“Why, what I may think after dinner is one thing, and what I may think before dinner is another.”
Mr Jopling, ‘Bleak House’.
It’s a fair assumption that not many of us contemplate the complex journey taken, from mouth to anus, of the food we eat. Once swallowed, the entire digestive process is involuntary and occurs without any conscious thought from the individual.
In 1822 American physiologist William Beaumont observed maceration was primarily a chemical process, not a mechanical one, courtesy of a window into the stomach of Alexis St Martin who had been left with a gastric fistula following an accidental shooting, The strong stomach acid essentially disinfected the wound from the inside out, making it safe not to sew up. Martin lived for another 58 years.
Food breakdown begins with chewing and saliva enzymes (early twentieth century health nut Henry Fletcher, aka the Great Masticator, recommended 100 chews per minute – Thomas Edison and Franz Kafka were advocates). The main digestive enzyme is amylase which breaks down starches into simple sugars the body can use. It is similar to enzymes found in laundry detergents for disintegrating stains. Histatin proteins in saliva have antimicrobial and antifungal properties and have been found to play a role in wound-closure.
Chewed food then becomes a lubricated, rounded mass known as bolus which moves down the widened oesophagus through peristalis, involuntary contracted muscle movements. Here the throat does all the work, and there are valves preventing an upward flow so food always lands in the stomach even if you eat while doing a hand-stand.
Sphincter muscles at each end of the oesophagus allow the bolus to pass. Heartburn occurs when the lower sphincter fails to close completely, allowing stomach acid to travel upward, irritating the tissue in the oesophagus and throat.
The stomach produces hydrochloric acid (the same stuff used to clean bricks) and the enzyme pepsin. These turn the bolus into a liquid called chyme which is slowly released into the small intestine. For a full meal, this process takes approximately two to three hours.
The acid and pepsin digest cells of the stomach’s protective layer, but the organ rebuilds itself.
A healthy adult has a new stomach lining every three days. Failure to do so causes ulcers.
On its way into your small intestine, chyme is met with bile produced by the liver to break down fats, and enzymes secreted by the pancreas that break down protein, carbohydrates and fats. The pancreas also releases bicarbonate that neutralizes any acid that’s made its way out of the stomach.
The small intestine is where the most important work of digestion occurs: that of further breaking down food into molecular components that can be absorbed into the bloodstream. Absorption of nutrients is conducted by microscopic projections along the lining of the small intestine called villi.
Once this breakdown of food and absorption of nutrients is complete, fibre, the undigested parts of plant food, is propelled into the large intestine. Fibre softens and bulks up the stool, and is essential for both digestive and overall health.
Most bacteria in our digestive systems can be found in our large intestine. Bacteria absorb nutrients that slip past the small intestine through fermentation, and help to support our immune systems. You’re aware of the work of bacteria when its process of fermentation produces a combination of swallowed air and gasses in the gastrointestinal tract causing intestinal gas.
The digestive system cannot break down or absorb certain components of foods, and those substances simply get pushed into the large intestine. Hordes of intestinal bacteria get to work, releasing a variety of gases in the process, including carbon dioxide, hydrogen and methane. Flatulence odour is caused by hydrogen sulphide which is more highly concentrated in women. This is balanced by men’s greater volume of gas per passage.
People pass gas on average fourteen times a day. It’s everyone’s problem thus really no-one’s.
In addition to fibre, the small intestine sends liquid into your large intestine, where it’s absorbed and stools are formed. Horace Fletcher called excreta ‘digestive ash’ and a healthy body should produce a few dry balls weekly, having an odour of hot biscuit. John Harvey Kellogg’s ideal was four loose logs a day.
The large intestine is made up of the ascending colon, the transverse colon the descending colon, the sigmoid colon, and the rectum. The stool is usually moved once or twice a day into the rectum in preparation for a bowel movement.
The average colon is approximately 8cm around. Hirschsprung’s disease is a rare condition that causes faeces to become stuck in the bowels. The enlarged colon of sideshow act the ‘human balloon’ can be seen in Philadelphia’s Mutter Museum. It contains 40 pounds of faeces is 71cm around.
In the 1600’s ‘The English Hippocrates’ Thomas Sydenham advocated horse riding to loosen an impacted bowel.
The digestive system is regulated by the enteric nervous system (ENS), made up of a tremendous amount of nerve cells which is regulated by the same neurotransmitters, most notably serotonin, found in the brain. This similarity has earned the ENS the title of the ‘Second Brain’. The brain and digestive system work in close partnership, hence the feelings of butterflies or diarrhoea when stressed. This collaboration is thought to be essential to our survival as a species.
A physician, talking to writer Mary Roach, bemoaned the lack of appreciation of the anus: this ring of muscle with nerves that has to discriminate between solid, liquid, and gas, and let it out accordingly. He said “No engineer could design something as multifunctional and fine-tuned as an anus. To call someone an a**hole is really bragging them up.”
Aldersley-Williams, Hugh. 2014. Anatomies: The Human Body, Its Parts and The Stories They Tell. Penguin.
Cedar, S.H. 2012. Biology for Health: Applying the Activities of Daily Living. Palgrave Macmillan.
Roach, Mary. 2014. Gulp. Oneworld Publications.
Worden, Gretchen. 2002. Mutter Museum: Of the College of Physicians of Philadelphia. Blast Books,U.S.
To cite this post : Gareth Miles, “The Natural Ordure of Things’”, Curious Histories (blog on oldoperatingtheatre.com), December 30th, 2016.
Gareth Miles is a Museum Officer at the Old Operating Theatre. He is involved with the museum’s education programme and leads historical and medical walks around the local area.