Blood supply
The urethra is supplied with arterial blood from branches of the deep pelvic artery (Arteria iliaca interna). This large artery divides into the arteria pudenda in the small pelvis. This, in turn, has many finer end branches, one of which is the so-called urethral artery (Arteria urethralis), which ultimately moves to the urethra. The venous outflow takes place via the urethral vein, which in turn flows into the deep pelvic vein (internal iliac vein) via the somewhat larger pudenda.
Function
For continence, i.e. the ability to hold urine, a flaccidity of the bladder on the one hand and the intact inner sphincter muscle at the transition from the bladder to the urethra (Musculus sphincter urethrae internus) on the other hand are required. The sphincter is also supported by a part of the muscular pelvic floor (Musculus sphincter urethrae externus). If this pelvic floor is too slack, as is often the case after several births, the patient cannot hold her urine and incontinence occurs under stress (e.g. when laughing, climbing stairs).
The urethra has its own nerve supply with vegetative nerve branches. These form a nerve plexus (plexus vesicalis) in the small pelvis. In order to initiate micturition (urination), a signal is sent to the brain via the nerves that a certain bladder filling is present, which can create the impression of an urge to urinate.
On the other hand, the brain can also use this signal to deliberately initiate the emptying of the bladder.This leads to tension of the bladder muscle (Musculus detrusor vesicae) and relaxation of the two bladder sphincters. The inner sphincter is controlled by the autonomic nervous system and is therefore independent of will. The outer sphincter is controlled by the central nervous system – the brain – and can thus relax independently of will. The urine enters the urethra, which uses gravity to move the urine towards the external urinary outlet.
Diseases of the urethra
Urethritis (inflammation of the urethra) is an inflammation of the mucous membrane of the urethra. A distinction is made between gonorrhoea (gonorrhea) and non-gonorrhoeic urethritis. The former is caused by the bacterium Neisseria gonorrhoea, the latter mostly by Chlamydia.
These are typical diseases that can be transmitted through unprotected sexual intercourse. The urethritis presents itself with a purulent discharge, itching and burning sensation when urinating. The doctor performs a smear from the urethra to detect the bacterium and administers antibiotics for therapy.
This is a relatively common congenital malformation of the male urethra. In hypospadias the urethra opens at the bottom of the penis, in epispadias at the top of the penis. A surgical correction should be performed in the 1st or 2nd year of life.
A very common disease is cystitis. This occurs mainly in women, as the urethra is significantly shorter in this case. Bacteria, mostly Escherischia coli from the intestine, can rise up and migrate through the urethra into the bladder.
Patients usually have an increased urge to urinate even when the amount of urine is small, pain when urinating, blood in the urine and lower abdominal pain. Therapy of choice is a one to three day antibiotic therapy. The dangers are on the one hand a repeated occurrence of the cystitis, on the other hand with e.g. weakened defense position an ascent of the germs over the ureters into the renal pelvis and over it to a renal pelvis inflammation (pyelonephritis).
Very many men in middle to old age have a benign enlargement of the prostate gland. Since the man’s urethra runs through the prostate, pressure and narrowing of the urethra (urethral stricture) quickly occurs. The patient then suffers from a weak urine stream, frequent urination, urinary stuttering, residual urine and dribbling after urination.
The complication is that the prostate gland narrows the urethra so much that urinary retention occurs. The patient has a very overstretched bladder, but cannot urinate at all because of the obstacle. Immediate relief via a catheter is absolutely necessary!
