Anatomy and Physiology of Urinary Incontinence

Control of urination is learned in early childhood through conscious training that later becomes mechanical. To establish and maintain this urinary continence and voiding control, it is essential that all genitourinary structures and the nervous and muscular structures that participate in its control are undamaged.

The genitourinary system is made up of two large structures:

The anatomical structures involved in the continence mechanism are:

• Genitourinary
  • Urinary bladder: it is the reservoir of urine due to the elasticity of its wall. The contractionary activity of the detrusor muscle, with involuntary muscle fibers, causes the bladder to empty when the internal sphincter opens.
  • Urethra: is the tube through which urine passes from the bladder to the outside. Along its path are the sphincters (involuntary interior and voluntary exterior), which are the doors to the passage of urine.
• Muscular:
  • Detrusor muscle: involuntary muscle fibers embedded in the bladder wall; when they contract, they push urine from the bladder into the urethra, initiating urination when the sphincters open.
  • Sphincters: The internal is involuntary and opens when the detrusor muscle contracts. The external one is voluntary, it opens when wanting to consciously initiate urination, or it closes more forcefully when it is not convenient to urinate, even when the internal sphincter opens and the detrusor contracts.
  • Pelvic floor muscles: they form the floor on which the bladder rests and through which the urethra passes. A correct pelvic floor keeps anatomical structures in place and ensures proper functioning.
• Nervous:
  • Peripheral nerves: the sacral nerves, which through the involuntary parasympathetic fibers that originate in the reflex center of urination (located in the sacral medulla) send stimuli for the contraction of the detrusor, in response to the stretching of the bladder wall, in a process without conscious control.
  • Spinal cord: From the bulb, fibers of the sympathetic nervous system are emitted (also involuntary) that cancel the effect of contraction of the sacral fibers, inhibiting urination.
  • Frontal cerebral cortex and medullary somatic nerves: in this case of voluntary control, they control the opening and closing of the external sphincter, in the case of wanting or not the emission of urine.
• Other structures:
  • Prostate: being located under the bladder and surrounding the first portion of the urethra in men, its growth can strangle it and make it difficult for urine to flow out. In the long term it can lead to overflow incontinence (the bladder never empties and is quickly too full to prevent the passage of urine)
  • Vagina and vulva: its atrophy in menopause causes deterioration in the function of the external sphincter, which loses contraction force.

These are the main anatomical elements involved in urinary continence, but in order to maintain correct continence, a conscious perception of the desire to urinate (central nervous system) and the adequate physical ability to reach the bathroom, remove clothes, and initiate urination is necessary. (locomotor system and central nervous system).

Taking into account these anatomical structures and their function, urinary incontinence will occur due to alteration of any of these requirements to be continent:

Proper Lower Urinary Tract Function:

• During the filling and storage of the bladder:
  • The bladder must accommodate progressive volumes of urine without involuntary contractions.
  • The urethral sphincter must remain closed preventing the exit of urine.
  • There is a feeling of bladder filling.
• During bladder emptying:
  • The bladder contracts properly.
  • There is an obstruction that prevents urine from coming out.
  • There is coordination between sphincter relaxation and bladder contractions.

Adequate physical function:

• Adequate mobility to reach the WC.
  • Skill in using the toilet or its substitutes and handling clothing.

Adequate cognitive functions:

• That allow the person to recognize the need to go to the toilet and find the toilet or a substitute (urinal, etc.)
  • That allows you to recognize the right time and place to urinate.

Motivations to be continent:

• Absence of architectural barriers and iatrogenic factors.
• Accessible toilets or substitutes.
• Caregiver availability.
• Avoid the use of drugs with side effects that compromise continence.