36. The lymphoid system. Definition and constituting elements. The thoracic duct and the right lymphatic duct – formation and tributaries. Movements of the lymph. Lymph capillaries and lymph nodes – morphological characteristic.

LYMPHOID SYSTEM

• The lymphatic System is a part of the circulatory system (It collects the excess body fluid and return it to the venous circulation) As well as a part of immune system (It circulates lymphocytes throughout the body).

• Lymphatic system is composed of:

1. Lymphoid organs (thymus, bone marrow, spleen) Primary secondery
2. lymph nodes
3. Lymph vessels
4. lymph

Structure of the wall of lymphatic vessels

Lymphatic vessels form an extensive and complex inter-connected network of channels, which begin as “porous” blind-ended lymphatic capillaries in tissues of the body and converge to form a number of larger vessels, which ultimately connect with large veins in the root of the neck.

• Main layers of the wall:

1. Endothelium:

• innermost layer
• Single layer of specialized cells
• Creating flap-like structures, that act as one-way valves.

allow fluid to enter the lymphatic vessel but prevent blackflow.

2. Basement membrane:

• Supportive layer
• Beneath the endothelium.

3. Anchoring filaments:

• Between endothelial cells and surrounding tissues.
• Anchore the endothelial to tissues

4. Smooth muscle layer: contract to move the lymph.
5. Connective tissue layer
6. Adventita: contains collagen fibers

In large lymphatic vessels