Constipation means different things to different people. This is because what one community considers as normal stool frequency and consistency may not be normal in another community. In general bowel movement of thrice a day to thrice a week can be considered normal.
Dr Chuah Seong York
Consultant Gastroenterologist
Pantai Hospital Ayer Keroh,
Melaka.
What make up the alimentary canal?
The alimentary tract is a long conduit consisting of the mouth as the entrance, oesophagus or gullet, stomach, small and large intestines. In general, the distance from the front teeth (incisors) to the bottom end of the oesophagus is 40 cm. The small bowel consists of duodenum (25 cm), jejunum (8 feet) & ileum (12 feet). Colon or large bowel can be divided into caecum, where the appendix arises as a blind appendage, ascending, transverse, descending, sigmoid colon and rectum. During colonoscopy the shortest distance from the anus, the exit of the digestive tract, to the caecum is 60 cm.
What does the colon do?
The colon has two main functions:
- Storage of faeces.
- Absorption of water.
From the above, it can be deduced that faeces closer to the anus will be more solid and bowel motion will be more liquid as it emits from the terminal ileum across the ileo-caecal valve into the caecum.
The urge to open one’s bowel will only be felt when faeces reaches the rectum. Therefore, even in its normal state, faeces would be present in the colon down to the sigmoid. Hence the practice of intermittently cleansing out the colon to detoxify is illogical.
The process of defaecation:
The ease of passage of a material through a conduit is dependent upon:
- consistency of the material.
- propulsion by the conduit.
It follows then that difficulty passing motion may be because the faeces are too hard or there is none or little urge to pass motion.
While there is no medical studies to show that drinking plenty of water and increasing dietary fibre content cure constipation, constipation is more prevalent in communities with low water and dietary fibre intake. Prolonged periods of immobility as in bedbound patients may also result in faecal impaction.
What are the other causes of constipation?
- Idiopathic (no apparent cause) constipation – usually affects females and runs in families.
- Irritable Bowel Syndrome – may be stress-related and after food poisoning.
- Presbycolon – “Presby” means “old”, hence “old colon”.
- Autonomic neuropathy, for example after many years of diabetes. This may be associated with erectile dysfunction.
- Colon obstructed by stricture, polyp or cancer.
- Under active thyroid.
- Medications for example morphine-like pain-killers, anti-psychotics and some anti-depressants.
How to categorise bowel obstruction?
- Causes within the lumen, for example food bolus or foreign body.
- Causes within the wall, for example stricture or tumour.
- Causes from without, for example compression by organs or tumours outside the bowel. Also kinking by adhesions or scars outside the bowel but within the abdominal cavity.
Under what circumstances can constipation be mistaken as diarrhoea (spurious diarrhoea)?
In some cases of incomplete colonic obstruction, the obstructed segment of colon allows only the softer, more liquid faeces to pass through giving the impression of diarrhoea. This can easily be diagnosed on colonoscopy or CT scan.
Sometimes with severe constipation, a large lump of faeces becomes impacted in the rectum resulting in the inability of the anus to close properly. This tends to occur with prolonged immobility. The softer, more liquid faeces from above seeps around the hard lump of faeces out via the incompetent anus again giving the impression of diarrhoea. This is known as “overflow diarrhoea” and can be easily diagnosed by a digital (the finger kind and not the computer type!) rectal examination. “Overflow diarrhoea” can be treated by manual digital evacuation of the impacted lump of faeces.
What is peristalsis and high amplitude propagated contractions?
From our science lessons during schooldays, many of us would have remembered peristalsis as the constant background low amplitude contraction and relaxation which propels the contents of the alimentary canal downwards. But occasionally our colon gives a massive push and this is known as high amplitude propagated contractions1, 2. High amplitude propagated contractions (HAPC) increase upon awakening and after meals. HAPC after meals may be known as the gastro-colic reflex.
What is gastro-colic reflex?
The urge to pass motion is strongest after a meal. This is because with distension of the stomach by food (or fluid), the stomach will inform the colon that there is new food entering the digestive tract, hence the colon better empty some of its contents in order to accommodate more faeces. This message from the stomach to the colon is known as the gastro-colic reflex.
For aeons parents have been using this gastro-colic reflex to help their constipated child defaecate without understanding its physiology. Many parents have this ploy of asking their constipated kid to sit or squat at the toilet bowl and feeding them water, thinking that the water will soften the stools. It doesn’t take a genius to work out that water entering the stomach is still 21 feet away from the large intestine where the faeces are! What the parents are effectively doing is distending the stomach with water to trigger off the gastro-colic reflex. The constipated child will then take the opportunity of the increased urge to defaecate.
How to avoid constipation?
- Respect your bowel request and avoid suppressing the urge to move your bowels. If you have to go, then drop everything including your work and go.
- Try to catch the high amplitude propagated contractions after meals, especially after breakfast.
- Exercise.
What are the types of laxatives?
- Bulking agent – fibre.
- Stool softener – lactulose (Duphalac Lactul).
- Flushers – Forlax and Fortrans.
- Osmotic laxative – Fleet.
- Stimulants – senna, Dulcolax, prucalopride (Resolor).
Closing Remark:
Henry Wheeler Shaw, a famous American humour writer and lecturer (AD 1818-1885) once said, “A good set of bowels is worth more to a man than any quantity of brain.”
Constipation is distressing and been able to defaecate sure is a gratifying experience.
References:
Chey WY, et al. The American Journal of Gastroenterology (2001) 96, 1499–1506.
Bharycha AE. Neurogastroenterology & Motility(2012) 24(11), 977-982.
