Chapter 39 The urinary tract and its relationship to gynaecology

The close connection of the bladder to the vagina and the short urethra give rise to more problems in a woman’s urinary tract than in a man’s. The anatomy of the urinary tract is described on page 343. The function of the urinary tract is to permit waste products of metabolism to be removed from the body in the urinary flow. For this reason the mechanics of micturition will be discussed first.

MECHANICS OF VOLUNTARY MICTURITION

The bladder fills as urine trickles down the ureters. To accommodate the urine the bladder distends, and it can accommodate 300–400 mL of urine without any increase in the resting intravesical pressure, which remains below 10 cmH₂O. In the resting state the urethrovesical junction is flat and there is an angle of about 90° between the bladder and the urethra (the urethrovesical angle) (Fig. 39.1A).

Fig. 39.1 Tracing from radiographs of the bladder and urethra. (A) At rest; (B) during micturition.

Continence is maintained because of the inherent tone of the urethra and by the muscles that envelop the urethrovesical junction and the proximal urethra, which keep the intraurethral pressure 7–10 cmH₂O higher than the pressure within the bladder.

When more than 350 mL of urine distends the bladder, cholinergic muscarinic stretch receptors in the bladder wall are stimulated. This causes the detrusor muscle to contract and the intravesical pressure rises. Paradoxically, the extension of the detrusor muscle, which surrounds the proximal urethra in a spiral fashion, relaxes, with the result that the intraurethral pressure falls below the intravesical pressure. By the age of 5 most children have learned to inhibit the detrusor contractions and to keep the urethra closed, so that micturition can be delayed until an appropriate time. In some women, this higher centre control cannot be maintained and micturition occurs inappropriately. A second line of defence against involuntary micturition is provided by the muscles forming the external urethral sphincter and the fibres of the pubococcygeal muscle that surround and support the distal urethra.

When the person is ready to pass urine the detrusor muscle is permitted to contract strongly, which raises the intravesical pressure above the intraurethral pressure. The detrusor contractions also cause funnelling of the bladder base and obliterate the urethrovesical angle (Fig. 39.1B).

At the same time, the person contracts the abdominal muscles, which raises the intravesical pressure further. These changes and the relaxation of the proximal urethral muscle permit urine to pass into the urethra. The person now relaxes the muscles surrounding the distal urethra, and urine is voided until the bladder is empty. When this occurs the detrusor ceases to be stimulated and relaxes, and the urethrovesical angle is restored. The proximal urethra contracts from its distal end to the urethrovesical junction, ‘milking’ back a few drops of urine into the bladder. Finally, the external sphincter closes.

URINARY INCONTINENCE (INVOLUNTARY MICTURITION)

As women grow older the incidence of urinary incontinence increases, often causing social isolation or psychological problems. In the 35–50-year age group 5% of women are incontinent at least once each week. By the age of 60, 15–20% of women complain of urinary incontinence, and by the age of 80 one woman in four is incontinent.

In women two main and two subsidiary forms of urinary incontinence occur. The two main forms are:

• Urge incontinence

• Urethral sphincter incontinence (genuine stress incontinence).

The two subsidiary forms are:

• Reflex incontinence

• Overflow incontinence.

Of the subsidiary forms, reflex incontinence is an involuntary loss of urine due to abnormal reflex activity in the spinal cord in the absence of a desire to pass urine. Overflow incontinence (urinary retention with overflow) occurs in:

• Motor neurone disease

• Urethral obstruction, which is rare in women

• Cases of chronic bladder distension.

The proportion of women complaining of the two main forms of incontinence is not known. The best estimates are shown in Table 39.1.

Table 39.1 Percentage prevalence of the types of urinary incontinence

Type of Incontinence	Age (Years)
	<70	>70
Urethral sphincter	50	26
Urge incontinence	20	33
Mixed	30	41

Urge incontinence (overactive bladder syndrome)

In this disorder the detrusor muscle contracts involuntarily. There are two categories of urge incontinence. In the first, sensory incontinence, the woman passes urine, not because of involuntary detrusor activity but because it hurts if she does not empty her bladder. The woman has to micturate frequently, often several times at night as well as during the day, and may have dysuria. In some cases there is obvious urinary tract infection. In others no evidence of this is found.

Only gold members can continue reading. Log In or Register to continue

Share this:

• Click to share on Twitter (Opens in new window)
• Click to share on Facebook (Opens in new window)

Related

Related posts:

1. Cardiovascular, respiratory, haematological, neurological and gastrointestinal disorders in pregnancy
2. Antepartum haemorrhage
3. The epidemiology of obstetrics
4. Ovulation and the menstrual cycle

Stay updated, free articles. Join our Telegram channel

Join