Basics of the Lymphatic System – Vocabulary Review

A comprehensive set of vocabulary flashcards covering structures, cells, and physiological concepts related to the lymphatic system, its organs, and its role in immunity, fluid balance, and digestion.

Lymphatic System

Network of vessels, tissues, and organs that returns excess interstitial fluid to the bloodstream and supports immune and digestive functions.

Interstitial Fluid

Fluid that bathes body cells; becomes lymph when it enters lymphatic capillaries.

Lymph

Name given to interstitial fluid once it has entered lymphatic vessels.

Lymphatic Capillaries

Blind-ended microscopic vessels that collect excess interstitial fluid to form lymph.

Collecting (Lymphatic) Vessels

Vessels that receive lymph from capillaries and contain valves like veins to prevent backflow.

Lymphatic Trunks

Large lymph vessels formed by merged collecting vessels; drain major body regions.

Collecting Ducts

Largest lymphatic vessels (right lymphatic duct & thoracic duct) that return lymph to subclavian veins.

Right Lymphatic Duct

Duct that drains lymph from the right upper limb, right thorax, and right side of head and neck into the right subclavian vein.

Thoracic Duct

Longer duct that drains lymph from the rest of the body into the left subclavian vein.

Subclavian Veins

Pair of veins that receive lymph from the collecting ducts and return it to the bloodstream.

Primary Lymphatic Organs

Sites where lymphocytes are produced and/or mature—red bone marrow and thymus.

Secondary Lymphatic Organs

Organs where lymphocytes are housed and extracellular fluids are filtered—lymph nodes, spleen, and MALT.

Red Bone Marrow

Primary lymphatic organ that produces all formed elements, including B and T lymphocytes.

Thymus

Primary organ in the mediastinum where T lymphocytes mature under the influence of thymosins.

Lymphocytes

Family of white blood cells (B cells & T cells) central to adaptive immunity.

B Cells

Lymphocytes that mature in bone marrow and can differentiate into plasma cells producing antibodies.

T Cells

Lymphocytes produced in bone marrow that mature in thymus; responsible for cell-mediated immunity.

Lymph Nodes

Small, encapsulated secondary organs that filter lymph and house large numbers of lymphocytes.

Spleen

Encapsulated organ in upper left abdomen that filters blood, removes old erythrocytes, and stores immune cells.

Mucosa-Associated Lymphoid Tissue (MALT)

Unencapsulated clusters of lymphatic nodules embedded in mucosal connective tissues of organs (tonsils, appendix, Peyer’s patches, etc.).

Diffuse Lymphatic Tissue

General term for loose aggregations of lymphocytes within organs; densest in lymph node cortex.

Lymphatic Nodule

Spherical cluster of densely packed lymphocytes; may contain a germinal center for lymphocyte production.

Germinal Center

Central region of a lymphatic nodule where active lymphocyte proliferation occurs.

Afferent Lymphatic Vessel

Vessel that carries lymph toward a lymph node for filtration.

Efferent Lymphatic Vessel

Vessel that carries filtered lymph away from a lymph node.

Capsule (of Lymph Node/Spleen)

Dense irregular collagenous connective tissue covering an organ.

Trabeculae

Connective-tissue extensions of a capsule that partition an organ into lobules.

Reticular Connective Tissue

Network of reticular fibers inside lymphatic organs that supports and filters cells and particles.

Hydrostatic Pressure Gradient

Difference in fluid pressure that drives movement of water into lymphatic capillaries.

Oncotic Pressure Gradient

Difference in protein-generated osmotic pressure; minimal role in normal lymph formation due to low tissue protein.

Sinusoidal Capillaries

Highly permeable capillaries in spleen that allow blood cells to exit for filtration.

Red Pulp (Spleen)

Region rich in erythrocytes and macrophages; removes aged red blood cells and stores blood.

White Pulp (Spleen)

Region surrounding central arteries rich in lymphocytes; site of immune surveillance of blood.

Peyer’s Patches

Large aggregates of MALT in the ileum of the small intestine.

Tonsils

MALT structures (pharyngeal, palatine, lingual) forming a ring of immune tissue around the pharynx.

Pharyngeal Tonsil

Single tonsil in the nasopharynx; also called adenoid.

Palatine Tonsils

Pair of tonsils at posterior oral cavity near soft palate.

Lingual Tonsils

Pair of tonsils at the posterior base of the tongue.

Vermiform Appendix

MALT-rich, worm-shaped extension of the large intestine that serves as an immune checkpoint.

Skeletal Muscle Pump

Rhythmic contraction of skeletal muscles that helps propel lymph through vessels.

Respiratory Pump

Changes in thoracic pressure during breathing that assist lymphatic return.

Perivascular Smooth Muscle Cells

Smooth muscle in lymphatic vessel walls that contract to aid lymph flow; possess α-adrenergic receptors.

Alpha-Adrenergic Receptors

Receptors on lymphatic smooth muscle that cause vasoconstriction when stimulated by sympathetic nerves.

Immune System Checkpoint

Site (e.g., lymph node, spleen, MALT) where immune cells monitor body fluids for pathogens.

Natural Flora

Beneficial microorganisms normally residing in the large intestine; harmful if they escape the gut.

Macrophages

Large phagocytic cells in spleen and other tissues that engulf pathogens and debris.

Blood Reservoir (Spleen)

Function in which the spleen temporarily stores healthy erythrocytes and platelets.

Thymosins

Hormone group secreted by thymic epithelial cells that direct T-cell maturation.

Lobule

Small compartment within an organ, formed by trabeculae (e.g., in thymus, spleen, lymph node).

Apoptosis

Programmed cell death; mechanism eliminating self-reactive T cells during thymic maturation.

Autoimmune Disease

Condition arising when immune cells attack the body’s own tissues, often due to faulty self-tolerance.

Alpha (α) Adrenergic Vasoconstriction

Sympathetic response that narrows lymphatic vessels to promote forward lymph flow.

Lacteal

Specialized lymphatic capillary in the small-intestinal villus that absorbs dietary fats.

Collecting Ducts (Right & Thoracic)

Terminal lymphatic vessels that empty lymph into the venous circulation.

Cortex (of Lymph Node)

Peripheral region of a lymph node containing dense aggregates of lymphocytes and nodules.

Medulla (of Lymph Node)

Central region of a lymph node with fewer lymphocytes and medullary cords.

Checkpoint System (Thymus)

Process ensuring only T cells that do not react to self-antigens mature and exit into circulation.