skin - 1st line of defense  

• 15% of an adult’s total weight
• oil/sweat glands >> low pH on surface >> many microorganisms killed
• prevents water loss
• lyxozyme - enzyme in sweat that digests bacterial cell walls
• stratum corneum - outer skin layer
  • cells constantly injured, worn, replaced
• stratum basale - innermost skin layer, produces new skin cells
• stratum spinosum - broad layer in middle of epidermis
• dermis - skin layer below epidermis, gives structural support
• mainly adipose (fat) cells below dermis
• other surfaces leading to outside - digestive tract, respiratory tract, urogenital tract
  • mucus traps microorganisms in bronchi, cilia sweeps mucus towards glottis to stomach

cellular counterattack - 2nd line of defense 

• uses nonspecific cellular/chemical devices to defend
• goes after any infection w/ leukocytes
• identity of pathogen doesn’t matter
• lymphatic system = central location for distribution of immune system cells
• macrophages - “big eaters”
  • ingests microbes through phagocytosis
  • uses oxygen-free radicals to destroy microbes
• neutrophils - most abundant leukocyte
  • can release chemicals (similar to bleach) to kill all cells in surroundings
• natural killer cells - destroys cells already infected by the microbe
  • drills hole into plasma membrane

complement system - in vertebrates, contains 20 proteins 

• proteins encounter bacterial/fungal cell wall >> forms membrane attack complex
• forms pore on membrane >> cell swells/bursts
• adds on to the effects of other body defenses
• interferons - messenger to warn other cells of the infection
  • alpha, beta, gamma
• prostaglandin - produces clotting to block spread of pathogens

inflammatory response - localized, nonspecific response to infection 

• infected cells release alarm signals >> blood vessels dilate >> increase blood flow >> area = red/warm
• neutrophils, then macrophages arrive to kill microbes
  • pus = mixture of dead pathogens, tissue, neutrophils
• temperature response - macrophages release interleukin-1 >> hypothalamus raises body temperature
  • fever >> stimulates phagocytosis, iron production
  • very high fever could start to denature enzymes