The rectum is continuous with the sigmoid colon proximally at the rectosigmoid junction (S3) and with the anal canal distally1. The rectum has a sacral flexure which follows the curve of the sacrum and the coccyx1. The anorectal flexure is an S-shaped flexure which has a sharp postero-inferior bend antero-inferior to the tip of the coccyx and it penetrates the pelvic diaphragm1. It maintained by the puborectal sling through the puborectalis muscle1. Lastly, the rectum also has lateral flexures due to transverse rectal folds1. There is a superior, intermediate and inferior lateral flexure1.
Relationships of the rectum1:
o Pelvic diaphragm (levator ani)
o Anococcygeal ...view middle of the document...
Lymphatic vessels from the inferior rectum drain to the sacral lymph nodes and then into the internal iliac lymph nodes1.
Sympathetic innervation of the rectum arises from the lumbar spinal cord segments via the hypogastric plexuses and the peri-arterial plexus of the superior rectal artery1. Parasympathetic and visceral afferent fibers to the rectum include the middle sacral spinal cord segments and ganglia1.
The anal canal is the terminal part of the colon1. It extends from the superior aspect of the pelvic diaphragm to the anus1. The anorectal line separates the anal canal and anus from the rectum1. Further, the anal canal is separated into the superior and inferior anal canal by the pectinate line1.
The internal anal sphincter1 consists of smooth muscle and it is involuntary1. It surrounds the upper part of the anal canal and its lower end is at the Hilton’s line1. The internal anal sphincter has autonomic nerve supply from the inferior hypogastric plexus1.
External anal sphincter1 is made up of striated muscle and the major muscles of the anal triangle1. It surrounds the lower part of the anal canal and it is supplied by the internal iliac artery which gives off the internal pudendal and finally the inferior rectal artery1. Innervation is by the inferior rectal nerve from the pudendal nerve (S2-S4) and a branch of S41.
The external anal sphincter constitutes three parts1,2:
1. Deep (superior anal canal) and it fuses with the puborectalis muscle at the anorectal junction. It is a thick and ring-shaped.
2. Superficial (pectinate line), which is deep to the subcutaneous part & attaches to the coccyx and perineal body.
3. Subcutaneous (inferior anal...