Term
| how many muscle layers are in the stomach wall? what are they? |
|
Definition
| 3, the circular and longitudinal (as seen in the rest of the GI) and the oblique - which does not start until the middle of the body and ends at the end of the antrum |
|
|
Term
| what do the fundus and the upper body of the stomach function as? why is this important? |
|
Definition
| the fundus and the upper body of the stomach function as reservoirs, which rugae (longitudinal folds) allow. this is important evolutionarily b/c it frees humans to grow and develop their brains rather than spending all their time eating |
|
|
Term
| what does a bolus of food become in the stomach? |
|
Definition
| chyme - which is partially digested food mixed w/acids and enzymes |
|
|
Term
| what does the stomach have to regulate in order to ensure chyme is emptied into the duodenum at a rate suitable for digestion and absorption? |
|
Definition
| the rate of emptying is regulated by the pyloric sphincter |
|
|
Term
| if not for what characteristic, would the stomach be considered a non-vital organ? |
|
Definition
| the stomach produces intrinsic factor which enables absorption and storage of vit B12 |
|
|
Term
| what are the 3 phases of gastric motility? |
|
Definition
| filling, mixing, emptying phase |
|
|
Term
| what characterizes the stomach's filling phase? |
|
Definition
| the stomach is able to function as a reservoir, mainly in the fundus and the body where there are weak or no contractions so food is not mixed there |
|
|
Term
| what kind of reflex is receptive relaxation? how does it occur? |
|
Definition
| receptive relaxation is a vagovagal reflex where stretch receptors to the vagal afferents carry impulses to the CNS, then vagal efferents carry impulses back to the stomach. (it is proven to be vagal b/c a vagotomy abolishes the reflex) |
|
|
Term
| how does cholecystokinin affect the stomach? where does it come from? |
|
Definition
| cholecystokinin increases gastric distensability and decreases emptying. it is produced in the small intestine in order to slow down the rate of chyme coming from the stomach |
|
|
Term
| how the different muscle layers of the stomach wall facilitate movement? |
|
Definition
| the upper longitudinal area of the stomach wall is continuous with the esophagus and the lower longitudinal area is continuous with the duodenum which smooths the transfer to and from the stomach. in the middle stomach (on the greater curvature) the longitudinal muscle has pacemakers which help coordinate contractions |
|
|
Term
| what are the slow waves in the stomach? |
|
Definition
| contractions w/out action potentials due to influx of Ca++ and varying Na+/K+ pump action |
|
|
Term
| what is the general progression of the basic electrical rhythm (BER) as the GI tract continues? |
|
Definition
| the BER is very slow in the stomach, then speeds up in the small intestine and gradually slows down again |
|
|
Term
|
Definition
| these cells set the BER, they function as the pacemakers in the stomach smooth muscle b/c they are more sensitive to signaling and are able to disperse depolarizations quickly via tight gap junctions in the muscle sheath |
|
|
Term
| what is the stratification of chyme in the stomach when it is functioning as a reservoir? |
|
Definition
| lipids sit on the surface/top and are digested last and water at the bottom and is digested rapidly due to the fact that the pyloric sphincter cannot ever completely close |
|
|
Term
| what is the function of the antrum and the lower portion of the stomach? |
|
Definition
| the antrum and lower portion of the stomach are thicker walled and function as "cement mixers" to mix and grind up chyme against the *closed pyloric sphincter (to keep bile from damaging the stomach wall) in a churning action called *retropulsion |
|
|
Term
| how does co-ingestion of protein/lipids help slow the absorption of alcohol in the stomach? |
|
Definition
| protein/lipids take the longest to get through the digestive tract, also slowing the absorption of anything else |
|
|
Term
| what is gastric emptying accomplished by? |
|
Definition
| coordination of the stomach, pylorus, and small intestine to push chyme collecting in the antrum of the stomach towards the small intestine. this activates intestinal receptors which then regulate the rate of chyme transferral to the small intestine thereafter |
|
|
Term
| what is the role of autonomic innervation on stomach emptying? |
|
Definition
| sympathetic inhibits stomach emptying and parasympathetic induces stomach emptying |
|
|
Term
| what kind of hormone are all gastric hormones? |
|
Definition
|
|
Term
| if the pH of chyme coming from the stomach is <3.5 how do duodenal chemo and stretch receptors respond? |
|
Definition
| duodenal chemo/stretch receptors send enteric signals and secrete secretin which slows the arrival of highly acidic chyme in the small intestine. |
|
|
Term
| if high levels of fat are in chyme coming into the small intestine, how do duodenal chemo and stretch receptors respond? |
|
Definition
| the duodenal chemo and stretch receptors secrete CCK and GIP which delay emptying of the fatty chyme and allow it to become further broken down |
|
|
Term
| how do duodenal chemo and stretch receptors respond to high levels of amino acids in chyme entering the small intestine? |
|
Definition
| the duodenal chemo and stretch receptors secrete gastrin which slows gastric motility |
|
|
Term
| what clinical factors can affect stomach emptying? |
|
Definition
| age, BMI, gender (females = slower), posture, disease states (DM can lead to gastroparesis, chron's etc), stress (increases gastric emptying rates), and depression (slows gastric emptying) |
|
|
Term
| what is the migrating motor complex? |
|
Definition
| these "housekeeping waves" occur between meals in bursts of 5-10 min all the way through the GI tract every 90-100 min until food is eaten again |
|
|
Term
| what are the only 2 "true" sphincters in the GI? |
|
Definition
| the upper esophageal sphincter and the external anal sphincter b/c they contain skeletal muscle and have a higher resting pressure than adjacent areas |
|
|
Term
| what are the three classifications of secretagogues (any substance that stimulates a secretory cell to secrete) in the GI? |
|
Definition
| neurocrine: NTs released from neurons that innervate secretory cells (e.g. ACh from vagus), endocrine (no duct): hormones released into blood (e.g. gastrin for G cells), and paracrine: substances released in close proximity to their target that travel via diffusion (e.g. histamine as an agonist for HCl secretion) |
|
|
Term
| what are the major secretions in gastric juice? |
|
Definition
| HCl, pepsionogen, intrinsic factor, mucous, somatostatin, gastrin, and histamine |
|
|
Term
| what is the role of HCl in gastric juice? |
|
Definition
| HCl denatures proteins, destroys bacteria, and converts Fe+3 to Fe+2 so it can be absorbed for Hb synthesis |
|
|
Term
| what is the role of pepsinogen in gastric juice? |
|
Definition
| pepsinogen is a gastric proenzyme that is converted into pepsin (protease) in the presence of HCl |
|
|
Term
| what is the role of intrinsic factor in gastric juice? |
|
Definition
| intrinsic factor functions as a vit B12 binding protein |
|
|
Term
| what is the role of mucous in the gastric juice? |
|
Definition
| mucous protects the stomach wall from HCl, pepsin, and mechanical trauma |
|
|
Term
| what is the role of somatostatin in gastric juice? |
|
Definition
| somatostatin is stimulated by high levels of H+ in the stomach lumen and shuts down its production. it is inhibited by vagal stimulation |
|
|
Term
| what is the role of gastrin in gastric juice? |
|
Definition
| gastrin stimulates HCl and histamine |
|
|
Term
| what is the role of histamine in gastric juice? |
|
Definition
| histamine stimulates HCl secretion |
|
|
Term
| what is the surface of the stomach wall lined with? |
|
Definition
| mucous cells with tight junctions along which HCO3- is secreted |
|
|
Term
| how low of a pH can the stomach wall stand? |
|
Definition
|
|
Term
| what cells are found in the gastric pits and what do they do? |
|
Definition
| G cells: stimulate acid production directly and through histamine. D cells: secrete somatostatin (inhibits acid). chief cells: secrete pepsinogen. enterochromaffin cells: secrete histamine, which stimulates acid. parietal cells: secrete HCl and intrinsic factor. mucous neck cells: secrete mucous and HCO3- |
|
|
Term
|
Definition
| due to metabolism, there is a surplus of CO2 and H20 which combine to form carbonic acid (H2CO3). carbonic acid dissociates into bicarb and H+. bicarb diffuses out and H+ is transported to the gastric pits where it combines ith Cl- (which is copious in the interstitium). |
|
|
Term
| what is the alkaline tide? |
|
Definition
| a rise in bicarb in the bloodstream as a result of HCl production (1:1 production) |
|
|
Term
| does HCl production depend on the type of food being digested? |
|
Definition
|
|
Term
|
Definition
| a zymogen (inactive precursor) that is cleaved to pepsin only in the presence of pH <3 to keep the stomach from digesting itself b/c pepsin is the major hydrolytic enzyme in the stomach |
|
|
Term
| what are the 3 phases of gastric secretion regulation? |
|
Definition
| cephalic phase: "reflex phase", occurs prior to entry. gastric phase: once food enters the stomach. intestinal phase: as chyme enters the duodenum |
|
|
Term
| what characterizes the cephalic phase? |
|
Definition
| the smell/sound of food preparation activate this phase and lead to stimulation through the medulla oblongata which then sets off parasympathetic APs into the stomach - specifically in the myenteric plexus which signals the chief cells, parietal cells, and G cells |
|
|
Term
| what did pavlov prove with his experiements on dogs? |
|
Definition
| pavlov made an esophageal stoma, through which any food going to the stomach would be diverted through and he found that the stomach still secreted HCl, gastrin, etc despite the fact that food never reached it. he also found that severing the vagus nerve above the diaphragm stopped these secretions - proving that the neuronal mediated pattern of activity was completely initiated by the senses. |
|
|
Term
| can the environment in a nursing home, if made more comfortable, increase caloric intake? |
|
Definition
|
|
Term
| what characterizes the gastric phase? |
|
Definition
| the gastric phase is responsible for most of the acid secretion of the stomach and is initiated by the presence of food in the stomach. |
|
|
Term
| how does the presence of food in the stomach initiate the gastric phase? |
|
Definition
| distention of the stomach activates a parasympathetic reflex, which sends APs up the vagus to the medulla oblongata which stimulates further stomach secretions. stomach distention also stimulates local reflexes which amplify stomach secretions |
|
|
Term
| what are the three mechanisms of the intestinal phase that inhibit chyme coming into the duodenum if its pH is less than 3? |
|
Definition
| 1) sensory input to the medulla from the duodenum inhibits motor input from the medulla to the stomach, *stopping secretion of pepsin/HCl via somatostain. 2) local reflexes inhibit gastric secretion. 3) secretin, gastric inhibitory polypeptide and CCK inhibit gastric secretions in the stomach |
|
|
Term
|
Definition
|
|
Term
|
Definition
| gastric inhibitory peptide, which is released by duodenum/jejunum epithelial cells and decreases gastric H+ secretion, increases insulin secretion. vasoactive intestinal peptide is released by the neuronal cells of the entire GI tract and decreases H+ secretion, stimulates pancreatic HCO3 secretion and relaxes GI smooth muscle/vasodilates |
|
|
Term
| what is gastric transit time? |
|
Definition
| an important metric that reflects the way the stomach and intestines handle a meal |
|
|
Term
| who was william beaumont? what did he learn? |
|
Definition
| an army surgeon who was able to perform tests on the town drunk who was shot in the stomach leaving an open fistula after the wound healed. beaumont studied the role of HCl, temperature and movement in digestion |
|
|
Term
| how much of cardiac output can go to the stomach at rest? |
|
Definition
|
|
Term
| why are the tissues lining the stomach so vulnerable to ischemia? |
|
Definition
| b/c they are constantly sloughing off, meaning there is constant mitotic activity, meaning that it needs a steady and reliable blood supply |
|
|
Term
| what is the positive feedback loop that occurs w/massive hemorrhage in the stomach? |
|
Definition
| massive hemorrage in the stomach leads to a fall in CO and arterial hypotension, this then leads to increased total peripheral resistance, redistribution to the vital organs and decreased splanchnic flow |
|
|
Term
|
Definition
| abdominal gurgling due to the passage of fluid and gas in the intestines which is enhanced w/increased GI motility |
|
|
