Pelvis Flashcards
(24 cards)
What is the origin and insertion of the piriformis, what sits directly anterior to it?
What is its nerve supply?
Origin - middle three pieces of the sacrum
Insertion - medial border of the greater trochanter.
Nerve supply - anterior border of S1 and S2
What is the levator ani composed of?
- Consists of pubococcygeus, and iliococcygeus.
- There fibres arise in continuity from the body of the pubis to the ischial spine across the obturator fascia, along a condensation of the fascia called the tendinous arch.
- The pubococcygeus arises from the anterior half of the tendinous arch.
- The medial aspect of pubococcygeus slings around the anorectal junction at the top of the anus and this is called puborectalis. It joins with fibres of the external anal sphincter.
- The iliococcygeus arise from the posterior half of the tendinous arch. Inserts onto the side of the coccyx and the anococcygeal raphe
What is the nerve supply of the levator ani?
Sacral plexus branches of S3-4
Puborectalis is also supplied by the inferior rectal branch of the pudendal nerve.
NB: the inferior rectal branch of the pudendal nerve supplies the external anal sphincter.
Describe the sensory supply to the perineum?
Pudendal nerve (S2-S4)
* Primary somatic nerve of the perineum
* Exits the pelvis via the greater sciatic foramen.
* Curves around ischial spine, re-enters via lesser sciatic foramen
* Travels through Alcocks canal and gives
○ Inferior rectal nerve - to anal canal and external anal sphincter.
○ Perineal nerve- to perineal muscles, posterior scrotum/labia, skin of perineal body.
○ Dorsal nerve of the glans/clitoris
Ilioinguinal (L1)
* Supplies skin at the root of the penis or mons pubis, anterior scrotum, labia majora.
Genitofemoral nerve (L1-L2)
* Genital branch supplies the cremaster muscle and skin of anterior scrotum.
Posterior femoral cutaneous nerve (S1-S3)
Perineal branch supplies posterior scrotum/labia
Anatomy of the internal iliac nerve?
Internal iliac artery
- The common iliac artery bifurcates at the pelvic brim opposite the SI joint.
- It then passes downwards and divides into short posterior and longer anterior divisions.
- There are 3 short posterior branches and 9 anterior branches
* Anterior branches can be divided into
○ Urinary
○ Reproductive
○ Digestive
○ Pelvic wall
Posterior branches
- Iliolumbar artery
- Supplies the iliac and lumbar areas,
- Lateral sacral artery
- Supplies the sacrum and adjacent muscles.
- Superior gluteal artery
- Leaves pelvis through greater sciatic foramen, above piriformis.
Anterior branches
- Urinary
- Superior vesical artery
○ Persistent patent proximal part of the foetal umbilical artery
○ Distal part becomes obliterated to form medial umbilical ligament.
○ Runs along pelvic side wall then turns medially to reach upper part of bladder. - Inferior vesical artery
○ Runs medially across the pelvic floor.
○ Supplies trigone and lower part of bladder, ureter, vas deferens, seminal vesicles and prostate.
- Superior vesical artery
- Reproductive
- Uterine artery
○ Passes medially across the pelvic floor at the base of the broad ligament.
○ Runs above the ureter.
○ When it reaches the uterus, runs upwards alongside the uterus to the tube - eventually anastomoses with the ovarian artery. - Vaginal artery
- Internal pudendal
○ Passes out of pelvis through the greater sciatic foramen below piriformis
○ Gives off the inferior rectal artery as it travels in the posterior aspect of the pudendal canal
○ Then gives off arteries to perineum, scrotum and dorsal artery of penis.
- Uterine artery
- Digestive
- Middle rectal artery
○ Frequently absent and small when present.
- Middle rectal artery
- Pelvic wall
- Obturator artery
○ In about 30% of people an accessory obturator artery can arise from the inferior epigastric artery and travels just medial to the lacunar ligament. This ligament is often divided when releasing a strangulated femoral hernia. - Inferior gluteal artery
- Leaves the pelvis through the Greater sciatic foramen
- Obturator artery
Anatomy of the anal canal
- Is usually about 4cm long.
- Consists of an internal and external sphincter
- The external anal sphincter is a continuation of the levator ani and is skeletal muscle.
- The internal anal sphincter is a continuation of the inner circular layer of rectal muscle.
- Internally lies the submucosa and mucus membrane
- The upper 1/3 of the anal canal has the anal columns. This is columnar mucosa
- At the lower end of the columns are the anal valves, into which open the anal sinuses/glands.
- At the level of the anal valves is the dentate line.
- Below the dentate line is the pecten area which extends down to the intersphincteric groove
- The lining of pecten is stratified non-keratinized squamous epithelium.
- Below the intersphincteric groove is stratified keratinized squamous epithelium.
- Anal cushions are located in the upper anal canal – these are submucosal masses comprising dilated venous spaces, arteriovenous anastomosis, and connective tissue.
- The dentate line divides the endoderm from the ectoderm.
What is the anatomy of the external anal sphincter?
Has a subcutaneous, superficial and deep part.
The motor and sensory supply is via the inferior rectal branches of the pudendal nerve
Nerve supply of the anal canal?
Sensory supply to the anal canal
- Above dentate line
* Sympathetic - inferior hypogastric plexus.
* Parasympathetic - pelvic splanchnic nerves - S2-S4
- Below dentate line
* Somatic nerve supply
○ Inferior rectal nerves - branches of the pudendal nerve (S2-S4)
Innervation of the anal sphincters
- External anal sphincter
* Somatic
○ Inferior rectal nerve (S2-4) - which is a branch of the pudendal nerve
○ Nerve to levator ani (S3-S4) - supplies the top.
- Internal anal sphincter
* Sympathetic - inferior hypogastric plexus
- Parasympathetic - pelvic splanchnic nerves (s2-S4)
What is the blood supply of the anal canal?
Superior rectal artery - supplies the upper end of the anal canal.
Lower end - via the inferior rectal vessels - branch of the pudendal artery.
Venous drainage of the anus
The upper anal canal drains via the portal systemic through the superior rectal vein and IMA, wheras the lower end is through the internal iliac vein – the anus is thus a site of porto-systemic anastomosis (at the region of anal columns).
What factors maintain faecal continence?
- contraction of puborectalis and the external sphincter
- maintenance of the angle between rectum and anal canal with abdominal pressure flattening the lower anterior rectal wall over the upper end of the canal
- presence of mucosal cushions in the canal.
What factors allow defecation?
- When increasing rectal pressure causes faeces to enter the upper anal canal, the external sphincter contracts and causes the contents to return back into the rectum
- The feeling of distension is conveyed within the spinal cord by gracile tracts
- Defaecation is allowed to occur by release of the cortical inhibition that developed during childhood training
- When abdominal pressure is increased, puborectalis relaxes and the anorectal angle straightens
- The colon and rectum contract to push faeces through
What are the boundaries of the ischiorectal fossa?
- The external sphincter and the sloping levator ani muscles form the medial wall of each fossa
- Lateral wall is formed by the ischial tuberosity and obturator internus.
- Posteriorly is the sacro-tuberous ligament
- Anteriorly is bound by the muscles of the urogenital diaphragm
- Posteriorly is bound by the sacrotuberous ligament overlapped by gluteus maximus.
- Posteriorly the two fossa communicate with each other providing a horse-shoe shaped path for the spread of infection.
What are the pelvic branches of the sacral plexus?
- Nerve to piriformis.
- Perforating cutaneous nerve
- Pierces gluteus maximus and supplies small area of skin on medial side of buttock.
- Posterior femoral cutaneous nerve
- Runs down below piriformis on the sciatic nerve.
- Supplies skin on posterior buttock, posterior thigh, to mid calf.
- Pelvic splanchnic nerves
- Sacral parasympathetic outflow
- Fibers joint inferior hypogastric plexus
- Motor to bladder, large intestine (splenic flexure downwards)
- Causes erection.
- Afferent fibers include those of distension, pain from bladder, lower cervix, lower colon, and rectum.
- Pudendal nerve
- Runs down and curls around Gluteal surface of sacrospinous ligament to enter pudendal canal.
- Is the nerve to the perineum.
- Supplies external anal sphincter, anal canal, perianal skin, and dorsal nerve of penis.
- Branches
○ Perineal nerve
§ Supplies posterior 2/3 of scrotum.
§ Motor to perineal and penis muscles
- Perineal branch of S4
- Supplies puborectalis
What is the branch of the sciatic nerve in the thigh, and what does it branch into?
Formed at the lower margin of the piriformis by the union of the tibial and peroneal parts.
Passes into buttock lying on the posterior surface of the ischium.
Passes vertically downwards into hamstring compartment - main trunk supplies all hamstring muscles and adductor magnus.
Divides into common peroneal and tibial branches - at the upper end of the popliteal fossa.
What is the path of the common peroneal nerve?
What are its branches?
What do its branches go on to supply?
- Runs medial to the head of biceps tendon in the popliteal fossa
- Crosses the lateral head of gastroc and curves around the neck of the fibula and enters peroneus longus.
- Divides into superficial and deep peroneal branches.
Deep peroneal branch
- reaches interosseous membrane and travels anterior to it.
- Ends by supplying the skin on the first interdigital cleft.
- supplies extensor muscles of the foot
- supplies the first web space.
Superficial peroneal nerve
- formed in the substance of peroneus longus
- emerges from the anterior border of peronus longus 1/3 of the way down the leg
- perforates the fascia to supply skin over lateral lower 1/3 of the limb and the dosrum of the foot (including medial aspect)
- supplies the lateral compartment muscles.
What is the main cutaneous branch of the tibial nerve
Sural nerve
- runs with the short saphenous vein.
- cutaneous supplie to posterior aspect of hte left and lateral aspect of the foot.
What is the general path of the tibial nerve
Enters apex of popliteal fossa.
Passes vertically down deep to the heads of gastrocnemius behind the knee joint.
Goes across the popliteus muscle.
Runs beneath the fibrous arch of soleus.
Sural nerve
* Cutaneous branch which is given off in the popliteal fossa - runs with the short saphenous vein.
* Receives tributaries from the common peroneal nerve (via the lateral sural cutaneous nerve)
Runs down with the posterior tibial vessels deep to soleus.
Is giving off muscular branches to posterior along its whole course.
Supplies the flexor compartment of the calf and the plantar muscles.
What are the layers of the testes - from skin to inside
- 7 layers
- Skin
- Dartos muscle.
- External spermatic fascia.
○ Derived from the aponeurosis of the external oblique. - Cremaster muscle and fascia.
○ Derived from the internal oblique muscle. - Internal spermatic fascia
○ Derived from transversalis fascia - Tunica Vaginalis
○ Double-layered serous membrane derived from peritoneum. - Tunica albuginea
Dense fibrous coating of the testes itself
What is the blood supply to the testes?
For each artery which supplies the testes - what artery do they arise from?
Testicular - arises from aorta.
Cremaster - arises from inferior epigastric.
Artery to the vas - arises from inferior vesical (internal iliac)
Explain the mesorectal fascia, parietal pelvic fascia, and Waldeyers fascia.
- Three layers of fascia posteriorly
- Mesorectal fascia
- Parietal pelvic fascia
- Pre sacral fascia
When performing TME - you are dissecting between the mesorectal fascia and the parietal pelvic fascia.
Waldeyer’s fascia is located at the level of S4 - is the distal aspect of the parietal pelvic fascia as it connects to the mesorectal fascia.
Divides the retro-rectal space into a pre-sacral space and pre-coccygeal space.
What is the inferior hypogastric plexus composed of?
Sympathetic nerves from the superior hypogastric plexus as well as parasympathetic pelvic splanchnic nerves from S2-S4
