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BIOLOGY 11 DIGESTIVE SYSTEM DIGESTIVE SYSTEM = digestive tract (=alimentary canal) plus associated glands and organs DIGESTION = breaking down of large complex molecules to simple molecules that can be used by body’s cells Molecules must be small enough to be absorbed by columnar epithelium of small intestine Organs involved: Digestive tract mouth pharynx esophagus stomach small intestine large intestine rectum anus Cavity in digestive tract is the lumen Associated glands: Salivary glands (3 pair) Liver Gall bladder Pancreas Glands in intestinal lining and stomach Digestive process Mouth Teeth Tongue & teeth Taste buds Salivary glands Parotid glands Submandibular glands Sublingual glands Saliva Pharynx Swallowing Soft palate seals nasal passage Epiglottis seals glottis Esophagus Peristalsis Cardiac sphincter - Stomach Functions Food storage Formation of chyme Initiation of protein digestion Gastric glands Gastrin hydrochloric acid release Mucus Pepsin Pyloric sphincter Small intestine Structure designed to increase surface area for absorption coiled circular folds villi microvilli 3 sections duodenum jejunum ileum Chyme contains nucleic acids polypeptides (from proteins) carbohydrates fats Chemoreceptors in duodenum wall detect type of food molecules present and pH (acidity) Glands in duodenum wall release hormones Secretin stimulates pancreas to secrete bicarbonate neutralizes acidity of chyme stimulates liver to produce bile Cholecystokinin (CCK) stimulates pancreas to secrete digestive enzymes stimulates gall bladder to release bile Liver produces bile Stimulated by presence of fats or low pH in chyme Bile breaks down large fat droplets into smaller droplets increases surface area for enzyme action Gall bladder stores bile When stimulated, gall bladder releases bile into intestine Pancreas releases digestive enzymes Pancreatic amylase polysaccharides (carbohydrates) disaccharides Lipases fats fatty acids + glycerol Nucleases RNA and DNA nucleotides Proteases polypeptides amino acids Absorption of most of water and all nutrients in small intestine Ileocaecal valve - one-way valve allows undigested material to pass into large intestine Large intestine Functions absorption of water from undigested food formation of feces anaerobic bacteria (E. coli) break down wastes produce gas produce vitamin K and B vitamins absorption of vitamins produced by E. coli vitamin K important for blood clotting factor storage of feces caecum - short pouch where small intestine joins large intestine appendix hangs off caecum colon - parts named for position or shape ascending colon transverse colon descending colon sigmoid colon rectum - muscular walls stores feces until elimination anal canal - two sphincters to control defecation internal anal sphincter - smooth muscle defecation reflex external anal sphincter - skeletal muscle control of defecation reflex Anus - opening through which defecation occurs