Lecture 18 - Anatomy (The perineum) Week 16.pdf

THE PERINEUM Thomas Wilson Graphics from Grant’s Method of Anatomy, Netters Atlas of Human Embryology, Larsen’s Anatomy, Human Embryology and Developmental Biology, Moore’s Before We Are Born, Analysis of Vertebrate Structure, McMinn’s & Abrahams Clinical Atlas of Anatomy, Human Anatomy Colour Atla...

THE PERINEUM Thomas Wilson Graphics from Grant’s Method of Anatomy, Netters Atlas of Human Embryology, Larsen’s Anatomy, Human Embryology and Developmental Biology, Moore’s Before We Are Born, Analysis of Vertebrate Structure, McMinn’s & Abrahams Clinical Atlas of Anatomy, Human Anatomy Colour Atlas & Textbook [email protected] Goal: 1) Notice the common patterns/differences between males and females 2) How we can use our phylogeny as a guide to help our understanding Outline: Outcomes: What the perineum is Identify & describe the features and borders of the perineum. Innervation of the perineum Identify the major nerves, arteries, muscles, spaces, pouches, membranes, diaphragms & fascia of the perineum & relate structure to function. Pouches, membranes, diaphragms & fascia Relate the structures of the perineum to their functions. Perineum as part of the body wall Describe & identify the homologues features of the perineum. Structure of the ‘perineal body wall’ “Near to those that carry things off by evacuation” Perineum: Pelvic floor & the things beneath it Separated into 2 angled triangles: 1. Anal triangle (open) 2. Urogenital triangle (closed) Special features: Anococcygeal raphe Perineal body Perineal membrane Includes the erectile tissues The pudendal nerve (S 234): general plan Exit the greater sciatic foramen  Enter the lesser sciatic foramen Pudendal vessels run inside the pudendal canal A fibrous canal in the internal obturator fascia (deep to obturator internus) Branches: 1. Inferior rectal (Skin of anal triangle / external anal sphincters) 2. Perineal: A. Posterior labial / scrotal (Skin of urogenital triangle) B. Supply to voluntary muscles of deep & superficial pouches 3. Dorsal nerve of penis/clitoris (skin & erectile tissues of penis/clitoris)  Medial view  The body wall is continuous & so is its fascia Fascia: Scarpa’s (superficial abdo wall) Colle’s (superficial perineal) Buck’s (deep penile) Covers male erectile tissues and extends with them as they grow Features: Perineal body Perineal membrane Deep pouch Superficial pouch Urogenital diaphragm (layer 3 urogenital muscles) NOTES: The body wall is continuous & so is its fascia Scarpa’s fascia from abdominal wall is continuous with Colles’ fascia Follow the green in the lower left image and orange in right images Colles’ is the superficial perineal fascia (AKA dartos fascia, superficial scrotal/penile) Closed posteriorly at the perineal body And the posterior border of the perineal membrane Deep perineal fascia: Contains male erectile tissues Buck’s fascia: Deep penile fascia / Investing perineal fascia Creates ‘compartments’ to contain things within  Evolution of the perineum: Another brick in the wall Perineum is a continuum of the body wall  1. Subcutaneus: Superficial external anal sphincter 2. External: Erectile tissue muscles 3. Internal: Deep external anal sphincter / urethral / vaginal sphincters 4. Transverse: Levator ani & coccygeus These perineal layers are, however, distinctly mammalian  Evolution of the perineum: Another brick in the wall (NOTES) The body wall is continuous Intercostal muscles  Abdominal wall muscles  AND perineal muscles Remember, fish don’t have pelvises, so pelvic girdle of higher vertebrates developed into this space of the body wall Tetrapods have 4 body wall muscle layers, but we usually only discuss 3… Most tetrapods keep the fish perineal plan, as they don’t septate their cloaca. Placental mammals, however, are the only higher vertebrates to septate their cloaca and thus have a different structural plan. The 4th and most superficial body wall layer houses a trunk muscle called Cutaneous Trunci in other mammals and is responsible for voluntary skin contraction. Its colloquial name is “the fly shaker.” The 4th layer is crucial in a mammalian perineal muscle sense, as it forms the superficial component of the external anal sphincter… A voluntary sphincter The other 3 layers of body wall in the perineum create the different layers of urogenital and pelvic floor musculature. Layer 1 (most superficial): Subcutaneous body wall Muscle: 1. Superficial external anal sphincter (voluntary!) Found in the anal triangle Layer 1 (most superficial): Subcutaneous body wall Space observed here: Ischiorectal / Ischioanal fossa Lateral wall: Obturator internus, ischiopubic rami Medial wall: Rectum & anus, urogenital tracts Floor: Open posteriorly, closed by urogenital diaphragm and pubic symphysis anteriorly Anterior recesses Layer 2 (Male): External body wall, Erectile tissue and muscle layer All of the following structures are found within the superficial pouch. Inferior to perineal membrane, but deep to colles fascia Perineal membrane forms the common anchor point for the erectile tissues: 1. Corpus-spongiosum (bulb, shaft, glans) 2. Corpus-cavernosum (crura, shafts) Covered and supported by muscles: 1. Bulbo-spongiosus (forms median raphe) 2. Ischio-cavernosus Extra contents for the male superficial pouch: Testes and spermatic cord  Layer 2 (female): External body wall, Erectile tissue and muscle layer Found in the superficial pouch, same as in males Homologous female erectile tissues: 1. Bulb of the vestibule (bulbs, neck, glans) 2. Clitoris (crura, body) Covered and supported by the same muscles: 1. Bulbo-spongiosus 2. Ischio-cavernosus Extra contents for the female superficial pouch: (homologous to prostate) Greater vestibular gland (homologous to bulbourethral gland) Layer 3: Internal body wall Muscles of the urogenital diaphragm are found within the deep pouch (the butcher’s tray analogy) Perineal membrane is the inferior border of this pouch Superior border is quite thin and indistinct Urethra and vagina must pass through this structure Within the urogenital triangle, these muscles support pelvic viscera and act as sphincters 1. External urethral sphincter Female only: 3. Compressor urethrae 4. Sphincter urethrovaginalis This layer is continuous posteriorly to: 5. Deep external anal sphincter Extra contents for the male deep pouch: Bulbourethral gland Layer 4 (deep): Transverse body wall, Pelvic floor layer The muscles of the pelvic floor are made up of 2 muscle, 1 of which has 3 parts to it. 1. Levator ani Puborectalis: Maintains recto-anal angle Pubococcygeus: Lift anal canal, vagina/prostate Iliococcygeus: Lift anal canal 2. Ischio-coccygeus (aka coccygeus) Fibrotic component is the sacrospinous lig. Summary notes: Diaphragms, Pouches, membranes, fascia & sphincters?? Urogenital diaphragm: Tissue diaphragm of the urogenital triangle It is the entire structure of the deep pouch with all contents The urogenital sphincter muscles (of 3rd layer) & fascia Deep pouch: Fascial pouch containing muscles of the urogenital diaphragm Roof: Fascia on top of these muscles (superior/internal/deep aspect) Floor: Fascia on the bottom of these muscles = Perineal membrane Extra contents of male deep pouch: Bulbourethral gland Superficial pouch: Space between perineal membrane & Colles’ fascia (~skin fascia) Contents: Erectile tissues and muscles of the 2nd layer Extra contents of superficial pouch: Para-urethral gland (homologous to prostate) Greater vestibular gland (homologous to bulbourethral gland) Testes and spermatic cord  Summary notes Layer 2 (Male): External body wall Muscle Origin Insertion Function 1. Bulbospongiosus Perineal body & Median raphe Bulb of penis & perineal membrane Remove urine from urethra & pulsatile ejaculation of semen 2. Ischiocavernosus Ischial ramus Crus of penis Blood from crura to body of penis Ischial tuberosity 3. Superficial transverse perineal Perineal body Stabilise the perineal body Summary notes Layer 2 (Female): External body wall Muscle Origin Insertion Function 1. Bulbospongiosus Perineal body Bulb of vestibule & Body of clitoris Blood from body of clitoris to glans 2. Ischiocavernosus Ischial ramus Crus of clitoris Blood from crura to body of clitoris Ischial tuberosity 3. Superficial transverse perineal Perineal body Stabilise the perineal body  Summary notes Layer 3 (Male): Internal body wall Muscle Origin Insertion Function 1. Deep external anal sphincter Surrounds superior aspect of anal canal Perineal body & anococcygeal lig. Closes anal canal 2. Deep transverse perineal Ischial ramus Perineal body Stabilise the perineal body 3. External urethral sphincter Ischiopubic ramus Urethra Compress the urethra, relaxes during micturition  Summary notes Layer 3 (Female): Internal body wall Muscle Origin Insertion Function 1. Deep external anal sphincter Surrounds superior aspect of anal canal Perineal body & anococcygeal body Closes anal canal 2. Deep transverse perineal Ischial ramus Perineal body Stabilise the perineal body 3. External urethral sphincter Ischiopubic ramus Urethra Compress the urethra, relaxes during micturition 4. ** Compressor urethrae ** Ischiopubic rami Itself, anterior to the urethra Accessory urethral sphincter Accessory urethral sphincter & helps to close the 5. ** Sphincter urethrovaginalis ** Perineal body Itself, anterior to urethra vaginal opening  Summary notes Layer 4 (deep): Transverse body wall, Pelvic floor layer, Both sexes Muscle Origin Insertion Function Puborectalis Tendinous arch across obturator Joins its counterpart at perineal body, Pelvic floor: support viscera, maintain Levator Ani Pubococcygeus fascia (posterior pubic bone to the anococcygeal ligament, coccyx, rectoanal angle (puborectalis), reinforce ischial spines) wrapping the anal canal anal sphincter, vaginal sphincter Iliococcygeus Ischiococcygeus (AKA coccygeus) Coccyx & lower sacrum Ischial spine & sacrospinous ligament Form pelvic floor, support viscera, flexes the (Sacral plexus S3-S4; NOT pudendal) coccyx after defecation