A 77-year-old woman comes to her physician for a routine checkup. Her only problem on review of systems is chronic constipation. The physical examination is unremarkable.

Questions:

5.1 Explain potential causes for constipation.

Constipation is the recurring problem of difficult, incomplete, infrequent defecation (<3 bowel movements per week). Normal defecation is variable, from 3 stools per day to 1 stool every 2-3 days. A digested meal reaches the cecum in 4 to 8 hours, but transit time through the colon may take days. Decreased intake of dietary fiber (<20 to 30 g per day) can precipitate this condition, as can "hard" water with an increased mineral content including calcium salts such as calcium carbonate. A wide variety of pathologic conditions can lead to constipation, from colonic inflammation (diverticulitis) to drugs to hypothyroidism to depression to neuromuscular problems such as autonomic neuropathy and multiple sclerosis.

5.2 What should be done?

At her age, a screening colonoscopy is indicated. In her case, there is a small 0.5 cm sessile polyp at 20 cm and a 0.8 cm pedunculated polyp at 35 cm which are snared, and on microscopic examination prove to be a hyperplastic polyp and a tubular adenoma respectively.

Radiopaque markers for colonic transit can be performed.

In the absence of underlying conditions, a dietary or functional process may be considered.

5.3 What treatment plans are useful?

Patients can be advised that simply increasing dietary fiber and maintaining adequate fluid intake will help significantly.

Laxatives may be used. Bulk laxatives such as metamucil (psyllium) are probably the first choice.

Fecal softeners such as docusates (Colace ®) are the next choice.

Osmotic laxatives such as milk of magnesia and "stimulant" laxatives such as castor oil or senna should be reserved for occasional use in acute treatment.

5.4 Describe normal gastrointestinal motility.

Swallowing initiates a primary peristaltic contraction that propels a food bolus into the stomach, with relaxation of the lower esophageal sphincter.

The interstitial cells of Cajal in the myenteric plexuses initiate slow waves of depolarization (opening calcium channels) and repolarization (opening potassium channels) in smooth muscle known as slow waves, with a frequency of about 3 to 12 per minute.

In the stomach, parasympathetic stimulation and gastrin increase motility while sympathetic stimulation and secretin diminish motility. Gastric emptying is faster for liquids than solids. Emptying is delayed when fat stimulates cholecystokinin production, and when acid stimulates duodenal hydrogen ion receptors to cause signaling via the myenteric plexus to the gastric smooth muscle.

In the small bowel, parasympathetic stimulation increases contraction while sympathetics have the opposite effect. There are both segmentation and peristaltic contractions to mix and propel digesting food.

In the large bowel, segmentation contractions occur in the proximal portion. About 1 to 3 mass movements propel feces into the distal colon where most remaining water is reabsorbed. The concentrated fecal mass is stored in the rectum until defecation, typically at 25% of capacity signaling the internal anal sphincter to relax, though the external sphincter is under voluntary control.

5.5 What causes ileus?

Ileus is reduced to absent bowel motility

Mechanical bowel obstruction leads to severe cramping pain. Bowel proximal to the point of obstruction dilates with air and fluid; the dilation attenuates the blood supply, leading to ischemia. Treatment is surgical.

Paralytic (adynamic) ileus results from non-obstructive causes. Blunt trauma activates opioid receptors to decrease motility. Peritoneal inflammation (from peritonitis) increases splanchnic nerve impulses to inhibit motility. There is generally minimal or no pain.

5.6 History of medicine.

For centuries, purgatives and emetics were part of standard medical practice, even though they benefitted few and harmed many people.

Purging of the bowel to rid the body of toxins was practiced into the mid-19th century. The most common purgative employed for this purpose was calomel, a form of mercurous chloride (six parts mercury to one part chlorine). Mercury is a poison, with toxicity to the kidney and nervous system in particular. The phrase 'mad as a hatter' refers to a 19th-century occupational disease from prolonged contact with mercury salts used in the manufacture of felt hats. Though mercury salts are poorly absorbed, they can be converted by bacteria to methyl mercury, which readily crosses cell membranes. Most atmospheric mercury emissions come from burning of coal, and when this settles into soil and water it is introduced into the food chain.

Tartaric acid naturally forms in grapes, and is a by-product of the wine industry. Cream of tartar (potassium hydrogen tartrate) can be combined with antimony oxide to produce tartar emetic (antimony potassium tartrate). The use of antimony as a medicine is first credited to a 15th century European cleric, who fed it to pigs on the monastery farm and observed that the pigs became healthier (in retropsect, probably because the antimony killed parasitic worms). He dismissed the deaths of several colleagues to whom he gave the antimony as unexplained, the scientific method having yet to be firmly established in experimentation. The usage of tartar emetic caught on with physicians of the time, and remained in usage for the next 400 years, since "purging" was considered a desirable effect in a sick person. Persons who vomited immediately were spared the poisoning from absorption.

Predating these "therapies" the Hippocratic Oath states, "I will not give a lethal drug to anyone if I am asked, nor will I advise such a plan;" which led to interpretation in the admonition to physicians, "primum non nocere," or "first do no harm."