Defecation and Bowel Emptying: How It Works

Defecation (bowel emptying) is the process of removing stool from the rectum through the anus. Understanding how this process works and which stool patterns are considered normal helps distinguish the norm from a condition that requires a doctor's consultation.

What defecation is and how it happens

The urge to defecate appears when the receptors of the rectum and pelvic floor are irritated by stool to a certain degree. When the rectum distends, a signal travels to the brain. The act of defecation in most cases occurs consciously: the internal sphincter opens, and the person controls the external sphincter. When it relaxes, the stool moves outward; if it does not come out completely, the abdominal muscles and diaphragm contract.

In a healthy adult, the rectal sensitivity threshold is no more than 25 milliliters, the minimum volume for relaxation of the internal sphincter is 10–20 milliliters, the threshold for a constant urge is no more than 220 milliliters, and the maximum tolerable volume is 110–280 milliliters. These parameters are measured by anorectal manometry.

What stool frequency is considered normal

In a person, defecation normally occurs about once a day — from one to two times a day to once every two days. Daily stool is not obligatory: constipation means fewer than three bowel movements per week, while the stool may be hard and dry, sometimes painful. Constipation is likely if there have been fewer than three bowel movements in the past week or they occur less often than usual, the stool is unusually large or small, dry, hard, or lumpy, as well as with straining or pain.

What the feeling of incomplete bowel emptying is

The feeling of incomplete emptying is a subjective sensation that the bowel has not been fully emptied after defecation. The feeling of incomplete emptying is considered a sign of constipation along with infrequent stool, its altered consistency, and straining. The sensation may be accompanied by bloating, abdominal pain, and nausea.

Possible causes of incomplete emptying

The most common causes of constipation include a lack of fiber, fluids, and movement, prolonged sitting or lying down, ignoring the urge to go to the toilet, a change in diet or daily routine, side effects of medications, stress, anxiety, and depression. Constipation is more common after age 65, during pregnancy, and after childbirth. Less often it is caused by diseases, such as diverticular disease or bowel cancer.

• infrequent stool and altered stool consistency;
• straining or pain during defecation;
• feeling of incomplete emptying;
• bloating, abdominal pain, nausea.

How a doctor assesses emptying disorders

The doctor clarifies the frequency of stool, its character, accompanying symptoms, and medications taken. Anorectal manometry is used to assess rectal sensitivity and sphincter function; colonoscopy and radiography of the lower gastrointestinal tract with a barium enema are also mentioned in diagnosis.

When to see a doctor

You should see a doctor if constipation does not improve with treatment, occurs regularly, is accompanied by regular bloating, blood in the stool, effortless weight loss, constant fatigue, abdominal pain, or a sudden change in bowel habits, as well as if constipation is associated with taking medications.

The feeling of incomplete emptying by itself is not a reason to call an ambulance; 103/112 — if a life-threatening condition occurs, for example, if peritonitis or bowel rupture due to hard stool is suspected.

This material is for reference: it describes mechanisms and guidelines but does not replace a doctor's consultation.

This content is for reference and does not replace a doctor's consultation. Medical disclaimer