The urethra is the tube that connects the mammalian urinary bladder to the urinary meatus. In placental mammals, the urethra transports urine through the penis or vulva during urination and semen through the penis during ejaculation.
The bladder is a hollow organ in humans and other vertebrates that stores urine from the kidneys before disposal by urination. In placental mammals, urine enters the bladder via the ureters and exits via the urethra. In humans, the bladder is a distensible organ that sits on the pelvic floor. The typical adult human bladder will hold between 300 and 500 ml before the urge to empty occurs, but can hold considerably more.
The human urinary system, also known as the urinary tract or renal system, consists of the kidneys, ureters, bladder, and the urethra. The purpose of the urinary system is to eliminate waste from the body, regulate blood volume and blood pressure, control levels of electrolytes and metabolites, and regulate blood pH. The urinary tract is the body's drainage system for the eventual removal of urine. The kidneys have an extensive blood supply via the renal arteries which leave the kidneys via the renal vein. Each kidney consists of functional units called nephrons. Following filtration of blood and further processing, wastes exit the kidney via the ureters, tubes made of smooth muscle fibres that propel urine towards the urinary bladder, where it is stored and subsequently expelled through the urethra during urination. The female and male urinary system are very similar, differing only in the length of the urethra.
Urination is the release of urine from the bladder to the outside of the body. Urine is released from the urethra through the penis or vulva in placental mammals and through the cloaca in other vertebrates. It is the urinary system's form of excretion. It is also known medically as micturition, voiding, uresis, or, rarely, emiction, and known colloquially by various names including peeing, weeing, pissing, and euphemistically going number one. The process of urination is under voluntary control in healthy humans and other animals, but may occur as a reflex in infants, some elderly individuals, and those with neurological injury. It is normal for adult humans to urinate up to seven times during the day.
Urinary incontinence (UI), also known as involuntary urination, is any uncontrolled leakage of urine. It is a common and distressing problem, which may have a large impact on quality of life. It has been identified as an important issue in geriatric health care. The term enuresis is often used to refer to urinary incontinence primarily in children, such as nocturnal enuresis. UI is an example of a stigmatized medical condition, which creates barriers to successful management and makes the problem worse. People may be too embarrassed to seek medical help, and attempt to self-manage the symptom in secrecy from others.
The parasympathetic nervous system (PSNS) is one of the three divisions of the autonomic nervous system, the others being the sympathetic nervous system and the enteric nervous system. The enteric nervous system is sometimes considered part of the autonomic nervous system, and sometimes considered an independent system.
Retrograde ejaculation occurs when semen which would be ejaculated via the urethra is redirected to the urinary bladder. Normally, the sphincter of the bladder contracts before ejaculation, inhibiting urination and preventing a reflux of semen into the bladder. The semen is forced to exit via the urethra, the path of least resistance. When the bladder sphincter does not function properly, retrograde ejaculation may occur. It can also be induced deliberately by a male as a primitive form of male birth control or as part of certain alternative medicine practices. The retrograde-ejaculated semen is excreted from the bladder during the next urination.
Onuf's nucleus is a distinct group of neurons located in the ventral part of the anterior horn of the sacral region of the human spinal cord involved in the maintenance of micturition and defecatory continence, as well as muscular contraction during orgasm. It contains motor neurons, and is the origin of the pudendal nerve. The sacral region of the spinal cord is the fourth segment of vertebrae in the spinal cord which consists of the vertebrae 26-30. While working in New York City in 1899, Bronislaw Onuf-Onufrowicz discovered this group of unique cells and originally identified it as “Group X.” “Group X” was considered distinct by Onufrowicz because the cells were different in size from the surrounding neurons in the anterolateral group, suggesting that they were independent.
Urinary retention is an inability to completely empty the bladder. Onset can be sudden or gradual. When of sudden onset, symptoms include an inability to urinate and lower abdominal pain. When of gradual onset, symptoms may include loss of bladder control, mild lower abdominal pain, and a weak urine stream. Those with long-term problems are at risk of urinary tract infections.
The internal anal sphincter, IAS, or sphincter ani internus is a ring of smooth muscle that surrounds about 2.5–4.0 cm of the anal canal. It is about 5 mm thick, and is formed by an aggregation of the smooth (involuntary) circular muscle fibers of the rectum. It terminates distally about 6 mm from the anal orifice.
The external sphincter muscle of the male urethra, also sphincter urethrae membranaceae, sphincter urethrae externus, surrounds the whole length of the membranous urethra, and is enclosed in the fascia of the urogenital diaphragm.
Bladder sphincter dyssynergia is a consequence of a neurological pathology such as spinal injury or multiple sclerosis which disrupts central nervous system regulation of the micturition (urination) reflex resulting in dyscoordination of the detrusor muscles of the bladder and the male or female external urethral sphincter muscles. In normal lower urinary tract function, these two separate muscle structures act in synergistic coordination. But in this neurogenic disorder, the urethral sphincter muscle, instead of relaxing completely during voiding, dyssynergically contracts causing the flow to be interrupted and the bladder pressure to rise.
Neurogenic bladder dysfunction, often called by the shortened term neurogenic bladder, refers to urinary bladder problems due to disease or injury of the central nervous system or peripheral nerves involved in the control of urination. There are multiple types of neurogenic bladder depending on the underlying cause and the symptoms. Symptoms include overactive bladder, urinary urgency, frequency, incontinence or difficulty passing urine. A range of diseases or conditions can cause neurogenic bladder including spinal cord injury, multiple sclerosis, stroke, brain injury, spina bifida, peripheral nerve damage, Parkinson's disease, multiple system atrophy or other neurodegenerative diseases. Neurogenic bladder can be diagnosed through a history and physical as well as imaging and more specialized testing. In addition to symptomatic treatment, treatment depends on the nature of the underlying disease and can be managed with behavioral changes, medications, surgeries, or other procedures. The symptoms of neurogenic bladder, especially incontinence, can severely degrade a person's quality of life.
The detrusor muscle, also detrusor urinae muscle, muscularis propria of the urinary bladder and muscularis propria, is smooth muscle found in the wall of the bladder. The detrusor muscle remains relaxed to allow the bladder to store urine, and contracts during urination to release urine. Related are the urethral sphincter muscles which envelop the urethra to control the flow of urine when they contract.
The urethral sphincters are two muscles used to control the exit of urine in the urinary bladder through the urethra. The two muscles are either the male or female external urethral sphincter and the internal urethral sphincter. When either of these muscles contracts, the urethra is sealed shut.
The external sphincter muscle of the female urethra is a muscle which controls urination in females. The muscle fibers arise on either side from the margin of the inferior ramus of the pubis. They are directed across the pubic arch in front of the urethra, and pass around it to blend with the muscular fibers of the opposite side, between the urethra and vagina.
In neuroanatomy, the pontine micturition center is a collection of neuronal cell bodies located in the rostral pons in the brainstem involved in the supraspinal regulation of micturition (urination). When activated, the PMC relaxes the urethral sphincter, allowing for micturition to occur. The PMC coordinates with other brain centers, including the medial frontal cortex, insular cortex, hypothalamus and periaqueductal gray (PAG). The PAG acts as a relay station for ascending bladder information from the spinal cord and incoming signals from higher brain areas.
Urodynamic testing or urodynamics is a study that assesses how the bladder and urethra are performing their job of storing and releasing urine. Urodynamic tests can help explain symptoms such as:
Overflow incontinence is a concept of urinary incontinence, characterized by the involuntary release of urine from an overfull urinary bladder, often in the absence of any urge to urinate. This condition occurs in people who have a blockage of the bladder outlet, or when the muscle that expels urine from the bladder is too weak to empty the bladder normally. Overflow incontinence may also be a side effect of certain medications.
Urethral resistance pressure is the pressure existing in urethra during urination or other conditions generated by the detrusor muscle. It forces urine into and through the urethra in order for micturition. In the urethra, part of that pressure is converted to dynamic (forward) pressure which helps voiding happen. On the other hand, static (lateral) pressure helps preventing involuntary dribbling. Decline in urethral resistance pressure is one of the contributing factors is some forms of incontinence for example stress incontinence as a result of atrophy in menopause.
