Anatomy and Physiology: The Lymphatic System

Vocabulary flashcards covering the major components, functions, capillaries, and collecting vessels of the lymphatic system.

Lymph

Excess tissue fluid carried by lymphatic vessels.

Edema

Swelling of the tissues, which is prevented by the lymphatic system transporting escaped fluids back to the blood.

Lacteals

Specialized lymphatic structures through which lipid absorption occurs.

Chyle

Milky white lymph fluid passing through lacteals, having a high fat content.

Lymphatic Capillaries

Close-ended vessels composed of simple squamous epithelium with overlapping walls forming flap-like mini-valves and anchored to connective tissue by filaments, lacking a basement membrane.

Mini-valves

Flap-like structures formed by the overlapping walls of lymphatic capillaries that close when internal pressure is higher, forcing fluid forward along the vessel.

Superficial Group of Lymphatic Capillaries

A group of capillaries that collects excess interstitial fluids from the dermis and subcutaneous tissue.

Deep Group of Lymphatic Capillaries

A group of capillaries that collects excess fluid from muscle, the viscera, and other deep structures.

Lymphatic Collecting Vessels

Larger vessels resembling small veins that collect lymph from capillaries, carry lymph to and away from lymph nodes, and return fluid to circulatory veins near the heart.

One-way Valves (Lymphatic Vessels)

Structures that give small lymphatic vessels a beaded appearance and prevent the backward movement of lymph when the vessel is compressed.

Compression Factors of Lymphatic Vessels

Skeletal muscle contractions during activity, periodic contractions of smooth muscle in vessel walls, and pressure changes in the thorax during breathing.

Right Lymphatic Duct

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

Thoracic Duct

Major lymphatic vessel that drains lymph from the lower body, left upper limb, and left side of the head and thorax, emptying into the left subclavian vein.

Harmful Materials Entering Lymph Vessels

Foreign pathogens and cellular waste carried in lymph, specifically bacteria, viruses, cancer cells, and cell debris.

Lymph Flow Pathway

The sequential pathway of fluid movement: blood capillaries, interstitial fluid, lymph capillaries, collecting vessels, lymph nodes, lymph trunks, lymph ducts, and subclavian veins.

Reticular Network in Lymphatic Tissue

Very fine reticular fibers forming an interlaced meshwork that suspends and houses lymphocytes and macrophages.

Lymph Nodes

Small rounded structures distributed along vessels that filter lymph before it enters the blood, varying in size from a small seed to a shelled almond.

Superficial Lymph Node Aggregations

Three major surface clusters located on each side of the body: cervical nodes (neck), axillary nodes (armpit), and inguinal nodes (groin).

Spleen

Lymphoid organ located in the left superior corner of the abdominal cavity that filters blood, destroys worn-out erythrocytes, and serves as a blood reservoir.

Trabeculae (Spleen)

Connective tissue extensions projecting from the capsule that divide the interior into small, interconnected compartments.

White Pulp

Splenic lymphatic tissue surrounding the internal arteries where lymphocytes mount immune responses against pathogens.

Red Pulp

Venous-associated splenic tissue consisting of a macrophage-rich fibrous meshwork and enlarged capillaries through which blood traverses before exiting.

Blood Pathway Exiting the Spleen

Passes through the red pulp before entering the splenic veins.

Functions of the Spleen

Filters blood, destroys worn-out blood cells, activates lymphocytes, produces fetal blood cells, and acts as a blood reservoir during hypovolemia.

Thymus

Roughly triangular, bilobed gland situated in the superior mediastinum that is most active during early stages of life.

Trabeculae (Thymus)

Connective tissue extensions radiating inward from the capsule that divide each thymic lobe into distinct lobules.

Thymic Cortex

Darkly staining outer region beneath the capsule that is densely populated with maturing lymphocytes.

Thymic Medulla

Lighter-staining inner core containing fewer lymphocytes where mature T cells collect prior to entering the bloodstream.

Thymosin

Hormone secreted by the thymus that promotes the development and functional maturation of T lymphocytes.

Functions of the Thymus

Directs T lymphocyte maturation, synthesizes thymosin, and releases functional immune cells into the circulation to establish defense against pathogens.

Tonsils

Small masses of lymphoid tissue located in the mouth and pharynx that protect against pathogens entering through the mouth and nose.

Palatine Tonsils

Paired lymphoid aggregations located on each side of the posterior opening of the oral cavity.

Pharyngeal Tonsil

A solitary lymphoid mass located near the internal opening of the nasal cavity.

Adenoids

The clinical term for an enlarged pharyngeal lymphoid mass that can obstruct and interfere with normal breathing.

Lingual Tonsil

Lymphoid tissue situated on the posterior surface of the tongue.

Mucosa-Associated Lymphatic Tissue (MALT)

A diffuse system of lymphoid tissue aggregations, including tonsils and intestinal clusters, located within mucous membranes to intercept pathogens.

Peyer's Patches

Lymphoid tissue clusters located in the wall of the ileum that capture and destroy bacteria in the small intestine.

Primary Site of Lymphocyte Origin

Red bone marrow, where hematopoietic stem cells generate both pre-B and pre-T immune cells.

Maturation Site of B Cells

Red bone marrow, where immature precursor cells develop into mature immunocompetent cells before entering the blood.

Maturation Site of T Cells

The thymus, where immature precursor cells migrate from the bone marrow, enlarge, and mature before entering the bloodstream.

Lymphocyte Proliferation Response

The immune process where B and T cells in lymphatic tissues respond to infection by dividing, increasing in number, and circulating via the blood to target pathogens.