10. Rectum and Anus Flashcards
is the most distal segment of the large intestine, and has an important role as a temporary store of faeces.
rectum
The rectum begins at the level of the
S3
How is Rectum
macroscopically distinct from the colon
- absence of taenia coli
- absence of haustra
- absence of omental appendices
course of the rectum is marked by two major flexures:
- sacral flexure
2. anorectal flexure
the course of the rectum, is marked by these three additional lateral flexures
superior,
intermediate,
inferior
anteroposterior curve with concavity anteriorly (follows the curve of the sacrum and coccyx).
sacral flexures
three lateral flexures (superior, intermediate and inferior) of the rectum are formed by
transverse folds of the internal rectum wall.
final segment of the rectum
ampulla
relaxes to accumulate and temporarily store faeces until defecation occurs.
ampulla
peritoneum covering of the rectum
- superior third of the rectum – the anterior surface and lateral sides are covered by peritoneum.
- The middle third – anterior peritoneal covering
- lower 1/3 – no peritoneum associated with it.
In males, the reflection of peritoneum from the rectum to the posterior bladder wall forms the
rectovesical pouch
In females, the peritoneum reflects to the posterior vagina and cervix, forming the
rectouterine pouch (pouch of Douglas)
rectum receives arterial supply through three main arteries:
Superior rectal artery – terminal continuation of the inferior mesenteric artery.
Middle rectal artery – branch of the internal iliac artery.
Inferior rectal artery – branch of the internal pudendal artery.
venous drainage of the recum is via
superior r.v -> portal venous system
middle and inferior rectal veins -> systemic venous system
Anastomoses between the portal and systemic veins are located in the wall of anal canal, making this a site of
portocaval anastomosis.
innervation of the rectum
Sympathetic nervous supply to the rectum is from the lumbar splanchnic nerves and superior and inferior hypogastric plexuses.
Parasympathetic supply is from S2-4 via the pelvic splanchnic nerves and inferior hypogastric plexuses. Visceral afferent (sensory) fibres follow the parasympathetic supply.
lymph drainage of rectum
pararectal lymph nodes, which drain into the inferior mesenteric nodes.
lymph from the lower aspect of the rectum drains directly into the internal iliac lymph nodes.
lower dilated portion of rectum
rectal ampulla
final segment of the gastrointestinal tract.
anal canal
fx of anal canal
important role in defecation and maintaining faecal continence.
this muscle surrounds the upper 2/3 of the anal canal. It is formed from a thickening of the involuntary circular smooth muscle in the bowel wall.
voluntary muscle that surrounds the lower 2/3 of the anal canal (and so overlaps with the internal sphincter). It blends superiorly with the puborectalis muscle of the pelvic floor.
anal canal is surrounded by these muscles
internal anal sphincyer
external anal sphincter
At the junction of the rectum and the anal canal, there is a muscular ring – known as the
anorectal ring
formed by the fusion of the internal anal sphincter, external anal sphincter and puborectalis muscle, and is palpable on digital rectal examination.
anorectal ring
superior aspect of the anal canal has the same epithelial lining as the rectum,
_____
columnar epithelium
in the anal canal, the mucosa is organised into longitudinal folds, known as
anal columns
anal columns are joined at their inferior ends by
anal valves
Above the anal valves are small pouches which are referred to a
anal sinuses
The anal valves collectively form an irregular circle – known as the
pectinate line / dentate line
This line divides the anal canal into upper and lower parts, which differ in both structure and neurovascular supply.
pectinate line
rectum
length
5 inches
anal canal
length
4 cm long
anal canal begins at level of this m. up to the anus
puborectalis m.
Above the pectinate line – derived from the
embryonic hindgut
Below the pectinate line – derived from the
ectoderm of the proctodeum
Inferior to the pectinate line, the anal canal is lined by
non-keratinised stratified squamous epithelium (known as the anal pecten
Inferior to the pectinate line, the anal canal is lined by non-keratinised stratified squamous epithelium (known as the anal pecten). It is a pale and smooth surface, which transitions at the level of the ____ to true skin (keratinised stratified squamous).
intersphincteric groove
above the pectinate line
arterial supply
Superior rectal artery (branch of inferior mesenteric artery)
Anastomosing branches from the middle rectal artery.
above the pectinate line
venous drainage
Superior rectal vein, which empties into the inferior mesenteric vein (portal venous system).
above the pectinate line
Nerve Supply
Visceral innervation via the inferior hypogastric plexus.
Sensitive to stretch
Lymphatics
above the pectinate line
internal iliac LN
below the pectinate line
arterial supply
Inferior rectal artery (branch of the internal pudendal artery)
Anastomosing branches from the middle rectal artery.
below the pectinate line
Venous Drainage
Inferior rectal vein, which empties into the internal pudendal vein (systemic venous system).
below the pectinate line
nerve supply
Somatic innervation via the inferior rectal nerves (branches of the pudendal nerve)
Sensitive to pain, temperature, touch and pressure.
below the pectinate line
lymphatics
Superficial inguinal lymph nodes
vascular cushions found within the anal canal of healthy individuals, which help with the maintenance faecal continence.
hemorrhoids
Pathological haemorrhoids are observed in people who
suffer from constipation, prolonged straining when defecating, or raised intra-abdominal pressure (e.g pregnancy, ascites).
Upon examination of the anal canal (with the patient in the lithotomy position), the haemorrhoids are typically located at the_____ o’clock positions.
3, 7 and 11
upper part of the anal canal is sensitive to
stretch
lower part of the anal canal is sensitive to
pain
temp
touch
pressure
painless protrusions of the anal canal covered by mucosa
contain dilated veins of the internal rectal venous plexus
internal hemorrhoids
painful enlargements covered by the skin that contain dilated veins of the external rectal venous plexus
external hemorrhoids
results from the failure of peristalsis in the aganglionic segment
hirschsprung disease/ congenital megacolon
ileal diverticulum
meckel diverticulum
persistence of remnant vitelline duct forming an outpouching located on antemesenteric border of ileum
meckel diverticulum
pain from foregut is perceived in
epigastric region
pain from midgut is perceived in
periumbilical
pain from hindgut is perceived in
hypogastric region
Rule of nerve supply
Foregut
P: Vagus
S: lower thoracic splanchnic nerves T5-T9
Rule of nerve supply
Midgut
P: Vagus n.
S: lower thoracic splanchnic nerves T5-T12
Rule of nerve supply
Hindgut
P: pelvic splanchnic nerves S2-S4
S: lower thoracic and lumbar splanchnic nerves T11-L2
preaortic lymphatics referred to as
celiac
superior mesenteric
inferior mesenteric LN
lymphatics below the pectinate line (perineum, genitalia, anal canal)
superficial inguinal LN
lymphatics of the anal canal above the pectinate line, bladder, uterus, vagina, prostate
internal iliac LN
is a disorder affecting either the lumbar or sacral plexus of nerves. They are rare syndromes, caused by damage to the nerve bundles.
lumbosacral plexopathy
main causes of lumbosacral plexopathy
diabetic amyotrophy (aka lumbosacral radioplexus neurophagy)
Idiopathic plexopathy -lumbosacral equivalent of Parsonage-Turner syndrome (which affects the brachial plexus).
tumors and other local invasions
tx for DM cause of lumbosacral plexopathy
high dose corticosteroids
