The Lymphatic System and Immunity

Comprehensive vocabulary flashcards covering the anatomy, physiology, and pathology of the lymphatic system, innate defenses, and adaptive immunity from Chapter 22.

Lymph

A clear, moving extracellular fluid component of the circulatory system that is collected from excess interstitial fluid by lymphatic vessels and returned to the venous bloodstream.

functions of the lymphatic system

maintenance of fluid balance inside the body and support to body’s immunity. part of immune system, transports tissue fluids, proteins, fats, etc to general circulation.

Components of lymphatic system

Vessels

Cells

Tissues

Organs

Vessels

transport lymph from tissues back to the bloodstream.

Cells

immune cells, especially lymphocytes and phagocytic cells.

Tissues

specialized lymphatic connective tissue containing many immune cells.

Organs

structures that house and support lymphatic and immune cells, such as lymph nodes, spleen, thymus, and tonsils.

Primary Lymphoid Organs

Organs that provide an environment for stem cells to divide, develop, and mature into immunocompetent lymphocytes; specifically the red bone marrow (where B cells mature) and the thymus (where T cells mature).

Red bone marrow

• produces lymphocytes; B cells mature

Thymus

T cells mature here

Secondary Lymphoid Organs (SLOs)

Sites where mature lymphocytes reside, encounter antigens, and initiate immune responses; includes lymph nodes, the spleen, tonsils, adenoids, and mucosa-associated lymphoid tissue (MALT) such as Peyer's patches and the appendix.

Right Lymphatic Duct

A major lymphatic duct that drains lymph from the right upper quadrant of the body (right side of the head and neck, right thorax, and right upper limb) and empties into the venous angle near the junction of the right internal jugular and right subclavian veins.

Thoracic Duct

The main lymphatic vessel that drains lymph from the entire lower body and the left upper body, emptying into the venous system at the left venous angle near the junction of the left internal jugular and left subclavian veins.

Lymphatic Capillaries

Microscopic, blind-ended vessels situated among blood capillaries with loosely overlapping endothelial cells anchored by filaments that form one-way flap valves to allow fluid entry when interstitial fluid pressure rises.

Lymphatic vessels

Lymph nodes are along lymphatic vessels,

Functions are

• Return excess interstitial fluid, proteins, and large particles to the bloodstream.

• Transport immune cells and lymph through lymph nodes.

• Lacteals in the small intestine absorb dietary fats and fat-soluble vitamins.

Lacteals

Specialized lymphatic capillaries located in the small intestine that absorb dietary fats and fat-soluble vitamins into the lymphatic circulation.

Lymphokinesis

The flow or movement of lymph through lymphatic channels, driven by pressure gradients generated by breathing movements and skeletal muscle contractions, and guided by numerous one-way valves.

Lymph Nodes

Small, oval or bean-shaped encapsulated lymphoid organs situated along lymphatic vessels where afferent lymph passes through sinus networks lined with macrophages and lymphocytes before exiting through an efferent vessel.

Functions of lymph nodes

Filtration and defense of pathogens

Lymphatic activation of b and T cells

Palatine Tonsils

Paired lymphoid nodules located on each lateral side of the throat (fauces) that help intercept and fight pathogens entering via the oral cavity.

Tonsil

Palatine

Pharyngeal lingual

Pharyngeal Tonsil (Adenoid)

A single lymphoid mass located in the posterior wall of the nasopharynx that protects against pathogens entering through the nasal passages.

Lingual Tonsils

A collection of lymphoid tissue situated at the base of the tongue that provides defense against ingested or inhaled pathogens.

Thymus

A primary lymphoid organ located in the anterior superior mediastinum behind the sternum that secretes thymic hormones like thymosin to facilitate T lymphocyte maturation; it is large in children and undergoes fatty atrophy after puberty.

White Pulp (of Spleen)

Splenic lymphatic tissue composed mostly of lymphocytes arranged around central branches of the splenic artery, serving immune defense against blood-borne antigens.

Red Pulp (of Spleen)

Splenic tissue composed of blood-filled venous sinusoids and splenic cords packed with macrophages and lymphocytes, serving to filter blood and remove damaged or aged erythrocytes and platelets.

Functions of spleen

Immune defense

Blood filtration

Removes and breaks down aged or damaged red blood cells and palate lets

Stores

Hematopoisis

Lymphoma

A cancer of lymphocytes that usually begins in lymph nodes or other
lymphatic tissues. Lymph nodes may normally enlarge during infection because
immune cells are actively multiplying; this is different from lymphoma.

Enlarged lymph nodes

Lymph vessels do not “widen into” lymph nodes. Lymph
nodes are separate structures located along lymphatic vessels and may become
enlarged and tender during infection.

Lymphedema

Abnormal tissue swelling caused by the accumulation of interstitial fluid when lymphatic vessels or nodes are obstructed, damaged, or surgically excised.

Elephantiasis

A severe, chronic form of lymphedema marked by pronounced tissue hypertrophy and skin thickening, frequently caused by parasitic worm obstruction of lymphatic vessels.

Innate Immunity

The rapid, nonspecific defense system present at birth that recognizes broad pathogen-associated molecular patterns without generating immunological memory.

Adaptive Immunity

A specific, antigen-targeted defense mechanism mediated by B and T lymphocytes that develops slowly upon initial exposure but produces long-lasting immunological memory.

Immunogenic

– capable of triggering an immune response.

Self Markers

Surface molecules on host cells, principally major histocompatibility complex (MHC) proteins, that identify body cells as self to prevent immune attack.

Non-Self Markers

Foreign antigens found on pathogens, transplanted tissues, or tumor cells that trigger detection and destruction by the immune system.

Self-Tolerance

The ability of the immune system to recognize and spare healthy host cells while selectively mounting responses against foreign or abnormal targets.

Pyrogens

Substances released by infectious microbes or immune leukocytes that act on the hypothalamus to elevate the body's thermoregulatory set point and induce fever.

Haptens

Small molecules that lack immunogenicity on their own but can stimulate an immune reaction when bound to a larger carrier protein.

Immunocompetence

The acquired ability of mature B and T lymphocytes to bind to a specific foreign antigen and execute an immune response.

Diapedesis

The migration of circulating leukocytes squeezing through intact endothelial capillary walls into surrounding injured or infected tissues.

Innate immunity first line defenses

The first line of defense consists mainly of mechanical and chemical
barriers that prevent pathogens from entering the body.

Innate Immunity: Second Line of Defense —
Inflammation

Inflammation is part of the second
line of innate defense. Tissue injury
or infection triggers an
inflammatory response that helps
contain the damage, remove
harmful agents, and begin tissue
repair.
Classic signs of inflammation are
redness, heat, swelling, and pain

Antigen-Presenting Cells (APCs)

Specialized immune cells—predominantly dendritic cells, macrophages, and B lymphocytes—that process foreign antigens and present peptide fragments bound to MHC proteins on their surface to activate T cells.

Natural Killer (NK) Cells

Innate granular lymphocytes (constituting approximately $5\text{--}20\%$ of circulating lymphocytes) that induce apoptosis in virus-infected and cancerous cells lacking MHC class I molecules using perforin and granzymes.

Interferons (IFNs)

Cytokines that combat viral infections and modulate immunity: $\text{IFN-}\alpha$ and $\text{IFN-}\beta$ inhibit viral replication in nearby cells, whereas $\text{IFN-}\gamma$ is produced by NK and T cells to activate macrophages.

Plasma Cells

Terminally differentiated effector cells derived from activated B lymphocytes that synthesize and secrete large volumes of specific antibodies into bodily fluids.

Antibody (Immunoglobulin)

A Y-shaped protein consisting of two identical heavy chains and two identical light chains joined by disulfide bonds, equipped with two identical antigen-binding sites in its variable regions.

Immunoglobulin M (IgM)

The initial antibody class secreted during the primary immune response; circulates primarily as a pentamer assembled with a joining (J) chain.

Immunoglobulin G (IgG)

The most abundant antibody class in circulation (accounting for roughly $75\%$ of serum antibodies); mediates the secondary immune response and can cross the placenta.

Immunoglobulin A (IgA)

An antibody class found predominantly in mucous membranes and external secretions such as saliva, tears, and breast milk, providing mucosal immunity.

Immunoglobulin E (IgE)

An antibody class that binds to mast cells and basophils, mediating allergic reactions and participating in defense against parasitic worms.

Immunoglobulin D (IgD)

An antibody class found almost exclusively on the surface of naïve B cells, where it functions as an antigen receptor involved in B cell activation.

Epitope

The specific chemical subunit or determinant on an antigen molecule that fits into and binds to the antigen-binding site of an antibody or T-cell receptor.

Opsonization

The process by which antibodies or complement proteins ($C3b$) coat a pathogen, making it readily recognizable and easily engulfed by phagocytes via Fc or complement receptors.

Complement System

A family of plasma proteins produced mostly by the liver that circulate in inactive forms and participate in innate defense through inflammation, opsonization, and cytolysis via the membrane attack complex (MAC).

Classical Pathway (Complement)

The complement pathway triggered when the $C1$ complex ($C1q, C1r, C1s$) binds to antibodies (IgG or IgM) that are attached to antigens on a microbial surface.

Alternative Pathway (Complement)

The complement cascade pathway that is triggered directly on microbial surfaces by surface molecules without requiring antibodies, leading to $C3$ cleavage.

Lectin Pathway (Complement)

The complement pathway activated when mannose-binding lectin (MBL) recognizes and binds to specific carbohydrates (such as mannose) on the surfaces of pathogens.

Secondary Immune Response

The accelerated, robust, and sustained antibody response (primarily IgG) mounted by memory B and T cells upon re-encountering a previously recognized antigen.

Clonal Selection Theory

The mechanism whereby a specific antigen binds only to a lymphocyte clone carrying a complementary receptor, selecting and stimulating that cell to undergo clonal expansion into effector and memory cells.

MHC Class I

Cell-surface proteins expressed on nearly all nucleated body cells that present endogenous, intracellular antigens to $\text{CD8}^+$ cytotoxic T cells.

MHC Class II

Cell-surface proteins expressed specifically on professional antigen-presenting cells (dendritic cells, macrophages, B cells) that present exogenous, processed peptide antigens to $\text{CD4}^+$ helper T cells.

Helper T Cells ($\text{CD4}^+$)

Effector T lymphocytes that recognize antigens displayed on MHC II and secrete cytokines to activate B cells, cytotoxic T cells, and macrophages.

Cytotoxic T Cells ($\text{CD8}^+$)

Effector T lymphocytes that recognize peptide antigens presented on MHC I and destroy infected, foreign, or cancerous cells by releasing perforin and granzymes to induce apoptosis.

Regulatory T Cells (Treg)

A subset of T lymphocytes (formerly known as suppressor T cells) that dampen immune reactions and preserve self-tolerance to prevent autoimmune tissue destruction.

Naturally Acquired Active Immunity

Long-lasting protection resulting from natural infection and exposure to a live pathogen, stimulating the host's own immune system to generate antibodies and memory cells.

Artificially Acquired Active Immunity

Long-lasting protection generated via vaccination (immunization), stimulating the body's immune cells to produce specific antibodies and memory cells without causing full clinical illness.

Naturally Acquired Passive Immunity

Immediate but short-lived protection conferred by the natural transfer of maternal antibodies to a fetus via the placenta or to a nursing infant via breast milk, without generating host memory cells.

Artificially Acquired Passive Immunity

Immediate, temporary protection provided by the clinical administration of preformed antibodies via injection or intravenous infusion.

Anaphylaxis

An acute, systemic hypersensitivity reaction triggered by IgE-mediated release of histamine from mast cells, causing severe broncho-constriction, impaired breathing, vasodilation, and gastrointestinal symptoms.

Systemic Lupus Erythematosus (SLE)

A chronic autoimmune disease in which the immune system produces autoantibodies against host tissues, causing inflammation in the skin, joints, kidneys, heart, and lungs, commonly manifesting as a butterfly-shaped rash across the face.

Erythroblastosis Fetalis

Hemolytic disease of the newborn caused when maternal anti-Rh IgG antibodies in an $\text{Rh}^-$ mother cross the placenta and lyse fetal $\text{Rh}^+$ red blood cells, causing fetal anemia and jaundice.

Autograft

A tissue graft transplanted from one anatomic location to another within the same individual.

Isograft

A tissue transplant transferred between genetically identical individuals, such as identical twins.

Allograft

A tissue transplant transferred between genetically non-identical individuals belonging to the same species.

Xenograft

A tissue graft transferred between individuals belonging to different species, such as animal tissue implanted into a human.