Term
| What two "tubes" connect to the stomach? |
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Definition
| The esophagus and the duodenum. |
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Term
| What are the 3 functions of the stomach? |
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Definition
| Store food, secrete HCl and enzymes that begin protein digestion, and create mixing movements to pulvorize food into chyme. |
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Term
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Definition
| Chyme is what the bolus becomes upon mixing with gastric juices in the stomach. |
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Term
| What are the three functional sections of the stomach? |
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Definition
LES and cardia
Fundus and body
Antrum and pylorus |
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Term
| What structures exist in the gastric mucosa, and are responsible for gastric juice production? |
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Definition
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Term
| What cells secrete pepsinogen? |
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Definition
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Term
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Definition
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Term
| What is the purpose of secreting pepsinogen and HCl separately? |
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Definition
| Pepsinogen is inactive, and only becomes active when meeting with HCl. Secreting these separately helps to stop the pepsin from digesting the stomach itself. |
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Term
| What is secreted in the stomach to absorb vitamin B12? |
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Definition
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Term
| What is secreted along with HCl and pepsinogen to ensure the stomach does not digest itself? |
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Definition
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Term
| What are the two distinct areas of the stomach that secrete gastric juices? |
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Definition
Oxyntic mucosa: lining of body and fundus
Pyloric gland area: lining of the antrum |
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Term
| What three types of gastric exocrine secretory cells exist in gastric glands (there are more but he mentioned these separately first)? |
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Definition
| Mucous cells, cheif cells, and parietal cells. |
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Term
| What are the three phases of gastric secretion? |
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Definition
| The cephalic, gastric, and |
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Term
| What occurs during the cephalic gastric secretion phase? |
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Definition
| Increased HCl and pepsinogen secretion occurs due to a cognitive stimulus. |
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Term
| What occurs during the gastric gastric secretion phase? (pardon my awkward wording) |
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Definition
| When food reaches the stomach the gastric secretions are increased even further from the cephalic phase. |
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Term
| What occurs during the intestinal gastric secretion phase? |
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Definition
| Inhibition from the filling intestines reduces the secretion rate of gastric juices. |
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Term
| What three stimulants originate in the stomach, causing an increase in pepsinogen secretion, and what secretes these stimulants? |
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Definition
Ach - from enteric neurons
Gastrin - from G cells in gastric antrum
Histamine - from ECL cells in gastric body |
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Term
| What absolutely must be present for parietal cells to produce HCl? |
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Definition
| Sch, gastrin, and histamine. |
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Term
| What structural change occurs to parietal cells upon becoming active? |
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Definition
| Increased HCl production causes enlargement of the tubulovesicles to form canaliculi. |
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Term
| Why is the acid gradient formed by HCl important to pepsin? |
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Definition
| Pepsin works best at a low pH. The HCl secretion is responsible for providing pepsin the optimal medium in which to act. |
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Term
| Not including the activation/support of pepsin what are three other important functions of HCl in the stomach? |
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Definition
| Breakdown of CT and muscle fibres, denaturing of proteins, and aiding of lysozyme to kill any ingested microbes. |
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Term
| What is the mediator of acid secretion (think membrane transporters)? |
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Definition
| A proton-potassium ATPase found on the luminal surface of the parietal cells. |
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Term
| Where does the proton in acid secretion "come from"? |
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Definition
| A molecule of CO2 enters from the plasma and is converted with H2O into H2CO3 by an enzyme known as Carbonic Anhydrase (CA). This then dissociates into HCO3- and H+. |
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Term
| What enzyme would you expect to find in large quantities within a parietal cell? |
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Definition
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Term
| What happens to the free bicarbonate formed within the parietal cells? |
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Definition
| On the basal membrane is a chloride-bicarbonate exchanger. This excretes bicarbonate into the plasma, and brings Cl- into the cell. |
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Term
| What happens to the chloride brought into the parietal cell by the chloride-bicarbonate exchanger? |
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Definition
| It is secreted into the lumen through a chloride channel along with the proton to form HCl. |
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Term
| How do Ach and gastrin stimulate the secretion of HCl? |
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Definition
| They activate their receptors on the basal surface (M3 and CCK2 respectively). This causes hydrolysis of PLC, which increases intracellular calcium, and a PKC cascade to increase activity of the proton-potassium exchanger. |
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Term
| How does histamine affect the actions of Ach and gastrin on the production of HCl? |
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Definition
| It activates its receptor (H2) which causes an increase in cAMP that can be then used in the cAMP-dependent protein kinase cascades started by Ach and gastrin. cAMP will also increase the activity of the proton-potassium exchanger directly. |
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Term
| What are the six cell types in the gastric pits (and what do they secrete)? Starting in and working out. |
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Definition
Neck cells - mucus and bicarb
Parietal cells - HCl and intrinsic factor
ECL cells - histamine
Chief cells - pepsinogen and gastric lipase
D cells - somatostatin
G cells - gastrin |
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Term
| How are ECL cells and parietal cells linked? |
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Definition
| ECL cells produce histamine which in turn activates the parietal cells. |
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Term
| I thought of lots of ways to make this work in flashcards but couldn't make it work... |
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Definition
| ...just go look at Figure 42-10 |
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Term
| Vagus nerve input directly activates what three cells through the enteric plexus? |
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Definition
| G cells, ECL cells, and parietal cells. |
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Term
| Amino acids and proteins entering the lumen from food directly activates what cells? |
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Definition
| G cells through the enteric plexus. |
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Term
| Gastrin produced by the G cells stimulates what cells? |
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Definition
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Term
| How are chief cells activated? |
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Definition
| An increase in [H+] in the lumen is a stimulus for enteric sensory neurons in the wall of the lumen. These neurons route through the enteric plexus to directly stimulate chief cells. |
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Term
| What three gastric cells does Ach have direct control over? |
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Definition
| Cheif, parietal, and ECL cells. |
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Term
| Define: Deglutition, eructation, flatulence, borborygmi, and chyme. |
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Definition
Deglutition: swallowing
Eructation: burping
Flatulence: intestinal gas
Borborygmi: rumbling in GI tract from gas
Chyme: bolus mixed with gastric/pancreatic juices |
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Term
| Why does HCl not penetrate the apical membranes of gastric cells? |
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Definition
| The apical membranes are impermeable to H+ so HCl is unable to pass through. |
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Term
| How is the pH gradient formed from the apical membranes to the lumen of the stomach? |
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Definition
| Mucus cells secrete mucin which creates a mucus layer full of bicarbonate. This bicarbonate allows a steady gradient from a pH of ~2 in the lumen to a pH of ~7 at the apical surface. |
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Term
| How does acid get past the mucus layer and into the lumen? |
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Definition
| Fingering. The parietal cells are under high pressure and thus produce a constant stream of acid "fingers" through the mucus layer. |
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