biology zoology blog benno meyer rochow diarrhoea

Dysentery, loose stool, running belly

It’s all unpleasant and called diarrhoea

Stomatologists are experts focusing on the structure and function and the surrounding area of that part of the body through which the food enters. Proctologists are interested in the structure and function of the part of the body from where the waste comes out. And psychologists are interested to study why (mostly) very young children in particular are so interested in their own faeces and find it so amusing to examine what they can produce from their rear ends. When, however, what comes out of there is a semi-liquid, brownish and soft and sticky, smelly slush, it’s certainly much less amusing.

I’m talking of diarrhoea of course and it used to be a topic in my class for the medical students on the autonomic nervous system. I remember that the dental students amongst them where the least interested in the lectures dealing with the nervous system – until I came to explain that ejaculation depended on the neurotransmitter noradrenaline from fibres of the sympathetic nervous system, while erections were the result of an innervation from the parasympathetic nervous system and the neurotransmitter acetylcholine. And now we have the connection to diarrhoea, for it is the sympathetic fibres of the autonomic nervous system with its noradrenaline that inhibits normal gut motility and causes the sphincter muscle to contract and forcefully eject the rectal content, but in contrast it’s the parasympathetic fibres of the autonomic nervous system that stimulates normal gut motility and leads to a relaxed state of the sphincter muscle. It’s actually a little bit more complicated as firstly internal and external sphincter muscles together control whether the rectal content should be expelled or retained (even moved back for further absorption of fluids and faecal solidification) and secondly, some control by the brain occurs on whether or not to defaecate at all (e.g. potty training).

In diarrhoea the problem is that the uptake of liquids from the gut via its so-called mucosa (the inner lining) cannot cope: either because too much liquid enters the gut passively due to osmotically active components in the gut or because the mucosa actively secretes excessive amounts of fluid into the gut. If the absorption of this excessive amount of fluid inside the gut is impaired, semi-liquid faeces begin to fill the intestine, accumulating in the rectum and ultimately distending the rectum’s wall to an extent that defaecation is triggered. The increase of the amount of faecal matter in the rectum stretches the rectum’s wall and that affects the sphincter muscles and gut motility, helping the rectal content to be released (considered to be a pleasurable experience under normal but not diarrhoea conditions). Given an average daily intake of let’s say 1.5 litres of liquids, the absorption of these liquids through the walls of the small intestine is the reason why normal faeces contain only about 10% of the ingested fluid. However, malabsorption of the fluid leads to diarrhoea and the main causes of such malabsorption in combination with increased secretion of fluid into the gut are pathogenic microorganisms as well as certain toxins present in some plants and animals.

The cholera bacterium Vibrio cholerae is probably the worst, but some viruses as well as microbes like the aquatic Giardia lamblia (in contaminated water) and others that develop in food stuffs that have gone off (especially meats, fish, milk and eggs), plus toxins in unripe fruit, spices and vegetables like broccoli and cauliflower, are also known to produce acute and watery diarrhoeas. Diarrhoea is really a response to help the body to get rid of some toxins, but if the running belly condition persists, it is best to use some anti-diarrhoea medicine and, of course, to replenish the lost fluid with clean water to which some salt and sugar should be added. An alcoholic beverage, however, won’t help at all.

© Dr V.B. Meyer-Rochow and, 2019.
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