Perineum Flashcards
What can the perineum be divided into?
2 triangles:
- Urogenital triangle
- Anal triangle
What are the 3 components of the anal triange?
- Anal aperture
- External anal sphincter
- Ischioanal fossa x2
Where are the ischioanal fossa’s located?
Spaces located laterally to anus (between ischial spine and anus)
Extend from skin of anal region (inferiorly) to pelvic diaphragm (superiorly)
What is the medial boundary of the ischioanal fossa?
Levator ani and external anal sphincter
What is the lateral boundary of the ischioanal fossa?
Obturator internus
What is the inferior boundary of the ischioanal fossa?
Subcutaneous tissue
What is the anal aperture?
Opening of anus
Where is the anal aperture located?
The anal aperture is located centrally in the triangle with the ischioanal fossae either side.
What do the ischioanal fossae contain?
Fat and connective tissue to allow expansion of anal canal during defecation
What else passes through the ischioanal fossa?
Pudendal neurovascular bundle (artery, nerve, vein)
What branch does the pudendal nerve/artery give off in the ischioanal fossa?
Inferior rectal nerve and inferior rectal artery
What does the inferior rectal nerve supply?
External anal sphincter, external urethral sphincter, levator ani
Helps with continence
Where does the pudendal nerve come from?
S2, S3, S4
What does the internal anal sphincter consist of?
Circular smooth muscle
What is the internal anal sphincter innervated by?
Autonomic fibres (as smooth muscle)
What is the external anal sphincter innervated by?
Pudendal nerve –> somatic control
What are the different parts of the external anal sphincter?
- Deep part
- Superficial part
- Subcutaneous part
Describe the deep part of the external anal sphincter
Fuses with fibres of levator ani including puborectalis
Maintains anorectal angle
What is the superficial part of the external anal sphincter attached to?
Anteriorly to the perineal body
What is the urogenital triangle covered by?
An additional layer of strong deep fascia; the perineal membrane, as well as the muscular urogenital diaphragm
What does the urogenital triangle merge with posteriorly?
The perineal body in the midline
What is found above and below perineal membrane?
Pouches on superior and inferior surfaces
Above - deep perineal pouch
Below - superficial perineal pouch
What are the boundaries of the urogenital triangle?
It is bounded by the pubic symphysis, ischiopubic rami, and a theorectical line between the two ischial tuberosities
What are the layers of the urogenital triangle (deep to superficial)?
- Deep perineal pouch
- Urogenital diaphragm
- Superficial perineal pouch
- Perineal fascia
- Skin
What is found superior to the UG diaphragm?
Deep perineal pouch
What is the UG diaphragm made up of?
- Superior layer of connective tissue
- Layer of striated muscle
- Inferior thick layer of fascia: perineal membrane
What does the layer of striated muscle of the UG diaphragm form?
External urethral sphincter, sphincter of vagina
What is found inferiorly/superficially to UG diaphragm?
Superficial perineal pouch
What is found within the superficial perineal pouch?
- Erectile tissue that forms the penis and clitoris (corpus cavernosum): found in men and women
- Corpus spongiosum/bulb of vestibule
Have 2 identical ones, one on either side of corpus spongiosum/vestibular bulbs
What is the corpus spongiosum?
A mass of erectile tissue alongside the corpora cavernosa of the penis
What is function of corpus spongiosum/the two cavernosa?
Expandable and sponge like, involved in process of penile erection
Corpora cavernosum fills with blood
What does the corpus spongiosum correspond to in females?
Female vestibular bulbs
What does the corpus spongiosum contain?
The urethra
Where does the corpus spongiosum terminate?
Dilates to form glans penis
What does the root/bulb of penis attach to?
Perineal membrane
How do the female vestibular bulbs differ from male corpus cavernosum?
Female bulbs don’t fuse but sit either side of vaginal opening
How do the female vestibular bulbs terminate?
Clitoris
What muscle is found around the vestibular bulb and bulb of penis?
Bulbospongiosus muscle
What muscle covers the corpora cavernosa?
Ischiocavernosus muscle
Where do external genitalia hang from?
Perineal membrane (superficial pouch)
What supplies the external genitalia?
Branches of pudendal artery and nerve
How do the pudendal artery/nerve enter the perineum?
Leave pelvis via greater sciatic foramen inferior to piriformis, curves around ischial spine to enter perineum via lesser sciatic foramen
