Voiding refers to the process by which the body eliminates waste. While commonly associated with urination, it also encompasses defecation. This bodily function ensures the removal of metabolic byproducts and undigested food, maintaining overall health.
The Process of Voiding
Normal urination involves a coordinated series of actions. Urine, produced by the kidneys, travels down the ureters and collects in the bladder. As the bladder fills, stretch receptors in its walls send signals to the brain, causing the sensation of needing to urinate. An adult bladder holds between 350 to 550 cubic centimeters (CCs) of liquid, with the urge to urinate felt around 150 to 250 CCs.
When urination is initiated, the brain sends signals that cause the detrusor muscle to contract. Simultaneously, the internal urethral sphincter, an involuntary muscle, relaxes. The external urethral sphincter, a voluntary muscle, then relaxes, allowing urine to flow out of the bladder through the urethra. This process is controlled by the central, autonomic, and somatic nervous systems, with brain centers like the pontine micturition center playing a coordinating role.
Similarly, defecation involves coordinated movement. Waves of muscular contraction, known as peristalsis, move fecal matter from the colon into the rectum. As the rectum fills and its walls stretch, signals are sent to the brain, prompting the urge to defecate. The internal anal sphincter, an involuntary muscle, relaxes, and the external anal sphincter, under voluntary control, also relaxes, allowing feces to pass.
Common Voiding Issues
Problems with voiding indicate underlying health concerns. Urinary incontinence is the involuntary leakage of urine. This can range from small drips with activities like coughing or sneezing (stress incontinence) to a sudden, strong urge to urinate that cannot be controlled (urge incontinence), often due to an overactive bladder. Weak pelvic floor muscles, nerve damage, or medical conditions can contribute to these issues.
In contrast, urinary retention involves difficulty emptying the bladder completely. This can lead to frequent urination of small amounts or a constant feeling of fullness. Causes may include blockages in the urinary system, such as an enlarged prostate in men, or weak bladder muscles that prevent contraction.
Painful urination, medically termed dysuria, is another common voiding complaint. This symptom points to an infection in the urinary tract, but it can also be associated with inflammation, irritation, or other conditions affecting the bladder or urethra. Frequent urination can stem from various factors including high fluid intake, bladder irritation from foods or drinks, or an overactive bladder.
Changes in bowel habits, such as chronic constipation (infrequent or difficult bowel movements) or diarrhea, also represent voiding issues. Constipation can occur when stool moves too slowly through the colon, allowing too much water to be reabsorbed, leading to hard, dry stools. These issues can be uncomfortable and may signal a need for medical evaluation.