Anatomy and Physiology of the Oesophagus

Back when they were teaching us the anatomy of the Oesophagus (mine is a med-school in Asia that follows the old Brit system according to which we’re taught each subject separately, not with respect to the systems with all the subjects hand-in-hand. I don’t know when these people will learn, but hey, this place is my way of taking out the frustration ), no one bothered to tell us that the lower part of the oesophagus was weaker than the upper one, which is why is bursts open in cases of Booerhaave Syndrome. Similarly, in physiology, no one bothered telling us the details regarding the lower oesophageal sphincter apart from the fact that it’s basically a sphincter! Yeah some over-the-top sorta geeky professors might have focused on the pressure inside the sphincter, but what’s the point of learning a mere number if we were to be taught the importance of that number after 4 years (in the last and hardest year of med-school in Pakistan). So yes, here’s the clinical scoop of the anatomy and the physiology of the oesophagus.

  • It begins at the level of the cricopharyngeus muscle BUT swallowing begins in the mouth and thus Dysphagia can be both oesophageal as well as pharyngeal, the pharynx being above the cricopharyngeus or the upper oesophageal sphincter.
  • It is around 25 cm long.
  • The distance of the upper oesophageal sphincter is 15 cm, aortic and bronchial constriction is 25 cm and the lower oesophageal sphincter is 40 cm from the incisor teeth > These aren’t just lame, boring numbers, you need to know these distances when performing endoscopy.
  • The upper half is made of skeletal muscle, although involuntary, and the lower half is made of smooth muscle which is arranged haphazardly, thus making this part of the oesophagus weaker than the upper one.
  • The nervous supply is from the vagus nerve which has connection with the myenteric plexus. Meissner’s submucosal plexus is sparse here.
  • The upper sphincter is normally closed and keeps air from entering the oesophagus as well as serving as a protective mechanism for prevention of regurgitation (that’s why problems in this region result in regurgitation in patients of myasthenia gravis).
  • The LOS (lower oesophageal sphincter) has a very pressure and is normally closed, only opening up during the passage of food into the stomach, letting air (that was swallowed with food) to pass up from the stomach and when one vomits. Here’s what they might not have explained in detail: Smoking, certain drugs, GIT hormones, gastric distention and food can cause this sphincter to open up, even when it’s not required to do so. That’s why smoking or large meals cause heartburn, since the sphincter remains open when it should be closed, thus letting the acid contents into the oesophagus causing heartburn or dyspepsia. The LOS is 3-4 cm long and maintains a pressure of 10-25 mm Hg.
  • In the lower region of the oesophagus, collaterals exist between the portal and the systemic circulation. These are the vessels that enlarge when people with liver disease (cirrhosis) develop portal hypertension and subsequently, oesophageal varices.

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