Urinary incontinence: Pathology review

In the Urology ward, two people are coming in. The first is Oleg, a 70 year old man who says that he frequently has to use the bathroom and also complains of a weak urinary stream. The second is Samantha, a 55 year old woman who says that she “pees” a little when she laughs. Samantha also has 2 children and both were born by vaginal delivery. Now, both these individuals seem to have urinary incontinence.

Urinary incontinence is a problem where the process of urination happens involuntarily, meaning that a person might urinate without intending to. This is particularly problematic because it affects a person’s personal hygiene as well as their social life in a way that can be very limiting.

Let’s talk about physiology real quick. Okay, so as urine flows from the kidneys into the bladder, the bladder starts to fill. Lining the bladder is a layer of transitional epithelium containing “umbrella cells”. These cells physically stretch out as the bladder fills, just like an umbrella opening up in slow-motion. This expansion is further aided by the relaxation of the muscular layer within the bladder’s walls, called the detrusor muscle. At some point, the bladder fills up with urine that will eventually exit the body through the urethra.

Now, the urethra is wrapped up in some muscles that can prevent urine from leaking out. The first one is the internal sphincter muscle, which is made of smooth muscle and is under involuntary control and typically opens up when the bladder is about half full. The second one is the external sphincter muscle, and it’s made of skeletal muscle and is under voluntary control. This is the reason that it’s possible to stop urine mid-stream by tightening up that muscle. Once urine has passed through the external sphincter muscle, it can no longer be stopped.

Now, when specialized nerves in the bladder wall sense that the bladder is about half full, they send impulses to the spinal cord at levels S2 and S3, also known as the micturition center, and to the pons of the brain. The spinal cord response is part of the micturition reflex and it causes an increase in parasympathetic stimulation and decrease in sympathetic stimulation which makes the detrusor muscle contract and the internal sphincter relax.