Human Anatomy and Physiology Immunology: Innate defenses

Overview Not organ associated but comprised of cells inhabiting lymph and body fluids Innate system Surface membranes: skin and mucosae Internal defenses: phagocytes, fever, NK cells, antimicrobial proteins, inflammation Adaptive system Humoral immunity (B cell) Cellular immunity (T cell)

Surface barriers Integument (skin) Epithelial membranes Multilayered skin Keratin stops bacterial enzymes and toxins Epithelial membranes Acidic skin secretions Acid stomach mucosa Saliva contains lysozyme Respiratory and digestive tract mucus

Internal barriers Phagocytes Macrophages “big-eaters” E.g. monocytes, neutrophils Phagocytosis - steps Engulf (1,2) Formation of vesicle (3) Lysozome fusion (4) Digestion Exocytosis (5)

Internal barriers Natural killer cells Non-specific killers (e.g. viruses, cancer cells) Recognize sugars on surface of target cell Attacks target cell’s membrane releasing perforins nuclear disintegration and inflammation

Internal barriers Inflammation Signs Inflammatory process Redness, heat, swelling, pain, impairment of function Inflammatory process Receptors on cell surface release chemicals (histamine, kinins, etc.) Cause small blood vessels to dilate = redness and heat Chemicals increase capillary permeability, fluid causes edema, edema causes pain

Inflammation Aids healing process Dilution of harmful substances Oxygen and nutrients Clotting proteins

Inflammation Phagocyte mobilization follows inflammation Process Leukocytosis (1) Margination (2) Diapedesis (3) Chemotaxis (4)

Internal barriers Viruses cannot replicate themselves How viruses work Antimicrobial proteins - interferon

Interferons Steps Virus enters host and replicates Infected cells secrete interferons Interferons stimulate production of antiviral proteins Antiviral proteins prevent virus replication

Internal barriers Fever Liver and spleen sequester iron and zinc during fever Speeds up metabolism