perineum anatomy Flashcards
perineum location
most inferior part of the pelvis between the thighs, separated from the pelvic cavity by the pelvic diaphragm and containing the anal and urogenital triangles
lithotomy position
lower limbs flexed at the hips and knees, abducted and supported in stirrups
ischiorectal fossa shape and contents
wedge shaped (horseshoe) space filled with fat, communicates posteriorly through the deep postnatal space but no anterior communication
ischiorectal fossa functions
passageway for neurovascular structures (pudendal nerve and internal pudendal vessels)
facilitates defecation by accommodating the movement and expansion of anal canal
ischiorectal fossa boundaries
base: skin
edges: junction of medial and lateral walls
medial walls: sloping levator Ani muscle and anal canal
lateral wall: obturator internus muscle, pudendal canal, ischial tuberosity
anteriorly: perineal body, urogenital diaphragm, anterior recess
posteriorly: recess, gluteus maximus, sacrotuberous ligament
what is the urogenital diaphragm?
double layered tough fibrous tissue that fills the urogenital triangles and gives attachment to the external genitalia
contents of the deep perineal pouch
• part of the membranous urethra
• external urethral sphincter muscle
• bulbourethral glands
• deep transverse perineal muscles
control and innervation of the external urethral sphincter
controls the flow of urine through the urethra, voluntarily controlled by the somatic nervous system and innervated by the pudendal nerve
location and function of the deep transverse perineal muscles
origin: internal surface of the ischial rami
insertion: the perineal body
function: provide structural support to adjacent pelvic and perineal structures (innervated by pudendal nerve)
testis descent movement
posterior abdominal wall –> abdomen –> through inguinal canal (thru deep inguinal ring to inguinal canal to superficial inguinal ring) –> scrotum (scrotal sac)
process of formation of tunica vaginalis
part of the peritoneum –> evaginates to form processus vaginalis –> closed off outpouching a few weeks before birth –> becomes the tunica vaginalis with fluid in-between the visceral and parietal layers
functions of fluid in tunica vaginalis layers
- lubrication of testes to reduce friction and prevent damage
- protection and cushion to absorb minor shock and trauma
- regulates temperature, keeping testes at optimal temp for spermatogenesis
hydrocele formation and types
formed by an abnormal collection of serous fluid between the two layers of tunica vaginalis
- communicating hydrocele : failure of processus vaginalis to obliterate, creating a potential space that gets bigger throughout the day due to gravity
- non-communicating hydrocele: due to injuries, infection, tumours, heart failure or liver disease, will not change in size
what is the hydrocele transillumination test?
shine a flashlight on the swollen scrotum, if the testicle transilluminated then it is a fluid filled mass and not a solid mass
coverings of the testes (superficial to deep)
- skin
- camper fascia
- scarpa fascia
- external oblique muscles
- internal oblique muscles
- transversalis fascia
- processus vaginalis (obliterates to become tunica vaginalis)
bulbourethral gland / Cowper’s gland functions
accessory sex gland in males that produces pre-ejaculatory fluids to neutralize acidic urine residue
penis function
male external genital organ used for micturition and sexual intercourse
parts of the penis (and their functions)
root: proximal part located in the superficial perineal pouch, contains the paired cylindrical corpora cavernosum (crus attached to perineal membrane and ischialpubic ramus) and single corpora spongiosum (bulb anchored to perineal membrane)
body: free part of the penis between the root and glans
glans: most distal end of the penis shaped by the bulbous expansion of the corpus spongiosum, membranous urethra passes through the corpus spongiosum here
type of skin covering the penis shaft
thin, loose, elastic and able to stretch during erection, lacks hair follicles and sebaceous glands and contains a prepuce (foreskin) covering the glans
phimosis pathology
inability to retract the prepuce covering the glans penis, treated by circumcision or resolving by puberty
complications include foreskin inflammation, UTI (poor hygiene), penile cancer risk
deep perineal pouch contents in females
part of female urethra, part of vagina, sphincter urethrae and deep transverse perineal muscles
parts of female external genitalia (anterior to posterior)
mons pubis
labia majora (hair bearing)
labia minora (non-hair bearing)
clitoris (homologous to male penis)
vestibule (area enclosed by labia minora)
fourchette (posterior meeting of labia minora)
female erectile tissues
paired cylindrical shaped corpora cavernosa (crus attached to perineal membrane and ischiopubic ramus), corpus spongiosum split into 2 to form 2 bulbs of the vestibule, uniting ventral to the urethral orifice to form spongiosum erectile tissue (glans of clitoris)
urethra length in males vs females
males: 20cm
females: 3-4cm
vagina relations
anterior to: rectum, anal canal, perineal body
posterior to: urinary bladder, urethra
upper end: expanded, receives the cervix
cervical-vaginal relations
cervix projects into vagina to form vaginal fornix (anterior, posterior, 2 lateral fornices) around the cervix margin - posterior fornix is covered by the peritoneum
what is the Pouch of Douglas
extension of the postero-inferior reflection of the peritoneal fold between the uterus and rectum
blood supply of the vagina
uterine, vaginal, internal pudendal arteries
lymph drainage of the vagina
upper 4/5: iliac nodes
lower 1/5: superficial inguinal nodes
nerve supply of the vagina
upper 4/5: inferior hypogastric plexus (stretch sensitive only)
lower 1/5: pudendal nerve (somatic innervation for touch and temperature)
vestibular/Bartholin’s gland anatomy
lies at the vaginal orifice and opens into the vaginal orifice by a single duct (homologous to the male Cowper’s gland)
presentation and treatment of a Bartholin cyst
presents as a cyst with localized pain, treat via incision and drainage
what does the per-vaginal examination during labour look for?
assesses the state of the cervix and the progressive descent of the fetus through the birth canal - looks for cervical effacement (where the cervix softens, thins and shortens) that occurs shortly before delivery
what to identify in a uterine bimanual examination
size: uterus should be orange-sized
shape: may be distorted by masses (eg large fibroids)
position: retroverted or anteverted
surface characteristics: smooth or nodular
tenderness: if present, may suggest inflammation
parts of the urethra in males (proximal to distal)
- preprostatic urethra (1-2cm)
- prostatic urethra (3-4cm, widest)
- membranous urethra (1-2cm)
- spongy/penile urethra (longest part)
membranous urethra anatomy
membranous urethra is surrounded by external urethral sphincter and formed from skeletal muscle (under voluntary control by the pudendal nerve)
spongy urethra anatomy
distal to membranous urethra and extends to /opens at external urethral orifice, surrounded by corpus spongiosum and wides distally at the navicular fossa (aka end of the penis)
membranous urethra rupture vs spongy urethra rupture
extravasation of fluid into retroperitoneal space + bladder and prostate floating in urine vs extravasation of fluid into superficial perineal pouch, scrotum, around penis and in the anterior abdominal wall
mechanism of erection and ejaculation
erotic stimulation –> parasympathetic fibers stimulated, relaxing the smooth muscles in the fibrous trabeculae + dilates the arteries –> cavernous spaces filled with blood –> blood filled space compresses the veins against the tunica albuginea –> blocks the backflow of blood, leading to pool of blood in the penis (erection) –> stimulation of sympathetic NS to close internal urethral sphincter during ejaculation
what is the perineal body?
fibromuscular structure located at the midline of the perineum, at the junction of the anal and urogenital triangles
attachments of the perineal body
bulbospongiosus muscle, deep+superficial transverse perineal muscles, external anal sphincter muscle, levator ani muscles
when is an episiotomy performed, and why?
performed to enlarge the birth outlet and facilitate the delivery of the fetus while preventing multiple tears in the birth canal
what structures are excised in a mediolateral episiotomy?
skin, subcutaneous tissues, superficial and deep transverse perineal muscles, bulbospongiosum, part of levator ani, posterior vaginal wall
supply and branches of the internal pudendal artery
internal pudendal artery is a branch of the anterior division of the internal iliac artery, exits the pelvis inferiorly via the greater sciatic foramen and reenters via the lesser sciatic foramen (to supply the skin and structures of the perineum, anal, and urogenital regions)
branches of the pudendal artery are the inferior rectal artery, the perineal artery, and the dorsal artery of the penis/clitoris
lymphatic drainage of the perineum
mostly into the superficial inguinal nodes, while glans penis and clitoris drain into the deep inguinal nodes, and the testes drain into the para-aortic lymph nodes
pudendal nerve roots and supply
arises from ventral rami of S2, S3, S4, supplies motor and sensory innervation + sympathetic autonomic fibres
leaves the pelvis through the greater sciatic foramen, curves around the sacrospinous ligament, enters the perineum through the lesser sciatic foramen
structures forming the pudendal canal
formed by the fascia of the obturator internus and deep pelvic fascia, pudendal nerve + internal pudendal artery + internal pudendal vein run thru the canal
pelvic splanchnic nerves roots and supply
arises from preganglionic nerves from the lateral horn of the spinal matter at sacral segments S2, S3, S4
what is the pudendal nerve block?
regional anaesthesia technique to provide perineal anaesthesia (bony landmark is the ischial spine)
penile musculature in males
- ischiocavernosus muscle spiralling over the corpora cavernosum to aid in support and movement
- bulbospongiosus muscle spiralling over the corpora spongiosum aiding in emptying the urethra
both are skeletal muscles innervated by the pudendal nerve
penile musculature in females
- ischiocavernosus muscle spiralling on the crura of the clitoris to compress it for clitoral engorgement
- bulbospongiosus muscle covering the vestibular bulb to contribute to clitoral erection
