Anatomy of the Bladder

The bladder is a hollow muscular organ situated behind the pubis symphysis.
It is composed of a crisscross of smooth muscle fibers known as the Detrusor muscle.
The Detrusor muscle has a rich cholinergic parasympathetic supply.
Contraction of the Detrusor muscle results in simultaneous reduction of the bladder in all its diameters.

The urethra is 3-5 cm in length and is a thin-walled muscular tube that drains urine from the bladder to outside the body.
Beneath the epithelium is a rich vascular plexus that contributes up to 1/3 of the urethral pressure.
The urethra has a minimal parasympathetic innervation, and its smooth muscles are innervated by sympathetic fibers.
Stimulation of these sympathetic fibers produces urethral contraction via α-adrenergic receptors.
β-adrenergic receptors produce Detrusor muscle relaxation.

The internal urethral sphincter (involuntary) is a thickening of the Detrusor muscle at the bladder-urethral junction.
The external urethral sphincter (voluntary) is a skeletal muscle that surrounds the urethra as it passes through the urogenital diaphragm.
The urogenital diaphragm is part of the pelvic diaphragm, which is the muscular portion of the pelvic floor that provides a stable base on which the bladder neck and proximal urethra rest.

The intra-urethral pressure at rest or with the stress of increased intra-abdominal pressure (IAP) remains higher than intra-vesical pressure by:
- Urethral mucosal resistance
- Periurethral vascular plexus pressure
- Resting intra-abdominal pressure
- Kinking of the urethra
- Contraction of the urogenital diaphragm
Urinary continence is the ability to hold urine at all times except during micturition.
Continence control is established via:
- Intraurethral pressure higher than intravesical pressure (neuromuscular)
- Fascial support around the urethra (anatomical position)
- Submucosal vascularity

As urine accumulates, the bladder stretches and stretch receptors are activated, causing a reflex that results in relaxation of the Detrusor muscle and contraction of the external urethral sphincter.
When about 200 ml of urine has accumulated, impulses are sent to the brain and one begins to feel the urge to urinate.
Activation of the micturition center in the pons signals parasympathetic neurons that stimulate contraction of the Detrusor and relaxation of the sphincters.
During micturition:
- Relaxation of pelvic striated muscle (pudendal nerve inhibition)
- Relaxation of the fascial support (parasympathetic effect)
  - Descent of the bladder neck
  - Funnelling of the urethra
  - Increase of urethro-vesical angle → 180°
  - Increase of urethral pubic angle → 45°
- Contraction of the Detrusor muscle (parasympathetic effect)

Definition: Involuntary leakage on effort, exertion, sneezing, or coughing.
Etiology: Intra-abdominal pressure exceeds the muscular strength of the sphincter.
Impaired urethral support, intrinsic sphincter deficiency, and weakness of the musculo-fascial support of the urethro-vesical junction.

Weakness of the musculo-fascial support of the urethro-vesical junction
Descent of the urethro-vesical junction so that the upper urethra is not situated above the urogenital diaphragm
Damage to either the pelvic floor musculature (levator ani) or pubourethral ligaments

The bladder neck is elevated by 2 fingers placed in the vagina on each side of the urethra without compressing it.
If no urine escapes during coughing, then bladder neck descent is the cause, and surgical repair will be successful.
If urine escapes on coughing, then weakness of the bladder neck will be the cause.

Definition: Involuntary leakage associated with a strong urge to pass urine that cannot be held back.
Etiology: Overlap of detrusor overactivity and impaired urethral sphincter function.

Definition: Involuntary leakage associated with urgency as well as exertion, effort, sneezing, or coughing.
Etiology: Overlap of detrusor overactivity and impaired urethral sphincter function.

Congenital or traumatic
Surgical trauma: The commonest cause, mostly surgical nowadays.
Obstetric trauma: It occurs in 2 types:
- Necrotic obstetric trauma
- Direct obstetric trauma
Inflammatory: Non-specific infections, pelvic abscess that opens in the bladder and vagina, specific infections (T.B. or bilharziasis), and neoplastic (e.g., advanced cases of cancer cervix, bladder, or vagina).

History and examination:
- Genito-urinary fistula: continuous (day and night) urine dripping
- Genuine stress incontinence: only drops of urine, not associated with the desire of micturition, usually on sudden cough or sneeze
- Urge incontinence: more than drops of urine, associated with the desire of micturition
- Retention with overflow: obvious neurologic affection or agonizing bladder pain with acute retention
- Nocturnal enuresis: only by night, may be psychological disorders
Specific investigations:
- Cases suspected to be genitor-urinary fistula: Methylene blue test
- Midstream urine to detect infection with pus cells
- Culture and sensitivity may be needed
- Urodynamic studies: Differentiate genuine stress incontinence from urge incontinence and diagnose mixed cases.

Genuine stress incontinence:
- Preventive: Avoid obstetric trauma, advise postnatal pelvic exercises, and replace therapy for menopausal females.
- Behavioral therapy: Restrict fluid, lose weight, treat constipation, and stop smoking.
- Repeated pelvic floor exercises (Kegel's exercises or passive by electric stimulation)
- Minimally invasive therapies: Pretibial nerve stimulation (PTN) and surgery.