TBL 23 Flashcards
What is the perineum?
It is a subcutaneous compartment immediately inferior to the pelvic diaphragm between the superomedial thighs.
When the lower limbs are abducted, the perineum is diamond-shaped extending from the pubic symphysis to the tip of the coccyx and between the ischial tuberosities.
What does the imaginary line between the tuberosities create?
anterior UG triangle (occupied by the genitilia and urethra) and posterior anal triangle (anal canal and anus)
central point = perineal body
What is the importance of the urogenital hiatus?
It enables the urethra and in females, the vagina, to exit the pelvic cavity.
What is the perineal membrane?
It is the fascial sheet that spans across the urogenital hiatus and stretches between the ischiopubic rami to cover the UG triangle.
It separates the UG triangle into the deep and superficial pouches.
What happens to the urethra in relation to the perineal membrane?
The urethra traverses the urogenital hiatus into the deep pouch, which is superior to the perineal membrane. After perforating the perineal membrane, the urethra enters the superficial pouch that is inferior to the perineal membrane.
What covers the perineal triangles?
Skin and subcutaneous fascia.
Like fascia of the anterolateral abdominal wall below the umblicus, the perineal fascia consists of a superficial fatty layer representing the continuation of Camper’s fascia and a deep fibrous layer (Colles fascia), that is a continuation of Scarpa’s fascia.
Describe Colles fascia in female perineum.
There is continuity of Scarpa’s fascia with Colles fascia here.
It extends to the perineal body, which marks the center of the posterior margin of the perineal membrane. Like the perineal membrane, Colles fascia only covers the UG triangle.
Describe Scarpas, dartos, and Colles fascia in males.
In males Scarpa’s fascia is continuous with the dartos fascia on the penis and scrotum.
Dartos (smooth) muscle joins the dartos fascia on the scrotum. Posterior to the scrotum, the dartos fascia is continuous with Colles fascia.
Colles fascia extends to the posterior margin of the perineal membrane.
Where does the perineal membrane stretch?
between the ischiopubic rami and it separates the deep and superficial pouches
What does the deep pouch contain?
It is the shallow space between the pelvic diaphragm and perineal membrane.
Contains the voluntary external urethral spincter and compressor urethrae, a slip of skeletal muscle from the pubococcygeus in females. Also has the deep transverse perineal muscle, which is a slip of involuntary smooth muscle from the muscluaris externa of the superior part of the anal canal (both sexes).
What is contained in the superficial pouch?
perineal membrane that acts as a foundation for the bulb and crura of the penis, body of the clitoris, associated erectile tissues (these are covered by thin sheets of skeletal muscle)
these structures of the superficial pouch are covered by dartos fascia in males and Colles fascia in both sexes
What is the superficial transverse perineal muscle?
slip of smooth muscle from the muscularis externa of the anal canal.
What happens to the perineal fascia in both sexes?
The fatty layer of the perineal fascia extends posteriorly into the ischioanal fossae, which are filled with white fat and surround the anal canal.
What is in the anal triangle? and what lies at the site of covergence?
anal triangle: voluntary external anal sphincter
site of convergence: perineal body, transverse perineal muscles and bulbospongiosus
Why is the anal triangle not separated into superficial and deep pouches?
perineal membrane and Colles fascia do not extend into the anal triangle.
What clinical consequences can occur if the perineal body is damaged during childbirth?
There will be a prolapse of pelvic viscera, including prolapse of the bladder (through the urethra), and prolapse of the uterus and/or vagina through the vaginal orifice.
Why is a mediolateral episiotomy preferable to a median episiotomy?
Episiotomy: surgical incision of the perineum and inferoposterior vaginal wall. it is used to enlarge the vaginal orifice to decrease excessive traumatic tearing of the perineum and uncontrolled jagged tears of the perineal muscles.
Mediolateral episiotomies result in lower incidence of severe laceration and are less likely to be associated with damage to the anal sphincters and canal. It circumvents the perineal body unlike the median episiotomy.
What forms the pudendal canal and what does it do?
Obturator fascia, which covers the medial surface of the obturator internus muscle, forms the pudendal canal.
The pudendal canal creates a horizontal passageway in the perineum for the internal pudendal artery and pudendal nerve (S2-S4).
What are the branches of the anterior division of the internal iliac artery?
anterior division of the internal iliac artery: pelvic viscera
Inferior gluteal arteries
pudendal artery: supplies the perineum
What is a branch of the posterior division of the internal iliac artery?
posterior division of internal iliac artery: posterior abdominal wall
superior gluteal artery
Where do the pudendal artery and nerve emerge from?
The greater sciatic foramen into the gluteal region.
They immediately hook around the sacrospinous ligament to traverse the lesser sciatic foramen into the perineum where they descend to the pudendal canal
What do the pudendal nerve and inferior rectal nerve do?
Pudendal nerve provides somatic motor and sensory fibers to the perineum.
The inferior rectal nerve (branch of the pudendal nerve) courses through the white fat of the ischioanal fossae to innervate the external anal sphincter and anus
What is the cloacal membrane? What is the cloaca divided into?
It respresents the fused surface ectoderm and cloacal endoderm.
The cloaca is divided into the anterior urogential sinus and posterior anorectal canal by the urorectal septum. The tip of the septum forms the perineal body.
What forms the genital tubercle? What happens caudal to the genital tubercle?
Mesenchymal cells migrate onto the surface of the cloacal membrane to form a pair of elevated cloacal folds that join cranially to form the genital tubercle.
Caudal to the genital tubercle, the cloacal folds are separated into anterior urethral folds and posterior anal fold.
What happens to the genital tubercle under the influence of testosterone?
The genital tubercle elongates rapidly to form the phallus
The phallus pulls the urethral folds forward thereby forming the lateral walls of the urethral groove. Closure of the groove forms the penile urethra.
What is hypospadias and where is it likely to occur?
Hypospadias: fusion of the urethral folds is incomplete and abnormal openings of the urethra occur along the inferior aspect of the penis, usually near the glans, along the shaft, or near the base of the penis.
What forms on the sides of the urethral folds?
another pair of elevations form the bilateral genital swellings
each genital swelling becomes a scrotal swelling composed of heavily pigmented skin that overlies the dartos fascia and muscle
What creates the scrotum?
During dissension of the testis and spermatic cord from the superficial ring of the inguinal canal, each genital swelling moves caudally to create half of the scrotum.
Midline fusion of the swellings forms the scrotal septum.
What happens to the prostatic urethra?
It becomes the membranous urethra in the deep perineal pouch.
What surrounds the urethra?
external urethral sphincter
What happens to the spongy (penile) urethra?
After perforating the perineal membrane, into the superficial pouch, the urethra courses through the root, body and glans of the penis.
How do the sites of the urine extravasation differ after injury to the penile and membranous urethra?
Penile urethra: superficial pouch
membranous urethra: deep pouch
What surrounds the penile urethra along its entire course?
Bulb of the penile root which is continuous with the corpus spongiosum
What do the crura of the penile root and corpus cavernosa do?
They are continuous with one another and course parallel to the urethra in the root and body of the penis
