Part III: Rectum Pg 109-112 Flashcards
Pelvic end of alimentary tract where feces accumulate prior to defecation
Rectum
Rectosigmoid junction located anterior to what vertebral level
S3
Is the rectum intraperitoneal, retroperitoneal or extraperitoneal or sub peritoneal?
- Superior third of rectum is retroperitoneal
- Inferior third of rectum is subperitoneal
What happens to the teniae coli as the transition from sigmoid colon to rectum?
Teniae coli of sigmoid colon expand into continuous layer on rectum
NOTE: Epiploic appendages, haustra and sacculations are also absent from rectum
What is the sacral flexure?
Where the rectum follows contour of sacrum and coccyx
What is the anorectal flexure?
Where the rectum takes a sharp turn at coccyx and pierces pelvic diaphragm
What is the functional significance of the anorectal flexure?
Approximately 80 degree posterior turn important for maintaining fecal continence
What maintains the 80 degree posterior turn of the anorectal flexure?
tonus of Puborectalis M at rest
- Puborectalis M must actively contract to resist peristaltic contractions in rectum and prevent defecation
Conscious initiation of defecation requires:
relaxation of Puborectalis M
3 sharp lateral flexures are present in rectum (superior, intermediate, inferior) and correspond to:
Transverse Rectal Folds of mucosa and submucosa
dilatable terminal region of the rectum lying above and supported by Levator Ani M
Ampulla
What is the function of the ampulla of the rectum?
Relaxes to hold accumulating fecal material prior to defecation
What is the function of the rectovesical pouch (in males), rectouterine pouch (in females) and pararectal fossae (in both sexes)?
All of these provide space for rectum to distend as it fills with feces
Posteriorly in both sexes, the rectum is associated with:
- Sacral vertebrae and coccyx
- Sacral plexuses and inferior ends of sympathetic trunks
- Median Sacral AV
Anteriorly in males, the rectum is associated with:
- Fundus of urinary bladder and terminal parts of ureters
- Ductus deferens, seminal vesicles and prostate
- Separated from these structures by rectovesical pouch
Anteriorly in females, their rectum is associated with
- Vagina, posterior fornix and cervix of uterus
- Separated from these structures by rectouterine pouch
What is the arterial supply to the proximal part of rectum?
Superior Rectal A - branches from Inferior Mesenteric A
What is the arterial supply to the anorectal junction and anal canal of the rectum?
Inferior Rectal A - branches from Internal Pudendal A
There are three arteries that supply the rectum. What are they?
- Superior Rectal A - branches from Inferior Mesenteric A
- Middle Rectal A - branches from Internal Iliac (anterior division)
- Inferior Rectal A - branches from Internal Pudendal A
What is the venous drainage of the rectum?
- Superior Rectal V drains to hepatic portal venous system
- Middle and inferior Rectal V drain to systemic system via Internal Iliac V
- Anastomoses between these veins create an important portacaval anastomosis
Lymphatic drainage of superior portion of the rectum is through:
pararectal to inferior mesenteric and lumbar nodes
Lymphatic drainage of inferior portion of the rectum is through:
internal iliac lymph nodes
Sympathetic innervation of the rectum is via:
lumbar splanchnic N through superior hypogastric plexus
NOTE: Possibly vasomotor but not functionally significant
Parasympathetic innervation of the rectum is via:
pelvic splanchnic N through inferior hypogastric plexus
Parasympathetic innervation to the rectum function:
Motor fibers to rectal muscularis externa
Visceral afferents (conveying both pain and/or distension) from the rectum pass through
pelvic splanchnic N to S2-S4
What happens to anal sphincters when the ampulla is empty?
- Internal Anal Sphincter M is contracted
- External Anal Sphincter M is relaxed
Defecation is controlled by innervation mediated through:
pelvic splanchnic N
When feces accumulates in ampulla and sufficiently distends it, what happens to the anal sphincters?
- Internal Anal Sphincter M reflexively relaxes
- External Anal Sphincter M reflexively contracts
What initiates the external anal sphincter M to reflexively contract?
visceral afferents in pelvic splanchnic N
Defecation requires voluntary override of:
reflexive External Anal Sphincter M contraction
NOTE: Puborectalis M also must voluntarily relax
Parasympathetic stimulation to the rectum during defecation does what?
increases peristaltic activity in rectum
The terminal part of large intestine (approximately 3cm) that extends from pelvic diaphragm (Puborectalis M) to anus
Anal canal
Thickened circular smooth muscle around the superior two-thirds of anal canal
Internal Anal Sphincter
Is the internal anal sphincter under voluntary or involuntary control?
Involuntary
NOTE: Normally contracted (sympathetic) to prevent leakage of feces or flatus but reflexively relaxes in response to pressure of feces/gas in rectal ampulla
Broad band of skeletal muscle surrounding inferior two-thirds of anal canal
External Anal Sphincter
Is the external anal sphincter under voluntary or involuntary control?
Voluntary
The external anal sphincter is attached anteriorly to ______ & posteriorly to _______.
- perineal body
- coccyx (via anococcygeal L)
The external anal sphincter blends superiorly with:
Puborectalis M
What voluntarily contracts to prevent defecation or relax to allow defecation?
External anal sphincter and puborectalis M
What innervates the external anal sphincter?
Inferior Rectal N (S4) from Pudendal N
longitudinal ridges of mucosa in superior half of anal canal
Anal columns
What part of the anus contains terminal branches of Superior Rectal AV
Anal Columns
What landmark is located at superior ends of anal columns
Anorectal Junction
What structure is located at inferior ends of anal columns
Anal Valves
The small recesses located just superior to anal valves in the anal columns that produce mucous to facilitate passage of feces
Anal sinuses
irregular line formed by anal valves
Pectinate lines
What is the arterial supply to the anal canal above the pectinate line?
Superior Rectal A (from Inferior Mesenteric A)
NOTE: Middle Rectal A forms anastomoses with Superior/Inferior Rectal A
What is the arterial supply to the anal canal below the pectinate line?
Inferior Rectal A (from Internal Pudendal A)
NOTE: Middle Rectal A forms anastomoses with Superior/Inferior Rectal A
What is the venous drainage of the anal canal superior to pectinate line?
Hepatic portal system via Superior Rectal V
What is the venous drainage of the anal canal inferior to pectinate line?
IVC via Inferior Rectal V, Internal Pudendal V
What is the lymphatic drainage of the anal canal superior to pectinate line?
internal iliac lymph nodes
What is the lymphatic drainage of the anal canal inferior to pectinate line?
superficial inguinal lymph nodes
Autonomic innervation to the anal canal above the pectinate line is via:
inferior hypogastric plexus
Sympathetic innervation of the anal function:
maintain tonus of Internal Anal Sphincter
Parasympathetic innervation of the anal canal function:
relax Internal Anal Sphincter and initiate peristalsis
Sympathetic and parasympathetic innervation is responsive to”
distension/stretching but insensitive to touching/cutting
Somatic innervation of the anal canal below pectinate line is via:
Inferior Rectal N (Pudendal N)
Somatic innervation to the anal canal function:
- Motor innervation to External Anal Sphincter
- Responsive to pain, touch, temperature
