Chapter 1

Digestion

1. Pathogen

   • Disease causing microorganism
     • Bacteria
     • Virus
     • Fungi
     • Disease is recognisable symptoms
       • Damage host tissues
       • Produce toxins
   • Causes infection
   • To cause disease, it must: Gain entry to host, Colonise tissues of host, Resist defences of host, Cause damage to host tissues

2. Entry to body

   • Interfaces
     • Excahnge surface/boundary, linking two systems
     • Skin
       • Effective barrier: forms thick, continous layer
       • Cut or abrasion - easier entry
     • Common entry for pathogenic microorganisms, due to some adaptations: thin, moist, sticky, large surface area, well supplied with blood vessels
   • Gas-exchange system
   • Digestive system
   • Adaptations: Thick mucous layer that covers exchange surfaces and forms a thick, sticky barrier, hard to penetrate - Production of enzymes, - production of stomach acid.

3. Chemical

   • Breaks down large, insoluble molecules, into smaller, soluble ones
   • Uses enzymes, called hydrolases
     • Hydrolysis is the splitting up of molcules by the addition of water
   • Examples of hydrolases: Carbohydrases, lipases, proteases.
   • Assimilation - the incorporation of molecules into body tissues
   • Absorption - taking soluble molecules into the body

4. Physical

   • Break down of large pieces of food into smaller ones by the means of structures, such as teeth
   • Makes it possible to ingest food
   • Provides a large surface area for chemical digestion
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