Immunity – Innate Host Defenses

Vocabulary flashcards covering innate host defenses: barriers, cells, processes, chemical mediators, and antimicrobial substances.

Immunity

The ability of an organism to ward off disease and infection.

Susceptibility

A lack of resistance to disease; the opposite of immunity.

Innate Immunity

Rapid, inborn defenses that protect against any pathogen without specific memory.

Adaptive Immunity

Slower, learned resistance that targets specific pathogens and develops memory.

Skin (Epidermis)

Outer layer of tightly packed epithelial cells containing keratin, forming a dry, shedding barrier to microbes.

Dermis

Inner connective-tissue layer of skin that supports the epidermis.

Keratin

Protective, water-resistant protein in epidermal cells that inhibits microbial entry.

Mucous Membranes

Epithelial linings of GI, respiratory, and genitourinary tracts that secrete mucus to trap microbes.

Mucus

Viscous glycoprotein secretion that traps microbes and prevents tract desiccation.

Lacrimal Apparatus

Tear-producing and drainage system that washes microbes from the eye.

Ciliary Escalator

Coordinated beating of cilia that moves mucus-trapped microbes away from the lungs.

Sebum

Oily skin secretion forming an acidic protective film (pH 3-5) that inhibits microbial growth.

Lysozyme

Enzyme in tears, saliva, perspiration, and urine that destroys bacterial cell walls.

Gastric Juice

Highly acidic stomach secretion (pH 1.2-3.0) that destroys most ingested microbes and toxins.

Leukocyte

General term for white blood cells involved in body defenses.

Neutrophil

Granulocytic WBC that is highly phagocytic and first to respond during infection.

Basophil

Granulocyte that releases histamine and participates in allergic responses.

Eosinophil

Granulocyte that is mildly phagocytic and toxic to parasites and helminths.

Monocyte

Circulating agranulocyte that matures into a macrophage in tissues.

Macrophage

Large phagocytic cell derived from monocytes; may be fixed or wandering.

Dendritic Cell

Phagocytic antigen-presenting cell found in skin, mucosa, and thymus.

Lymphocyte

Agranulocytic WBC group that includes T cells, B cells, and Natural Killer cells.

T Cell

Lymphocyte that mediates cellular immunity and orchestrates adaptive responses.

B Cell

Lymphocyte that differentiates into plasma cells to produce antibodies (humoral immunity).

Natural Killer (NK) Cell

Lymphocyte that kills virus-infected or tumor cells by releasing perforin and granzymes.

Hematopoiesis

Formation of blood cellular elements in red bone marrow from stem cells.

Phagocyte

Cell that ingests and destroys microbes or particles via phagocytosis.

Phagocytosis

The ingestion of microbes or particles by a cell, involving chemotaxis, adherence, ingestion, and digestion.

Opsonization

Coating of a microbe with serum proteins to enhance phagocyte attachment and ingestion.

Chemotaxis

Movement of phagocytes toward chemical signals released by microbes or damaged cells.

Phagolysosome

Fusion of a phagosome with a lysosome where ingested microbes are digested.

Inflammation

Local defensive response characterized by pain, redness, heat, swelling, and sometimes immobility.

Histamine

Vasoactive mediator from mast cells/basophils causing vasodilation and increased permeability.

Kinins

Plasma peptides that attract neutrophils (chemotaxis) and augment vasodilation.

Prostaglandins

Mediators from damaged cells that intensify histamine/kinin effects and ease phagocyte passage.

Leukotrienes

Mediators from mast cells/basophils that increase vessel permeability and help phagocyte attachment.

Margination

Process where phagocytes stick to blood vessel endothelium at the site of inflammation.

Diapedesis

Migration of phagocytes through endothelial gaps to reach infected tissue.

Fever

Abnormally high body temperature triggered by cytokine-induced hypothalamic reset.

Cytokine

Small protein messenger released by cells that regulates immune responses.

Complement System

Serum protein cascade (C1–C9) that enhances immunity via cytolysis, opsonization, and inflammation.

Membrane Attack Complex (MAC)

Ring of complement proteins that forms pores in microbial membranes, causing cytolysis.

Classical Pathway

Complement activation route triggered by antibody–antigen complexes.

Alternative Pathway

Complement activation route initiated directly by microbial surface molecules.

Lectin Pathway

Complement activation route started by mannose-binding lectin attaching to pathogen surfaces.

Interferons (IFNs)

Host cytokines that inhibit viral replication and activate phagocytes.

Iron-Binding Proteins

Molecules (e.g., transferrin, lactoferrin) that sequester iron to limit bacterial growth.

Antimicrobial Peptides (AMPs)

Short peptides that inhibit cell wall synthesis, disrupt membranes, and destroy microbes.

Genetic Resistance

Inherited traits (e.g., sickle cell trait) that confer selective protection against specific pathogens.

First Line of Defense

Physical and chemical barriers such as skin, mucous membranes, and normal microbiota.

Second Line of Defense

Innate internal mechanisms including phagocytes, inflammation, fever, and antimicrobial substances.

Lymphatic System

Network of vessels, lymph, nodes, and tissues that transports immune cells and filters pathogens.