Rectum Flashcards
Just above the pelvic diaphragm, generate the urge to defecate
Ampulla of rectum
Contains 3 transverse rectal folds (Houston valves)
Mucosa
Submucosa
Inner circular layer of smooth muscle
Blood supply of rectus
Inferior mesenteric artery via the superior rectal artery
Venous drainage of the rectum
Superior rectal vein –> IMV –> portal vein
Autosomal dominant
Mutation in APC anti-oncogene, ras proto-oncogene, DCC anti-oncogene & p53 anti-oncogene
MC site: rectosigmoid colon
Familial adenomatous polyposis (FAP)
Adenomatous polyps + multiple osteomalacia
Gardner syndrome
Adenomatous polyps + gliomas
Turcot syndrome
Mutations on HNPCC gene
R sided tumors - iron deficiency anemia
L sided tumors - obstruction & bloody stools
MC site of metastasis: liver because sigmoid vein & superior rectal vein drain into portal system
Posterior mets may involve the sacral nerve plexus –> sciatica
Colonic adenocarcinoma
IBD, always involve the rectum & extends proximally, no skip areas
May lead to toxic megacolon
Ulcerative colitis
Protrusion of full thickness of rectum through the anus (vs mucosal prolapse which is the protrusion of just the rectal mucosa)
Anal incontinence (stretching of internal & external sphincters or stretch injury to pudendal nerve
Rectal prolapse
Divided into upper & lower portion by the Pectinate line
Surrounded by 2 sphincters:
- internal anal sphincter (smooth muscle, involuntary, via autonomic innervation)
- external anal sphincter (striated muscle, voluntary, via pudendal nerve)
Upper anal canal mucosa extends into longitudinal folds (anal column, columns of Morgagni)
- Pectinate lime is defined by the base of anal columns
- anal valves are found at the base of anal columns
- behind the anal valves are anal sinuses into which anal glands open
Anal canal
Location: from anorectal junction (perineal flexure to Pectinate line)
Blood supply: superior rectal artery
Venous drainage: superior rectal vein ➡️ IMV ➡️ portal system
Lymphatic drainage: deep nodes
Innervations:
- motor: autonomic for internal anal sphincter
- sensory: stretch only, no pain sensation
Embryonic derivation: endoderm (hindgut)
Epithelium: simple columnar
Tumors: no palpable enlarged superficial nodes, no pain
Hemorrhoids:
- internal (varicosities of superior rectal veins)
- covered by rectal mucosa
- no pain
Upper anal canal
Location: from Pectinate line to anal verge
Blood supply: inferior rectal artery (branch of internal pudendal artery)
Venous drainage: inferior rectal vein ➡️ internal pudendal vein ➡️ internal iliac vein ➡️ IVC
Lymphatic drainage: superficial inguinal nodes
Innervations:
- motor: somatic (pudendal nerve) for external anal sphincter
- sensory: pain, temp, touch
Embryonic derivation: ectoderm (proctodeum)
Epithelium: stratified squamous
Tumors:
- palpable enlarged superficial nodes
- +pain
Hemorrhoids:
- external (varicosities of inferior rectal veins)
- covered by skin
- +pain
Lower anal canal
+feces ➡️ pressure-sensitive receptors in ampulla of rectum
Motor:
- pelvic splanchnic nerve (parasympathetic, S2-4)
- ⬆️ peristalsis
- relax the internal anal sphincter
If external sphincter & puborectalis muscle are also relaxed ➡️ defecation
If external anal sphincter & puborectalis muscle are contracted ➡️ feces move back into sigmoid colon for storage
- HYPOGASTRIC PLEXUS & LUMBAR SPLANCHNIC NERVE amidsanal sphincter
Defection reflex
Begins at S3, ends at the tip of coccyx (anorectal junction), where puborectalis muscle forms s U-shaped sling that causes a 90% perineal flexure
Rectum
