Inside Your Health: Constipation Part 1

Inside Your Health: Constipation Part 1

Constipation has many causes, and it usually results from a combination of multiple factors. Consequently, many widely circulated constipation remedies online may be effective for some individuals while offering little benefit to others. Fully understanding the root causes of constipation is the key to finding a tailored solution. To understand how constipation occurs, one must first understand gastrointestinal physiology.

How does the human body produce and excrete stool?

After food undergoes digestion and nutrient absorption in the stomach and small intestine, the remaining intestinal contents are transported into the colon, commonly known as the large intestine, via small bowel peristalsis. The colon consists of the ascending colon, transverse colon, descending colon, and sigmoid colon. Stool gradually moves along this pathway toward the rectum and anal opening. The primary function of the colon is the absorption of water and electrolytes.

As mucosal cells in the colon absorb electrolytes, they drive the passive absorption of water. Studies indicate that the colon can absorb approximately 1.5 liters of water per day, with roughly 0.3 liters retained in the stool to prevent it from becoming excessively dry or hard, thereby maintaining smooth bowel movements. However, if one contracts a gastrointestinal infection from pathogens such as cholera, the intestinal tract's ability to absorb electrolytes may be blocked. This causes fluid to remain in the intestinal lumen, resulting in diarrhea.

How does the human body control the excretion of stool? The physiological control mechanism of defecation is highly complex. To regulate the release of fecal matter, the body utilizes the puborectalis muscle alongside the internal and external anal sphincters to prevent involuntary passage from the rectum. Without these mechanisms, uncontrolled defecation could occur during daily activities 🫢

The entire defecation process involves precise muscular coordination. Contraction of the puborectalis muscle maintains a 80 to 100 degree angle in the anorectal junction, preventing stool from directly entering the anal canal. During defecation, the puborectalis muscle and both anal sphincters relax. Concurrently, increased intraabdominal pressure, pelvic floor descent, and rectal contraction work in unison to complete fecal expulsion, functioning like a perfectly coordinated system.

Under normal conditions, neural signals triggering colonic motility and contraction become more prominent upon waking in the morning or following food intake. These peristaltic movements facilitate the transit and expulsion of stool through the intestinal tract. This physiological reflex explains why many individuals experience a bowel movement shortly after eating breakfast or drinking water.