Chapter 20 – The Lymphatic System and Lymphoid Organs & Tissues

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

Lymph

Protein-containing interstitial fluid that has entered lymphatic vessels.

Lymphatic Vessels (Lymphatics)

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

Lymphatic Capillaries

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

Minivalves

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

Anchoring Filaments

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

Collecting Lymphatic Vessels

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

Lymphatic Trunks

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

Right Lymphatic Duct

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

Thoracic Duct

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

Cisterna Chyli

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

Lacteals

Specialized lymphatic capillaries in intestinal villi that absorb dietary fats.

Chyle

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

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.

Lymph Nodes

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

Afferent Lymphatic Vessels

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

Subcapsular Sinus

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

Medullary Cords

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

Hilum

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

Efferent Lymphatic Vessels

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

Lymphoid Tissue

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

Diffuse Lymphoid Tissue

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

Lymphoid Follicle (Nodule)

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

Germinal Center

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

Primary Lymphoid Organs

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

Secondary Lymphoid Organs

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

Spleen

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

White Pulp

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

Red Pulp

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

Thymus

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

Thymic Corpuscles (Hassall’s Corpuscles)

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

Blood-Thymus Barrier

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

MALT (Mucosa-Associated Lymphoid Tissue)

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

Tonsils

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

Palatine Tonsils

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

Pharyngeal Tonsil (Adenoid)

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

Tonsillar Crypts

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

Peyer’s Patches

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

Appendix (Vermiform Appendix)

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

T Cells (T Lymphocytes)

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

B Cells (B Lymphocytes)

Lymphocytes that differentiate into plasma cells to secrete antibodies.

Plasma Cells

Antibody-producing descendants of activated B cells.

Macrophages

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

Dendritic Cells

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

Reticular Cells

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

Lymphangitis

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

Lymphedema

Severe localized edema resulting from blocked or removed lymphatic vessels.

Lymphadenopathy

General term for any disease or enlargement of lymph nodes.

Buboes

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

Elephantiasis (Filariasis)

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

Hodgkin’s Lymphoma

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

Non-Hodgkin’s Lymphoma

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

Sentinel Node

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

Splenomegaly

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

Tonsillitis

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

Vasa Vasorum

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

Immune Response

Coordinated defensive reaction of immune cells to antigens.

Antigen

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