Chapter 20 – The Lymphatic System and Lymphoid Organs & Tissues

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Vocabulary flashcards covering key structures, cells, mechanisms, and clinical terms related to the lymphatic system and lymphoid organs & tissues.

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57 Terms

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Lymph

Protein-containing interstitial fluid that has entered lymphatic vessels.

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Lymphatic Vessels (Lymphatics)

One-way drainage network that returns excess tissue fluid and leaked proteins to the bloodstream.

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Lymphatic Capillaries

Blind-ended microscopic vessels whose overlapping endothelial cells form flaplike minivalves that admit interstitial fluid.

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Minivalves

Overlapping endothelial cell flaps in lymphatic capillaries that open when interstitial pressure rises and close when internal pressure increases.

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Anchoring Filaments

Collagen fibers attaching lymphatic endothelial cells to surrounding tissue, preventing vessel collapse when pressure rises.

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Collecting Lymphatic Vessels

Larger channels that receive lymph from lymphatic capillaries; possess the same three tunics as veins but thinner walls and more valves.

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Lymphatic Trunks

Large vessels formed by the union of collecting lymphatic vessels; drain major body regions (lumbar, intestinal, bronchomediastinal, subclavian, jugular).

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Right Lymphatic Duct

Duct that drains lymph from the right upper limb, right side of head, and right thorax into the venous circulation.

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Thoracic Duct

Largest lymphatic duct; drains lymph from the rest of the body into the venous circulation.

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Cisterna Chyli

Enlarged sac at the origin of the thoracic duct that collects lymph from intestinal and lumbar trunks.

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Lacteals

Specialized lymphatic capillaries in intestinal villi that absorb dietary fats.

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Chyle

Milky, fat-laden lymph carried by lacteals from the small intestine.

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Lymph Transport Mechanisms

Low-pressure propulsion aided by skeletal-muscle pumps, respiratory pressure changes, arterial pulsations, and rhythmic contraction of smooth muscle in lymphatic vessel walls.

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Lymph Nodes

Secondary lymphoid organs that filter lymph and house lymphocytes; bean-shaped, encapsulated structures along lymphatic vessels.

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Afferent Lymphatic Vessels

Vessels carrying lymph into a lymph node on its convex surface.

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Subcapsular Sinus

Large bag-like sinus just beneath the capsule of a lymph node where lymph first enters.

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Medullary Cords

Inward extensions of cortical tissue in a lymph node’s medulla containing B cells, T cells, and plasma cells.

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Hilum

Indented region of an organ (e.g., lymph node, spleen) where blood vessels, nerves, or efferent lymphatics exit.

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Efferent Lymphatic Vessels

Vessels draining lymph from a lymph node at its hilum; fewer than afferent vessels, slowing lymph flow.

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Lymphoid Tissue

Reticular connective tissue that houses lymphocytes and provides surveillance and proliferation sites.

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Diffuse Lymphoid Tissue

Loose arrangement of lymphoid cells and reticular fibers found in almost all body organs and mucous membranes.

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Lymphoid Follicle (Nodule)

Solid, spherical collection of lymphoid cells with a reticular fiber stroma; often contains a germinal center.

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Germinal Center

Light-staining region in a lymphoid follicle where rapidly dividing B cells predominate.

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Primary Lymphoid Organs

Red bone marrow and thymus—sites where B and T lymphocytes mature.

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Secondary Lymphoid Organs

Sites where mature lymphocytes first encounter antigens: lymph nodes, spleen, tonsils, Peyer’s patches, appendix, and other MALT.

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Spleen

Largest lymphoid organ; filters blood, recycles RBC components, stores platelets/monocytes, and provides immune surveillance.

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White Pulp

Lymphocyte-rich regions of the spleen surrounding central arteries; site of immune functions.

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Red Pulp

Spleen tissue where old RBCs and pathogens are destroyed; contains splenic cords and sinusoids.

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Thymus

Primary lymphoid organ in the superior thorax where T lymphocyte precursors mature.

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Thymic Corpuscles (Hassall’s Corpuscles)

Concentric whorls of epithelial cells in the thymic medulla involved in regulatory T cell development.

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Blood-Thymus Barrier

Barrier preventing bloodborne antigens from reaching immature T cells in the thymus.

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MALT (Mucosa-Associated Lymphoid Tissue)

Diffuse collections of lymphoid tissue in mucous membranes that guard body entryways.

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Tonsils

Ring of lymphoid tissue around the pharynx that traps and destroys pathogens entering in food or air.

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Palatine Tonsils

Largest tonsils located at the posterior oral cavity; most often infected.

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Pharyngeal Tonsil (Adenoid)

Tonsil in the posterior wall of the nasopharynx; called adenoid when enlarged.

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Tonsillar Crypts

Epithelium-lined invaginations in tonsils that trap bacteria, promoting immune memory.

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Peyer’s Patches

Large clusters of lymphoid follicles in the distal small intestine wall; monitor intestinal bacteria.

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Appendix (Vermiform Appendix)

Tubular offshoot of the large intestine rich in lymphoid follicles; prevents bacterial breach and generates memory cells.

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T Cells (T Lymphocytes)

Lymphocytes that manage immune responses and can directly attack infected cells.

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B Cells (B Lymphocytes)

Lymphocytes that differentiate into plasma cells to secrete antibodies.

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Plasma Cells

Antibody-producing descendants of activated B cells.

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Macrophages

Phagocytes that engulf pathogens and help activate T cells; reside on lymphoid reticular fibers.

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Dendritic Cells

Antigen-capturing cells that migrate to lymph nodes to activate T cells.

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Reticular Cells

Fibroblast-like cells producing the reticular fiber stroma of lymphoid tissues.

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Lymphangitis

Inflammation of lymphatic vessels causing tender red streaks along their path.

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Lymphedema

Severe localized edema resulting from blocked or removed lymphatic vessels.

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Lymphadenopathy

General term for any disease or enlargement of lymph nodes.

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Buboes

Inflamed, pus-filled lymph nodes overwhelmed by pathogens; characteristic of bubonic plague.

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Elephantiasis (Filariasis)

Massive edema of limbs or scrotum due to lymphatic blockage by parasitic worms.

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Hodgkin’s Lymphoma

Malignancy of lymphoid tissue marked by Reed-Sternberg cells; high cure rate with therapy.

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Non-Hodgkin’s Lymphoma

All other lymphoid tissue cancers; includes fast-growing and slow-growing forms.

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Sentinel Node

First lymph node to receive drainage from a cancerous area; tested to assess metastasis.

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Splenomegaly

Enlargement of the spleen due to infectious microbes or blood disorders.

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Tonsillitis

Inflammation of the tonsils, usually bacterial, causing sore, swollen tonsils.

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Vasa Vasorum

Small blood vessels supplying the walls of larger lymphatic or blood vessels.

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Immune Response

Coordinated defensive reaction of immune cells to antigens.

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Antigen

Any substance—bacterial toxin, virus, mismatched RBC, cancer cell—that provokes an immune response.