Anatomy&Phys I Notes - Digestion 11:28:00...

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Digestion 26/09/2011 11:28:00 The job of the digestive system is to break down food so that your body can  absorb nutrients While being broken down, food goes through the  alimentary canal Accessory organs  aid in digestion Add chemicals, etc. to food Technically part of the digestive system, but not part of the digestive tract  because food never passes through accessory organs Ex: salivary gland, liver, pancreas, gallbladder Layers of tissue in alimentary canal Lumen : the opening/empty space in an organ Mucosa : the innermost lining around the lumen o Cells excrete mucous to trap bacteria, protect cell, lubricate food Submucosa : layer that lies outside the mucosa o Full of blood vessels and nerve endings  o Supports the mucosa Muscularis : layer that lies outside the submucosa o The tongue and muscularis of esophagus are striated muscle; all other  muscularis consist of two layers of smooth muscle Inner circular layer: smooth muscle fibers that wrap around a  long axis Outer longitudinal layer: smooth muscle fibers that extend  parallel to the long axis o Coordination of these two layers   rhythmic  peristalsis Adventitia/Serosa : the outermost (most distant from lumen) layer o When it is attached to a surrounding tissue, called adventitia o When it lies adjacent to the peritoneal cavity, called serosa o Made of a lot of collagen fiber
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Pathway of Food Mouth o Teeth, especially molars, crunch, chew and grand food to increase  surface area o Tongue rubs food onto palette o Saliva: made up of water, mucus and enzymes Dissolves salts and carbohydrates Surrounds bacteria (if present) Lubricates as you swallow Salivary amylase : a type of enzyme that breaks down starch  into simple sugars, making things sweet Salivary lipase : a type of enzyme that digests lipids Salivary salts  lower the pH of saliva, making it difficult for some  bacteria to survive Eating sugar   sticks to teeth   bacteria grow  bacteria excrete acid   cavity due to low pH Vomit   teeth erosion due to low pH o Hardly any absorption of nutrients Pharynx o Push back tongue and lift up larynx   epiglottis seals respiratory track  (trachea)   swallow to esophagus Esophagus o Passes food from pharynx, past heart and lungs, to stomach o Moves by peristalsis (wave-like contractions) o Lining of esophagus secretes mucus to lubricate food Stomach o Muscles surrounding stomach churn the food o Gastrin  (hormone) stimulates secretion by gastric glands Parietal cells secrete HCl, which kills bacteria and denatures 
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