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Vocababble: Digestive System

BER = base electrical rhythm, cycles of depolarization that originate in the stomach and spread via gap junctions among the cells of the digestive tract (electrical impulses traveling among cells like the syncytium of the heart). They rhythm is 3-12 pulses per minute. The stomach muscles contract from these depolarization cycles, but the rest of the digestive tract requires additional stimulus to generate an action potential to stimulate smooth muscle contraction

action potential = a sufficient depolarization of a neuron membrane to trigger propagation to the synapse.

interstitial cells = in the stomach, are non-neural cells resembling fibroblasts that generate (propagate???) BERs. They are located between the outer longitudinal and inner circular layers of the muscularis externa, in the same region as the myenteric plexi.

stimuli for depolarization = activation of gut action = distention of muscles in stomach, intestine, parasympathetic stimulation (vagal via acetylcholine), hormones (gastrin, CCK)

stimuli for hyperpolarization = inhibition of gut action = sympathetic nervous stimulation, epinephrine in blood

constricting/mixing waves = in the stomach, respond to pacemaker in middle of stmoach, concentric contractions of smooth muscle, milking action, squeezes stuff into they pyloric region. The contractions are stronger there, and when the pyloric sphincter is closed the chyme reverses direction and is squirted back into the stomach, mixing the contents with every swish.

bolus = blob of foodstuff

steps of swallowing = 1) chew (hopefully) then take bolus to back of mouth via pushing up with tongue against hard palate (conscious) 2) nasopharynx closes (unconscious from here on) 3) larynx raises, glottis closes 4) peristaltic contractions move bolus down esophagus due to reticular center programming

dysphagia = trouble swallowing, common in ALS

aspiration pneumonia = common in people who have trouble swallowing, incomplete closure of glottis allows foodstuff to get into trachea and lungs providing food for bacteria in wrong place

UES and LES functions and anatomy = UES is upper esophageal sphincter, LES is lower. Both sphincters are closed and the esophagus is relaxed between swallows. The glossopharyngeal and vagal nerves are involved in swallowing. The relaxation of the UES and LES are specifically mediated by the vagus nerve, VIP and NO. During swallowing the cricopharyngeus muscle relaxes and that opens the UES. The LES relaxes when food travels down the esphagus and the peristaltic wave hits, letting the bolus drop into the stomach. When the LES fails you have GERD, gastro-esophageal reflux disease, where the acid from the stomach digests the lower esophagus causing trouble.

three types of esophageal peristalsis = primary is regular peristalsis that delivers a bolus from the mouth to the stomach. Secondary is the contractions that occur when something is stuck in your throat, and your body senses the distention and keeps trying to swallow it down. This is still functional progressing peristalsis. Tertiary is disorganized muscle contraction of the esophageal smooth muscle, chaotic and nonfunctional.

VIP = vasoactive intestinal peptide, relaxes gut smooth muscle, comes from pancreatic islet cells

transient relaxation of esophageal sphincters = what has to happen for swallowing, mediated by VIP or vagus

chyme = food and stomach secretions mixed into an acidic paste

retropulsion = the backward motion of chyme during mixing waves, when it gets to the pyloris and the valve is closed, and the chyme squirts back through the concentric contracted part of the stomach into the body.

gastric emptying = one way movement of chyme from stomach into duodenum, lipids empty from the stomach last because they float on top of everything else

stomach distention = a stimulus that weakly encourages emptying. if you're full, it wants to move on through.

duodenal activity = a stimulus that slows gastric emptying. The duodenum sense neurological and hormonal signals that say "slow down with the acid stuff, we've got our hands full trying to digest what you've already sent". The duodenum senses acid, non-isotonic solutions and fat, and that stimulates CCK and vagal action to slow stomach emptying.

gastrin = a hormone released due to vagal stimulation that causes increase in stomach acid and motility, and a slowing of gastric emptying

CCK = cholecystokinin = a brush border hormone provoked when stomach contents hit the duodenal I-cells, kicks off intestinal phase of digestion including gall bladder contraction, slowing of gastric emptying, increased intestinal motility, etc.

secretin = another brush border hormone provoked by fat and acid in the duodenum, causes the release of bicarbonate from duct cells to buffer acids, slows gastric emptying, also reduces acid production in stomach.

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