Overarching Function

The lymphatic system is considered part of the immune system and circulatory system. It helps maintain body fluid balance, removes cellular wastes, absorbs fat, and protects the body from foreign microorganisms.

Basic structures and functions

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Macroscopic structures

  1. Lymph node

    See the diagram above. Lymph nodes are bean-like structures part of the lymphatic system. There are more than a hundred lymph nodes that connect via lymphatic vessels throughout the body. Lymph nodes filter substances that travel through the lymphatic fluid, and they contain lymphocytes (white blood cells) that help the body fight infection and disease.

  2. Thymus gland

    The thymus gland is located above the heart. It contributes the the activation of T cells, which is a kind of lymphocyte that are produced in the bone marrow but mature in the thymus gland.

Microscopic structures

  1. B lymphocytes (aka B cells)

    B lymphocytes are located in all lymphatic tissues. They produce antibodies that specifically react to a foreign antigen. An antigen is a foreign substance in the body that triggers an immune response. It can bind to an antibody or T cell.

    In the lymphatic tissues, the macrophage (phagocytic cell), with the processed antigen on its surface, binds to a helper T cell, which activates the helper T cell. The helper T cell then activates antibody secretion in B cells and another type of T cell. Some B cells continue to manufacture antibodies through mitosis. Some activated B cells remain as memory cells, which can respond quickly to the same antigen when there’s a second exposure. The Antibody-Mediated Response in the diagram below illustrates the process described above.

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  2. Lymphatic fluid (aka Lymph)

    Lymph is the plasma part of the blood. It is a clear fluid that contains oxygen, nutrients, and white blood cells. It leaks out of the capillaries to “bathe” all cells in the body. They circulate around the cells, then is collected by lymphatic vessels, which brings them back to the circulatory system via the veins near the heart.

Connection to other systems

The lymphatic system works with the circulatory system and the immune system. Lymph needs the circulatory system to travel throughout the body. B cells helps the immune system produce antibodies that target a specific antigen, which is then carried to different parts of the body through the circulatory system.

Differences between a frog and human

The lymphatic systems between a frog and human are essentially the same.