Perineum Flashcards
What are the Boundaries of the Perineum?
- Located inferior to the pelvic diaphragm (coccygeus + levator ani)
- Bounded by the inferior pelvic aperture (pelvic outlet)
- A line drawn between the ischial tuberosities divides the perineum into two triangles
1) Urogenital (UG) Triangle (anterior to the line)
2) Anal Triangle (posterior to the line)
What makes up the Anal Triangle
- Ischioanal fossae
- Anal Canal
Describe the Ischioanal fossae
- Fat filled spaces on either side of the anal canal; allow for dilation of anal canal
- Lateral wall of each fossa: formed by obturator internus and ischial tuberosity
- Medial wall of each fossa: formed by the levator ani and external anal sphincter
- Each fossa projects anteriorly into the UG triangle, forming anterior recesses, these recesses facilitate the spread of infection between the UG and anal triangles
- The fossae also communicate with one another posterior to the anal canal; this communication facilitates the spread of infection between the left and right sides of the anal triangle.
Describe the Anal Canal
- Begins at anorectal flexure and ends at the anus
- Anal columns-vertical folds in the mucosal lining
- Anal valves-crescent shaped folds that unite the anal columns inferiorly
- Pectinate line-irregular line at the level of the anal valves
Describe what is superior to the pectinate line
- Anal canal is derived from the hindgut (endoderm)
- Supplied/drained by superior rectal vessels (origin: inferior mesenteric vessels) with minor supply/drainage via the middle rectal vessels (origin: internal iliac vessels)
- Lymph drains to the internal iliac lymph nodes
- Parasympathetic and sympathetic innervation similar to the hindgut; visceral sensory innervation (sensitive to stretch/ischemia but not pain/temp/touch)
Describe what is Inferior to the pectinate line
- Anal canal is derived from ectoderm
- Supplied/drained by inferior rectal vessels (origin: internal pudendal vessels from internal iliac)
- Lymph drains to the superficial inguinal lymph nodes
- Somatic innervation via the inferior rectal nerve (branch of the pudendal nerve); sensitive to pain/temp/touch
Describe the Portal-caval anastomosis related to the rectum and anal canal
- Proximal drainage into the superior rectal vein (portal system)
- Distal drainage into the inferior rectal vein (caval system)
- In cases of portal hypertension, the increased volume of blood in the inferior rectal veins leads to external hemorrhoids (note: internal hemorrhoids occur most commonly in the absence of portal hypertension, and are thought to be related to a breakdown of the muscle walls of the anal canal, leading to prolapse).
What are the anal sphincters?
Internal anal sphincter
External anal sphincter
Describe the Internal anal sphincter
- Smooth muscle sphincter; thickening of the superior 2/3 of the anal canal
- Sympathetic innervation (via lumbar splanchnic nerves) stimulates its contraction (preventing defecation)
- Parasympathetic innervation (via pelvic splanchnic nerves) relaxes it (allowing defecation to occur)
Describe the External anal sphincter
- Skeletal muscle sphincter surrounding the inferior 2/3 of the anal canal
- Somatic motor innervation (via inferior rectal nerve) stimulates its contraction (‘potty’ training involves learning how to control this sphincter)
What makes up the female External genitalia
- Collectively, the female external genitalia are called the vulva or pudendum
1) Mons pubis
2) Labia majora
3) Labia minora
4) Vestibule
Describe the Mons pubis
- Located anterior to the pubic symphysis
- Covered with pubic hair and filled with fat and connective tissue
Describe the Labia majora
- Fat filled folds containing the round ligament of the uterus
- Covered with pubic hair
- Correspond to the scrotum in males
Describe the Labia minora
- Thin folds (no fat, no hair) located on either side of the midline
- The labia minora join together superior to the clitoris to form the prepuce
Describe the Vestibule
- Space between the labia minora
- Contains the openings of the urethra and vagina (hymen is a mucous membrane that spans the vaginal orifice)
What are the Erectile tissues in the female
- Clitoris
- Bulbs of the Vestibule (paired structures)