THE SIGNIFICANCE OF THE BLADDER

During Pregnancy

• Frequency of Micturition: Is common during the first 12 weeks because during this time the uterus is still a pelvic organ, and so is the bladder. As the uterus grows, there will be no room, and so the bladder is compressed by the growing uterus, causing frequency of micturition.

• Physiological changes: Due to hormonal action (progesterone activity) on the muscle of the ureters, making them relaxed and kinked, can also cause frequency.

• At 36 weeks: There is frequency again because of the engaging head pressing on the bladder.

• Infections: Frequency can also be due to infections like urinary tract infections (UTI), which occur in 2% of all pregnant mothers.

• Retention of urine: This can occur around 12 weeks in a retroverted gravid uterus. The growing uterus pulls up the cervix and becomes impacted. The discomfort of this full bladder is only relieved by catheterization.

• Incontinence of urine (Stress Incontinence): About the 36th week of pregnancy, as the fetal head engages, urine drips when a patient coughs, sneezes, or laughs.

During Labour

• Frequency: In the occipito-posterior position, pressure is exerted on the sacral plexus nerve. This sends stimulus to the nerves of the bladder (sympathetic and parasympathetic) through the Lee-Frankenhauser plexus. Sometimes there is then an urge to pass urine, but the patient is unable to do so.

• Retention: Pressure on the sacral plexus can also cause a lack of stimulus to the bladder. During labor, the urethra also stretches from 4cm to 15cm. If the bladder is kept full until labor is well advanced, there are great difficulties in passing urine, and even catheterization is difficult.

• Incontinence: If the bladder is not emptied in the first stage of labor, there will be dripping of urine with each expulsive contraction in the 2nd stage of labor.

• Complications of a Full Bladder in Labor:

  • A full bladder causes delay in the 1st and 2nd stage of labour by inhibiting good uterine contractions.

  • As a result of this delay, there is going to be prolonged pressure of the descending head on the bladder wall. The full bladder will be nipped between the head and the symphysis pubis, causing bruising of the bladder wall.

  • Then, as the pressure continues, the blood supply will be cut off. As a result, there will be necrosis of that compressed part, leading to slough which can detach and leave a hole known as a vesicovaginal fistula (VVF), causing incontinence of urine.

  • The urethra is also bruised, potentially causing a urethral-vaginal fistula.

• In 3rd stage of labour: A full bladder can cause serious complications, e.g., Postpartum Hemorrhage (P.P.H) and retained placenta. It is therefore very important to keep the bladder empty at all stages of labour.

During the Puerperium

• Frequency: Due to polyuria brought about by physiological changes, especially during the first 48 hours. Some of the protoplasm which had grown ten times in thickness and 10 times in width are now broken down and excreted by the kidneys through the bladder in the form of urine. Uterine involution also recurs, leading to frequency of micturition.

• Retention: This can occur in cases that are confined to bed. Early ambulation is therefore important. If a patient is not used to a bedpan, she can fail to empty the bladder.

  • Embarrassment or lack of privacy can also cause retention.

  • Pain from stitches or a bruised perineum can make a patient fail to pass urine.

  • Insufficient stimulus due to pressure during labour.

  • An overstretched bladder during labour may later on lose its muscle tone, leading to retention.

• An injury: In the puerperium, the bladder should be palpated so as to detect residual urine which may accumulate and be a predisposing factor to urinary infection due to stasis or stagnation.

• Secondary P.P.H: Can be caused by a full bladder.

• Incontinence: Due to a major degree of trauma during the 1st and 2nd stage of labour which resulted in V.V.F.

• Stress Incontinence

Mechanism of Micturition (Note: Original text labeled this ‘Stress Incontinence’)

1. The sensation of a full bladder is conveyed to the brain by sensory sympathetic nerves.

2. Then at a suitable time, the voluntary nerve relaxes the membranous sphincter.

3. The sympathetic nerve relaxes the internal urethral sphincter.

4. The parasympathetic nerve causes the Detrusor muscle to contract, and this results in the pulling of the internal urethral meatus by the bell muscles.

5. Then intra-abdominal pressure is increased, and urine is passed with a bearing-down movement.

THE URETHRA

Definition

This is the channel leading from the bladder to the surface of the body by which the urine is voided.

Situation

It runs from the apex of the trigone to the external anterior vaginal wall.

Shape

It is tubular.

Size

In the female, it is about 4cm (1.5 inches) long but is capable of elongating, as it does during labour when the bladder becomes an abdominal organ. This stretches the urethra to 10cm and makes catheterization difficult. It is introduced in the anterior vaginal walls.

Gross Structure

• Internal meatus: Where it meets the neck of the bladder.

• External meatus: The opening in the vestibule.

• Urethral crypts: Small, blind ducts open from the wall of the urethra. The lowest ones at each side of the urethral orifice are known as Skene’s ducts.

Microscopic Structure

• Stratified epithelium lines the lower half of the urethra.

• Transitional epithelium lines the upper half.

• Connective tissue lies beneath the epithelium.

• The muscle coat is arranged in two layers:

  1. Inner layer of longitudinal fibers

  2. Outer layer of longitudinal fibers

• The muscle is thickened around the internal meatus to form the sphincter muscle. The external meatus is surrounded by the membranous sphincter.

• The urethra needs no outer protection because it is embedded in the anterior wall of the vagina.

Blood Supply

Inferior vesicle arteries and pudendal arteries.

Venous Drainage

By the corresponding veins.

Lymphatic Drainage

By internal iliac glands.

Nerve Supply

Sympathetic nerves to the internal sphincter. The membranous sphincter is under the control of the will and is supplied by the pudendal nerve.

Supports

It is given by the anterior vaginal wall and pelvic floor muscle.

Functions

It forms a canal through which urine can be eliminated from the body.