U4 AOS1 Topic 4: Lymphatic System

It is a network of vessels throughout the body in which a fluid known as lymph flows. It is an important component of both immune system and circulatory system.

 Functions of lymphatic system:

·        Transport of antigen presenting cells and pathogens.

·        Site of leukocyte production and “clonal expansion”.

Components of lymphatic system:

In addition to lymphatic vessels and lymph, there are some tissues involved in lymphatic system such as primary and secondary lymphoid tissues.

·        Primary lymphoid tissue includes bone marrow and thymus where lymphocytes are created and matured. Lymphocytes are produced in bone marrow. B lymphocytes remain and mature in bone marrow whereas T lymphocytes travel to thymus to mature.

·        Secondary lymphoid tissue includes lymph nodes and spleen where mature lymphocytes are maintained and adaptive immune response is initiated.

Mechanism of lymphatic system:

The lymphatic system works by the following stages:

1.   Fluid from the blood vessels leaks into body tissues.

2.   Fluid from the tissue containing pathogens and antigen presenting cells drains into lymphatic capillaries present throughout the tissue by the process of “lymphatic drainage”.

3.   Fluid which has drained into lymphatic capillaries has now become lymph and travels through the valve containing lymphatic vessels in one direction only i.e. toward the lymph nodes and away from body tissues.

4.   Afferent lymphatic vessels take the lymph towards the lymph nodes where clusters of B and T lymphocytes are present. The pathogens and antigen presenting cells in the lymph when pass through the lymph nodes interact with lymphocytes to initiate adaptive immune response and allows clonal expansion and differentiation. This process is called as “lymphatic surveillance”.

5.   The antibodies and activated cytotoxic T cells produced in adaptive immune response are transported into lymph via efferent lymphatic vessel which takes the lymph away from lymph nodes.

6.   Lymphatic vessels join with veins so that lymph can enter the blood circulation.