31.2 Immune System KEY CONCEPT The immune systems consists of organs, cells, and molecules that fight infections.

31.2 Immune System Infections are caused by different types of pathogens. Bacteria: –single-celled organisms –cause illness by destroying cells –release toxic chemicals –Ex: food poisoning Viruses: genetic material surrounded by a protein coat. –force host cells to make more viruses –very small –Ex: flu, cold, AIDS

31.2 Immune System Fungi –multicellular or single-celled. –take nutrients from host cells by piercing healthy cells –occur in warm and damp places –Ex. Athlete’s foot Protozoa single-celled organisms. –use host cells to complete their life cycles –take nutrients from host cell –Ex. Malaria

31.2 Immune System Parasites –multicellular organisms. –grow and feed on a host –possibly kill the host

31.2 Immune System Pathogens can enter the body in different ways. Indirect contact: does not require touching an infected individual. – touching an infected surface – breathing in infected air –vectors (carry a pathogen and transmit into healthy cell) –ex: insects or food Direct contact: requires touching an infected individual. –kissing –sexual intercourse –hand shaking

31.2 Immune System Many body systems protect you from pathogens. The immune system is the body system that fights off infection and pathogens. Many other tissues and systems help the immune system. –Skin is a physical barrier to infection. –Mucous membranes trap pathogens entering the body. –The circulatory system transports immune cells.

31.2 Immune System Cells and proteins fight the body’s infections. White blood cells attack infections inside the body. –Phagocytes engulf and destroy pathogens. –T cells destroy infected cells. –B cells produce antibodies, which deactivate the pathogen.

31.2 Immune System

Three types of proteins fight off invading pathogens. –Complement proteins weaken pathogen membranes. –Antibodies make pathogens ineffective. –Interferons prevent viruses from infecting healthy cells. antibody pathogens

31.2 Immune System Immunity prevents a person from getting sick from a pathogen. In all immunity, pathogens are destroyed before you get sick. Passive immunity occurs without an immune response. –mother’s milk –genetics Active immunity occurs after a specific immune response

31.2 Immune System Vaccines control pathogens and disease –Injected with antibodies that have been exposed to the pathogen. -Gives instant but short- term protection. –Given mild or dead version of the pathogen. -Your body makes the antibodies itself for long-term protection. -Memory B cells stay for a long time, ready for another attack from the same organism. Vaccines artificially produce acquired immunity.