66 Pelvic diaphragm. Nerves and arteries of the pelvic cavity Flashcards
What is the false pelvis?
The posterior abdominal wall, iliacus covering the iliac bones
What is the true pelvis/ lesser pelvis/ pelvic cavity
Inferior to the arcuate lines on the iliac bones (equivalent to the pelvic brim or pelvic inlet)
What muscle lines the pelvic lateral wall?
Obturator internus
What muscle forms the pelvic floor/ diaphragm?
Levator ani
What is the perineum?
- Diamond-shaped
- Pudendal region below the pelvic floor/ diaphragm
- Containing the external genitalia and urethra anteriorly with the anal canal and ischioanal fossa posteriorly
What are the structures which form a hammock for the pelvic visceral/ organs?
- Pelvic side walls - obturator internus
* Pelvic floor/ diaphragm - elevator ani
What structures rest on the levator ani that forms the pelvic floor/ diaphragm?
- Bladder
* Prostate
Perineum is divided into deep and superficial compartments anteriorly by what?
Perineal membrane
Pelvis brim/ inlet (of true pelvis) formed by?
- Pubic symphysis
- Pubic crest
- Pectineal line on superior pubic ramus
- Arcuate line of ilium
- Sacroiliac joint
- Sacral ala and sacral promontory (S1)
Pelvic outlet formed by?
- Pubic symphysis
- Ischiopubic ramus
- Ischial tuberosity
- Sacrotuberous ligament
- Sacrum and coccyx
Pelvic outlet is hugely important in what scenario?
Childbirth
What triangles are the diamond-shaped perineum divided into?
- Anterior: urogenital triangle
* Posterior: anal triangle
Changes to female pelvis?
Must accommodate childbirth • Lighter • More rounded • Wider • Oval inlet
Changes to male pelvis?
- Heavier
- Heart shaped inlet
- Narrowed outlet (due to more acute sub-pubic angle and enriched upon by the ischial spines)
Ligaments of the pelvis?
- Sacrospinous
• Triangular
• From ischial spine to adjacent sacrum and coccyx - Sacrotuberous
• Broader
• From ileum, sacrum and coccyx to ischial tuberosity
Both ligaments form the greater and lesser sciatic foramina
What are the 3 passages through the pelvis floor?
- Greater sciatic foremen:
• Above piriformis -Superior gluteal nerve and vessels
• Below piriformis - Sciatic nerve + inferior gluteal vessels - Lesser sciatic foramen:
• Pudendal nerve + internal pudendal vessels - Obturator canal
• Obturator nerve and vessels
What is the piriformis?
- From sacrum —> greater trochanter
- Forms the posterosuperior pelvic wall
- Divides the greater sciatic foramen
- Innervation: S1, S2, occasionally L5
What is the obturator internus?
• From obturator membrane and adjacent bone
—> greater trochanter
• Forms the lateral pelvic wall with its overlying obturator fascia that gives origin to the pelvic floor/ diaphragm muscle (elevator ani)
• Innervation: nerve to obturator internus - L5, S1, occasionally S2
Tendinous arch (thickening of obturator fascia) is for the attachment of what muscle?
Levator ani
What muscles make up the pelvic wall?
- Obturator internus - lateral
2. Pirifromis - posterosuperior
What muscles make up the pelvic floor/ diaphragm?
- Coccygeus
2. Levator ani
What is the coccygeus (aka ischiococcygeus)?
- Overlies sacrospinous ligament
- Blends with the elevator ani posteriorly
- Innervation: S4, S5
What parts make up levator ani? Innervation?
- Iliococcygeus:
• Innervation: S3, S4 - Pubococcygeus - subdivided into:
• Puborectalis posteriorly
• Pubovaginalis (female) or puboprostaticus (male) anteriorly around the urogenital opening
• Innervation: S3, S4 (occasionally pudendal nerve S2, S3, S4)
What muscles make up pubococcygeus in females and males?
- Females:
Puborectalis + Pubovaginalis - Males:
Puborectalis + Puboprostaticus
Importance of the levator ani as a bowl of the pelvic floor?
- Supports the visceral organs
- Maintains urinary and faecal continence
- Weakness may cause incontinence or prolapse
Where does each side of the levator ani meet and form?
Each side meets in the midline to form:
- Anococcygeal body (a.k.a. raphe or ligament)
- Perineal body (a.k.a. central tendon of perineum) - anterior to anal canal and posterior to vagina (females)
Actions of levator ani?
- Supports the pelvic viscera
- Makes the rectoanal angle more acute aiding rectal continence
- Augments the external anal and urethral sphincters
- Forms a vaginal sphincter
Lymphatic drainage of the pelvis?
- Lumbar/ para-aortic
- Inferior mesenteric
- Iliac: common, external, internal
- Inguinal: superficial + deep
- Sacral
- Pararectal
Lymph nodes may be found on the lateral pelvic walls alongside the obturator neuromuscular bundle
What structures are under voluntary control in the pelvis?
- Pelvic floor/ diaphragm muscles
- External urethral
- External anal sphincters
Pelvic nerves overview
- Somatic - conscious, voluntary
- Autonomic - visceral, subconscious, involuntary as always to complement each other both sympathetic and parasympathetic
- Afferent (sensory) and efferent (motor) for each of the above
What makes up the somatic pelvic nerve supply?
- Lumbo-Sacral plexus:
• Ventral rami of spinal nerves L4, L5 (lumbosacral trunk) and S1-4 emerge from anterior sacral foramina - Pudendal nerves:
• S2-4 to perineum (sensory for external genitalia) and voluntary sphincters (motor for external urethral and external anal)
• Direct branches from S3 + S4 to pelvic floor/ diaphragm muscles
Pudendal nerve overview
- Pudendal nerve (S2-4) passes out of the greater sciatic foramen and into the buttock
- Curves posterior to the ischial spine, sacra-spinous ligament and coccygeus
- Before running forwards into the perineum below levator ani
What makes up the autonomic pelvic nerve supply?
- Sympathetic trunks:
• Bilateral and extending into the pelvis to give sacral splanchnics - Superior hypogastric plexus:
• Sending branches to the right and left pelvic plexus (a.k.a. inferior hypogastric) - Parasympathetic pelvic splanchnics: from S2, S3, S4
The thoracic sympathetic trunk gives which splanchnics?
- Greater splanchnic nerve derived from T5 to T9 (foregut)
- Lesser splanchnic nerve derived from T10 _ T11 (midgut)
- Least splanchnic nerve derived from T12 (hindgut)
Relationship between splanchnic servers and pelvis?
- Splanchnic nerves form the preaortic (prevertebral) plexus and synapse in ganglia at the celiac trunk, SMA + IMA
- The preaortic plexus passes into the pelvis as the superior hypogastric plexus that becomes the pelvic plexus (inferior hypogastric)
The thoracic sympathetic trunk gives which splanchnics?
- Greater splanchnic nerve derived from T5 to T9 (foregut)
- Lesser splanchnic nerve derived from T10 _ T11 (midgut)
- Least splanchnic nerve derived from T12 (hindgut)
Relationship between splanchnic servers and pelvis?
- Splanchnic nerves form the preaortic (prevertebral) plexus and synapse in ganglia at the celiac trunk, SMA + IMA
- The preaortic plexus passes into the pelvis as the superior hypogastric plexus that becomes the pelvic plexus (inferior hypogastric)
What does the preaortic (prevertbral) plexus form?
Forms superior hypogastric plexus that branches right and left to become the pelvic plexus (inferior hypogastric)
What is the pelvic plexus (inferior hypogastric) augmented by?
Sacral splanchnic nerves from the sympathetic trunk in the pelvis
What nerves does the pelvic splanchnic nerves send?
Parasympathetic afferents and efferents to the pelvic plexus from S2, 3, 4
Pelvic splanchnics?
- Aka nervi erigentes
- Afferent and efferent parasympathetic fibres derived from S2, 3, 4
- They join the pelvic plexus that is BOTH parasympathetic (cholinergic) and sympathetic (adrenergic)
Pelvic plexus (inferior hypogastric):
• Derived from?
• Carry which fibres
• Augmented by?
- Derived from the superior hypogastric plexus that descends over the sacrum and is from the the preaortic (prevertebral) plexus
- Therefore, essentially carrying fibres from the lesser and least splanchnic nerves T10, 11, 12
- Augmented by sacral splanchnic nerves
- Afferent and efferent
Anatomical relations of pelvic plexus?
Lateral to: • rectum • seminal vesicles + prostate (male) • cervix + vaginal fornicles (female) • posterior aspect of bladder
Lies in an angle between the internal iliac and inferior vesical arteries
What is the blood supply of the pelvis?
• Internal iliac artery branches from the common iliac artery opposite the sacroiliac joint at the level of the L5 disc
• Internal iliac artery divides into anterior + posterior trunks
• Supplies:
- buttock + medial thigh
-posterior pelvic + abdominal walls
- pelvic viscera
- perineum
• Its gluteal branches contribute to important anastomoses around the hip - may form a collateral circulation for the lower limb
What is the blood supply of the pelvis?
• Internal iliac artery branches from the common iliac artery opposite the sacroiliac joint at the level of the L5 disc
• Internal iliac artery divides into anterior + posterior trunks
• Supplies:
- buttock + medial thigh
-posterior pelvic + abdominal walls
- pelvic viscera
- perineum
• Its gluteal branches contribute to important anastomoses around the hip - may form a collateral circulation for the lower limb
Venous drainage of the pelvis
- Internal iliac vein drains equivalent areas to the artery
- Joins the external iliac veins to from the common iliac vein that meets its opposite to form the IVC at the level of L5
- Most pelvic viscera have an extensive venous plexus that drains into the internal iliac or internal pudendal vein
- Anal canal is a site of port-systemic anastomosis
Venous drainage of the pelvis
- Internal iliac vein drains equivalent areas to the artery
- Joins the external iliac veins to from the common iliac vein that meets its opposite to form the IVC at the level of L5
- Most pelvic viscera have an extensive venous plexus that drains into the internal iliac or internal pudendal vein
- Anal canal is a site of port-systemic anatomosis
