USMLE Step 1 Review 03 06 Anatomy Stomach 2

USMLE Step 1 Review 03 06 Anatomy Stomach 2

 

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Begin 03 06 Anatomy Stomach 2 Transcription

What is the normal capacity of the stomach?

  • About 1200-1600mL.

What is the name for the wrinkled folds of mucosa in the stomach?

  • The rugai or rugae.

What is the term for the few long longitudinal rugae along the lesser curvature inside the stomach?

  • The gastric pathway.

Some of the rugae run in an oblique or transverse direction, how are they referred to?

  • Reserve folds.

These reserve folds of rugae demarcate mucosal niches, and what are these niches called?

  • Digestive chambers.

What is the purpose of these digestive chambers?

  • To hold larger pieces of food for further digestion.

How many layers of muscle form the stomach?

  • Three layers.

What kind of muscle is in the outermost layer?

  • Longitudinal muscle.

What is the second or middle layer?

  • Circular muscle.

What is the innermost layer?

  • Oblique muscle.

What layers present in the stomach but absent in the esophagus?

  • The innermost oblique muscle.

In the same way that a sling for a broken arm hangs over the shoulder, the innermost oblique layer hangs like a sling from what area?

  • The cardiac notch.

Where the innermost oblique muscle hangs over the cardiac notch, like a sling over a shoulder the middle circular muscle fibers wrap around this sling as it comes off the cardiac notch and these two together form what collar?

  • The collar of Helvetius, surrounding the cardiac neck of the stomach.

Just deep to the layer of the innermost oblique muscles is what tissue?

  • The submucosa.

And what nervous plexus is in the submucosa?

  • The submucosal plexus also called Meissner’s plexus.

(What) Two types of structure’s does Meissner’s plexus, the submucosal plexus innervate?

  • The muscularis mucosa and the glands.

What structure is deep to the submucosa?

  • The muscularis mucosa.

And what is deep to the muscularis mucosa?

  • The lamina propria of the stomach mucosa.

And then what is deep to the lamina propria?

  • The mucosa.

Now hydrochloric acid and the gastric juices is secreted by what type of cells in the stomach mucosa?

  • Parietal cells.

And pepsinogen is released by what type of cells in the mucosa?

  • Chief cells.

And what two types of cells in the mucosa secrete mucin?

  • The surface cells and the mucous cells.

And what is the other cell in the mucous membrane of the stomach which secretes substances which inhibit or excite the other cells?

  • The endocrine cells.

All of these cells taken together form what layer of the stomach mucosa?

  • The epithelial layer.

And what is the more superficial layer of the stomach mucosa?

  • The lamina propria.

Now the mucous, parietal and chief cells form glands, these glands tend to be grouped together in little depressions, what are the names for these little depressions where they are grouped together?

  • Gastric pits.

Which kind of cell predominates in the base of the glands?

  • The chief cells.

And what do they produce?

  • Pepsinogen.

What does pepsinogen have to turn into before it becomes active upon protein?

  • Pepsin.

Once the pepsinogen is released by the chief cells, what acts upon it to turn it into pepsin?

  • The hydrochloric acid of the stomach.

At what pH range?

  • 1.5 to 2.

What cells are scattered among the chief cells along the tubules of the gastric glands?

  • The parietal cells.

And what do parietal cells produce?

  • Hydrochloric acid.

What two substances do the parietal cells actually secrete apically into the lumen?

  • Hydrogen ions and chloride ions.

At the same time, what do they release basally?

  • Bicarbonate ions.

What other substance is produced by parietal cells?

  • The intrinsic factor.

And what is the purpose of intrinsic factor?

  • Absorption of vitamin B12.

In what location?

  • In the ileum.

Lying in the outlet ducts of the gastric pits are what type of cells?

The mucous cells.

At the very top of the outlet duct where it is completely into the lumen of the stomach, these mucous cells are also called?

  • Surface cells.

And both of these surface and mucous cells produce?

  • Mucin.

What’s the pH of Mucin?

  • Neutral, about 7.

Now stomach activity, both motion and secretions, is influenced by what two factors?

  • Gastrointestinal hormones and by the vagus nerve, cranial nerve ten.

What three types of cells are within the gastric glands within the fundus and body of the stomach?

  • Mucous and surface cells, parietal cells and chief cells.

The glands which are in the one centimeter wide cardiac region contain what type of cells? Only mucous cells. Again, what type of cell predominates in the gastric pits of the pylorus?

  • Again mucous cells.

What measurable quality can be use to distinguish the antrum from the body of the pylorus?

  • The pH, the pH becomes distinctly more neutral as you move from the antrum into the body.

What is the name of the phase where the stomach is stimulated even though its empty by sensory impressions such as taste, smell and sight?

  • The cephalic phase.

In the cephalic phase, gastric secretions are stimulated by what?

  • Nervous impulses from the vagus nerve.

If the vagus nerve is cut is there a cephalic phase of gastric stimulation?

  • No.

What is the second phase of gastric stimulation?

  • The gastric phase.

What is it stimulated by?

  • Food entering the stomach.

And what is the actual mechanism of stimulation?

  • Endocrine stimulus.

Finally, what phase begins as the chyme is emptied from the stomach into the duodenum?

  • The intestinal phase.

Is there much in the way of gastric secretion during the intestinal phase?

  • No.

In the cephalic phase how does the vagus stimulate the parietal cells to release hydrochloric acid?

  • By the release of acetylcholine.

What hormone carried through the blood stimulates the parietal cells to release hydrochloric acid, mostly during the gastric phase?

  • Gastrin.

And the hormone Gastrin is produced by what type of endocrine cell?

  • The G cells.

We’ll come back to g cells in a moment. What paracrine agent works upon the parietal cells to cause them to release more hydrochloric acid?

  • Histamine. Histamine is classified a paracrine agent because it reaches the parietal cells by diffusion rather than through the blood.

Where does this histamine come from?

  • Mast cells in the stomach.

Finally the G cells that produce the Gastrin, which is the hormone that travels to the parietal cells through the blood, the G-cells are stimulated by two substances, what are they?

  • GRP or Gastrin releasing peptide and protein digestion products.

Where does the GRP come from?

  • It is also released by the vagus nerve.

What paracrine agent inhibits both parietal cells and G-cells?

  • Somatostatin.

What cells produce Somatostatin?

  • D cells.

Now these D-cells producing the inhibitory Somatostatin are themselves inhibited by what substance from what structure?

  • Acetylcholine from the vagus.

****END OF TRANSCRIPTION****

 

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