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Digestive System (Oral Cavity (Salivary Glands (pharynx (esophagus…

- - - - passage way for food
      - esophagus
        
        flat muscular tube that is collapsed when not performing PERISTALSIS. Peristalsis is the distal movement of food through alternating contracting and relaxing segments of the alimentary canal
        
        stomach
        
        Has a muscosal barrier to protect itself from the stomach acid. This layer contains a thick layer of mucus, tight junctions between cells, and has the ability to quickly replace damaged epithelial cells
        
        Storage tank that can expand from 50 mL to 4 L.
        Turns bolus --> chyme
        
        Propulsion through peristalsis. Mechanical breakdown through churning and pummeling of chyme through the muscularis externa circular, longitudinal and oblique smooth muscle layers.
        
        Digestion: pepsin starts enzymatic digestion of proteins. HCl unfolds proteins to prepare for the SI. Lingual and gastric lipase beings fat digestions, but is only a minor contribution to the breakdown of fat.
        
        absorption of lipid-soluble alcohol and aspirin occurs here
        
        small Intestine: major organ of digestion and absorption
        
        Large Intestine
        
        Rectum: function is defecation
        
        Anal Canal: the last segment of large intestine. about 3 cm long; function: defectation
        
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        Reflexes
        
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        Ascending Colon
        
        travels up the right side of the abdominal cavity
        
        Tranverse Colon
        
        travels across the abdominal cavity
        
        Descending Colon
        
        down the left side of of posterior abdominal wall
        
        Sigmoid Colon
        
        S-shaped and joins the rectum
        
        Digestive Process: digestion: some food is remaining and are digested by gut bacteria (some produce Vitamin K and B vitamins). Absorption: absorbs most of remaining water, electrolytes and vitamins produced by bacteria. Propulsion: propels feces toward feces. Defecation: reflex triggered by rectal dissension; eliminates feces from the body. temporarly stores until dedication can occur.
        
        Reflexes
        
        Gastrocolic Reflex- Stimulates contractions in the large intestine, triggered by the presence of food in the stomach
        
        Appendix
        
        A subdivision of the large intestine
        
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        Structure: provides increased surface area for absorption
        
        Villi
        
        Finger-like projections of the mucosa. Absorbes nutrients and electrolytes. Each contains capillaries and lymphatic capillaries called lacteal
        
        Circular folds
        
        deep, permanent folds of mucosa and submucosa
        
        Microvilli
        
        long densely packed cytoplasmic extensions of the absorptive cells of mucosa called the brush boarder that contain enzymes. These enzymes complete digestion of carbohydrates and proteins
        
        Intestinal Crypts
        
        Goblet Cells
        
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        Enterocytes
        
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        enteroendocrine cells
        
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        Paneth Cells
        
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        Stem Cells
        
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        Duodenum
        
        Jejunum
        
        Ileum
        
        Digestion Process:
        Mechanical Breakdown through propulsion: segmentation by smooth muscle, mixing contents with intestinal juices. Uses short peristaltic waves moving food along tract.
        Digestion: enzymes delivered from pancreas and brush board enzymes attached to microvilli membranes complete digestion of all classes of food.
        absorption: breakdown products of carbohydrates, proteins, fat, nucleic acid, vitamins, electrolytes, and water through active and passive transport.
        Bile from liver emulsifies fats for digestion of lipids and fat-soluble vitamins.
        
        Hormones
        
        Cholecystokinin released from duodenum of small intestine inhibits secretions in the stomach, stimulates the gallbladder to contract, and increases pancreatic juice production in the pancreas
        
        Secretin is produced in the duodenum of the small intestine and it acts on the liver to increase bile output, the stomach to inhibit gastric gland activity, and the pancreas to increase pancreatic juice production
        
        Motilin is made in the duodenum of the small intestine and it acts on the small intestine to initiate the migrating motor complex (MMC)
        
        Somatostatin (shared production with the stomach)
        
        Reflexes
        
        Enterogastric Reflex- prevents acid secretion in the stomach
        
        Gastroileal Reflex- strengthens the process of segmentation in the ileum and relaxes ileocecal valve
        
        Hormones-
        
        Gastrin produced in the stomach mucosa stimulates contractions in the small intestine and relaxes ileocecal to allow chyme to pass from the stomach to the small intestine
        
        Somatostatin is produced by the stomach and the small intestine. It inhibits pancreatic secretions, inhibits blood flow in the GI tract, inhibits bile release in the gall bladder, and inhibits gastric secretions
        
        Serotonin- stimulates contraction of stomach muscle
        
        Histamine- Activates parietal cells in stomach mucosa to produce HCl
        
        contains the gastroesphageal sphincter, keeps orfice closed when food is not being swallowed and contains mucus cells to protect the esophagus from stomach acid. Controlled by the swallowing center in medulla and lower pons
- - - - yellow-green, alkaline solution that contains bile salts, bile pigments, cholesterol, triglycerides, phospholipids, and electrolytes
        
        only bile salts and phospholipids aid digestive process
        
        bile salts go through enterohepatic circulation to recycle 95% of it
  - - - stores bile that is not immediately needed for digestion
  - - - these enzymes include proteases (for proteins), amylase (for starch), lipases (for fats) and nucleases (for nucleic acids