Nonspecific Defenses of the Host

1. Nonspecific Defenses of the Host

2. The Immune System

3. The First Line of Defense Surface Barriers

4. Epidermis (Skin) • Intact surface is rarely penetrated by microbes • Stratum Corneum is made of dead keratinized cells that form an armor plating • Dead karatinized cells are constantly sloughing off

5. Epidermis • Dry: Most areas of the skin are too dry for microbial growth. • Acidic: (pH 5): The sebaceous glands produces sebum, an unsaturated fatty acid. • Temperature: slightly cooler than 37 degrees • Resident microflora: The natural flora out competes pathogenic organisms.

6. Mucous Membranes • Mucous membranes are surfaces areas lining the Respiratory, G.I., and urogenital tracts. • These membranes are considered to be outside the body. • Mucous membranes are involved in either secretion or absorption and thus cannot be covered with an armor of dead cells. • Membranes must be bathed in fluids (warm, wet environments that would readily colonize bacteria if they were not protected by a number of defenders.

7. Defense of the Mucous Membrane • Goblet cells produce mucus, a thick sticky substance composed of polysaccharide and protein. • Mucus contains carbohydrate structures similar to the ones on mucosal cells surfaces • Mucus traps bacteria before they can reach membrane. • Muco-ciliary escalator pushes microbes and debris outside the respiratory system • M-cells funnel bacteria into waiting phagocyts

8. Eyes (lacrimal apparatus • Washing action of tears along with the blinking action of the eyelid mechanically removes bacteria and debris • Lysozyme attacks peptidoglycan layer of bacteria

9. Stomach • Low pH and digestive enzymes kill microbes and endospores that enter the GI tract.

10. Reflexes • Types: Coughing sneezing, blinking, vomiting • Function: Expel microbes and toxins

11. Earwax Antibacterial and insect repellent