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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 04 05 Anatomy Teniae colie Below
Begin 04 05 Anatomy Teniae colie Transcription
What three structures travel down three sides of the cecum to come together and form a three pointed star at the origin of the appendix which can be used as a guide by surgeons to locate the origin of the appendix?
- The teniae colie.
And what are the teniae colie composed of?
- Bands of longitudinal muscle.
Now these three bands of longitudinal muscle that are the teniae colie that run the length of the colon and are spaced equidistantly around the outside of the colon are condensations of muscle from where?
- From the longitudinal muscle that covers the entire surface of the ileum.
And where do these teniae colie run to?
- All the way to the rectosigmoid junction.
What happens to the teniae colie at the rectosigmoid junction between the sigmoid colon and the rectum?
- They spread out and unite to form a longitudinal muscle layer that completely surrounds the rectum.
What layer is beneath the teniae colie that run the length of the colon and beneath the longitudinal muscle that surrounds the rectum?
- The circular muscle layer.
And what quality of the teniae colie cause the colon to be bunched into baggy segments?
- The teniae colie are shorter than the length of the colon.
And what are the short baggy segments of the colon called?
- Haustra, also known as sacculations.
How do the teniae colie end up shorter than the colon?
- They stop lengthening before the colon does during development.
What is the name of the internal folds that separate the haustra?
- Semilunar folds.
Which of the teniae colie runs free of attachments to the mesentery or omentum, is anterior on the cecum and ascending colon, is also anterior on the left on the descending colon and sigmoid colon, and is posterior on the transverse colon?
- Tenia libera.
And what thin layer of tissue covers the tenia libera on its course?
- One layer of peritoneum.
Which of the teniae colie runs on the medial side of both the ascending and descending colons, along the line where the peritoneum hits the side of these sections of colon and climbs over to cover them and also runs along the transverse colon where the transverse mesocolon attaches?
- Tenia mesocolica.
In the normal position of the transverse colon, on what side is the tenia mesocolica?
- Along the superior side toward the back.
What special feature of the positioning of the transverse colon causes the tenia mesocolica to end up on the transverse colon’s superior posterior aspect?
- Because the transverse colon flops over forward and hangs down from the right and left colic flexures in a loop suspended from above and behind by the transverse mesocolon.
Finally, which of the teniae colie runs on the lateral side of the ascending and descending colons along the line where the peritoneum returns to the posterior abdominal wall after climbing over the front of the ascending and descending colons and also runs along the anterior side of the transverse colon along the line where the greater omentum originates?
- Tenia omentalis.
There are small appendages of fat hanging from the colon at intervals especially along the lines of the three teniae colie and what are these called?
- Epiploic appendices.
In the same way that a pouch of peritoneum forms the transverse mesocolon to suspend the transverse colon, there is another pouch of peritoneum which suspends the sigmoid colon.
What is it called?
- Sigmoid mesocolon.
Similarly, what the pouch of small intestine mesentery which suspends the appendix and which accounts in part for the variability in position of the appendix?
- The mesoappendix.
What three parts of the large intestine, then, are wrapped completely within pouches of peritoneum and are designated as being within the peritoneum or being intraperitoneal?
- The appendix, transverse colon, sigmoid colon.
Student doctor, which four parts of the large intestine, then, are covered only on the anterior side by peritoneum, are attached on the posterior side to the posterior wall of the trunk and are designated as being retroperitoneal?
- Cecum, ascending colon, descending colon, and the upper half of the rectum.
Student doctor, which parts of the large intestine then, lie within the abdominal cavity?
- The appendix, transverse colon, sigmoid colon.
What defines the abdominal cavity that is part of the intra-abdominal space?
- The abdominal cavity is that portion which is lined with peritoneum.
What is the name of the intra-abdominal space which is between the peritoneum and the posterior trunk?
- This is the retroperitoneal space.
Which part of the large intestine is not covered on at least one side by peritoneum?
- The lower half of the rectum.
What two structures together divide the abdominal cavity into an upper and lower abdomen?
- The transverse colon and the transverse mesocolon.
What structure connects the transverse colon with the greater curvature of the stomach?
- The gastrocolic ligament.
And what larger peritoneal structure is this gastrocolic ligament a part of?
- The greater omentum.
In an abdominal x-ray, looking at the transverse colon and right and left colic flexures, in what state would they be seen much more superior, when the large intestine is filled or empty?
What structure containing muscle fibers, when contracted, helps open the ileocecal valve to allow small intestine contents to pass into the cecum?
- The mesocolic band or tenia mesocola, which is not the same as tenia mesocolica.
Where do the muscle fibers of the mesocolic band originate from?
- These also originate from the longitudinal layer of muscle in the lower ileum and as there is motility in the lower ileum, this in turn, causes the mesocolic band to open the ileocecal valve.
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