Chapter 21: The Lymphoid and Immune Systems

Comprehensive vocabulary flashcards covering the components, functions, and disorders of the lymphoid and immune systems as described in Kenneth S. Saladin's Anatomy & Physiology, 10th Edition.

Microbiome

The microorganisms that reside on and in the human body, many of which are beneficial while some have the potential to be harmful.

Pathogen

Any organism that causes disease, such as E. coli.

Immune system

A cell population that inhabits all organs and defends the body from agents of disease, rather than a single organ system.

Lymphoid (lymphatic) system

A network of organs and vein-like vessels that recover fluid, inspect it for pathogens, activate immune responses, and return the fluid to the bloodstream.

Cyclospora cayatanensis

A parasite endemic to tropical and subtropical regions that causes Cyclosporiasis, characterized by explosive diarrhea, bloating, and fever.

Lymphedema

Swelling caused by an interference or blockage in lymphatic drainage.

Immune surveillance

A function of the lymphoid system where fluid picks up foreign cells and chemicals from tissues and passes through lymph nodes where immune cells stand guard.

Lacteals

Specialized lymphatic vessels in the small intestine that absorb dietary lipids not absorbed by blood capillaries.

Lymph

A clear, colorless fluid, similar to plasma but low in protein, that originates as tissue fluid taken up by lymphatic vessels.

Right lymphatic duct

A collecting duct that receives lymph from the right arm, right side of the head, and thorax, and empties into the right subclavian vein.

Thoracic duct

A larger, longer collecting duct beginning at the cisterna chyli that receives lymph from below the diaphragm, left arm, and left side of the head, neck, and thorax.

Neutrophils

Antibacterial leukocytes found in the lymphoid system.

Natural killer (NK) cells

Lymphocytes that patrol the body to attack and destroy infected host cells, transplanted cells, and cancerous cells.

T lymphocytes (T cells)

Lymphocytes that mature in the thymus and kill infected or cancerous cells or recruit other lymphocytes.

B lymphocytes (B cells)

Lymphocytes that, when activated, differentiate into plasma cells to produce antibodies for specific agents.

Macrophages

Large phagocytic cells that act as antigen-presenting cells (APCs) by displaying antigens on their surface to alert other immune cells.

Dendritic cells

Antigen-presenting cells (APCs) found in the skin, mucous membranes, and lymphoid organs.

Primary lymphoid organs

Organs where T and B cells become immunocompetent, including red bone marrow and the thymus.

Secondary lymphoid organs

Locations where immunocompetent cells migrate and populate, including lymph nodes, tonsils, and the spleen.

Spleen

The body’s largest lymphoid organ; it serves as an 'erythrocyte graveyard' for old RBCs and monitors blood for foreign antigens.

Lymphadenitis

A swollen, painful lymph node that is responding to a foreign antigen.

Metastasis

A process where cancerous cells break free from a primary tumor, travel through the body (often via lymphatic vessels), and establish new tumors.

Innate immunity

Defenses present from birth that provide broad, nonspecific protection at the point of invasion and lack immune memory.

Adaptive immunity

The third line of defense characterized by systemic effects, specificity to individual pathogens, and memory.

Acid mantle

A thin film of lactic and fatty acids from sweat and sebum on the skin that inhibits bacterial growth.

Lysozyme

An enzyme found in mucous membranes that destroys bacterial cell walls.

Interferons

Proteins secreted by virally infected cells that serve as an 'alarm' to stimulate neighboring cells to synthesize antiviral proteins.

Complement system

A group of $30$ or more globular proteins that contribute to inflammation, immune clearance, phagocytosis, and cytolysis.

Perforins

Proteins released by NK cells that polymerize to form a ring and create a hole in the plasma membrane of an enemy cell.

Granzymes

Protein-degrading enzymes secreted by NK cells that enter through perforin holes to induce apoptosis.

Pyrexia

An abnormal elevation of body temperature, commonly known as fever.

Exogenous pyrogens

Fever-producing agents originating outside the body, such as glycolipids on bacterial and viral surfaces.

Stages of fever

The sequence of abnormal body temperature elevation consisting of onset, stadium, and defervescence.

Cytokines

Small proteins like interferons and interleukins that function in chemical communication between cells.

Cellular (cell-mediated) immunity

A form of adaptive immunity where T lymphocytes directly attack and destroy foreign or diseased host cells.

Humoral (antibody-mediated) immunity

A form of adaptive immunity mediated by antibodies that tag extracellular pathogens for destruction.

Natural active immunity

The production of one’s own antibodies or T cells as a result of natural exposure to an antigen.

Artificial active immunity

The production of one’s own antibodies or T cells as a result of vaccination.

Natural passive immunity

Temporary immunity resulting from antibodies produced by another person, such as a fetus acquiring antibodies through the placenta.

Antigen (Ag)

Any molecule with a large molecular weight (over $10,000$ amu) and structural complexity that can bind an antibody and distinguish self from nonself.

Antibody monomer

The structural unit of an antibody composed of four polypeptide chains (two heavy and two light) linked by disulfide bonds.

IgG

The predominant monomer antibody in the secondary immune response that constitutes $80\%$ of circulating antibodies.

IgM

A pentamer antibody in plasma and lymph that is predominant in the primary immune response and has strong agglutinating abilities.

MHC proteins

Proteins encoded by the major histocompatibility complex that act as structurally unique cell 'identification tags' for an individual.

Cytotoxic T cells ($T_{C}$)

The class of T cells that carry out the actual attack and destruction of diseased or foreign cells.

T cell recall response

The rapid immune response occurring during re-exposure to a pathogen due to long-lived and numerous memory T cells.

Agglutination

An antibody action where enemy cells are clumped together to immobilize them for clearance by phagocytes.

Hypersensitivity

An excessive immune reaction against antigens that are normally tolerated, including allergies, alloimmunity, and autoimmunity.

Severe combined immunodeficiency disease (SCID)

A hereditary lack of both T and B cells, leaving individuals vulnerable to opportunistic infections.

Acquired immunodeficiency syndrome (AIDS)

A nonhereditary disease caused by HIV where helper T cell counts drop below $200\,cells/µL$, crippling the immune response.