digestive system functions - ingestion: selective intake of food - digestion: mechanical and chemical breakdown of food - absorption: uptake of nutrient molecules into blood or lymph - defecation: elimination of feces mechanical breakdown: physical breakdown of food into smaller particles chemical breakdown: hydrolysis reactions breaking macromolecules into monomers microscopic anatomy of alimentary canal (from inside to out) 1. mucosa a. part of alimentary canal that is in contact with food b. lamina propria: loose connective tissue immediately deep to mucosa c. muscularis mucosa: creates grooves and ridges that increase surface area 2. submucosa a. blood/lymph vessels b. controls mucosa 3. muscularis externa a. 2 layers i. circular 1. drives food forward to keep it from moving backward ii. longitudinal 1. peristalsis: contraction of longitudinal muscle which sweeps food down alimentary canal 4. serosa a. adventitia: fibrous connective tissue that replace serosa in the pharynx, some parts of the esophagus, and rectum enteric nervous system - nervous network ● esophagus, stomach, intestines ○ motility, secretion, blood flow ○ motility: movements of digestive system ● nerve plexuses ○ submucosal plexus ( long ) ■ secretory activity ■ controls muscularis mucosa ○ myenteric plexus ( short ) ■ controls muscularis externa ■ GI tract motility ( peristalsis ) ■ contractions digestive tract regulation 1. long reflexes a. submucosal
b. extrinsic c. autonomic NS control i. parasympathetic fibers of vagus nerve ii. stimulates motility and secretion d. includes CNS 2. short reflexes a. myenteric b. intrinsic c. stimulates muscularis externa i. responds to stretching/chemicals d. excludes CNS saliva - moistens mouth, inhibits bacterial growth, dissolves molecules to enable taste bud stimulation, and starts dissolving fat and starch contains: ● mucous ● electrolytes ● lysozyme ● IgA (antibody) ● salivary amylase: begins to break down starch ● lingual lipase: begins to dissolve fat deglutition - swallowing center in brain - bolus: chewed food about to be swallowed - food down esophagus stretches myenteric nerve plexus - triggers contraction for circular muscle to guide bolus further down 1. oral (buccal) phase a. voluntary control b. tongue collects food in a bolus and pushes it down to esophagus 2. pharyngeal phase a. soft palate and root of tongue block any food from re-entering mouth b. breathing is suspended and epiglottis covers the trachea 3. esophageal phase a. peristalsis (myenteric / short) b. bolus stimulates stretch receptors c. circular muscle above bolus pushes food downward d. longitudinal muscle below bolus contracts gastric pits - indentations in the stomach that contain gastric glands 1. mucous cells
a. mucous: protects stomach lining i. rich in bicarbonates (alkaline) 2. parietal cells a. HCl b. intrinsic factor: enables vit.b12 absorption c. ghrelin: appetite stimulator 3. chief cells a. pepsinogen : breaks down proteins once activated to pepsin by HCl b.
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- Summer '17
- Kyle Harris