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Unformatted text preview: 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 ← 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 proteins (makes them more vulnerable to pepsin-attack) Chief cells secrete pepsinogen...
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This note was uploaded on 04/06/2012 for the course BIO 323 taught by Professor Staff during the Spring '08 term at Washington University in St. Louis.
- Spring '08