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12. Lymphoid system




< Lymph, immunity >


Fig. 12-1.


Lymphocyte, a part of white blood cell (Fig. 11-8), and plasma (Fig. 11-17) may get out of the capillary (Fig. 11-10). When the lymphocyte and plasma are collected into lymphatic vessel, lymph is formed. Lymph circulates throughout the lymphatic vessel (Fig. 12-7).


Fig. 12-2.

Unlike the blood (Fig. 11-3), lymph contains just white blood cells (in particular, lymphocytes).



Fig. 12-3.


Immunity is activated by antigen. Main cell in the immunity is the lymphocyte and the macrophage that is a modified monocyte (Fig. 11-8).



Fig. 12-4.


Cell-mediated immunity involves antigen-specific T lymphocyte and macrophage. A macrophage’s cytoplasm contains much lysosome (Fig. 16-10).



Fig. 12-5.


In contrast, humoral immunity refers to antibody production by plasma cell that is modified B lymphocyte. By binding its specific antigen, the antibody causes destruction of an antigen either independently or by the help of macrophage.


< Lymphoid organs >



Fig. 12-6.


Lymphoid organs (namely, lymph node, spleen, tonsil, and thymus) contain the lymphocytes and initiate the immunity.



Fig. 12-7.


Lymph nodes are widely present in the lymphatic vessels (Fig. 12-1). A lymph node is full of T and B lymphocytes (Fig. 12-4) (Fig. 12-5). If the lymphocyte is like a police officer, the lymph node is like police station.


Fig. 12-8.


Lymphatic vessel can be the route for cancer cells to spread, which is called metastasis. The lymph node, equipped with the lymphocytes, is acting as filter for the cancer cells.



Fig. 12-9.


The lymph node becomes enlarged in various diseases which may range from trivial infection to life-threatening cancer.



Fig. 12-10.


Lymph is transported through lymphatic vessel, which becomes larger and larger as proceed (lymphatic trunk, thoracic duct or right lymphatic duct) and enters the vein (Fig. 12-11). So, it can be said that lymph comes from the blood vessel (Fig. 12-1) and also empties into the blood vessel.


Fig. 12-11. Thoracic duct, right lymphatic duct, lymphatic trunks.


Pay attention to the chyle cistern where the intestinal lymphatic trunk, the two lumbar lymphatic trunks empty. While the “intestinal” lymphatic trunk conveys lymph from the abdominal cavity (mostly “intestine”), the lumbar lymphatic trunks convey lymph from the abdominal wall, pelvis, perineum, and lower limbs. The chyle cistern leads to the thoracic duct, the biggest highway for lymph (Fig. 12-10).

Terminal portion of the thoracic duct travels to the left side to receive lymph from the left jugular, left subclavian, and left bronchomediastinal lymphatic trunks. The three lymphatic trunks drain lymph from the left head and neck, left upper limb, and left thorax (lung and mediastinum) (Fig. 10-6), respectively.

In conclusion, the thoracic duct receives lymph from the whole body except the right head and right neck, right upper limb, and right thorax, for which the right lymphatic duct is responsible.

Junction of the subclavian and internal jugular veins (Fig. 10-64) is the site into which the thoracic duct and right lymphatic duct drain.


Fig. 12-12.


The spleen is in contact with the pancreas; but the spleen has no functional relationship with the pancreas that belongs to digestive system and endocrine system (Fig. 9-18).


Fig. 12-12a.


The spleen is protected by the left R9–R11 (Fig. 6-3).


Fig. 12-13.


The spleen purifies blood like the lymph node that cleanses lymph (Fig. 12-7).


Fig. 12-14.


The spleen removes old red blood cells (Fig. 11-4).


Fig. 12-15.


The spleen is enlarged for various reasons, such as cancer and leukemia.


Fig. 12-16. Palatine tonsil.


When you open your mouth wide in front of a mirror, you can see the palatine tonsil between the palatoglossal and palatopharyngeal arches (Fig. 4-16).



Fig. 12-17. Tonsils around fauces.


In the nasopharynx and oropharynx, the pharyngeal, palatine, and lingual tonsils are located. Among them, the lingual tonsil is situated at the posterior 1/3 of tongue (Fig. 4-7).


Fig. 12-18.


The tonsil is frequently enlarged against illnesses such as the common cold.



Fig. 12-19.


The thymus in the superior mediastinum is hidden by the manubrium of sternum (Fig. 1-19) (Fig. 10-5). The thymus is widely known as the site of T (thymus) lymphocyte maturation.



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