PHYSII Midterm Material
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| What the fundus in the stomach? | Top are above the LES
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| Does the body or the antrum of the stomach have a thicker amount of smooth muscle? | The antrum has a thicker amount
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| What is the significance in the difference in thickness of smooth muscle in the stomach? | It is important for gastric motility; more smooth muscle means greater strength of contraction
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| Where is the pyloric sphincter located? | Between the stomach and the duodenum of the small intestine
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| What are the three divisions of the stomach? | Fundus, body, antrum
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| What are the three main functions of the stomach? | storage, HCl secretion, and mixing
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| Why does the stomach secrete HCl? | To begin protein digestion
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| What is the end product in the stomach after mixing pulverized food with gastric secretions? | Chyme
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| What is the stomach volume when it is empty? When its full? | 50mLs; 1500 mLs
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| What fold change in volume occurs between an empty and full stomach? | A 30 fold change
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| What two small changes occur to allow volume change in the stomach? | Stomach wall tension and intragastric pressure
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| What folds in the stomach flatten during food intake? | Rugae
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| What reflex occurs during stomach relaxation? | Receptive relaxation; allows stomach to accommodate an increased volume without increasing pressure
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| What is receptive relaxation triggered by? | eating and mediation by the vagus nerve
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| What happens if you consume more than 1.5L of food? | The stomach will become overdistended and cause an increase in intragastric pressure and discomfort
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| What size particles can enter the duodenum? | smaller than 1 cubic millimeter
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| What happens during gastric emptying | After initial peristaltic wave from fundus toward pyloric sphincter occurs, vigorous contractions continue in the antrum and peristalsis propel small amounts of chyme forward through partially open sphincter
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| What happens during gastric emptying (2) | Strong repetitive antral contractions propel small chyme amounts through pyloric sphincter. Retropulsion occurs when peristaltic contractions reach pyloric sphincter and closes it. Chyme is tossed back into antrum for further mixing with each contraction
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| What three stomach factors modify the rate of gastric emptying? | amount of chyme (MAJOR FACTOR), stomach distension, and chyme fluidity (ADF!)
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| How does stomach distension increase stomach motility? | directly effects stretch of smooth muscle, involves intrinsic plexuses and vagus nerve, and by gastrin
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| How does fluidity affect gastric emptying? | Increased chyme fluidity allows faster emptying while decreased fluidity slows emptying.
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| For a 1.5L meal, how long does it take to empty gastric contents into the duodenum? | 3 hours
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| What four duodenal factors modify rate of gastric emptying? | fat, acid, distension, and hypertonicity (FADH!)
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| What type of receptors are stimulated by duodenal factors on gastric emptying? | duodenal receptors; trigger neural/hormonal response, decrease smooth muscle excitability and decrease rate of gastric emptying
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| What neural response occurs after stimulation of duodenal receptors? | enterogastric reflex
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| What is the enterogastric reflex mediated by? | Short intrinsic nerve plexuses and long autonmic nerves
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| What hormonal response occurs after stimulation of duodenal receptors? | Release of enterogastrones (secretin & CCK) from DUODENAL MUCOSA
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| What does fat in the duodenum do to modify rate of gastric emptying? | inhibits emptying of gastric contents (slower than carbs)
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| What mediates fat in the duodenum? | CCK (secreted by I cells in the duodenum and jejunum mucosa)
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| What does acid in the duodenum do to modify rate of gastric emptying? | inhibits emptying of gastric contents
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| What mediated acid in the duodenum? | enteric nervous system reflexes
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| How is HCl chyme from stomach in duodenum neutralized? | sodium bicarbonate in the duodenum secreted from the PANCREAS
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| What effect does un-neutralized protons in duodenum have? | inhibits gastric emptying until complete neutralization occurs BUT inactivates pancreatic enzymes
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| How does hypertonicity occur in the duodenum? | when absorption rate of amino acids and glucose does not keep up with protein and carbohydrate digestion and stay in chyme; causes water to cross duodenal wall and lumen to cause INTESTINAL DISTENSION (increased osmolarity)
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| What does hypertonicity in the duodenum do to modify rate of gastric emptying? | Reflexively inhibits gastric emptying to prevent increased osmolarity of duodenum
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| What does distension of the duodenum do to modify rate of gastric emptying? | inhibits gastric emptying to allow duodenum time to catch up from presence of CHYME
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| What cells in the stomach secrete gastric digestive juices? | Cells in oxyntic gastric mucosa (fundus and body) and pyloric gland area mucosa (antrum)
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| What structures in the stomach lumen produce gastric digestive juice? | Gastric pits
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| What is the base of gastric pit called? | gastric GLAND
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| What cells occur between gastric pits and cover the gastric mucosa? | surface epithelial cells
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| What cells line gastric pits and entrance of glands? | Mucous cells that secrete thin watery mucus
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| What cells line the deeper parts of gastric glands and secrete pepsinogen? | Chief cells
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| What cells line the deeper parts of the gastric glands and secrete HCl? | Parietal (oxyntic) cells
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| What cells occur in gastric glands and secrete histamine? | enterochromaffin-like (ECL) cells
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| What other types of cells occur in the pyloric gland area mucosa of the stomach? | G and D cells
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| What do G cells secrete? | gastrin
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| When do G cells secrete gastrin? | In response to eating
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| What are the two actions of gastrin? | Stimulate proton secretion from parietal cells and growth of gastric mucosa
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| Growth of gastric mucosa is also known as what? | a trophic effect
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| What occurs during Zollinger-Ellison Syndrome? | Gastrin secreting tumors are present in the pancreas or duodenum that increase proton secretion and gastric mucosa hypertrophy; cause duodenal ULCERS and STEATORRHEA (reduced fat absorption)
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| What do D cells in the stomach pyloric glands secrete? | Somatostatin
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| What does somatostatin inhibit? | HCl secretion, release of gastrin and histamine
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| What is the process of HCl secretion by parietal cells in the stomach? | After water and carbon dioxide form carbonic acid and bicarb, the extra protons are excreted by a proton-potassium exchange into the lumen and chlorine follows by diffusion. Bicarb is excreted into the blood by a bicarb chloride exchanger (alkaline tide)
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| What enzyme catalyzes the formation of carbonic acid from water and carbon dioxide? | Carbonic anhydrase
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| What two channels consume ATP in the production of HCl in parietal cells? | Proton pump (proton potassium exchanger) and sodium potassium ATPase (sodium out; potassium in)
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| What are three agonists in proton secretion from parietal cells? | ACh from vagus nerve, gastrin from G cells, and histamine from ECL cells
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| What type of receptors do proton secretion agonists work on? | Ach works on M3 receptors, gastrin works on CCK(b) receptors, and histamine works on H(2) receptors
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| What does atropine do in the regulation of proton secretion? | Blocks M3 receptors from interacting with ACh
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| How do ACh and gastrin increase proton pump activity? | both receptors activate G(q) subunit that secretes IP3 and calcium to trigger pump activity
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| How does histamine increase proton pump activity? | activate Gs subunit that secretes cAMP to trigger pump activity
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| What are two antagonists in proton secretion from parietal cells? | Somatostatin and prostaglandins
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| How do somatostatin and prostaglandins inhibit proton pump activity? | Activate G(i) complex to inhibit production of cAMP
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| What does cimetidine do in the regulation of proton secretion? | Blocks H(2) receptors from interacting with histamine (no cAMP production)
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| What are the three functions of hydrochloric acid in digestion? | activates pepsinogen, aids in connective tissue and protein breakdown, and kills most ingested microorganisms (helps salivary lysozyme)
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| What activates pepsinogen when its secreted into the intestinal lumen? | Hydrochloric acid by cleavage
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| What type of process is pepsin on pepsinogen? | Autocatolytic/self activating process on same enzyme molecules (creates more pepsin)
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| What does pepsin do? | Initiates protein digestion by splitting amino acid linkages into peptides
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| What are the three phases of gastric secretion? | Cephalic, gastric, and intestinal
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| What happens during the cephalic phase? | Increased HCl and pepsinogen secretion due to conditioned reflexes (swallowing, hypoglycemia, etc)
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| What direct effect occurs in the cephalic phase by vagal stimulation? | stimulation of parietal cells to release ACh and increase HCl secretion from parietal cells
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| What indirect affect occurs in the cephalic phase by vagal stimulation? | Stimulation of G cells to release gastrin that is circulated to parietal cells
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| When does the gastric phase occur? | When food is in the stomach
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| What happens during the gastric phase of gastric juice secretion? | HCl is released from stimulus from amino acids, small peptides, and stomach distension;
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| What stimulations trigger stomach distension in the gastric phase | direct vagal stimulation of parietal cells and indirect stimulation of parietal cells by gastrin
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| What affect do amino acids and peptides have during the gastric phase of gastric juice secretion? | directly stimulate gastrin release!
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| What are the two most potent amino acids in the gastric phase? | phenylalanine and typtophan
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