Abdomen 3 - Large Intestine, Rectum & Anal Canal Flashcards
what are the 4 parts of the colon?
ascending (on right side)
transverse
descending
sigmoid
what is the primary function of the large intestine?
mainly absorbs water and electrolytes
what is the taenia coli? where do they extend from exactly?
three longitudinal muscle bands - extend from the base of the appendix to the rectosigmoid junction
what type of muscle is the taenia coli?
longitudinal muscle
what happens to the taenia coli past the rectosigmoid junction?
spread out & form a continuous muscle later
what are haustra?
pouches/saccules of the colon (give it a segmented appearance) separated by semilunar folds
what separates individual haustra?
semilunar folds - don’t fully encircle colon’s lumen
what are omental appendices?
small fatty projections from the colon’s surface
what feature gives the colon its segmented appearance?
haustra
what separates the pouches of the colon?
semilunar folds
what are the fatty projections off the colon’s surface?
omental appendices
do semilunar folds go all the way around the colon’s lumen?
no - they separate the haustra but don’t form a continuous ring
muscle layers of the colon?
inner circular muscle
outer longitudinal muscle - forms the taenia coli
where does the taenia coli extend from?
from the base of the appendix to the rectosigmoid junction - forms a continuous muscle layer past the rectum
what is the first part of the large intestine?
cecum
where is the cecum located regionally?
in the lower right quadrant - within the iliac fossa
what is the peritoneal status of the cecum?
intraperitoneal (but lacks a a mesentery; it’s closely related to the posterior abdominal wall)
function of the ileocecal valve?
acts as a passive valve to prevent backflow of colonic contents
is the ileocecal valve an anatomical sphincter?
no - has minimal circular muscle, just passively prevents backflow of colonic contents
what is the primary function of the cecum in humans?
water absorption
where does the appendix originate from?
extends as a blind-ended diverticulum from the cecum - inferior to the ileocecal junction
what anatomical structure helps locate the base of the appendix?
McBurney’s point
- located 1/3 of the way along a line from the anterior superior iliac spine (ASIS) to the umbilicus
what is the most common position of the appendix?
retrocecal (position highly variable)
what is the significance of the taenia coli in relation to the appendix?
taenia coli converge at the base of the appendix - forms a continuous outer longitudinal muscle layer
what are the two main functions of the appendix?
immunological role - contains mucosa-associated lymphoid tissue
reservoir for gut flora - helps restore beneficial bacteria after infections
what is appendicitis?
inflammation of the appendix
what are the two main causes of appendicitis?
- lymphoid hyperplasia - often following infections
- fecalith/ hardened stool - blocks lumen, leads to fluid build-up and distension
why does pain in appendicitis start as vague and then become well-localized?
initial pain is visceral pain referred to the T10 dermatome (periumbilical region)
as inflammation spreads to the parietal peritoneum it becomes sharp & localised at McBurney’s point
visceral peritoneum has autonomic innervation; parietal peritoneum has somatic innervation - explains transition between general colicky pain to well-defined sharp pain
key diagnostic sign of appendicitis?
transition from poorly localized, colicky pain to sharp, well-defined pain in the right lower quadrant (McBurney’s point)
why is a ruptured appendix dangerous?
can lead to peritonitis - release of bacteria/faeces into peritoneal cavity, causing infection
what is the common surgical approach to removing the appendix?
appendectomy - incision at McBurney’s point
where is McBurney’s point? what is it used for?
located 1/3 of the way along a line from the anterior superior iliac spine (ASIS) to the umbilicus
used to locate the position of the appendix
what is the mesoappendix?
portion of mesentery connecting the appendix to the posterior abdominal wall & (terminal) ileum
mainly connects appendix & post. ab walk; small slip of it connects it to ileum
what does the mesoappendix connect?
mainly connects appendix to the posterior abdominal wall
small slip of it connects appendix to terminal ileum
peritoneal relationship of the ascending colon?
secondary retroperitoneal
what structure of the ascending colon forms a potential space lateral to it?
right paracolic gutter
what is the clinical significance of the right paracolic gutter?
potential space lateral to the ascending colon
allows for fluid movement between the liver and pelvis - important in infection spread
where does the ascending colon extend between?
ileocolic junction to hepatic (right colic) flexure
what happens to the ascending colon at the hepatic flexure?
turns 90° to the left - goes below liver & under gallbladder fundus
once the colon turns at the hepatic flexure, what is its relationship relative to the liver & galbladder?
below liver (inferior)
under gallbladder fundus (posterior)
what is the longest part of the colon?
transverse colon - approx. 50cm
what is the most mobile part of the colon? why?
transverse colon
intraperitoneal organ - has a mesenteric connection via the greater omentum/ gastrocolic ligament connecting it to the stomach AND it blends with the transverse mesocolon
peritoneal classification of the transverse colon?
intraperitoneal - suspended by transverse mesocolon
where is the midgut-hindgut boundary in the transverse colon?
2/3 of the way along the transverse colon (or at the splenic flexure) - no clear anatomical landmark
what is the transverse mesocolon?
double layer of peritoneum - suspends the transverse colon to the posterior abdominal wall
what surgical significance does the transverse mesocolon have?
provides access to the omental bursa (lesser sac) via two surgical routes
how does the transverse mesocolon affect abdominal compartmentalization?
separates the greater sac into the supracolic and infracolic compartments
how is the transverse mesocolon connected to the greater omentum?
its anterior layer merges with the posterior layer of the greater omentum
where does the descending colon extend between?
from the splenic flexure to the sigmoid colon
what is the peritoneal classification of the descending colon?
secondary retroperitoneal - fused with the posterior abdominal wall during gut rotation
what paracolic gutter is closely related to the deacending colon?
left paracolic gutter
what is the function of the left paracolic gutter?
allows for fluid movement between the pelvis and upper abdomen
how does infection spread differently via the left vs. right paracolic gutter?
right paracolic gutter provides a direct path between the pelvis and liver for infection spread
left paracolic gutter doesn’t - BUT infections can still spread from the lesser omentum → omental foramen → subhepatic space → right paracolic gutter → pelvis
what is the peritoneal classification of the sigmoid colon?
intraperitoneal - suspended by the sigmoid mesocolon
where does the root of the sigmoid mesocolon extend from and to?
from the left iliac fossa to S3
why is the sigmoid colon prone to volvulus?
has the longest mesentery in the large intestine - more mobile & more prone to twisting/volvulus
which colonic mesentery is more prone to volvulus?
sigmoid colon
what is the main function of the sigmoid colon?
final water absorption (even though most of the water has already been absorbed)
what is the state of stool by the time it reaches the sigmoid colon?
more solid - most of the water has been absorbed
where in the colon is diverticulosis most likely to occur? why?
sigmoid colon
has highest pressure build-up & weak areas where blood vessels penetrate between the taenia coli
what are the main causes of diverticulosis?
ageing
low fibre diet
increased intraluminal pressure - e.g. chronic constipation, straining
weak points int he bowel wall
which region of the colon has the most weak points in the bowel wall? what does this mean, clinically?
sigmoid colon - has the weakest areas with only one muscle layer between taenia coli where blood vessels penetrate
more prone to diverticulosis & diverticulitis
exactly where along the sigmoid colon are diverticula more likely to form?
in the gaps between taenia coli - weakest areas; only one muscle layer there
what is diverticulosis?
formation of small outpouchings (diverticula) in the mucosa and submucosa through weak spots in the muscle layer
what is diverticulitis?
infection & inflammation of diverticula
in what abdominal region would you expect pain with divertculitis?
left lower quadrant
symptoms of diverticulitis?
left lower quadrant pain
fever
blood in faeces
in what abdominal region would you expect diverticulitis pain?
left lower quadrant
which medication class increases the risk of diverticulitis and why?
opioids - they slow bowel motility, increasing constipation and pressure build-up
which one of these ISN’T a symptom of diverticulitis?
A: left lower quadrant pain
B: left kidney pain
C: fever
D: blood in stool
B: left kidney pain
what is volvulus?
twisting of a mobile part of the intestine - leads to lumen obstruction and ischemia
what happens as a consequence of when an intestinal loop twists around itself?
bowel obstruction & no passage of faeces
ischaemia - vessel compression with twisting
which locations of the intestine are more prone to volvulus? why?
sigmoid colon
ileum & jejunum loops
- have long mesenteries
if volvulus doesn’t resolve spontaneously, what complications can arise?
severe constipation
ischaemia
necrosis
treatment for persistent volvulus?
potential surgery
at what vertebral level does the rectum begin?
S3 - at rectosigmoid junction
what are the peritoneal relations of the three 1/3s of the rectum?
upper 1/3 = intraperitoneal
middle 1/3 = retroperitoneal
lower 1/3 = subperitoneal
peritoneal classification of the middle 1/3 of the rectum?
retroperitoneal
peritoneal classification of the lower 1/3 of the rectum?
subperitoneal
peritoneal classification of the upper 1/3 of the rectum?
intraperitoneal
what happens to the taenia coli at the rectosigmoid junction?
merge into a continuous longitudinal muscle layer (no longer three separate bands)
what is the anorectal flexure?
an 80-degree posterior bend where the rectum perforates the pelvic diaphragm
what is the landmark at which the rectum perforates the pelvic diaphragm? why is this important?
anorectal flexure - the 80 degree bend helps maintain continence
how does the anorectal flexure change during defecation?
straightens to allow stool to pass more easily
where is the lowest point of the peritoneal cavity in MALES?
rectovesical pouch - between rectum & bladder
where is the lowest point of the peritoneal cavity in FEMALES?
rectouterine pouch - between rectum & uterus
why is the rectouterine pouch clinically significant?
fluid collects here in certain clinical conditions - ascites, peritonitis, ruptured ectopic pregnancy
fluid can be collected to test for these conditions (infection/ ruptured ectopic pregnancy)
how can fluid be collected from the rectouterine pouch?
needle inserted through the posterior fornix of the vagina
