The urethral sphincters are two

muscle Skeletal muscles (commonly referred to as muscles) are organs of the vertebrate muscular system and typically are attached by tendons to bones of a skeleton. The muscle cells of skeletal muscles are much longer than in the other types of muscl ...

s used to control the exit of

urine Urine is a liquid by-product of metabolism in humans and in many other animals. Urine flows from the kidneys through the ureters to the urinary bladder. Urination results in urine being excretion, excreted from the body through the urethra. Cel ...

in the

urinary bladder The urinary bladder, or simply bladder, is a hollow organ in humans and other vertebrates that stores urine from the kidneys before disposal by urination. In humans the bladder is a distensible organ that sits on the pelvic floor. Urine enters ...

through the

urethra The urethra (from Greek οὐρήθρα – ''ourḗthrā'') is a tube that connects the urinary bladder to the urinary meatus for the removal of urine from the body of both females and males. In human females and other primates, the urethra con ...

. The two muscles are either the

male Male (symbol: ♂) is the sex of an organism that produces the gamete (sex cell) known as sperm, which fuses with the larger female gamete, or ovum, in the process of fertilization. A male organism cannot reproduce sexually without access to ...

or female external urethral sphincter and the

internal urethral sphincter The internal urethral sphincter is a urethral sphincter muscle which constricts the internal urethral orifice. It is located at the junction of the urethra with the urinary bladder and is continuous with the detrusor muscle, but anatomically and ...

. When either of these muscles contracts, the

is sealed shut. The external urethral sphincter originates at the

ischiopubic ramus The ischiopubic ramus is a compound structure consisting of the following two structures: * from the pubis, the inferior pubic ramus * from the ischium, the inferior ramus of the ischium It forms the inferior border of the obturator foramen and ...

and inserts into the intermeshing muscle fibers from the other side. It is controlled by the deep perineal branch of the

pudendal nerve The pudendal nerve is the main nerve of the perineum. It carries sensation from the external genitalia of both sexes and the skin around the anus and perineum, as well as the motor supply to various pelvic muscles, including the male or fem ...

. Activity in the nerve fibers constricts the urethra. * The

internal sphincter muscle of urethra The internal urethral sphincter is a urethral sphincter muscle which constricts the internal urethral orifice. It is located at the junction of the urethra with the urinary bladder and is continuous with the detrusor muscle, but anatomically and ...

: located at the bladder's inferior end and the urethra's proximal end at the junction of the urethra with the urinary bladder. The internal sphincter is a continuation of the

detrusor The detrusor muscle, also detrusor urinae muscle, muscularis propria of the urinary bladder and (less precise) muscularis propria, is smooth muscle found in the wall of the bladder. The detrusor muscle remains relaxed to allow the bladder to stor ...

muscle and is made of

smooth muscle Smooth muscle is an involuntary non-striated muscle, so-called because it has no sarcomeres and therefore no striations (''bands'' or ''stripes''). It is divided into two subgroups, single-unit and multiunit smooth muscle. Within single-unit mus ...

, therefore it is under

involuntary Involuntary means ''unintended''. An involuntary action is one that is unintentional, i.e. without volition or will; see volition (psychology) and will (philosophy). ''Involuntary'' may also refer to: * ''Involuntary'' (film), a 2008 Swedish film ...

or autonomic control. This is the primary muscle for prohibiting the release of

. * The

female Female (Venus symbol, symbol: ♀) is the sex of an organism that produces the large non-motile ovum, ova (egg cells), the type of gamete (sex cell) that fuses with the Sperm, male gamete during sexual reproduction. A female has larger gamet ...

or male external sphincter muscle of urethra (sphincter urethrae): located in the

deep perineal pouch The deep perineal pouch (also deep perineal space) is the anatomic space enclosed in part by the perineum, and located superior to the perineal membrane. Structure The deep perineal pouch is bordered inferiorly by the perineal membrane, also kno ...

, at the bladder's distal inferior end in females, and inferior to the prostate (at the level of the

membranous urethra The membranous urethra or intermediate part of male urethra is the shortest, least dilatable, and, with the exception of the urinary meatus, the narrowest part of the urethra. It extends downward and forward, with a slight anterior concavity, be ...

) in males. It is a secondary sphincter to control the flow of urine through the urethra. Unlike the internal sphincter muscle, the external sphincter is made of

skeletal muscle Skeletal muscles (commonly referred to as muscles) are organs of the vertebrate muscular system and typically are attached by tendons to bones of a skeleton. The muscle cells of skeletal muscles are much longer than in the other types of muscl ...

, therefore it is under voluntary control of the somatic nervous system.

Sex differences

In males and females, both internal and external urethral sphincters function to inhibit the release of urine. In males, the

functions to prevent reflux of seminal fluids into the male bladder during ejaculation. Females do have a more elaborate external sphincter muscle than males as it is made up of three parts: the sphincter urethrae, urethrovaginal muscle, and the compressor urethrae. The urethrovaginal muscle fibers wrap around the vagina and urethra and contraction leads to constriction of both the vagina and the urethra. The origin of the compressor urethrae muscle is the right and left

inferior pubic ramus In vertebrates, the pubic region ( la, pubis) is the most forward-facing (ventral and anterior) of the three main regions making up the coxal bone. The left and right pubic regions are each made up of three sections, a superior ramus, inferior r ...

and it wraps anteriorly around the urethra so when it contracts it squeezes the urethra against the vagina. The external urethrae, like in males, wraps solely around the urethra. Congenital abnormalities of the female urethra can be surgically repaired with

vaginoplasty Vaginoplasty is any surgical procedure that results in the construction or reconstruction of the vagina. It is a type of genitoplasty. Pelvic organ prolapse is often treated with one or more surgeries to repair the vagina. Sometimes a vaginoplas ...

Function

The internal urethral sphincter provides involuntary control of urination. The external urethral sphincter provides voluntary control of urination. Any damage to these muscles can lead to

urinary incontinence 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 geria ...

Clinical significance

The urethral sphincter is considered an integral part in maintaining urinary continence, and it is important to understand its role in some conditions: * Stress urinary incontinence is a common problem related to the function of the urethral sphincter. Weak pelvic floor muscles, intrinsic sphincter damage, or damage to the surrounding nerves and tissue can make the urethral sphincter incompetent, and subsequently, it will not close fully, leading to stress urinary incontinence. In women, childbirth, obesity, and age can all be risk factors, especially by weakening the pelvic floor muscles. In men, prostate surgery (

prostatectomy Prostatectomy (from the Ancient Greek language, Greek , "prostate" and , "excision") as a medical term refers to the surgical removal of all or part of the prostate gland. This operation is done for benignity, benign conditions that cause urina ...

TURP Transurethral resection of the prostate (commonly known as a TURP, plural TURPs, and rarely as a transurethral prostatic resection, TUPR) is a urology, urological operation. It is used to treat benign prostatic hyperplasia, benign prostatic hype ...

, etc) and radiation therapy can damage the sphincter and cause stress incontinence. *

Neurogenic bladder dysfunction Neurogenic bladder dysfunction, or 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 bladde ...

can involve a malfunctioning urethral sphincter. *

Urge incontinence Overactive bladder (OAB) is a condition where there is a frequent feeling of needing to urinate to a degree that it negatively affects a person's life. The frequent need to urinate may occur during the day, at night, or both. If there is loss ...

can happen when the urethra can't hold the urine in as the bladder contracts uncontrollably.

References

External links

* - "Muscles of the female urogenital diaphragm (deep perineal pouch) and structures located inferior to it." {{Portal bar, Anatomy Perineum Urinary system Urethra

Sex differences

Function

Clinical significance

See also

References

External links