Exam 2 Review:  Chapter 20:  Lymphatic Organs & Pathology Terms

primary lymphatic organ - Those organs in which lymphocytes are produced or in which they mature; in the human, they are the red bone marrow and the thymus gland.

red bone marrow - The type of marrow tissue found in spongy bone and marrow cavities where the various blood stem cells reside and where new red blood cells, white blood cells, and platelets are produced for release into the circulation.

thymus gland - A lobed endocrine organ located in the mediastinum, deep to the sternum, which is responsible for the maturation of T lymphocytes; it produces a number of local hormones including thymosin to contribute to T lymphocyte maturation; the thymus is at its largest at birth and shrinks over time, being replaced by fibrous connective tissue, and is usually absent by the end of the second decade of life; the thymus is regulated primarily by local hormones.   [See autopsy specimen of human thymus below.]

secondary lymphatic organ  - Those organs in which mature lymphocytes are found and where they play active roles in immune defense reactions; in the human, they include the red bone marrow, the lymph nodes, the spleen, the tonsils and the various isolated microscopic lymphatic nodules, especially those found in lamina propria of mucous membranes of the GI tract, respiratory tract, urinary tract, and reproductive tract, i.e., “MALT” = mucosa-associated lymphatic tissue; lymphatic tissues are regulated primarily by local hormones.

lymph node - Any of the small discrete (encapsulated) bodies (secondary lymphatic organs) located along the lymphatic vessels, particularly at the neck, armpit, and groin, and in the thoracic and abdominal cavities, which receive lymph (interstitial fluid = intercellular fluid = tissue fluid) from the lymphatic circulation through afferent lymphatic vessels; they consist of a capsule, an outer cortex and an inner medulla; they filter microorganisms and foreign particles from the lymph fluid; they are also a frequent site of antigen-presentation and lymphocyte activation and proliferation; during infection, they may become swollen with activated lymphocytes; lymphatic tissues are regulated primarily by local hormones.  aka -- lymph glands [Note:  although nicknamed "lymph glands," they are not glandular nor epithelial in origin.]

spleen - A large, dark-red, oval, highly vascular, fragile secondary lymphatic organ, located in the human body to the left of the stomach below the diaphragm, organized into areas of red pulp and white pulp; its functions include acting as a blood reservoir, phagocytizing old, worn, or damaged blood cells, filtering foreign substances from the blood, participating in immune defenses and housing mature lymphocytes and macrophages; lymphatic tissues are regulated primarily by local hormones.

Spleen - gross specimen with splenic pulp visible Spleen - stained specimen identifying red and white pulp

red pulp (of spleen) -Those portions of the spleen acting as a blood reservoir, organized into splenic cords (containing a meshwork of loose reticular tissue housing macrophages, lymphocytes, plasma cells, erythrocytes, platelets, and granulocytes) separated by endothelium-lined capillary sinuses (containing primarily macrophages and erythrocytes); the presence of large numbers of erythrocytes gives these portions of the spleen their distinctive red color in fresh unstained specimens; blood flow through these portions of the spleen is sluggish, but in hemorrhagic emergencies, smooth muscle in the splenic capsule can contract and expel this blood from this reserve.

white pulp (of spleen) -Those portions of the spleen localized around the many small central arteries of the spleen; each central artery is surrounded by a thin layer of T lymphocytes while the surrounding reticular connective tissue is rich in lymphatic nodules containing B and T lymphocytes; these lymphocytes are involved in immune defenses; the absence of erythrocytes outside of the central arteries gives these portions of the spleen their distinctive white color in fresh unstained specimens; lymphatic tissues are regulated primarily by local hormones.

lymphatic nodule - Microscopic collections of unencapsulated, relatively spherical masses of dense aggregates of small B lymphocytes in an outer core and a central mass of antigen-presenting macrophages and larger, more metabolically active, proliferating B lymphocytes and plasma cells termed the germinal center; this is a site for proliferation and differentiation of lymphocytes in active immune responses; these structures are located in the walls of various organs, especially tubular organs lined by mucosal membranes; lymphatic tissues are regulated primarily by local hormones.

MALT = mucosa-associated lymphatic tissue - The general term used for the various aggregations of lymphoid tissue found associatied with the mucous membranes of the respiratory and digestive tracts; the consist of lymphatic nodules within the connective tissues walls of these tubular organs; these lymphocytes are involved in immune defenses; lymphatic tissues are regulated primarily by local hormones.

tonsils - Small oral masses of lymphoid tissue covered by mucous membranes, especially either of two such masses embedded in the lateral walls of the opening between the mouth and the pharynx, which help, in a limited fashion, protect the throat from potential infections; in addition to the large paired pharyngeal tonsils, there are smaller lingual and palatine tonsils; lymphatic tissues are regulated primarily by local hormones.

Normal Pharyngeal Tonsils Inflamed Pharyngeal Tonsils

 

metastasis - A secondary cancerous growth formed by transmission of cancerous cells from a primary growth (original site) to one or more sites elsewhere in the body, usually by way of the blood vessels or lymphatics; the potential for metastasis is a characteristic of almost all malignant cancers.

Hodgkins disease - A malignant cancer; a progressive, sometimes fatal lymphoma of unknown cause, marked by progressive (but painless) enlargement of the lymph nodes, followed by enlargement of the spleen, and liver; bone marrow transplantation may be useful for selected patients who have relapsed following treatment with radiation and chemotherapy.

List:

2. the forms of lymphatic tissue in the body:  (a) structural and (b) developmental and give examples of each form or category.

Structural* Developmental*
[1] discrete, encapsulated lymphatic organs:  thymus, lymph nodes, spleen

[2] diffuse, unencapsulated lymphatic tissues: red bone marrow, MALT = mucosa-associated lymphatic tissue, isolated lymph nodules

[1]  primary lymphatic organs:  Those in which lymphocytes are produced or mature: red bone marrow, thymus gland.

[2]  secondary lymphatic organs:  Those in which mature lymphocytes play active roles in immune defense reactions: red bone marrow, lymph nodes, spleen, tonsils and various isolated microscopic lymphatic nodules, especially those found in lamina propria of mucous membranes of the GI tract, respiratory tract, urinary tract, and reproductive tract, i.e., “MALT” = mucosa-associated lymphatic tissue.

[*Note:  The structural and developmental categories are separate categories.  Do not draw the conclusion that all primary lymphatic organs are discrete and encapsulated, while all secondary lymphatic organs are diffuse and unencapsulated.  That is not the case.  Red bone marrow (primary) is unencapsulated; lymph nodes and the spleen (secondary) are encapsulated.]

3. The organs of the lymphatic system and the functions of each.

Lymphatic System Organs Function(s)
red bone marrow site of production of leukocytes, site of anti-self screening and maturation of B lymphocytes
lymph nodes physical filtration of lymph, site of antigen-presentation between macrophages and lymphocytes, site of activation of specific clones of B and T lymphocytes
spleen physical filtration of blood, site of removal and phagocytosis of aged and damaged blood cells, site of antigen-presentation between macrophages and lymphocytes, site of activation of specific clones of B and T lymphocytes
tonsils site of antigen-presentation between macrophages and lymphocytes, site of activation of specific clones of B and T lymphocytes
“MALT” = mucosa-associated lymphatic tissue site of antigen-presentation between macrophages and lymphocytes, site of activation of specific clones of B and T lymphocytes
thymus site of anti-self screening and maturation of T lymphocytes

 
4. the locations where MALT lymphatic tissue is found.

          in the lamina propria of mucous membranes of the conjunctival sacs, GI tract, respiratory tract, urinary tract, and reproductive tract

5. the four tissues which do not contain lymphatic capillaries.

          any epithelial tissue, nervous tissue, cartilage, red bone marrow, spleen

Explain:

2. How lymphatic tissue varies in its distribution and organization in various parts of the body.  Give examples. 

Lymphatic tissue varies in distribution by being localized and concentrated in regions near to potential invasion sites for micro-organisms (in the lamina propria of mucous membranes, and in lymph nodes along the lymphatic vessel drainage channels.  There is also more lymphatic tissue in the head and trunk and less in the limbs.

Lymphatic tissue varies in organization by being either [1] discrete, encapsulated lymphatic organs (thymus, lymph nodes, spleen) or [2] diffuse, unencapsulated lymphatic tissues (red bone marrow, MALT = mucosa-associated lymphatic tissue, isolated lymph nodules)