Ch. 21 Immune System

The immune system provides resistance against disease & is made of 2 intrinsic systems:

1. Innate (nonspecific) defense system:

   • the 1st & 2nd lines of defence

     • 1st: external body membranes

     • 2nd: antimicrobial proteins, phagocytes, & other cells

2. Adaptive (specific) defense system":

   • 3rd line of defense: attacks particular foreign substances (longer to react)

PART 1 - INNATE DEFENSES

Innate system uses 1st & 2nd lines of defense to stop attacking pathogens

21.1 First Line of Defense: Surface Barriers

• surface barriers are skin & mucous membranes w/ their secretions

  • physical barrier protects against most

  • keratin is resistant to weak acids & bases, bacterial enzymes, & toxins

• skin & mucosae produce protective chems that inhibit/destroy pathogens

  • Acid: acidity of skin inhibits pathogen growth called acid mantle

  • Enzymes: lysozyme of saliva, respiratory mucus, & lacrimal fluid kill many pathogens; enzymes in stomach kill many as well

  • Mucin: sticky mucus lining digestive & respiratory tract trap microorganisms

  • Defensins: antimicrobial peptides that inhibit microbial growth

  • Other chems: lipids in sebum & dermicidin in sweat are toxic to some bacteria

21.2 Second Line of Defense: Cells & Chemicals

• Innate system necessary of pathogens invade deeper tissues

  • phagocytes, natural killer (NK) cells, inflammatory response (macrophages, mast cells, WBCs), antimicrobial response (interferons), fever

• Many 2nd line cells have pattern recognition receptors that recognize & bind tightly to structures on microbes, disarming them

  • toll-like receptors (TLRs) play main role in triggering immune response. humans have 11, each recognizing particular microbe

o Phagocytes: WBCs that ingest & digests pathogens

• Neutrophils: most abundant, but die fighting; become phagocytic on exposure to infectious material

• Macrophages: develop from monocytes & are chief phagocytic cells

  • free macrophages: wander thru tissues

  • fixed macrophages: permanent residents of organs

• Phagocytosis: cellular process of engulfing & destorying bacteria

  1. phagocytes recognizes & adheres pathogen’s carb 'sign’

     • some microorganisms have external capsules dining their surface carbs, evading phagocytosis

     • opsonization: immune system uses antibodies/proteins as opsonins that coat pathogens

  2. cytoplasmic extensions (pseudopods) bind to & engulf particle in vesicle called phagosome

  3. phagosome fuses w/ lysosome, forming phagolysosome

  4. phagolysosome is acidified, & lysosomal enzymes eat particles

  5. indigestibles & waste is exocytosed

• Helpter T cells trigger macrophages to produce respiratory burst which kills pathogens reistant to lysosomal enzymes by…

  • releasing cell-killing free radicals

  • producing oxidizing chems (H₂O₂)

  • increasing pH & osmolarity

o Natural killer (NK) cells: