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66 Cards in this Set
- Front
- Back
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type of food person seeks is determined by |
appetite |
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amount of food person eats determined by |
hunger |
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anterior teeth (incisors) |
strong cutting action |
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posterior teeth (molars) |
grinding action |
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closing force of jaw muscles |
55 pounds on incisors and 200 pounds on molars |
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innervation of chewing muscles |
motor branch of fifth cranial nerve, controlled by nuclei in brainstem |
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chewing reflex |
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 |
fruits and veggies-indigestible cellulose membranes around nutrient portions that must be broken |
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deglutition |
swallowing |
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swallowing stages |
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 |
posteriorly into pharynx by P of tongue upward and backward against palate |
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automatic pharyngeal muscle contractions step 1 |
soft palate pulled upward to close off posterior nares-prevent food reflux |
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automatic pharyngeal muscle contractions step 2 |
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 |
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 |
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 |
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 |
strangulation |
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fxn of upper esophageal spincter during respiration |
prevents air from entering GI tract |
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most sensitive area for initiating pharyngeal stage of swallowing |
ring around pharyngeal opening, tonsillar pillars |
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sensory signals from tonsillar pillars |
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 |
5, 9, 10, and 12 CNs and a few of upper cervical nerves |
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esophagus primary peristalsis |
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 |
8-10 secs |
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food transmision to stomach time |
5-8 secs if upright due to gravity |
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secondary peristaltic waves of esophagus |
result from distention of esophagus-continue until all food emptied into stomach |
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what neurons initiate secondary waves |
intrinsic circuits in myenteric plexus |
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stomach and somewhat duodenum state when food is coming |
wave of relaxation via myenteric inhibitory neurons (also allows relaxation of lower esophageal sphincter) |
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achalasia |
lower esophageal sphincter doesn't relax satisfactorily |
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orad portion of stomach |
first 2/3 of body |
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caudad potion of stomach |
remainder of body plus antrum |
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limit of food in completely relaxed stomach |
0.8-1.5 L |
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what secretes digestive juices in stomach |
gastric glands-in entire wall of body except narrow strip on lesser curvature |
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constrictor waves |
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 |
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 |
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 |
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 |
promotes-enhances pyloric pump |
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inhibitory reflexes from duodenum to stomach |
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 |
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 |
fats in duodenum |
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most potent hormonal inhibitor of stomach from upper small intestine |
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 |
stimulate secretion of insulin from pancreas |
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mixing contractions of small intestine (segmentation contractions) |
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 |
background excitation from myenteric nerve plexus-as indicated when atropine blocks |
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peristaltic waves |
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 |
3-5 hours |
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gastroenteric reflex |
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 |
gastrin, CCK, insulin, motilin, and serotonin |
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secretin and glucagon on small intestinal motility |
inhibit |
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gastroileal reflex |
chyme blocked until another meal eaten-this intensifies peristalsis and moves chyme into large intestine |
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peristaltic rush |
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 |
intense irritation (infectious diarrhea) |
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chyme V that enters cecum each day |
1500-2000 ml |
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reflexes from cecum to iliocecal sphincter and ileum are mediated by |
myenteric plexus and extrinsic autonomic nerves (espeically prevertebral sympathetic ganglia) |
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Haustrations (aka mixing movements) in colon |
large circular constrictions; ~2.5 cm of circular muscle contracting |
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3 longitudinal muscle strips in colon |
teniae coli |
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feces expelled each day |
80-200 ml |
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time to move chyme through colon |
8-15 hours |
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mass movement sequence in large intestine |
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 |
gastrocolic and duodenocolic reflexes-transmitted via autonomic nervous system |
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what prevents continual dribble of fecal matter through anus |
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 |
pudendal nerve |
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intrinsic reflex of defecation mediated by |
local enteric nervous system in rectal wall; normally weak by itself |
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parasympathetic defectaion reflex |
sacral segments of spinal cord via pelvic nerves; greatly intensify peristaltic waves |
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peritoneointestinal reflex |
results from irritation of peritoneum-strongly inhibits excitatory enteric nerves and an cause intestinal paralysis |
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renointestinal and vesicointestinal reflexes |
inhibit intestinal activity as result of kidney or bladder irritation |
