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66 Cards in this Set
- Front
- Back
type of food person seeks is determined by
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appetite
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amount of food person eats determined by
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hunger
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anterior teeth (incisors)
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strong cutting action
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posterior teeth (molars)
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grinding action
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closing force of jaw muscles
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55 pounds on incisors and 200 pounds on molars
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innervation of chewing muscles
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motor branch of fifth cranial nerve, controlled by nuclei in brainstem
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chewing reflex
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presence of bolus of food in mouth first initiates reflex inhibition of mastication (lower jaw drop), drop initiates stretch reflex of jaw muscles-rebound contraction; repeat
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what is chewing most important for and why
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fruits and veggies-indigestible cellulose membranes around nutrient portions that must be broken
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deglutition
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swallowing
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swallowing stages
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voluntary stage-initiates; pharyngeal stage-involuntary-food through pharynx into esophagus; esophageal stage transports food to stomach
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where is food in voluntary swallowing stage
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posteriorly into pharynx by P of tongue upward and backward against palate
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automatic pharyngeal muscle contractions step 1
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soft palate pulled upward to close off posterior nares-prevent food reflux
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automatic pharyngeal muscle contractions step 2
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palatopharyngeal folds pulled medially-form sagital slit through which food must pass into posterior pharynx; lasts <1 sec
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automatic pharyngeal muscle contractions step 3
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vocal cords strongly approximated-larynx pulled up and anterior by neck muscles; cause epiglottis to swing backward over larynx opening
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automatic pharyngeal muscle contractions step 4
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pulls up and enlarges opening to esophagus-upper 3-4 cm esophageal muscular wall relaxes (upper esophageal sphincter)
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automatic pharyngeal muscle contractions step 5
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entire muscular wall of pharynx contracts beginning in superior part and spreading downward propeling food by peristalsis into esophagus
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what can destruction of vocal cords or muscles around cause
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strangulation
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fxn of upper esophageal spincter during respiration
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prevents air from entering GI tract
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most sensitive area for initiating pharyngeal stage of swallowing
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ring around pharyngeal opening, tonsillar pillars
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sensory signals from tonsillar pillars
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sensory trigeminal and glossopharyngeal nerves into medulla then into/close to tractus solitarius
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motor impulses from swallowing center to pharynx and upper esophagus transmitted by
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5, 9, 10, and 12 CNs and a few of upper cervical nerves
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esophagus primary peristalsis
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simple continuation of peristaltic wave that begins in the pharynx
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how long does the peristaltic contraction beginning in pharynx take to reach stomch
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8-10 secs
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food transmision to stomach time
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5-8 secs if upright due to gravity
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secondary peristaltic waves of esophagus
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result from distention of esophagus-continue until all food emptied into stomach
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what neurons initiate secondary waves
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intrinsic circuits in myenteric plexus
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stomach and somewhat duodenum state when food is coming
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wave of relaxation via myenteric inhibitory neurons (also allows relaxation of lower esophageal sphincter)
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achalasia
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lower esophageal sphincter doesn't relax satisfactorily
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orad portion of stomach
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first 2/3 of body
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caudad potion of stomach
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remainder of body plus antrum
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limit of food in completely relaxed stomach
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0.8-1.5 L
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what secretes digestive juices in stomach
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gastric glands-in entire wall of body except narrow strip on lesser curvature
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constrictor waves
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weak peristaltic mixing waves in mid to upper portions moving toward antrum; about once every 15-20 seconds when food present
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hunger contractions
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occur when stomach has been empty for several hours or more; rhythmical peristalic contractions in body of stomach
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what occurs when hunger contractions fuse
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cause continuing tetanic contraction that sometimes lasts 2-3 minutes; usually do not begin until 12-24 hours after last ingestion of food
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contraction of pyloric sphincter
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open enough for water and other fluids to empty from stomach to duodenum with ease; prevents food passage until almost fluid consistency
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gastrin and stomach emptying
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promotes-enhances pyloric pump
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inhibitory reflexes from duodenum to stomach
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1) directly through enteric nervous system 2)through extrinsic nerves that go to prevertebral sympathetic ganglia and back through inhibitory sympathetic nerve fibers 3) slighltly via vagi to brain stem; all inhibit pyloric pump and increase pyloric sphincter tone
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what can initiate enterogastric inhibitory reflexes
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1) distention 2) irritation 3) acidity 4) osmolality of chyme 5) breakdown products of chyme (proteins, somewhat fats)
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stimulus for hormone release that cause stomach inhibition
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fats in duodenum
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most potent hormonal inhibitor of stomach from upper small intestine
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cholecystokinin (CCK)-released by jejunum mucosa in response to fat in chyme; blocks gastrin
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main effect of gastric-inhibitory peptide (GIP) at physiologic concentrations
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stimulate secretion of insulin from pancreas
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mixing contractions of small intestine (segmentation contractions)
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chop chyme 2-3 times per minute; localized concentric contractions lasting a fraction of a minute; resemble chain of sausage
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what are contractions not effective without
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background excitation from myenteric nerve plexus-as indicated when atropine blocks
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peristaltic waves
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toward anus at 0.5-2 cm/s; very weak-die out after 3-5 cm; net movement ~1cm for chyme
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time for chyme to travel from pylorus to ileocecal valve
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3-5 hours
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gastroenteric reflex
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initiated by distension of stomach and conducted through myenteric plexus from stomach down along wall of small intestine
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hormonal factors that enhance peristalsis
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gastrin, CCK, insulin, motilin, and serotonin
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secretin and glucagon on small intestinal motility
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inhibit
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gastroileal reflex
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chyme blocked until another meal eaten-this intensifies peristalsis and moves chyme into large intestine
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peristaltic rush
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initiated partly by nerous reflexes (autonomic NS and brain stem) and partly by intrinsic enhancement of myenteric plexus; powerful peristaltic contractions traveling long distances within minutes
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what causes peristaltic rush
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intense irritation (infectious diarrhea)
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chyme V that enters cecum each day
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1500-2000 ml
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reflexes from cecum to iliocecal sphincter and ileum are mediated by
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myenteric plexus and extrinsic autonomic nerves (espeically prevertebral sympathetic ganglia)
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Haustrations (aka mixing movements) in colon
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large circular constrictions; ~2.5 cm of circular muscle contracting
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3 longitudinal muscle strips in colon
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teniae coli
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feces expelled each day
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80-200 ml
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time to move chyme through colon
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8-15 hours
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mass movement sequence in large intestine
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constrictive ring in response to distended/irritated colon; 20 or move cm colon distal to this ring lose haustrations and contract as a unit, propelling fecal material; a series persist 10-30 minutes
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what facilitates mass movements in colon
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gastrocolic and duodenocolic reflexes-transmitted via autonomic nervous system
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what prevents continual dribble of fecal matter through anus
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1) internal sphincter immediately inside anus 2) external anal sphincter (striated voluntary muscle)
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what nerve sends fibers to external anal sphincter
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pudendal nerve
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intrinsic reflex of defecation mediated by
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local enteric nervous system in rectal wall; normally weak by itself
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parasympathetic defectaion reflex
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sacral segments of spinal cord via pelvic nerves; greatly intensify peristaltic waves
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peritoneointestinal reflex
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results from irritation of peritoneum-strongly inhibits excitatory enteric nerves and an cause intestinal paralysis
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renointestinal and vesicointestinal reflexes
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inhibit intestinal activity as result of kidney or bladder irritation
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