The Immune System

Pathogens Defined: microorganisms that cause disease Viruses: turn cells into virus making factories Bacteria: prokaryotes that can release toxic chemicals Fungi: pierce cells and absorb the nutrients Protozoans: single cells protista (eukaryotes) Parasites: grow and feed on a host

Pathogens (contd) Some carried by wind, water, direct contact, indirect contact… Some carried by vectors Vector: object that carries a pathogen Examples: Malaria – mosquitos carry the protozoan Black Death – carried by flea’s of mice West Nile Virus – carried by birds, but spread by mosquitos

The Skin 1st line of defense: physical barrier Oils & sweat destroy some pathogens Some cells burst Some cells shrivel

Mucus Membranes Coat the openings of the body Nose, mouth, ears, eyes, genitals, anus Lined with cilia & sticky fluids to trap pathogens

White Blood Cells Job: Search & destroy Phagocytes: surround & engulf invaders Phagocytosis Lymphocytes: T cells: destroy infected body cells B cells: Inactivate invaders

Defense Proteins Complimentary Proteins Weaken cell membrane Attract phagocytes Cause microbes to stick to wall of blood vessel

Defense Proteins Antibodies Made by B cells Bind to cell membrane of pathogen Prevents pathogen from binding to host cells Causes pathogens to clump More susceptible to phagocytes Weakens the cell membrane Causes them to burst

Defense Proteins Interferon Produced by virus infected cells Stimulates uninfected cells to create infection preventing enzymes

Vaccination Prevents infections (not a cure) Memory cells developed without actually getting the disease Vaccine Contains antigens of a pathogen Weakened pathogen is injected Stimulates the production of memory cells Speeds up immune response if you encounter the unweakened virus