There are three levels of nonspecific host defenses: mechanical, chemical, and cellular. Mechanical defenses include physical barriers like skin and mucous membranes, as well as cilia and mucus in the respiratory tract that trap microbes. Chemical defenses secrete antimicrobial substances like oils, acids, and peptides. Normal microbiota on the skin and in the gut inhibit the growth of pathogenic bacteria. Cellular defenses include phagocytic white blood cells that engulf microbes, lymphocytes and antibodies in the immune system, and processes like inflammation and fever that fight infection.

1. Nonspecific Defenses of the Host

10. Phagocytosis

11. Phagocytosis WBC engulfing bacteria. Note pseudopods.

13. Inflammation 6. Phagocyte Migration and Phagocytosis 7. Tissue Repair.

14. FEVER Hypothalamus controls body temperature. Interleukin-1 released from phagocytes. Hypothalamus releases prostaglandins. Prostaglandins raise body temperature. Skin temperature remains cold causing chills. Once IL-1 removed, fever breaks.

16. Complement

17. Interferons Interferons -IFNs- anti-viral. Prevent viral replication.

19. Mechanisms of Peptide Action