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Please note: This question is neither homework nor seeking medical advice. I'm simply asking for a factual, objective, biological explanation of the various neuro-motor diseases/illnesses that can act as the underlying cause to LES malfunction.

The primary function of the lower esophageal sphincter (LES) is to prevent stomach acid from backwashing into the esophagus. This sphincter is an involuntary muscle, and so, for it to malfunction (unable to fully or properly close), it must be the result of an underlying neuro-motor (autonomic) disease or condition.

What such condition attacks this sphincter/valve, thereby causing it to malfunction and not operate properly? How exactly does this condition effect the sphincter biologically/neurologically?

Update

Looks like the Vagus Nerve (10th Cranial) innervates this sphincter, so I guess the question is: What neuro-motor diseases attack the Vagus Nerve or cause it to malfunction?

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  • $\begingroup$ Try looking up acid reflux disorders. My aunt has this as well as Multiple Sclerosis and it causes this muscle to spasm, she has to drink water slowly in small sips to calm it down. $\endgroup$
    – SolarLunix
    Aug 30, 2015 at 10:40

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This is called achalasia. According to UpToDate, the mechanism for this diseases are generally unknown. What is known, however, is that the esophagus has a neural system called the myenteric plexus and if these ganglion cells in the esophagus are damaged in any way (e.g. physically, followed by Wallerian degeneration, or the primary process of degeneration after physical damaging of neurons), it can lead to lower esophageal dysfunction as these neurons regulate the inhibition of the contraction of this sphincter muscle. Dysinhibition leads to a closed sphincter.

Yes, you are right in that the vagus nerve is the primary route of the myenteric plexus to the central nervous system, so damage here might result in dysfunction as well.

Histological studies have reported fewer myenteric neurons in people with achalasia, and inflammatory cells in the region, perhaps suggesting infection or autoimmune etiology 1.

Additionally, from the UpToDate article, Chagas Disease has been associated with this disease. Chagas disease is a parasitic disease caused by the species Tropanosoma Cruzi, and these parasites multiply within cells, causing them to burst.

Check out pathophysiology of achalasia on websites such as UpToDate.

1 "Histopathologic features in esophagomyotomy specimens from patients with achalasia." Goldblum JR, Rice TW, Richter JE. Gastroenterology. 1996;111(3):648.

EDIT:

I answered the opposite, but the principles still apply. Here is a wonderful resource on this topic ("Physiology of esophageal motility," http://www.nature.com/gimo/contents/pt1/full/gimo3.html. It includes a diagram showing the vagal neural pathway and the main neurotransmitters responsible for each action (relaxation and contraction).

enter image description here

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    $\begingroup$ Thanks @Biomed_guy (+1) - however it appears that achalasia occurs when the LES closes and cannot reopen. I am interested about the opposite: what would cause the LES to remain largely open and unable to close? $\endgroup$
    – smeeb
    Aug 30, 2015 at 23:49
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    $\begingroup$ Sorry about that. However, we are close. Just as there are inhibitory neurons on the LES, there are also excitatory neurons with a different set of neurotransmitters. $\endgroup$
    – Biomed_guy
    Aug 31, 2015 at 2:41
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    $\begingroup$ Thanks again @Biomed_guy (+1) - so let me see if I understand this. You're stating that anytime there is damage to the Vagus Nerve and/or the myoenteric plexus, that LES can malfunction as a result, yes? If so, then to me, it stands to reason that the root problem either lies in this plexus, anywhere along the Vagus nerve, or the place in the brain that the Vagus nerve feeds into (which, correct me if I'm wrong here, but I believe is the medulla oblongata). Can you confirm that the root of the problem has to lie in one of these areas (or any others you can think of)? Thanks again! $\endgroup$
    – smeeb
    Aug 31, 2015 at 13:53
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    $\begingroup$ I believe I am qualified to guide but not necessarily completely confirm. Indeed, the medulla and vagus has been implicated for LES dysfunction (ncbi.nlm.nih.gov/m/pubmed/12061915) Keep in mind that diseases like GERD may not always be caused by neurological dysfunction. But if you're thinking neurological, than this is a valid thought. $\endgroup$
    – Biomed_guy
    Aug 31, 2015 at 17:34
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    $\begingroup$ Thanks for the update @Biomed_guy (+1) - last followup (I promise): you are correct in thinking that I am assuming a neurological cause for GERD. I am very interested in your statement that "GERD may not always be caused by neurological dysfunction." Can you elborate on this and perhaps give some examples? To me, it has to be neurological in nature, because the LES is an involuntary muscle. If you know of non-neurological root causes for LES, please fire away! By "root" causes, I don't mean "obesity", because that's just a vague blanket phrase that doesn' explain the physiology... $\endgroup$
    – smeeb
    Aug 31, 2015 at 17:42

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