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62 Cards in this Set
- Front
- Back
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What is the lymphatic system?
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Consists of cells, tissues and organs that monitor internal fluid compartments and react to the presence of potentially harmful substances.
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What are the various tissues of the lymphatic system?
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Diffuse lymphatic tissue
Lymphatic nodules Tonsils Lymph nodes Spleen Thymus Lymphatic vessels |
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What do the various tissues of the lymphatic system serve as?
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Serve as sites where lymphocytes proliferate, differentiate, and mature.
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What are the major features of the lymphatic system?
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Protect against invading pathogens or antigens.
Distinguish self from non-self. Lymphatic system widely distributed. Immune cells transported through body via lymphatic vessels or bloodstream |
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Where are Primary Lymphoid Organs?
What occurs here? |
- Bone marrow and thymus.
- Cells undergo antigen-independent proliferation and differentiation. |
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What are Secondary Lymphoid Organs?
What occurs here? |
- Lymph nodes, spleen, tonsils, cell aggregates.
- Cells undergo antigen-dependent activation |
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What are the cells of the immune system?
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Lymphocytes and various supporting cells
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What are the characteristics of the lymphocytes?
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- 7-8 microns diameter.
- Dark, round nucleus. - Sparse basophilic cytoplasm. - Found in peripheral blood, lymph nodes, spleen, thymus, tonsils, appendix, and CT of many other tissues (e.g., GI tract, respiratory tract). - Responsible for immunologic surveillance |
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What are the three types of lymphocytes?
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B Cells
T Cells Natural Killer cells |
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What are the characteristics of B cells?
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-20-30% of circulating lymphocytes
- Originate in bone marrow - Mature in bone marrow - Migrate to secondary lymphoid organs - When activated, differentiate into Plasma cells |
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What are the characteristics of T cells?
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- 60-80% of circulating lymphocytes
- Originate in bone marrow - Mature in thymus - Migrate to secondary lymphoid organs - Respond to cell-bound antigens (viral, fungal-infected, & tumors) (helper T cells and cytotoxic T cells, etc.) |
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What are the characteristics of NK (natural killer) cells?
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- 5-10% of circulating lymphocytes
- Kill virus-infected and tumor cells - Larger than B and T cells; indented nucleus |
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What are the characteristics of plasma cells?
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- Activated B-lymphocytes
- Plasma cells are located in CT and lymphoid tissues only - Produce antibodies in response to cell-free and cell-bound antigens |
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What are the characteristics of macrophages?
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- Located in peripheral tissues
(NOT in circulation). - Derived from blood monocytes. - 12-15 microns diameter. - Functions are phagocytosis and antigen presentation |
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What do lymphatic vessels provide?
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Route by which cells and large molecules pass from the tissue spaces back to the blood
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What is lymph fluid composed of?
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Electrolytes, 2-4% protein, lymphocytes
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What does MALT stand for?
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Mucosa-associated lymphatic tissue
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What does GALT stand for?
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Gut-associated lymphatic tissue
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What does BALT stand for?
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Bronchus-associated lymphatic tissue
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What is the site of initial immune response?
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Diffuse Lymphatic Tissue
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What are the characteristics of the diffuse lymphatic tissue?
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- Stroma (reticular fibers and cells) and lymphocytes not enclosed by capsule.
- Found mostly in GI tract and respiratory tract (lamina propria). - Also may contain plasma cells and eosinophils. - After contact with antigen, cells travel to lymph nodes. |
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What are the lymphatic nodules?
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- Sharply defined concentrations of B lymphocytes contained within a meshwork of reticular fibers.
- Not encapsulated |
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What are the germanic centers of the lymphatic nodules?
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- Lighter staining nuclei of proliferating B lymphocytes and plasma cells.
- Develops when a lymphocyte that has recognized an antigen returns to a nodule and undergoes proliferation. - Macrophages, reticular cells and follicular dendritic cells are present |
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What are the Aggregated lymphatic nodules?
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Tonsils, Peyer’s Patches, and Vermiform appendix
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What are Peyer’s Patches?
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Aggregated lymphatic nodules in ileum containing T and B lymphocytes.
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Where is the palatine tonsil located?
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Located between palatopharyngeal and palatoglossal arches in pharynx; encapsulated
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Where is the pharyngeal tonsil located?
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(adenoids): roof of the pharynx
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Where is the lingual tonsil located?
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base of the tongue
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Lymph drains via _____ lymphatic vessels
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Efferent
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What are the characteristics of lymph nodes?
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- Oval or bean-shaped, 1mm – 2cm.
- Enclosed by capsule (dense irregular CT). - Trabeculae extend from capsule to separate cortical nodules. |
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How are lymph nodes arranged in the body?
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Distributed throughout body in series along lymphatic vessels.
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What is the role of lymph nodes?
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- Involved in body’s defense against microorganisms and spread of tumor cells.
- Lymph derived from tissue fluid is filtered by at least one lymph node before returning to the circulation. |
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What is the lymph flow through a lymph node?
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- Arteries and veins enter at hilum.
- Major capillary beds form in cortex. - Lymph enters node via many afferent vessels. - Lymph exits node via one large efferent vessel at hilum |
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What are the three layers of a lymph node?
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Cortex
Medulla Paracortex (Deep Cortex) |
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What is associated with the Lymph Node cortex?
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- Cortical nodules contain B lymphocytes surrounding a germinal center.
- Dendritic cells localized with T cells (antigen-presenting cells) - Follicular dendritic cells associated with B cells in germinal centers. - Macrophages and plasma cells |
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What is associated with the Lymph Node medulla?
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- Medullary cords separated by sinuses (lined by endothelium).
- B lymphocytes, macrophages, plasma cells, and dendritic cells. - No germinal centers. |
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What is associated with the Lymph Node paracortex (deep cortex)?
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Contain mostly T lymphocytes.
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What supports lymph node parenchyma?
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Reticular fibers
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What are the two routes of lymphocyte entry into the lymph node?
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- Via lymph vessels
- Circulation via high endothelial (post-capillary) venules in deep cortex. |
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The endothelial lining of sinus of the lymph node is incomplete; what does this allow?
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Reticular cell and macrophage processes to form meshwork in sinus.
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What happens as the lymph travels through the cortex of the lymph node?
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As lymph travels through cortex to medulla, antigens and cancer cells are trapped and phagocytized by macrophages (which present to lymphocytes).
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What are HEV's?
What do they do? What is their distribution? |
- High endothelial venules in paracortex (deep cortex)
- Signal lymphocytes to enter lymph node - 90% of lymphocytes enter lymph node via HEVs. - 35% of fluid that exits lymph node is from circulation (HEVs). |
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Why do lymph nodes enlarge?
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Enlarge (swollen glands) due to lymphocyte proliferation in germinal centers.
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What retards flow to enhance filtration in the lymph node?
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Macrophage and reticular cell processes form meshwork
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What is the largest lymphatic organ?
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Spleen
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What is the role and function of the spleen?
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Monitor blood immunologically (filter): removal of senescent RBC’s and macromolecular antigens, phagocytize bacteria and present antigens, generate T and B lymphocytes
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Trabeculae within the spleen contain what?
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Contractile myofibroblasts to help discharge RBCs
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Where is the hilum of the spleen?
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On medial surface for passage of splenic arteries and veins, nerves, and efferent lymphatic vessels.
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What are embedded in the trabeculae of the spleen?
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Arteries and veins
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What are PALS?
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periarteriole lymphatic sheath
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What is the white pulp of the spleen?
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Lymphatic (splenic) nodules are localized expansions of the PALS
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What is the red pulp of the spleen?
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Splenic sinuses filled with blood, separated by splenic cords (reticular cells and fibers, macrophages, lymphocytes, dendritic cells, plasma cells, granulocytes).
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What do Macrophages of the spleen phagocytize?
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Senescent red blood cells
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What is the movement of blood through the spleen?
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splenic artery > trabecular artery > central artery > penicillar arteriole > splenic cords > splenic sinuses > pulp vein > trabecular vein > splenic vein
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What is open circulation of the spleen?
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- open circulation occurs in humans
- penicillar arteries open directly into splenic cords - exposes blood more efficiently to macrophages |
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What is the role of the Thymus?
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- Differentiation and maturation of T-lymphocytes (thymic cell “education”)
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What are the characteristics of the Thymus?
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- Bilobed mass enclosed by capsule.
- In superior mediastinum. - No germinal centers (no antibody production). - Lobules incompletely separated by trabeculea in cortex (with blood vessels, nerves, and efferent lymphatic vessels). - Each lobule composed of cortex and medulla. - Trabecula not in medulla - Lymphatic tissue replaced by adipose tissue at puberty. |
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What do the macrophages of the thymus phagocytize?
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Apoptotic T cells
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What is the distinguishing feature of thymic medulla?
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Thymic (Hassall’s) corpuscles
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What are the characteristics of Thymic (Hassall’s) corpuscles?
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Concentric mass of type VI epithelioreticular cells.
Joined by desmosomes. Contain keratohyaline granules. Secrete compounds that influence T cell differentiation. |
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What are the characteristics of the thymic blood supply?
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- Small arteries enter the medulla from trabecula to form capillary beds in the cortex.
- Blood vessels surrounded by a sheath of connective tissue in the medulla. - Give rise to capillary beds in cortex. |
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What are the characteristics of the Blood-thymus barrier?
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- Developing T-lymphocytes are protected from exposure to bloodborne antigens.
- Prevents autoimmune responses. - Endothelium of capillary wall (with thick basal lamina and occluding junctions) - Macrophages in perivascular CT (phagocytize antigenic molecules) - Type I epithelioreticular cells (basal lamina and occluding junctions) |
