Anatomy: Perineum I and II Flashcards
a. The urogenital triangle
1. The urogenital triangle is the area in the angle between the two ischiopubic rami. The urogenital triangle contains the urethral and vaginal (female) openings, the erectile tissues, and muscles important for the function of perineal structures.
b. The anal triangle
1. The anal canal is the central structure in this triangle.
Urogenital triangle in the male:
External genitalia
Superficial perineal space
Deep perineal space
The perineum of the male contains the penis and scrotum.
The penis is the male copulatory organ that also conveys the urethra. The penis is divided up into the root, located in the superficial perineal pouch, and the body, which is suspended from the pubic symphysis.
The body of the penis is expanded at the distal end to form the glans. The skin at the end of the penis is extended to envelope the head of the penis. This fold of skin is called prepuce. The frenulum of the prepuce connects the prepuce to the glans on the ventral surface.
Inguinal canal. The inguinal canal is the route that allows the passage of testes from abdominal cavity to scrotum. It contains the spermatic cord.
- Ductus deferens
- Testicular artery
- Testicular vein (pampiniform plexus)
- Genitofemoral nerve
- The scrotum is a fibromuscular sac for the testes and associated structures. It is a multilayered structure that is created during the descent of the testes through the inguinal canal.
- The layers include (from outside), the skin, the dartos muscle, Colles fascia, the external spermatic fascia, the cremaster muscle, the internal spermatic fascia and the tunica vaginalis.
Dartos Reflex
- The Dartos reflex is a somato-autonomic reflex that depends upon an intact T11-L2 segment.
- It manifests as a slow elevation of the testis and retraction of the penis. It can be used to assess spinal cord injury at this level.
Cremaster Reflex
- The Cremaster reflex is a somatic reflex that relies on L1-L2.
- Stimulation of the inner thigh results in a quick elevation of the testis.
Which type of hernia (direct or indirect) traverses the inguinal canal?
- Hernias that traverse the inguinal canal are indirect.
- In children, these are the most common type of hernia.
- They arise lateral to the inferior epigastric vessels.
The testes are suspended in the scrotum by the spermatic cord and are responsible for the production male germ cells (sperms) and male hormones (mainly testosterone).
- The outer surface of the testes is covered by a fibrous covering, the tunica albuginea.
- The epididymis carries sperm from the testes to the ductus deferens and is formed by the dense coiling of the efferent ductules and the duct of the epididymis. The head of the epididymis rests on the superior part of the testis and is composed of efferent ductules. The body of the epididymis is composed of the duct of the epididymis, and the tail of the epididymis is continuous with the ductus deferens.
- The blood supply to the testes is from the testicular arteries, branches of the abdominal aorta.
- The venous drainage is through the testicular veins, which form an anastomosing network in the spermatic cord called the pampiniform plexus.
The superficial perineal space, or superficial perineal pouch, is the most superficial part of the urogenital triangle. The erectile bodies of the perineum and the associated muscles occupy this space. The superficial perineal space is bounded by the perineal membrane superiorly and the membranous layer of the superficial fascia of the perineum (Colles’ fascia) inferiorly. (It is called Scarpa’s fascia on the abdomen). Colles’ fascia encloses the superficial space by attaching to the ischiopubic rami and the posterior edge of the urogenital diaphragm, thus separating the superficial perineal space from the ischioanal fossae of the anal triangle. The superficial perineal space is open only anteriorly.
Contents of the superficial perineal space in the male:
- Muscles that cover the erectile bodies and the superficial transverse perineal muscle
- Part of the urethra
- Erectile bodies
The male urethra is divided up into several sections:
- The prostatic urethra- traverses the prostate gland
- The membranous urethra
a. narrowest part of the urethra
b. begins at the apex of the prostate and ends at the bulb of the penis - Spongy urethra a. longest part of the urethra b. ends at urethral orifice
The erectile bodies of the male perineum are the two dorsal erectile bodies and a single ventral erectile body of the penis.
- Each of the two dorsal erectile bodies of the penis consists of two individually named portions.
a. The crus of the penis (2) is the proximal portion of the dorsal erectile body. They are attached to the ischiopubic ramus.
b. The corpus cavernosum (2) of the penis is the longer, more distal portion of the dorsal erectile body. They are adjacent in the shaft of the penis. - The ventral erectile body of the penis consists of three individually named portions.
a. The enlargement at the proximal end of the ventral erectile body is the bulb of the penis. The bulb is attached to the perineal membrane. The urethra descends into the bulb from the urogenital diaphragm.
b. The long portion of the ventral erectile body distal to the bulb is the corpus spongiosum. The spongy portion of the urethra continues through this.
c. The enlargement at the distal end of the ventral erectile body is the glans of the penis. This expands dorsally to cap the ends of the corpora cavernosa. The terminal part of the spongy portion of the urethra passes through the glans.
•The blood supply of the erectile bodies is through deep arteries of the penis (crus and corpus cavernosum) and artery to the bulb (bulb of the penis, corpus spongiosum and glans), which are branches of the internal pudendal artery.
- The deep perineal space is bounded by the perineal membrane inferiorly and the inferior fascia of the pelvic diaphragm superiorly. It is essentially the same as the urogenital diaphragm.
- The urogenital diaphragm is a muscular and fascial shelf that spans between the two ischiopubic rami. It contains:
a. The perineal membrane - the inferior fascia of the urogenital diaphragm that forms the roof of the superficial perineal space.
b. the external urethral sphincter muscle
c. deep transverse perineal muscles.
•In addition, the deep space contains: The membranous part of the urethra Bulbourethral glands The ducts of these glands descend through the perineal membrane into the bulb of the penis to join the urethra.
The internal pudendal artery and the dorsal nerve of the penis pass forward in the urogenital diaphragm.
•Relationship between the Pelvic Diaphragm and the Urogenital Diaphragm The edges of the urogenital hiatus of the pelvic diaphragm are attached to the upper surface of the urogenital diaphragm such that the prostate gland rests upon the urogenital diaphragm as well as the pelvic diaphragm.
- Mons pubis Rounded prominence anterior to the pubic symphysis
- Labia majora Folds of skin extending from the mons pubis toward the anus.
- Labia minora Hairless folds of skin that surround the vestibule of the vagina
- Clitoris The clitoris has two attachments from the labia minora: ventrally at the frenulum of the clitoris and dorsally at the prepuce of the clitoris.
As in the male, the superficial perineal space is between the Superficial (Colles’) fascia and the perineal membrane in the urogenital triangle. Also as in the male, the erectile bodies and the associated muscles occupy this space.
Muscles of the superficial perineal space
- The superficial transverse perineal muscles
- The bulbospongiosus muscle
- The ischiocavernosus muscles
The erectile bodies of the female perineum have counterparts of the dorsal and ventral erectile bodies of the male perineum.
- The two dorsal erectile bodies of the female perineum are the dorsal erectile bodies of the clitoris. Each of the two dorsal erectile bodies of the clitoris consists of two individually named portions.
a. The crus of the clitoris is the proximal portion of the dorsal erectile body. It is attached to the ischiopubic ramus.
b. The corpus cavernosum of the clitoris is the more distal portion of the dorsal erectile body. It is adjacent to its counterpart on the opposite side in the shaft of the clitoris. - The ventral erectile bodies of the female perineum are not one continuum of erectile tissue as in the male.
a. The bulbs of the vestibule of the vagina, are the counterparts of the bulb of the penis. The vestibular bulbs lie at the sides of the vestibule of the vagina, which is the space between the two labia minora. The vagina and the urethra open into this space. The vestibular bulbs are attached to the perineal membrane. The clitoris does not have a corpus spongiosum therefore the bulbs of the female perineum are separate from the erectile tissue of the clitoris.
b. The glans of the clitoris fits like a cap over the ends of the corpora cavernosa.
The greater vestibular glands in the female are analogous to the bulbourethral glands in the male. The ducts of the greater vestibular glands open into the lower part of the vagina.
- The perineal membrane As in the male, the perineal membrane is the inferior fascia of the urogenital diaphragm that forms the roof of the superficial perineal space. Deep to the perineal membrane is the deep space of the urogenital triangle.
- The external urethral sphincter/compressor urethrae muscle
- The deep transverse perineal muscles The internal pudendal artery and the dorsal nerve of the clitoris pass forward in the urogenital diaphragm.
In the female, the urethra and vagina pass through the urogenital diaphragm.
Relationship between the Pelvic Diaphragm and the Urogenital Diaphragm In the female, the edges of the urogenital hiatus of the pelvic diaphragm are attached to the upper surface of the urogenital diaphragm such that the neck of the bladder rests upon the urogenital diaphragm as well as the pelvic diaphragm.
Anal Triangle
A. The anal triangle 1
. The anal canal is the central structure in this triangle.
- At either side of the anal canal is the ischioanal fossa, a wedge-shaped space. The base of the wedge is the span between the ischial tuberosity and the anal canal. The roof is the converging obturator internus muscle and the levator ani muscle.
Ischioanal fossa
- Fat filled
- Continuous posteriorly
- Can be infected – perianal abcess
- Supports rectum –starvation can result in rectal prolapse
Muscles of the anal canal
Internal anal sphincter – smooth muscle
External anal sphincter- skeletal muscle
Levator ani- skeletal muscle
Perineal Body
•The perineal body (central tendon of the perineum) is a mass of connective tissue to which muscles of the perineum and the pelvic diaphragm attach.
- It is located in front of the anal canal.
- It provides attachment for muscles of both the urogenital and anal triangles
(A) Fecal incontinence can result from damage to the anal sphincter during vaginal delivery. The perineal body is the site of convergence of several muscles of the urogenital diaphragm anterior to the anus: the bulbospongiosus, external anal sphincter, and perineal muscles. A severe medial perineal laceration may result in damage to the anal sphincter, leading to incontinence. Perineal tears are common during vaginal deliveries, particularly in the setting of prolonged labor, babies large for gestational age, and in older mothers.
The internal pudendal artery is a branch of the internal iliac artery. The internal pudendal artery passes to the greater sciatic foramen and exits the pelvic cavity just above the ischial spine. From there, it runs around the back of the ischial spine and then traverses the lesser sciatic foramen into the perineum. From its entrance to the perineum it is conducted through the pudendal canal. The pudendal canal is a conduit in the obturator internus fascia on the lateral wall of the ischioanal fossa. The pudendal canal conducts the internal pudendal artery, the internal pudendal vein, and the pudendal nerve to the deep perineal space.
Branches of the internal pudendal artery:
- The inferior rectal artery supplies the anal sphincter muscles. These branches anastomose with branches of the middle rectal artery.
- The perineal artery supplies the superficial space and terminates into:
a. posterior scrotal or posterior labial branches. - the artery of the bulb of the penis or artery of the bulb of the vestibule.
- The terminal branches of the internal pudendal artery are:
a. the deep artery of the penis or clitoris.
b. the dorsal artery of the penis or clitoris.
The external pudendal arteries are branches of the femoral artery on the front of the thigh. The external pudendal arteries pass medially across the front of the thigh to the external genitalia. They supply the scrotum/labia majora.
- The superficial external pudendal artery.
- The deep external pudendal artery.
- Inferior rectal vein: blood from inferior to the pectinate line in the anal canal drains into the inferior rectal vein. The inferior rectal vein anastomoses with the middle rectal vein (internal iliac vein). Blood from above the pectinate line drains into the superior rectal vein (inferior mesenteric vein). The anastomoses between the inferior and superior rectal vein make this a one of the sites of Portal-Systemic anastomoses.
- Venous drainage of the superficial perineum is via the posterior labial or scrotal veins to the perineal v. and then to the internal pudendal vein.
- Venous drainage of the anterior perineum and the surface of the penis/clitoris is into the external pudendal veins (femoral vein).
The venous drainage of the testes is via the testicular veins, which form a venous network called the pampiniform plexus. This plexus provides a counter-current exchange to cool the blood the in the testicular artery that supplies the testes. This decreased temperature is essential for normal sperm production and maturation.
The pudendal nerve:
- Is derived from ventral primary rami of spinal nerves S2, S3 and S4.
- The pudendal nerve accompanies the internal pudendal artery
- The pudendal nerve passes through the gluteal region around the back of the sacrospinous ligament very near the attachment of the ligament to the ischial spine.
- The pudendal nerve enters the perineum through the lesser sciatic foramen and enters the pudendal canal with the internal pudendal artery.
- The pudendal nerve innervates the striated muscles and most of the skin of the perineum.
Branches of the pudendal nerve.
- The inferior rectal nerve. The inferior rectal nerve is both a muscular and cutaneous nerve, innervating the external anal sphincter and the skin around the anus and the lining of the anal canal up to the pectinate line.
- The perineal nerve. The perineal nerve distributes very extensively both to perineal muscles and to perineal skin. It supplies muscular branches to all the muscles of the superficial perineal space (ischiocavernosus, bulbospongiosus, superficial transverse perineal) and to all the musculature of the deep perineal space (sphincter urethrae and deep transverse perineal). It supplies cutaneous branches to most of the skin of the perineum. Its terminal branches are the posterior scrotal or posterior labial nerves, which are cutaneous nerves for the more posterior parts of the scrotum or labia majora.
- The dorsal nerve of the penis or clitoris. The dorsal nerve of the penis or clitoris serves all the skin of the penis or clitoris, supplying not only branches to dorsal skin but also sending branches around the shaft to ventral skin.
Motor innervation of the anal canal
- The innervation of the internal anal sphincter muscle is from sympathetic fibers from the superior rectal and hypogastric plexus. The internal anal sphincter contracts in response to sympathetic stimulation.
- The innervation of the external anal sphincter is from the inferior rectal nerve. Thus, damage to the pudendal nerve (and thus inferior rectal nerve) during childbirth can result in fecal incontinence.
Sensory innervation of the anal canal.
- As with venous drainage, there are separate sensory innervations for the parts of the anal canal above and below the pectinate line.
a. Above the pectinate line, the sensory innervation of the anal canal is from visceral afferent fibers. These are fibers of the pelvic splanchnic nerves. This area is not sensitive to temperature or cutting, but is sensitive to stretch.
b. Below the pectinate line, the sensory innervation of the anal canal is cutaneous sensory innervation. The sensory fibers serving this part of the anal canal are fibers of the inferior rectal branch of the pudendal nerve.
