The urethral sphincters are two

muscle Muscle is a soft tissue, one of the four basic types of animal tissue. There are three types of muscle tissue in vertebrates: skeletal muscle, cardiac muscle, and smooth muscle. Muscle tissue gives skeletal muscles the ability to muscle contra ...

s used to control the exit of

urine Urine is a liquid by-product of metabolism in humans and many other animals. In placental mammals, urine flows from the Kidney (vertebrates), kidneys through the ureters to the urinary bladder and exits the urethra through the penile meatus (mal ...

in the

urinary bladder The bladder () is a hollow organ in humans and other vertebrates that stores urine from the Kidney (vertebrates), kidneys. In placental mammals, urine enters the bladder via the ureters and exits via the urethra during urination. In humans, the ...

through the

urethra The urethra (: urethras or urethrae) is the tube that connects the urinary bladder to the urinary meatus, through which Placentalia, placental mammals Urination, urinate and Ejaculation, ejaculate. The external urethral sphincter is a striated ...

. The two muscles are either the

male Male (Planet symbols, symbol: ♂) is the sex of an organism that produces the gamete (sex cell) known as sperm, which fuses with the larger female gamete, or Egg cell, ovum, in the process of fertilisation. A male organism cannot sexual repro ...

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 f ...

. 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 bones inferior pubic ramus * from the ischium, the inferior ramus of the ischium It forms the inferior border of the obturator for ...

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 is a Mixed nerve, mixed (motor and sensory) nerve and also conveys Sympathetic nervous system, sympathetic Autonomic nervous system, autonomic fibers. It carries sensation from the exter ...

. 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 f ...

: 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 urinary bladder, bladder. The detrusor muscle remains relaxed to allow th ...

muscle and is made of

smooth muscle Smooth muscle is one of the three major types of vertebrate muscle tissue, the others being skeletal and cardiac muscle. It can also be found in invertebrates and is controlled by the autonomic nervous system. It is non- striated, so-called bec ...

, therefore it is under involuntary or autonomic control. This is the primary muscle for prohibiting

urination Urination is the release of urine from the bladder through the urethra in Placentalia, placental mammals, or through the cloaca in other vertebrates. It is the urinary system's form of excretion. It is also known medically as micturition, v ...

. * The

female An organism's sex is female ( symbol: ♀) if it produces the ovum (egg cell), the type of gamete (sex cell) that fuses with the male gamete (sperm cell) during sexual reproduction. A female has larger gametes than a male. Females and ...

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 from the apex of the prostate proximally to the bulb of ur ...

) 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 muscle (commonly referred to as muscle) is one of the three types of vertebrate muscle tissue, the others being cardiac muscle and smooth muscle. They are part of the somatic nervous system, voluntary muscular system and typically are a ...

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

Function and sex differences

In males and females, both

internal Internal may refer to: *Internality as a concept in behavioural economics *Neijia, internal styles of Chinese martial arts *Neigong or "internal skills", a type of exercise in meditation associated with Daoism * ''Internal'' (album) by Safia, 2016 ...

and external urethral sphincters function to prevent the release of urine. The internal urethral sphincter controls involuntary urine flow from the bladder to the urethra, whereas the external urethral sphincter controls voluntary urine flow from the bladder to the urethra. 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 significant effect on quality of life. Urinary incontinence is common in older women ...

. In males, the internal urethral sphincter has the additional function of preventing the flow of

semen Semen, also known as seminal fluid, is a bodily fluid that contains spermatozoon, spermatozoa which is secreted by the male gonads (sexual glands) and other sexual organs of male or hermaphrodite, hermaphroditic animals. In humans and placen ...

into the male bladder during

ejaculation Ejaculation is the discharge of semen (the ''ejaculate''; normally containing sperm) from the penis through the urethra. It is the final stage and natural objective of male sexual stimulation, and an essential component of natural conception. ...

. Females do have a more elaborate external sphincter muscle than males as it is made up of three parts: the sphincter urethrae, the 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 pubis or pubic bone () forms the lower and anterior part of each side of the hip bone. The pubis is the most forward-facing (ventral and anterior) of the three bones that make up the hip bone. The left and right pubic bones ar ...

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 ...

Clinical significance

The urethral sphincter is considered an integral part of maintaining urinary continence, and it is important to understand its role in some conditions: *

Stress urinary incontinence Stress incontinence, also known as stress urinary incontinence (SUI) or effort incontinence is a form of urinary incontinence. It is due to inadequate closure of the bladder outlet by the urethral sphincter. Pathophysiology Stress incontinence i ...

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") is the surgical removal of all or part of the prostate gland. This operation is done for benignity, benign conditions that cause urinary retention, as well as ...

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 (BPH). As the name ind ...

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

Neurogenic bladder dysfunction Neurogenic bladder dysfunction, often called by the shortened term neurogenic bladder, was technically termed neurogenic lower urinary tract dysfunction by the International Continence Society. It refers to urinary bladder problems due to disease ...

can involve a malfunctioning urethral sphincter. *

Urge incontinence Overactive bladder (OAB) is a common 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. Loss of bl ...

can happen when the urethra cannot hold the urine in as the bladder contracts uncontrollably. *

Retrograde ejaculation 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 ...

can occur in men when the internal urethral sphincter fails to adequately contract during ejaculation.

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

Function and sex differences

Clinical significance

See also

References

External links