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GI Physiology - Motility

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yupuhefa's version from 2012-03-13 20:52

Section

Question Answer
What comprises the upper esophogeal sphincter?Cricopharyngeus (most important), Inferior Constrictor, and Proximal Esophagus
Scleroderma affects what type of muscle? Smooth muscle
Is swallowing voluntary or involuntary?Both, has components that are voluntary while others that are involuntary
Normal gastric emptying half (time it takes for half of solid food to be emptied from stomach)85 minutes
Increased glucose intake leads to what effect on gastric emptying?The higher the glucose intake, the longer it takes to empty the stomach
How are indigestible, >3mm objects get pushed out of stomach?Occurs during the fasting state when the Migrating Motility Complex begins to work
What is the effect of vertigo on gastric emptying?Slows emptying
What are the two mechanisms of muscle relaxation in the fundus/body of the stomach in response to eating?1. Receptive Relaxation is mediated by myenteric plexus when peristalsis reaches the lower esophagus; 2. Vago-vagal reflex in response to increased volume/stretch of the stomach
What is the function of motilin? What is the most commonly used Motilin receptor agonist?When in a fasting state, motilin increases in the blood leading to rapid peristalsis/MMC in the stomach; this will push any remaining food out of stomach (MMC = Migratory Motor Complex); Erythromycin stimulates motilin receptor to cause stomach emptying
What is the entero-gastric reflex? What is it activated by?The duodenum signals the stomach to slow down empyting; occurs in three ways: 1. When dudodenum stretched, ascending myenteric nervous system stimulates inhibitory neurons in the stomach; 2. Sensory fibers from duodenum travel to sympathetic ganglion and stimulate inhibitory fibers going back to stomach; 3. Sensory fibers in vagus nerve travel to CNS centers and causes inhibition of stomach; This reflex is activated by stretch, decreased pH, irritation, hypo or hypertonic solutions (affects water/ion homeostasis), Protein/Fat, glucose
Why do hyper and hypotonic solutions in the duodenum inhibit stomach emptying?These solutions would negatively affect water/ion balance, therefore the chemoreceptors in the duodenum are stimulated and the stomach is inhibited
What are I cells?They produce Cholecystokinin --> 1. Causes Gallbladder contraction to increase bile/bicarbonate; 2. Stimulates acini in the Pancreas that secrete pancreatic enzymes; 3. Inhibits smooth muscles (decreased gastric motility) NOTE: This has nothing to do with I-cell disease, which is a disorder characterized by release of lysosomal enzymes from the cell instead of storing them in lysosomes
What are the functions of Secretin?1. It stimulates pancreatic secretion of bicarbonate rich solution; 2. Slows down stomach; 3. Increases Bicarbonate release from glands of Brunner
What factors stimulate gastric function?Parasympathetic nervous system, Motilin, and Gastrin
What factors inhibit gastric function?Sympathetic nervous system, GIP (Gastric Inhibitory Peptide), and CCK (Cholecystokinin)
What is the relationship of I cells and I-cell Disease?There is no relationship; I cells produce and secrete CCK which induces secretion of pancreatic enzymes and slows down stomach; I-cell Disease is a lysosomal storage disease caused by a defect in a phosphotrasnferase in the Golgi apparatus (Loss of Mannose-6-phosphate tagging) --> This leads to lysosomal enzyme release from the cell instead of them being tagged to go to lysosomes --> Manifests with mental retardation, coarse facial features, congenital hip dislocation and other bone problems
What are the causes of pyloric stenosis? What is the classical symptom of this condition?1. Congenital (especially male infants); 2. Chronic peptic ulcer disease leading to inflammation and scarring; 3. Cancer/Malignancy --> These all cause vomiting that does not contain bile (Non-bilius vomiting)
What is gastroparesis? What are common symptoms?Stomach becomes semi-paralyzed, so food remains in the stomach for a long time --> Leads to nausea/vomiting, feeling of satiation even when eating very little
What is the gastro-ileal/gastro-enteric reflex?When the stomach is distended, motility in the small intestine is increased --> Works through myenteric plexus, vago-vagal reflex, or primary sensory fibers inhibiting sympathetic ganglion (increases motility)
What is peristaltic rush/power propulsion?When the small intestine is overly distended or irritated and wants to rapidly push its content into the large intestine; This is associated with abdominal pain/cramps and is classically caused by infectious diarrhea; NOTE: This also occurs in the opposite direction during vomiting (can induce with administration of apomorphine)
What is the function of the MMC?To "clean out" the stomach, small intestine, and bile duct during a fasting state (triggered by high levels of the hormone motilin in the fasting state)
What is the ceco-ileal reflex? How is it controlled?When pressure in the cecum increases, it causes constriction of the ileo-cecal sphincter to prevent backflow; This is mediated by the myenteric plexus and sympathetic ganglion (via primary sensory fibers)
What are haustrations?Circular contractions of the large intestine reduce lumenal area while Tinea coli also constrict and shorten the large intestine; The ballooned segments inbetween the ringed contrictions are called haustra; The movements that create haustra are called haustrations
What are segmental propulsions?Propulsive movements that move material between haustra
What is mass movement in the large intestine?A strong constriction ring --> The haustrations distal to the ring disappear and the entire segment constricts, causing propulsion of material distally; NOTE: Occurs in different frequency in different people per day
How is the colon stimulated to increase motility?The gastro-colic reflex and via duodenal-colic reflex
Is the internal or external anal sphincter voluntary?External is voluntary
What two factors can trigger secondary peristalsis in esophagus?Piece of remnant food in esophagus or Acid
Distinguish the activity front of MMC from activity going on in intestinePeristalsis at the rate of slow waves
Phase IIIdetect regular contractions
Phase IIdetect irregular contractions
Where is bile reabsorbed?In the terminal Ileum
What is the effect of apomorphine?Induces vomiting via power propulsions going orally
How do stimulant laxitives such as castor oil and senna?They work by triggering release of 5-HT which irritates bowel and causes power propulsion
What is the difference between haustrations in the large intestine and the mixing program in the small intestine?Physiologically, the only difference is that haustrations occur at a slower rate than the mixing program
What muscles are most important in maintaining fecal continence?Puborectalis and External Anal Sphincter
What controls the internal anal sphincter? What controls the external?Internal = Enteric nervous system; External = Sacral outflow
Describe what normally occurs when the rectum is distendedThe internal anal sphincter relaxes via the rectoanal reflex and the external anal sphincter/puborectalis contract in response to sensory stimulation in the lining of the anal canal (continence)
What muscles are responsible for fecal continencePuborectalis and External Anal sphincter
What occurs to anal sphincter function in spinal cord injury vs in Hirschprung's disease?In spinal cord injury, voluntary control of the external anal sphincter is lost so it does not contract in response to rectal distension but the relaxation of smooth muscle in the internal anal sphincter is intact; However, in Hirschprung's disease the opposite occurs. Control of smooth muscle is lost because of loss of enteric ganglia --> Therefore upon distention of the rectum, the external anal sphincter contracts but the smooth muscle of the internal anal sphincter fails to relax
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