USMLE Step 1 Review 03 10 Anatomy Small Intestine 1

USMLE Step 1 Review 03 10 Anatomy Small Intestine 1


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Begin 03 10 Anatomy Small Intestine 1 Transcription

Now we’re going to look at the small intestines.

What are the three parts of the small intestines?

  • The duodenum, jejunum, ileum.

Which of the three parts of the small intestines is the shortest and the most thickest part?

  • The duodenum.

The duodenum is more or less what shape?

  • In the shape of a C.

There are four defined parts to the duodenum, what are they?

  • The superior or first part, the descending or second part of the duodenum, the horizontal or third part of the duodenum, and the fourth part of the duodenum is the ascending part.

The superior first part of the duodenum actually has three alternative names, what are they?

  • The ampula of the duodenum, the duodenal cap or the duodenal bulb.

What is a distinguishing feature about the lumen of the first part of the duodenum, the superior part?

  • The mucosa is smooth.

Now the vertical portion or the convexity of the duodenum is on what side?

  • It is toward the right.

The duodenum curves around what structure?

  • The head of the pancreas.

Where does the duodenum lie in relation to the spinal column?

  • It lies mainly to the right of the vertebral column.

And what  vertebral level is the superior part or first part of the duodenum?

  • At the level of the twelfth thoracic to the first lumbar vertebrae.

Now the descending or second part of the duodenum is at what vertebral layer?

  • The third to fourth lumbar vertebrae.

The horizontal third part is at about what level?

  • The top of the fourth lumbar vertebrae.

And then the ascending or fourth part of the duodenum climbs back up to about what level?

  • Back up to about the first to second lumbar vertebrae.

The ascending or fourth part of the duodenum ends in a sharp bend back down what is this bend called?

  • The duodenojejunal flexure.

And what does it mark the beginning of?

  • The jejunum.

And again the superior of first part of the duodenum is suspended by?

  • The hepatoduodenal ligament. So it is intra peritoneal.

What is the relation of the second, third and fourth parts of the duodenum to the peritoneum?

  • They are all retroperitoneal.

What two organs is the first part of the duodenum inferior to?

  • The right lobe of the liver and the gallbladder.

Now I said the duodenum curves around the head of the pancreas.

What is the relationship of the stomach to the pancreas?

  • The stomach overlies the rest of the pancreas.

What retroperitoneal organ lies to the right of the second or descending portion of the duodenum?

  • The right kidney.

The second or descending part of the duodenum also passes deep underneath what other structure?

  • The right hand side of the transverse colon.

The third or horizontal portion of the duodenum is deep to what structure?

  • Deep to the small intestines, more specifically to coils of jejunum, somewhat to the right of midline.

Ok, now this third or horizontal portion of duodenum, which is deep to coils of jejunum and deep to transverse colon overlies and crosses over what two structures from right to left?

  • It first crosses the inferior vena cava and then at the midline it crosses over the abdominal aorta.

And what two structures come down from underneath the pancreas to over the third or horizontal section?

  • The superior mesenteric artery and vein.

And which is on the right and which is the left?

  • The superior mesenteric vein is on the right and the artery is on the left.

We’ll come back to these in more detail later.

If one were doing an endoscopic exploration of the duodenum from the pylorus, what quality of the mucosa would signal to you that you had entered the second portion of the duodenum, the ascending portion?

  • You would begin to see circular folds.

What’s the other name for these circular folds?

  • The circular folds of kerkring.

What two types of tissue make up the circular folds?

  • Mucosa and submucosa.

Now as we are coming down the descending portion or second portion of the duodenum with our scope about a third of the way down we might see a very tiny aperture in the posterior wall, this is not always there , what would this be called if it’s there?

  • The minor duodenal papillae, in constant.

And this is an opening for what duct that is not always present?

  • The accessory pancreatic duct.

What’s the other name for this?

  • The accessory pancreatic duct of santorini.

Now a little more than half way down we’d see a much larger aperture projecting into the lumen from the posterior wall, and what would this be called?

  • This would be the major duodenal papillae.

And what’s the other name for it?

  • The major duodenal papillae of Vater.

And what two ducts merge here to empty into the duodenum at the major duodenal papillae?

  • The common bile duct and the pancreatic duct.

What is the name for the sphincter in the major duodenal papillae which controls the secretion of substances from the common bile duct or the pancreatic duct?

  • The sphincter of hepatopancreatic ampula.

What’s the other name?

  • The sphincter of Oddi.



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