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B313-13-Perineum & Triangle

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Daniel Howell

on 27 November 2018

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Transcript of B313-13-Perineum & Triangle

Perineum & Urogenital Triangle
The Perineum
The perineum is a shallow compartment of the body bounded by the pelvic outlet:
pubic symphysis, anteriorly
ischiopubic rami, anterolaterally
ischial tuberosities, laterally
sacrotuberous ligaments, posterolaterally
sacrum & coccyx, posteriorly
The Perineum
Surface is the narrow region between the thighs

Forms a diamond shape when lower limbs are abducted; extending from the mons pubis anteriorly along the medial (inside) of thighs laterally, and gluteal folds to gluteal cleft posteriorly
Divided into two triangles:
urogenital triangle
anal triangle
Muscles of the Perineum
The deepest muscles of the perineum are the puborectalis, pubococcygeus, iliococcygeus, and coccygeus muscles

The middle layer is the external urethral sphincter, compressor urethrae, and deep transverse perineal (DTP)

The superficial layer is ischiocavernosus, bulbospongiosus, superficial transverse perineal (STP), and external anal sphincter

The perineal body is a central support for the pelvic diaphragm

The bublourethral gland is said to be embedded in the external urethral sphincter (pg. 379) or DTP (fig.3.52)
During parturition, the baby's head may be too large to pass through the vaginal orifice

Left alone, death may result for baby and mother, or the perineum may tear producing jagged edges

Episiotomy = surgical incision of the perineum to enlarge vaginal orifice
median episiotomy = incision from orifice through perineal body toward anus
mediolateral episiotomy = incision from orifice posterolaterally, avoid the perineal body and anal sphincter
Male External Genitalia
Urethra has four parts
intramural part
prostatic urethra
membranous urethra
penile (spongy) urethra
Male Urogenital Triangle
The scrotum is a cutaneous fibromuscular sac for the testes, inferior to pubic symphysis, posteroinferior to penis

Bilateral formation of the scrotum and penis evident as the scrotal and penile raphe (and perineal raphe)

The penis is the male copulatory organ and conveys both urine and semen through urethra
The caliber of the urethra is not constant (membranous urethra most narrow)

The ducts of the bulbourethral glands open into the proximal spongy urethra
Male Urogenital Triangle
Penis consist of root, body, and glans (dorsum anterior of flaccid penis)

Glans is covered with foreskin (prepuce) unless circumcised

Erectile tissue of the penis
corpus spongiosum
corpora cavernosa

The urethra passes through the corpus spongiosum

Erectile tissues engorged with blood to produce erection
Male Urogenital Triangle
Root of the penis consist of crura and bulb, surrounded by ischiocavernosus and bulbospongiosus muscles

Crura attached firmly to ischial rami
Female Urogenital Triangle
Includes the external genitalia and perineal muscles

External genitalia includes:
mons pubis
labia majora & minora
urethral orifice
vaginal orifice

All the structures enclosed by labia minora lie with the vestibule
Female Urogenital Triangle
Prominent labia majora surround pudendal cleft, within which the labia minora and vestibule

The labia minora are fat-free, hairless folds of skin

Like the penis, the clitoris has a glans and prepuce (clitoral hood) and consists of erectile tissue
Female Urogenital Triangle
The labium majus is largely filled with the terminus of the round ligament of the uterus

Like the penis, the clitoris is attached to the ischial rami via crura made of erectile tissue
Female Urogenital Triangle
The greater and lesser vestibular glands moisten the vestibule and vagina, especially during sexual arousal.
Infection of Greater Vestibular Glands
The greater vestibular (Bartholin) glands are usually not palpable, but can enlarge to 4-5 cm and be palpated if infected / inflammed

Occlusion of the the duct can lead to a cyst
The Hymen
A thin, membranous structure that partially covers the vaginal orifice

Sometimes used as a virginity test in past cultures

However, the hymen is often torn prior to intercourse

Imperforate hymen = the hymen is completely closed; causes vaginal flow obstruction
Imperforate Hymen
Bulging perineum shown caused by an imperforate hymen in a 20 yo female
Daniel Howell, PhD
Liberty University

Male & Female
Male & Female
Corona ("crown") = a ridge around perimeter of glans

A sulcus demarcates glans from body (shaft) of penis

Frenulum = a bridge of skin connecting glans to shaft
Frenulum = a bridge of skin
Urogenital Triangle
Male & Female
Incidence ~1:5000

congenital disorder caused by failure of the hymen to perforate during fetal development

sporadic occurence; no genetic cause apparent

Treated by surgical incisions in the hymen or removal of hymen (hymenotomy)
is the surgical removal of the prepuce (foreskin) of the penis

Permanently exposes the glans penis

Prescribed by God in Genesis 17

Now somewhat controversial today in the United States

Confers medical benefits (prevents the spread of STDs, including AIDS, in both men and women)
Complications from Circumcision
skin bridge
may form from improper healing from circumcision

Usually, the inner lining of remaining foreskin adheres to the glans

May cause painful erections and need surgical correction

Meatal stenosis
accounts for 26% of complications (shown here in 3yo patient)
The Scrotum & Testis
Scrotum = loose, sac-like structure that houses testes outside the main body cavity
The Scrotum & Testis
Sperm that is not released by ejaculation is reabsorbed into body

Reabsorption achieved by epithelial cells of testes, epididymis, and vas deferens; assisted by macrophages following vasectomy
Main purpose of scrotum is temperature regulation
Sperm develop at 35-36 degrees Celcius
Cremaster muscle
Dartos musle
Penile Erection via Hydrostatic Skeleton
Upon sexual stimulation, neurons from the brain extending to the penis promote the release of nitric oxide (NO, a vasodilator) and other agents that open afferent arteriole sphincters, increasing blood flow to the penis.

Dilation of erectile tissue blood vessels engorges erectile tissue with blood

Engorged tissues cause penis to become bigger and rigid (erection) and constricts veins that drain blood (to maintain erection)

Orgasm halts NO release and agents that promote sphincter vasoconstriction; blood drains, penis resumes flaccid state (detumescence)
Penis contains three masses of erectile tissue
2 corpora cavernosa
1 corpus spongiosum surrounding urethra
Male External Genitalia
Includes the external genitalia and perineal muscles

External genitalia includes
shaft (body)
glans (head)
foreskin if not circumcised
urethral meatus
Penile Erection
The internal urethral sphincter is closed during erection (penile tumescence)
prevents semen from entering bladder during ejaculation
prevents urine from exiting bladder during erection

The neurotransmitter norepinephrine prevents erections by causing vasocontriction and contraction of erectile capillary sphincters
During REM sleep, norepinephrine release (and other neurotransmitters) is reduced to prevent acting out dreams
Reduction of norepinephrine causes vasodilation and erection in the penis
REM is prolonged prior to waking, often leading morning erections ("morning wood").
A congenital defect (1:250 males) in which the urethral meatus is not located in the usual position

The opening (meatus) occurs on or near the glans in 90% of cases
Unlike most other mammals, humans lack a penis bone (os penis, or baculum)
BIOL 313
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