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Pharynx & Esophagus
Involved in TRANSPORT
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Stomach
- Mechanical Disruption
- Absorption of H20 & alcohol
- Chyme empties through the pyloric valve
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Small Intestine
Chem. & Mech. digestion & Absorption
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Large Intestine
Absorbs: Electrolytes & Vitamins (B&K)
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GI Tract Layers
- 1. Mucosal
- 2. submucosal
- 3. muscularis
- 4. serosa
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Peritoneum
Visceral layer that covers organs
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Peritonitis
- Accute INFLAMMATION of the peritoneum
- CAUSE: contamination by infectious microbes during SURGERY or from rupture of abdominal organs
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Saliva functions
- 1. wet food to swallow easier
- 2. dissolves food for tasting
- 3. chem. digestion of STARCH starts here (salivary amylase)
- 4. lysozyme helps destroy bac.
- 5. prevents INFECTION as it has rinsing action
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During INCREASE in salivation
- sight, smell, sounds, memory of food, tongue stimulation - rock in mouth
- parasympathetic nn (CN 7&9)
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When Salivation is STOPPED
- dry mouth when you are afraid
- SYMPATHETIC nerves acting
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Mumps (action and symptoms)
- Attacks the PAROTID gland
- Vaccine available (since 1967)
- Symptoms:
- 1. INFLAMMATION & enlargement of parotid gland
- 2. Fever, sour throat (esp. swallowing sour foods)
- 3. Swelling on one or both sides
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Mechanical Digestion in mouth
- called Mastication
- involves: breakdown of food into pieces and MIXES food w/saliva to form a BOLUS
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Chemical digestion in mouth
- amylase: Starch digestion @ pH 6.5-7 in mouth
- When bolus & enzyme hit pH 2.5, gastric juices hydrolysis END
- lingual lipase: (secreted by glands in TONGUE) begin BREAKDOWN of triglyerices into Fatty A & glycerol
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Esophagus
- Voluntary phase: tongue pushes food to back of oral cavity
- Involuntary phase: soft palate & uvula lifted to close off nasopharynx, & vocal cords CLOSE
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Steps involved in swallowing (ESOPHAGUS)
- Upper sphincter relaxes when larynx is lifted
- Lower sphincter relaxes as food comes towards stomach
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Gastroesophageal Reflex disease
- When LOWER sphincter FAILS to open (feels like chest pain)
- If lower sphincter fails to CLOSE...stomach acid enters esophagus (causes HEARTBURN-GERD)
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If you have a weak sphincter
- do NOT eat large meals
- to prevent GERD, avoid: coffee, chocolate, tomatoes, onions, fatty foods & mint
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Pyloric sphincter abnormalities
- PyloroSPASM: muscle fibers of sphincter FAIL to relax, trapping food in stomach, inducing VOMITING
- Pyloric Stenosis: NARROWING of sphincter, indicated by PROJECTILE vomiting. Needs surgery correction
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Mucosa & gastric glands role
- HCL converts Pepsinogen from CHIEF cell to PEPSIN
- Intrinsic factor: absorption of vit. B12 for RBC production
- Gastric hormone
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Gastric hormone fxns
- 1. releases gastric juice
- 2. increases gastric motility
- 3. relaxes pyloric sphincter
- 4. constricts esophageal sphincter, PREVENTING entry (keep it moving)
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Types of Mechanical Digestion Processes
- 1. Gentle mixing waves: every 15-25s, mix BOLUS w/gastric juice = chyme
- 2. More vigorous waves: go from stomach to pyloric region
- 3. Intense waves: near pylorus, open & squirt 1-2tsp w/each wave
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Chemical Digestion
- This is where PROTEIN digestion occurs
- HCL transforms pepsinogen to pepsin and that breaks peptide bonds b/w aa's
- FAT digestion also continues: triglycerides in milk fat
- HCL kills microbes (low pH)
- Mucous cells protect stomach walls from being digested
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Vagus nerve
Increases STOMACH muscle and GLANDULAR activity
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Nervous control
keeps stomach alive
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If caffeine or protein present?
- G-cells secret gastrin into the bloodstream
- Gastrin hormone INCREASES stomach glandular secretions
- sphincter relaxation occurs
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Intestine role in digestion
- Stretch receptors in duodenum SLOW stomach activity & increase intestinal activity
- SYMPATHETIC nerves SLOW stomach activity
- Hormonal influences: secretin (decreases stomach secretions), CCK (decreases stomach emptying), Gastric inhibitory peptide (decreases stomach secretions, motility & emptying)
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When there is distention & stomach contents
increase in Gastrin hormone SECRETION and Vagal nerve impulses
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Pancreatic juice
- pH of 7.1-8.2
- contains H20, enzymes & sodium bicarb.
- has Digestive enzymes
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Pancreatitis
Inflammation of pancreas (occurs with the MUMPS)
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What is involved in REGuLATING pancreatic secretions?
- SECRETIN: high acid in intestine causes increase in sodium bicarb release
- GIP(gastric inhibitory peptide): f-acid & sugars cause INCREASE insulin release
- CCK: fats & proteins cause INCREASE digestive enzyme release
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Bile
- 1Qt is secreted by liver per DAY
- yellow-green
- composed of H20 & cholesterol & bile salts (Na&K)
- contains bilirubin - bile pigments
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Pathway of bile
- Flows through bile capillaries into hepatic ducts
- these ducts form a COMMON hepatic duct
- the Common hepatic duct joins with Cystic duct to form: COMMON BILE Duct
- This empties into the DUODENUM
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Liver fxns:
- 1. turns proteins into GLUCOSE
- 2. turns triglyerides into GLUCOSE, also stores some fat
- 3. synthesizes cholesterol & lipoproteins
- 4. stores excess glucose as GLYCOGEN (and can turn back to glucose when needed)
- 5. detoxifies the blood by removing drugs & hormones
- 6. Stores vitamins (fat soluble such as ABDEK)
- 7. Stores Iron & Copper
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Location of digestive hormones
- Gastrin: stomach, gastric & ileocecal sphincters
- GIP: stomach & pancreas
- Secretin: Stomach, liver & pancreas
- CCK: stomach, pancreas, gallbladder, sphincter of Oddi
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Microvilli
- Increases surface area
- Involved in Absorption & Digestion
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Brush border enzymes (types and role)
- Types: Maltase, Sucrase & Lactase
- Role: carb digestion- Act on Disaccharides to produce Monosacchardies (fruc, gluc & galac)
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lactose intolerant
- mucosal cells in small intestines fail to produce lactase
- Essential for digestion of lactose sugar in milk
- results: diarrhea, gas, abdominal cramps
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Protein digestion in stomach
- HCL denatures proteins
- Pepsin turns proteins into peptides
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Protein digestion in pancreas
- digestive enzymes: split peptide bonds
- brush border enzymes: aminjopeptidase or dipeptidase
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Lipid Digestion in Mouth
lingual lipase
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Lipid Digestion in Small intestines
- Fats emulsified by BILE
- Pancreatic lipase: splits into f acids & monoglycerides
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Nucleic Acid digestion
In pancreatic juice: ribonuclease (digests RNA) & deoxyribonuclease (digests DNA)
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Electrolyte Absorption
Ca+ absorp. requires vit D & PTH (osteoclast activity)
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H20 Absorption
- 9L fluid dumped into GI tract/day
- Small intestine reabsorbs 8L
- Large intestine reabsorbs 90% of last L
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Large Intestine Mechanical Digestion
- Haustral churning
- Gastroilial reflex
- Gastrocolic reflex: moves FECES into rectum
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Large Intestine Chem. Digestion
- NO enzymes secreted-only mucus
- bacteria ferment:
- 1. undigested carbs into CO2 & meth. gas
- 2. undigested proteins into simpler substances (ie indoles--odor)
- 3. turn bilirubin into simpler substances that produce color
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Large intestine Absorption & feces formation
- electrolytes absorbed: Na+ & Cl-
- 3-10hrs, 90% of H20 removed from chyme
- feces formed: dead epithelial cells, undigested food (ie cellulose), bacteria
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Problems w/defecation
- Diarrhea: chyme passes too quickly thru intestine (not all H20 reabsorbed)
- Constipation: decreased intestinal MOTILITY (too much H20 reabsorbed). Drink H20, exercise & fiber to remedy
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