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46 Cards in this Set
- Front
- Back
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Describe the differences in molar vs incisor in terms of location, function, and maximum pressure.
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Incisors, anterior, cutting, 50 lbs.
Molars, posterior, grinding, 200 lbs |
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What nerve innervates muscles of mastication?
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CN 5 motor branch
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Describe the chewing reflex in the mouth.
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You put food in the mouth- the muscles of mastication are inhibited and the jaw drops.This drop then leads to a stretch reflex of the jaw muscles that causes a rebound contraction.This is then repeated again and again.
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Why do we chew our food?
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1) Physically breaks it down
2) Prevents excoriation of GI tract 3) Increase SA for digestion. |
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What are the stages of swallowing?
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Voluntary, pharyngeal, esophageal.
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Describe the voluntary stage of swallowing?
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In the voluntary stage, food is voluntarily squeezed into the pharynx by the tongue.
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Describe the pharyngeal stage of swallowing?
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1) THe soft palate is pulled up to prevent food from going into the nasal passages
2) the palatopharyneal foldsdeviate medially- this forms a slit through which food must pass to be swallowed. Vocal cords approximated, larynx pulled up, anteriorly - to cause epiglottis to cover opening of larynx (close trachea) 4) Upward movement of larynx opens esophagus and esophageal spincter relaxes, allowing food movement. 5) The pharynx contracts and propels food into the esophagus. 6) Respiration interrupted |
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What nerve innervates the upper 1/3 of esophagus? Why is only the upper 1/3 innervated by this nerve?
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Glossopharyngeal. This is because only the upper 1/3 is skeletal muscle. The rest is SM.
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How does the esophageal phase of swallowing work?
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Primary peristalsis is the continuation of the wave that began in the pharynx. This takes 8-10 seconds to reach the stomach, and food takes only 5 seconds due to gravity. If the esophagus is not completely emptied, secondary peristalsis can occur- this persists even without the vagus, meaning myenteric plexus controls it.
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What is receptive relaxation of the stomach?
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When the esophageal peristaltic wave reaches the stomach, myenteric inhibitory neurons release VIP, triggering a wave of relaxation in the stomach so that it can receive food.
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What is the normal state of the gastroesophageal sphincter? What is the pathological state?
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Normal: gastroesophageal sphincter tonically constricted until wave of relaxation hits. Then it relaxes via the reeceptive relaxation mechanism and food can pass into the stomach. In the pathological state, achalasia, the gastroesophageal sphincter does not relax, leading to megaesophagus.
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What pressure does the gastroesophageal sphincter normally have?
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The gastroesophageal sphincter, which is the last 3 cm of the esophagus, has a pressure of 30 mmHg.
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Why have a tonically constricted gastroesophageal sphincter?
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The purpose is to prevent reflux.
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What is another mechanism that prevents reflux into the esophagus
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The esophageal valve is the final portion of the esophagus that extends into the stomach slightly. When intra-abdominal pressure goes high, it collapses.
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Which disease produces a bird beak appearance during barium study?
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Achalasia
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What is a hiatal hernia?
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The Lower esophageal sphincter protrudes into the thoracic cavity and becomes patent dt negative pressure in thorax.
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What are the functions of the stomach?
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1) Allows you to eat more food than can be processed
2) Kills bacteria 3) Mixture of food with secretions to create chyme 4) slow empyting of chyme into duodenum at appropriate rate 5) mixes food with pepsin and acid to break down collagen. |
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What is the vagovagal reflex?
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With food entry, vagovagal reflex from stomach to brain
stem (and back) to reduce wall tone in the fundus and body – bulging outward – keeps pressure in stomach low |
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T/F Majority of the contractions in the stomach are strong mixing contractions?
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False. Most are weak, and just promote mixing.
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Describe the strong contractions in the stomach?
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Pyloric pump -intense peristaltic contractions (20% of total contractions) of the time in the antrum promote emptying of the stomach. With emptying, contractions move further up the stomach. each contraction empties a few ml of chyme into duodenum.
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How does the composition of the pyloric sphincter differ?
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The pyloric sphincter is tonically constricted and much THICKER than antrum.
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How does the pyloric sphincter's tonic constriction benefit digestion?
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This tonic tone is tight enough to prevent solid food to pass, but still loose enough to let some chyme slip in. The degree of constriction is under neural and humoral control.
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What is the term that describes solid food being forced back into the stomach for more mixing
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Retropulsion
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How long does stomach empyting typically take? What are factors that enhance its emptying?
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2-3 hours
1) High food VOLUME not pressure - stretch reflex via myenteric plexus - increasing pyloric pump, decreasing pyloric sphincter. 2)Gastrin mildly enhances stomach emptying (secreted in response to meat). Increases H+ secretion |
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What are factors that inhibit stomach emptying?
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DENR - duodenal enterogastric reflexes. nerves from duodenum to prevertebral sympathetic nerves to stomach. Inhibits vagal tone - slows pyloric pump, increases pyloric sphincter.
And then the hormones CCK Secretin Enterogastrone GIP |
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What are the factors that activate the DENR-
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duodenal distension
irritation of duodenal mucosa duodenal acidity of chyme (since duodenum is where pancreatic juice released needs more time to neutralize) high or low osmolarity Breakdown products of protein/fats (need more digestion time) |
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In the SI, how fast are propulsive movements of chyme? are they strong like they are in the stomach?
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In the SI, chyme movements are not strong like they are in the stomach. They travel only 5 cm at 1-2 cm / sec velocity. Chyme takes about 4 hours to empty out.
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Which hormones increase stomach motility?
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GM
Gastrin Motilin |
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Which hormones inhibit stomach motility?
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GECS
GECS GIP, Enterogastrone, CCK, secretin |
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Which hormones promote SI motility?
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CIGS
CCK, INSULIN, Gastrin, Serotonin |
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Which hormones inhibit SI motility?
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GIP
VIP Secretin Glucagon |
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What is peristaltic rush?
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The ANS/ENS initiate forceful peristalsis dt intense irritation - rapid clearing of SI
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Do peristaltic contractions occur when you are fasting?
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Yes every 90 minutes or so to empty the GI contents and prevent bacteria overgrowth. This is mediated by motillin.
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What kind of motor complexes are responsible for backwards peristalsis?
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Retrograde motor complexes. Irritation of these triggers nausea and vomitting- causes reverse peristalsis.
si -> stomach -> vomit |
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What are the functions of the ileocecal valve?
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Prevent fecal matter from flowing back into the SI.
Can withstand pressures of 60 cm H20 |
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What are the functions of the ileocecal sphincter?
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The ileocecal sphincter slows empyting of ileal contents into the cecum. This facillitates absorption.
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What is the ileocecal sphincter controlled by?
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Controlled by cecum reflexes
Cecum distension: increases tone, inhibits ileal peristalsis Cecum irritation (appendicitis): can cause sphincter spasm and ileal paralysis Mediated by myenteric plexus and ANS (via prevertebral sympathetic ganglia) Opens after a meal via gastroileal reflex |
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What are the functions of the colon?
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The proximal half is to reabsorb water and electrolytes to form feces
The distal half is to store fecal matter until expulsion |
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What are the two movement types of the colon?
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Mixing movements- haustrations.
Propulsive movements- mass movements |
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What are haustrations?
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These are similar to the segmentation movements in the SI- large constrictions occur, almost to occlusion. The longitudinal muscle (tenae coli) then constricts. Together these cause bulging of the unconstricted regions called haustrations.These have some propulsive component to them and they have a roll and dig movement for more affective absorption.
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What are mass movements?
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From the cecum to the sigmoid, these propulsive movements move the feces through the colon. A constrictive ring occurs in response to a distended part of the colon. Then distal colon loses its haustrations and contracts as a unit, propelling the feces forward.
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What reflexes facilitate the mass movements?
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Gastrocolic and Duodenocolic after meals via ANS.
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T/F most of the time the rectum is empty of feces
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True, a partially week sphincter exists between the sigmoid colon and rectom and it also has a sharp angulation. The mass movement fills the rectum.
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What happens when fecal matter enters the rectum?
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The urge for defecation is felt immediately. The rectum contracts and the anal sphincters relax.
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What is the difference between the internal and external anal sphincter?
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The internal anal sphincter is under autonomic control (SM). The external anal sphincter is under voluntary control (skeletal muscle) and is controlled by the pudendal nerve.
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How does the defecation reflex work?
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When feces enter the rectum, they distend the rectum, which causes signals to spread through the myenteric plexus to initiate peristaltic waves, forcing the feces towards the anus. The internal anal sphincter is relaxed from the myenteric plexus. If the external one was also relaxed, defecation occurs. This is relatively weak and must be fortified by a parasympathetic defecation reflex-stretch in rectum causes pelvic nerves (PNS) to intensify the peristaltic signal and relax internal sphincter
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