SDL - Perineum and External Genitalia Flashcards
What is the perineum bounded by superiorly and inferiorly?
The perineum is the area inferior to the pelvic floor, bounded by the pelvic outlet and limited inferiorly by the skin.
Where does the rectum become the anal canal?
At the U-shaped sling created by puborectalis (anorectal angle)
How is the anal canal divided into 2 separate parts?
By the pectinate line
What is the upper 2/3 of the anal canal derived from?
Derived from the embryonic hindgut (endoderm)
Where is lower 1/3 of the anal canal derived from?
Derived from the ectoderm of the proctodeum.
Describe the epithelial lining of the upper 2/3 of the anal canal?
Columnar epithelium (same as rectum) but mucosa organised into longitudinal folds, known as anal canals which are joined together at their inferior ends by anal valves. Above the anal valves are anal sinuses (pouches that contain glands which secrete mucus)
Describe the epithelial lining of the lower 1/3 of the anal canal?
Non-keratinised stratified squamous epithelium (anal pecten).
Transitions to true skin (keratinised stratified squamous) at level of sphincteric groove
Describe the arterial supply of the upper 2/3 of the anal canal?
Superior rectal artery (branch of IMA), anastomosing branches from the middle rectal artery
Describe the arterial supply of the lower 1/3 of the anal canal?
Inferior rectal artery (branch of internal pudendal artery). Anastomosing branches from middle rectal artery
Describe the venous drainage of the upper 2/3 of the anal canal?
Superior rectal vein which empties into inferior mesenteric vein (portal venous system)
Describe the venous drainage of the lower 1/3 of the anal canal?
Inferior rectal vein which empties into internal pudendal vein (systemic venous system)
Describe the lymphatic drainage of the upper 2/3 of the anal canal?
Internal iliac lymph nodes
Describe the lymphatic drainage of the lower 1/3 of the anal canal?
Superficial inguinal lymph nodes
Describe the nerve supply of the upper 2/3 of the anal canal?
Visceral innervation via the inferior hypogastric plexus. Sensitive to stretch.
Describe the nerve supply of the lower 1/3 of the anal canal?
Somatic innervation via the inferior rectal nerves (branches of the pudendal nerves). Sensitive to pain, temperature, touch and pressure.
What is the mucosa of the upper anal canal arranged into?
Longitudinal folds called anal columns
What are the inferior ends of the anal columns linked by?
Ridges called anal valves
What is the pectinate line formed by?
The ring formed by the anal valves is termed the pectinate line
What does the pectinate line mark?
marks the approximate boundary between the embryologically different regions of the anal canal
What surrounds the anal canal?
internal and external anal sphincters
Describe the internal anal sphincter
around the upper two-thirds of the canal, is the thickened lower end of the circular smooth muscle of the rectum.
Describe the external anal sphincter
striated muscle surrounds the lower two-thirds of the canal. It comprises subcutaneous, superficial and deep parts
What type of muscle is the internal anal sphincter?
Circular smooth
What type of muscle is the external anal sphincter?
Striated
What is the deep part of the external anal sphincter closely related to?
related posteriorly to the fibres of puborectalis