Chapter VI - Urinary System

Urethra and Urinary tract Infections

Urethral Sphincter

The flow of urine from the urinary bladder is controlled by a group of muscles collectively called the urethral sphincter, named for their proximity to the urethra. Both sexes have at least two areas of muscle: the internal sphincter, or bladder neck; and the external, or distal, sphincter.

In males the internal and external urethral sphincters are more powerful, able to retain urine for twice as long as females, and are furthermore backed up by the tertiary rings of urethral sphincters along the length of the penis.

Both sexes can use the levator ani, the voluntary muscle of the pelvic floor, to control urination. In females this muscle is more important because of the weakness of the urethral sphincters. Kegel exercises are a form of exercise intended to strengthen the pelvic floor muscles.

Urinary incontinence is the inability to control urination, and is more common in women than men.

Urethra

The urethra is a tube, which connects the urinary bladder to the outside of the body. The urethra has an excretory function in both sexes, to pass urine to the outside, and also a reproductive function in the male, as a passage for sperm.

The external urethral sphincter is a smooth muscle that allows voluntary control over urination.

Men have a longer urethra than women. This means that women tend to be more susceptible to infections of the bladder (cystitis) and the urinary tract. The length of a male's urethra, and the fact it contains a number of bends makes catheterization more difficult.

In the human female, the urethra is about 1-1.5 inches (2.5-4 cm) long and opens in the vulva between the clitoris and the vaginal opening. In the human male, the urethra is about 8 inches (20 cm) long and opens at the end of the penis.

The urethra is divided into three parts in men, named after the location:

• The prostatic urethra crosses through the prostate gland. There is a small opening where the vas deferens enters.
• The membranous urethra is a small (1 or 2 cm) portion passing through the external urethral sphincter. This is the narrowest part of the urethra.
• The spongy (or penile) urethra runs along the length of the penis on its ventral (underneath) surface. It is about 15-16 cm in length, and travels through the corpus spongiosum.

Histology
The epithelium of the urethra starts off as transitional cells as it exits the bladder. Further along the urethra there are stratified columnar cells, then stratified squamous cells near the external meatus (exit hole). There are small mucus secreting urethral glands.

Medical problems of the urethra

• Hypospadias and epispadias are forms of abnormal development of the urethra in the male, where the opening is not quite where it should be (it occurs lower than normal with hypospadias, and higher with epispadias). A chordee is when the urethra develops between the penis and the scrotum.
• Infection of the urethra is urethritis, said to be more common in females than males. Urethritis is a common cause of dysuria (pain when urinating).
• Related to urethritis is so called urethral syndrome.
• Passage of kidney stones through the urethra can be painful and subsequently it can lead to urethral strictures
• Endoscopy of the bladder via the urethra is called cystoscopy.
• Urethral Stricture-A urethral stricture is internal damage to the urethra caused by injury or disease such as urinary tract infections or other forms of urethritis.

G-spot
The Gräfenberg spot' or G-spot is named after German gynecologist Ernst Gräfenberg. It is a small area in the genital area of women behind the pubic bone and surrounding the urethra. It is the same as, or part of, the urethral sponge, the site of Skene's glands.

Stimulation of the G-spot (through the front wall of the vagina) is said to promote a more vigorous and satisfying orgasm, and is possibly the cause of female ejaculation from the Skene's glands, contained in the urethral sponge. Such stimulation requires a somewhat opposite thrust to that required to obtain maximal clitoral stimulation via the penis, called "riding high". The stimulation of the G-spot is thought to be more intense for women beyond their thirties, because of changes in tissue structure inside the vagina allowing easier access to the G-spot. Some women believe their thirties are their sexual peak because of this reason.

Urethral Sounding
Sounding or urethral sounding is a medical activity using probes called sounds to increase the inner diameter of the urethra and to locate obstructions in the urethra. Sounds are usually made of stainless steel and come in two main types: the Van Buren (named after its inventor, William Holme Van Buren), which has a J-shaped curve at one end, and the Dittle, which is straight. The curved variety may inhibit the ability to gain an erection. A urethral sound may be connected to a special electrical device for use in erotic electrostimulation.

The use of urethral sounding in this way can potentially be damaging to the urethra. The dangers include tearing or cutting of the urethra and the possibility of urinary tract infection.

Urinary Tract Infection
A urinary tract infection (UTI) is an infection of the urinary tract. An infection anywhere from the kidneys to the ureters to the bladder to the urethra qualifies as a urinary tract infection.

Symptoms & Signs

• Urethritis: discomfort or pain at the urethral meatus or a burning sensation throughout the urethra with micturition (dysuria).
• Cystitis: pain in the midline suprapubic region and/or frequent urination
• Hematuria (bloody urine)
• Cloudy and foul-smelling urine

Common organisms that cause UTIs include Escherichia coli and Staphylococcus saprophyticus. Less common organisms include Proteus mirabilis, Klebsiella pneumoniae, and Enterococcus spp.

UTIs are most common in sexually active women, and increased in diabetics and people with sickle-cell disease or anatomical malformations of the urinary tract.

Treatment
Most uncomplicated UTIs can be treated with oral antibiotics such as trimethoprim, cephalosporins, Macrodantin, or a fluoroquinolone (e.g. ciprofloxacin, levofloxacin). Patients with recurrent UTIs may need further investigation. This may include ultrasound scans of the kidneys and bladder or intravenous urography (X-rays of the urological system following intravenous injection of iodinated contrast material).