Pelvic Prime's Anatomy Academy Series
Constipation
Constipation is a condition where passing stool becomes difficult, or bowel movements occur infrequently. Symptoms may include:
Straining
Feeling as if the bowels are not completely emptied
Needing to use fingers to assist with stool passage
Bloating
Having hard stools.
According to the updated Rome IV criteria, functional constipation is diagnosed when two or more of the following criteria are met within the past three months:
Straining during more than 25% of bowel movements
Hard or lumpy stools in more than 25% of bowel movements
A sensation of incomplete evacuation in more than 25% of bowel movements
A sensation of anorectal blockage in more than 25% of bowel movements
The need to use fingers to help pass stool in more than 25% of bowel movements
Fewer than three bowel movements per week
Diarrhea should not be present unless it is induced by laxatives.
How Common is Constipation?
The prevalence of constipation varies significantly, ranging from 2% to 30%, depending on the population and the criteria used for diagnosis. Globally, chronic idiopathic constipation affects approximately 14% of people, making it one of the most common gastrointestinal disorders.
In the United States, constipation affects around 63 million people, with a prevalence ranging from 2% to 27%. It has considerable socioeconomic impacts, costing over $1.5 billion in emergency department visits and over $1 billion in laxative purchases in 2011 alone.
Globally, constipation affects quality of life similarly. Women with constipation tend to report a lower quality of life than men. Constipation is also frequently associated with premenstrual syndrome in up to 48% of women of childbearing age.
Constipation is also common in children, with 95% of cases being functional and often related to behavioral withholding after an unpleasant stool event.
Anatomy and Pathophysiology of Constipation
The anal canal, about 4 cm in length, connects to the rectum at the anorectal junction. The puborectalis muscle surrounds this junction, forming a 90 to 110-degree angle at rest. The muscle layer of the gastrointestinal tract thickens at the anal canal, forming the internal anal sphincter.
The external anal sphincter, a somatic muscle, continues with the puborectalis muscle and the levator ani. The internal anal sphincter and the area above the dentate line are controlled by sympathetic nerves from the pelvic plexus, while the external anal sphincter and the area below the dentate line are controlled by branches of the pudendal nerve.
Normal Bowel Movements
The process of defecation involves the movement and storage of stool, absorption of water and electrolytes, and coordinated muscle actions. Disruptions in any of these processes can lead to constipation.
Motility: The colon moves stool through peristalsis and mass movements, which occur a few times daily and lead to defecation.
Mass movements are high-amplitude contractions that propel stool forward.
Peristalsis is facilitated by serotonin, a chemical that promotes intestinal muscle contractions.
Fluid and Electrolytes: Adequate hydration is crucial for regular bowel movements, as the colon absorbs about 1 to 2 liters of fluid daily. Medications like pro-secretory drugs and osmotic laxatives can increase the fluid content in the intestines, softening stool and promoting bowel movements.
Diet: A diet high in processed grains, low in fiber, insufficient fluids, and low physical activity can contribute to constipation.
A recommended diet includes 30 to 40 grams of fiber and more than 2 liters of water daily.
Fiber increases stool bulk, absorbs water, and promotes healthy gut bacteria.
Causes and Risk Factors
Constipation can be classified as primary or secondary.
Primary Constipation: Includes normal transit constipation, irritable bowel syndrome with constipation (IBS-C), slow-transit constipation, and obstructed defecation syndrome (ODS).
Normal Transit Constipation and IBS-C: These conditions are common, affecting up to 70% of people with chronic constipation. They are often related to stress and do not involve abnormal bowel transit or pelvic floor dysfunction. IBS-C can cause abdominal pain and is diagnosed by ruling out other causes.
Slow Transit Constipation: Characterized by slow movement of stool through the colon, often due to nerve or muscle issues in the intestines. Symptoms include a reduced urge to defecate and lack of rectal fullness.
Obstructed Defecation Syndrome (ODS): Involves difficulty emptying the rectum, excessive straining, and the need for physical assistance to pass stool. It can be caused by mechanical issues like rectal prolapse or functional issues like muscle coordination problems.
Secondary Constipation: Caused by other medical conditions or lifestyle factors, including:
Endocrine and metabolic disorders (e.g., diabetes, hypothyroidism)
Neurological disorders (e.g., spinal cord injury, Parkinson's disease)
Psychological issues (e.g., depression, anxiety)
Certain medications (e.g., opiates, antidepressants)
Other Factors
There is no strong evidence linking genetics to constipation. However, factors that increase the risk of constipation include:
Insufficient physical activity
Low fiber and water intake
Obesity
Older age
Being female
Factors that can improve or relieve constipation:
Regular exercise: recommendation is exercising for at least 30 minutes per day
Adequate fiber
Water intake: Recommendation is drinking 2 liters of water daily
References: Bo, K., Berghmans, B., Mørkved, S., & Van Kampen, M. (Eds.). (2023). Evidence-Based Physical Therapy for the Pelvic Floor (3rd ed.). Elsevier.