

Anemia: A condition in which the number of red blood cells (RBCs) or hemoglobin is lower than normal

Allergy: An inflammatory response caused by a hypersensitivity to a substance (Anspaugh et al., 2022)

Antibody: A protein produced by B lymphocytes to fight an antigen (protein that the body perceives to be causing harm); also called immunoglobulin (Anspaugh et al., 2022)

Antigen: A protein that causes an immune response

Autoimmune disease: A disease in which the immune system begins to attack cells of the animal’s own body

Immune (adjective): Having immunity to a pathogen (Anspaugh et al., 2022)

Immunity: The body’s ability to fight a disease-causing organism. After an infection, memory cells remain in the body for a long time and can very quickly mount an immune response against the same pathogen if it tries to re-infect (Anspaugh et al., 2022).

Immunization: The process of inducing immunity artificially with weakened or killed pathogens (Anspaugh et al., 2022)

Lymphoma: A form of cancer in which masses of malignant T and/or B lymphocytes collect in lymph nodes, the spleen, the liver, and other tissues (Anspaugh et al., 2022)

Example

Splenomegaly: Enlargement of the spleen

Vaccine: An agent administered by injection, orally, or by nasal spray that induces an immune response to a particular infectious disease (Anspaugh et al., 2022)

Common Procedures

Fine needle aspiration: A sampling procedure in which cells are aspirated using a needle – this sample can be used for cytology

Splenectomy: The surgical removal of all or part of the spleen

References

Anspaugh, K., Goncalves, S., Jackson-Osagie E., & Smith, S. Q. (2022). Medical terminology: An interactive approach. LOUIS: The Louisiana Library Network. https://louis.pressbooks.pub/medicalterminology/, licensed under CC BY 4.0

Image Credits
(images are listed in order of appearance)

Anatomy and physiology of animals Circulationof lymph w major lymph nodes by Sunshineconnelly, CC BY 3.0

Large lymphocyte-2 by Guy Waterval, Apache Licence-2.0

Lymphoma in golden by Joel Mills, CC BY-SA 3.0