USMLE Step 1 Review 03 11 Anatomy Small Intestine 2

USMLE Step 1 Review 03 11 Anatomy Small Intestine 2


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Let’s continue our USMLE Review with Anatomy from the Gold Standard USMLE Step 1 Audio Review program.

Play USMLE Audio MP3 03 11 Anatomy Small Intestine 2 Below


Begin 03 11 Anatomy Small Intestine 2 Transcription

In terms of gross appearance, what is the difference between the circular folds in the duodenum, the jejunum and the ileum. Let’s start with the duodenum.

In the duodenum the circular folds are coarse and a little bit widely spaced. How about the jejunum?

  • In the jejunum, the circular folds are thin and very closely spaced.

And in the ileum?

  • They’re almost absent in the ileum. And those circular folds that can be distinguished are very shallow and very widely spaced.

What two structures can be seen microscopically on the circular folds and the mucosa of the duodenum, jejunum and ileum?

  • Villi and crypts.

What can be seen with an electron microscope?

  • Microvilli.

Now the circular folds are prominent in both the duodenum and jejunum and are different in their spacing in the duodenum and jejunum.

However what is different on the circular folds between the villi and crypts in the duodenum and the jejunum?

  • First the duodenum. The villi are high and often leaf shaped and the crypts are shallow.

And in the jejunum?

  • The jejunum has numerous high circular folds but the villi are not as long as in the duodenum and the crypts are deeper.

What happens in the folds and villi in the ileum?

  • They progressively disappear getting shorter.

(What) glands are found only in the duodenum?

  • Brunner’s glands.

And what do Brunner’s glands produce?

  • Mucus.

What cell found throughout the small intestines also produces mucus?

  • Goblet cells.

The Brunner’s glands in the duodenum are found where?

  • In the submucosa.

Ok working from the luminal side of both the circular folds and the mucosa, in the duodenum, we first have?

  • The villi.

And then we have?

  • The crypts.

The villi and crypts are both part of what layer?

  • The epithelial mucosal layer.

Deep to the villi and crypts which is the epithelial mucosal layer what layer comes next?

  • The lamina propria.

Which is what kind of mucosal layer?

  • Connective tissue mucosal layer.

And then what is deep to the lamina propria both in the circular folds and in the flat mucosa between them?

  • The muscular epithelial layer.

Also called the?

  • Muscularis mucosa.

Now these three layers the lamina epithelialis, the lamina propria, and the muscularis mucosa together form what type of mucosa?

  • The tunica mucosa.

Deep to the tunica mucosa and of course deep to the muscularis mucosa, what is our next layer?

  • The tela submucosa.

Also called?

  • The connective tissue mobile layer.

Now in our circular folds we have the muscularis mucosa layer which is of course deep to the lamina propria and then the lamina epithelialis with the crypts and villi.

What tissue comes up between the two muscularis mucosa layers forming the circular fold?

  • The Tela submucosa again coming up between them.

And what structure found only in the duodenum is found within this tela submucosa?

  • Brunner’s glands.

Now traveling further out from the lumen, we now encounter another layer, what is the next layer?

  • The stratum circulare or circular muscle layer.

And then what layer is outside the stratum circulare?

  • The stratum longitudinali or the longitudinal muscle layer.

Now these two layers the inner circular muscle layer and the outer longitudinal muscle layer both make up what layer?

  • The tunica muscularis.

What layer then covers the tunica muscularis?

  • The peritoneum.

And finally what layer covers this visceral peritoneum?

  • The serosa.

For those organs which are retroperitoneal, the part of the organ which is not in contact with the peritoneum is covered instead outside the longitudinal muscle layer with what layer?

  • The tunica adventitia.

Which is also known as?

  • The connective tissue layer.

Now on the mucosa in the jejunum and the ileum, we see nodules here and there, somewhat infrequent in the jejunum and much more frequent in the ileum, what are these nodules?

  • They are solitary lymph follicles.

In the ileum and somewhat in the colon, we see aggregates of these lymph follicles, what are these called?

  • Peyer’s patches.



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