Lymphatic system is a closed system of lymph channels or lymph vessels, through which lymph flows. It is a one-way system and allows the lymph flow from tissue spaces toward the blood.


Lymphatic system arises from tissue spaces as a meshwork of delicate vessels. These vessels are called

lymph capillaries. Lymph capillaries start from tissue spaces as enlarged blind-ended terminals called capillary bulbs. These bulbs contain valves, which allow flow of lymph in only one direction. There are some muscle fibers around these bulbs. These muscle fibers cause contraction of bulbs so that, lymph is pushed through the vessels. Lymph capillaries are lined by endothelial cells. Capillaries unite to form large lymphatic vessels. Lymphatic vessels become larger and larger because of the joining of many tributaries along their course. The structure of lymph capillaries is slightly different from that of the blood capillaries. Lymph capillaries are more porous and the cells lie overlapping on one another.

This allows the fluid to move into the lymph capillaries and not in the opposite direction.


Larger lymph vessels ultimately form the right lymphatic duct and thoracic duct. Right lymphatic duct opens into right subclavian vein and the thoracic duct opens into left subclavian vein. Thoracic duct drains the lymph from more than two third of the tissue spaces in the body.


Lymph vessels are situated in the following regions:

1. Deeper layers of skin

2. Subcutaneous tissues

3. Diaphragm

4. Wall of abdominal cavity

5. Omentum

6. Linings of respiratory tract except alveoli

7. Linings of digestive tract

8. Linings of urinary tract 9. Linings of genital tract

10. Liver

11. Heart.

Lymph vessels are not present in the following structures:

1. Superficial layers of skin

2. Central nervous system

3. Cornea

4. Bones

5. Alveoli of lungs.


Lymph nodes are small glandular structures located in the course of lymph vessels. The lymph nodes are also called lymph glands or lymphatic nodes.


Each lymph node constitutes masses of lymphatic tissue, covered by a dense connective tissue capsule.

The structures are arranged in three layers namely cortex, paracortex and medulla Cortex Cortex of lymph node consists of primary and secondary lymphoid follicles. Primary follicle develops first. When

some antigens enter the body and reach the lymph nodes, the cells of primary follicle proliferate. The active proliferation of the cells occurs in a particular area of the follicle called the germinal center. After proliferation of cells, the primary follicles become the secondary follicle. Cortex also contains some B lymphocytes, which are usually aggregated into the primary follicles. Macrophages are also found in the cortex.


Paracortex is in between the cortex and medulla. Paracortex contains T lymphocytes.


Medulla contains B and T lymphocytes and macrophages. Blood vessels of lymph node pass through medulla.

Lymphatic Vessels to Lymph Node

Lymph node receives lymph by one or two lymphatic vessels called afferent vessels. Afferent vessels divide into small channels. Lymph passes through afferent vessels and small channels and reaches the cortex. It circulates through cortex, paracortex and medulla of the lymph node. From medulla, the lymph leaves the node via one or two efferent vessels.

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