Term
| Briefly describe the type of motility that's going on in the GI tract during a fasting state. |
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Definition
| The Migrating Myoelectric Complex. Begins 3-4 hours after eating, sweeps undigested material into the colon. Active mid-stomach to the terminal ileum. Four phases, just phase 3 is important. |
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Term
| Describe the role of the hormone motilin in the MMC. |
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Definition
| Motilin stimulates phase 3, which is where the major series of contractions occurs that sweeps material into the colon. Phase three lasts 10 minutes. Motilin is secreted from the M cells of the small intestine. |
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Term
| What are the differences between primary esophageal peristalsis and secondary? Talk about innervations too. |
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Definition
| Primary esophageal peristalsis is normal, occurs under control of the medullary centers of the brain. If something gets stuck in the esophagus, secondary peristalsis takes over. This process is under local enteric nervous system control, via the myenteric plexus (M for motility). |
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Term
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Definition
| A smooth muscle disorder with the lower esophageal sphincter. It's constantly contracted so food is backed up. This can be surgically fixed, but patients will typically have acid reflux issues since the sphincter will remain relaxed. |
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Term
| What's Hirschsprung's Disease? |
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Definition
| Lack of innervation to the internal anal sphincter smooth muscle. The sphincter doesn't relax, and you get a back up of shit. Leads to megacolon. |
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Term
| How can the stomach accommodate such a large volume of food? |
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Definition
| Because vagal stimulation relaxes the stomach, allowing it to expand and keep the intraluminal pressures constant. If vagus nerve is cut or during bariatric surgery, intraluminal pressure will rise with small food intake. Patient feels full faster. This receptive relaxation is vagally mediated via vasoactive intestinal peptide (VIP). |
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Term
| What determines how long it takes for the stomach to empty its contents? |
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Definition
| The composition of the chyme/food. Fatty foods take longer to clear, followed by acidic foods. Salty foods clear fastest. |
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Term
| What pumps determine the basal electrical rhythm? |
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Definition
| Na/K ATPases. These pump 2K+ in for 3Na+ out, and they determine the BER. |
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Term
| Describe the rate of contractions produced via the BER in the stomach vs small and large intestines. |
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Definition
| We get 3 contractions a minute in the stomach, which is better served for mixing. 10-12 contractions a minute in the small intestines, which helps in propulsion. Contractions in the colon can be fast or slow, depending on if the body wants to clear food or store it. |
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Term
| The opening of what channels cause a slow wave depolarization? |
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Definition
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Term
| Describe how slow waves can be stimulated locally or systemically. |
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Definition
| Locally, mechanostretch receptors detect and initiate a contraction. System contractions are more uniform throughout the GI tract, and are caused by hormones or vagal stimulation. |
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Term
What favors depolarization of slow waves?
Hyperpolarization? |
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Definition
| Parasympathetic activity, gastrin, motilin, CCK favor more contractions. Hyperpolarization is favored by sympathetic activtity, Vasoactive Intestinal Peptide (VIP) (remember this is the hormone that helps with receptive relaxation --> fewer contractions). |
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Term
| Describe the role of interneurons in peristalsis |
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Definition
| Interneurons allow for fine coordination of contractions. Behind the bolus, motor neurons contract, while in front of the bolus, they relax the smooth muscle. |
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Term
| What are two instances in which propulsion via peristalsis doesn't proceed towards the anus? |
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Definition
| During vomiting, and in the rectum when defecation reflex is voluntarily stopped. In these cases reverse peristalsis occurs. |
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Term
| What types of nervous control are segmentation and peristalsis under? Which one is responsible for most propuslion? |
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Definition
| Peristalsis is under extrinisic control via the vagus. Segmentation is thought to be under intrinsic control via enteric nervous system. Segmentation is responsible for most movement. |
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Term
| What two factors influence bile secretion into duodenum? |
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Definition
Vagal stimulation: relaxes the sphincter of oddi. Vagal stimulation occurs upon eating.
CCK: contracts gall bladder. CCK is released once chyme enters duodenum. |
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Term
| What role does fever play in giving you diarrhea? |
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Definition
| An increase in temperature makes the Na/K pumps more active, so you get a faster BER. This can lead to diarrhea as the food moves faster through the GI tract. |
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Term
| What's the difference between segmentation in the small intestine and in the colon? |
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Definition
| In the colon, instead of smooth circular muscle contracting to produce segments, longitudinal muscle called taneia coli work slowly to segment colon, forming haustrae. |
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Term
| Describe the role of gastrin and vagal stimulation in the gastrocolic reflex. |
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Definition
| Upon eating, gastrin secretions in the stomach and vagal stimulation will create mass movements in the small intestine, where the haustrae smooth out, allowing feces to get into rectum. Clearing out old food to make room for new food, basically. |
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Term
| Talk about the defecation reflex. |
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Definition
| Rectal stretch receptors allow relaxation of the internal anal sphincter, allowing feces to get into anal canal. If you hold it in long enough, the urge to poop goes away until something else causes further stretching of rectum. |
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Term
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Definition
| When you're holding it in, and eventually you try to manually activate the defecation reflex. |
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