Abdomen 4 Flashcards
what forms the large intestine
- caecum
- ascending colon
- transverse colon
- descending colon
- sigmoid colon
blood supply to GIT?
foregut - coeliac trunk T12
midgut - SMA L1
hindgut - IMA L3
Explain the development of midgut
Because the intestines are so long, they herniate out through the abdominal wall into the umbilical cord, twist around the superior mesenteric artery and enter back
What is the term given when the gut contents is protruding from the umbilical ring in a baby? why?
Omphalocele
Usually because rectus abdominis fails to develop properly
Malrotation of the midut
50% due to chromosomal abnormality
If surgical repair is possible, positive prognosis
What is the term given to outpouching of the ileum in babies?
What is the cause of this?
Meckel’s diverticulum
Vitelline duct connects the growing foetus to the yolk sac
The vitelline duct fails to degenerate resulting it in attaching to the ileum leading to the outpouching
Ulceration or bleeding caused
What part of the GIT does the vitelline duct attach to?
ileum
where are the main sites for absorption?
jejunem (mostly) and illeum - 95%
What is the start and end of the jejunum and ileum?
In which quadrant can we find the jejunum and ileum
Duodenojejunal flexure to ileocaecal junction
Jejunum = LLQ
Ileum = RLQ
What is the mesentery?
What does it contain?
Suspends the jejunum and ileum (both intrapeitineal) from the posterior abdominal wall
Contains
Superior mesentaric artery (L1 from abdominal aorta)
Superior mesenteric vein (joins with splenic to form portal)
Lymph nodes, fat and autonomic nerves)
What is the route of the mesentery?
mesentry is attached to posterior abdo wall via roots - oblique course
- Duodenojejunal flexure to sacro-iliac joint
what does the IMV join with?
IMV –> splenic vein –> portal vein to be processed by liver
jejunum and ileum structure differences:
- lumen
- wall
- vasa recta, blood supply
- peyer’s patches: aggregation of lymphatic tissue
- mesentery
What does the large intestine extend from?
What is its main function?
Ileocaecal junction to anus
Water and salt absorption
Label the parts of the colon/ large intestine on the X-ray
where does cecum reside?
next to right illiac fossa, before becoming the ascending colon
where are the Paracolic gutters and clin rel
Lateral to ascending and descending colons - fills up if burst appendix
what is the ileal orifice?
ileocecal valve - entrance to cecum from ileum
where half digested food enters the colon (cecum)
What are features of the colon which help us identify it to the small intestine?
Contains
Haustra - sacculations
Teniae coli - 3 longitudinal bands of muscle
Omental appendices - fat pouches
HOT
Label the diagram of the colon
Where in the colon do we find the boundary between the midgut and hindgut?
Midgut and hindgut is split in the 2/3 transverse colon
what vessel provides the caecum?
ileocolic artery –> branch of SMA
What junction is found in the caecum?
What supplies the caecum?
Where does this artery come from?
Ileocaecal junction
Ileocolic artery which is a branch of the superior mesenteric artery
What is the relationship of the appendix to the peritoneum?
How can its position vary?
Appendix is intraperitoneal = contains mesoappendix
position varies:
What is the relationship of the opening of the appendix to the ileocaecal opening
The orifice of the appendix is inferior to the ileocaecal opening
What artery is appendix supplied by?
Supplied by appendicular artery = branch of ileocolic artery
Vermiform appendix = mesoappendix?
what is the mesoappendix and what does it contain
If it is intraperitoneal it is called the mesoappendix (the mesentery)
appendix intraperitoneal so its mesentry is called mesoappendix
- contains blood vessels such as appendicular artery
What is appendicitis?
Inflammation of appendix stretching visceral peritoneum.
Faeces slip down the caecum (iappendix) and inflame the appendix
Where is pain from appendicitis felt?
- Pain is referred to peri-umbilical region (T10) - innervation from lesser splanchnic nerve
- Later pain in right lower quadrant: irritant of parietal peritoneum lining posterior abdominal wall.
What is McBurney’s point?
1/3 from the ASIS and umbilicus (where appendix leaves the cecum)
Demarcates position of appendix and pain
What is the relationship of the ascending colon to the peritoneum?
Ascending colon is secondary retroperitoneal
-During development, the ascending colon was covered in visceral peritoneum, but it migrates backwards to reside along the posterior abdominal wall
-In 75% of people, this occurs fully
-In some people it will still often have mesentery
Which gutter is located at the ascending colon? What is its clinical significance?
Right paracolic gutter is located here = fluid can track and build up in subhepatic and hepatorenal recess
What marcates the termination of the ascending colon?
The right hepatic (colic) flexure
What is the blood supply to the ascending colon?
Which artery supplies the transverse colon?
Where does this branch from?
superior mesenteric artery,
right colic
middle colic - running in the transverse mesocolon going to supply the transverse colon
Where does the transverse colon start and terminate?
What is its relationship to the peritoneum?
Starts at right hepatic (colic) flexure and ends at the splenic flexure
Intraperitoneal = contains transverse mesocolon
Level of L1
at what point does the transverse colon switch from midgut to hindgut?
and so Give the difference in arterial, ParaSym and Sym supply at the boundary of the midgut and hindgut
2/3rds distally
- Arterial supply: Superior mesenteric artery to inferior mesenteric artery
- Parasympathetic innervation: Vagus nerve (CNX) to pelvic splanchnic nerve (S2 – S4)
- Sympathetic innervation: Lesser splanchnic nerve to lumbar splanchnic nerve
Which colic region gains access to lesser sac?
Note how the greater omentum and transverse colon have fused
Supracolic region is everything above the transverse mesocolon
what is above and below the transverse mesocolon (abdominal compartments)
above = superacolic
below = inferocolic
what is above and below the transverse mesocolon (abdominal compartments)
above = superacolic
below = inferocolic
What vessel does the SMV unite with to form the hepatic portal vein
Splenic vein
What is important about the marginal artery of drummond?
Anastomosis between SMA and IMA
Collateral supply to colon if there is a blockage
Where does the descending colon end?
What is its relationship to the peritoneum?
What gutter is present lateral to descending colon?
Splenic flexure to sigmoid colon
Secondary retroperitoneal (but 33% still have mesentary)
Left paracolic gutter located laterally
What is the relationship of the sigmoid colon to the peritoneum?
What is the root of the sigmoid mesocolon (begin and end)
Intraperitoneal = contains sigmoid mesocolon
From left iliac fossa to level of S3
Where can we find the rectosigmoid junction? (sigmoid mesocolon)
s3
What is diverticulosis?
Often found in sigmoid colon due to weaker muscle here
What is diverticulitis?
(most common in sigmoid colon)
Outpouching of colonic mucosa and submucosa through weakness of muscle layers
inflammation of the outpouches (in diverticulosis)
label what u can:
what are transverse rectal folds
what is rectal ampulla
what is anorectal flexure
thickening of circular muscle layers
dilated lower portion - important for continence
as the gut perforates - the levator ani muscle to become continuous with the anus
Which muscle does the gut perforate to become continuous with the anus?
Levator ani this will form the pelvic diaphragm
It is a collection of three muscles: Puborectalis, pubococcygeus and ileococcygeus
Rectum and continence control
-Rectum pierces levator ani muscle; forms part of the pelvic diaphragm (also important for continence)
-Sharp bend backwards helps control continence 80 degrees
What is the importance of the pectinate line
(not to be confused with arcuate line)
Line represents the termination of the hindgut, therefore a change in the peritoneal coverings, epithelial lining, blood supply, venous drainage and innervation
-Everything above and below it has a different cell type, blood supply and lymph drainage
-Everything below the line is somatic, a lot more sensitive
-Thus hemorrhoids below this line are more painful
What is the clinical significance of the region below the pectinate line?
Innervated by somatic branches meaning it will be more sensitive e.g Haemorrhoids
How does the epithelium, artery and vein anatomy differ above the pectinate line?
Compare the internal and external anal sphincters: location, muscle type, voluntary/involuntary and innervation
label what u can
How does the epithelium, artery, and venous drainage change below the pectinate line?
How does the innervation and lymphatic drainage anatomy change below the pectinate line?
Epithelium = Stratified squamous epithelium
Arterial = Middle and inferior rectal
Venous drainage = Middle and inferior (systemic circulation!)
Innervation becomes somatic = Inferior rectal nerves
Lymphatic drainage = Superificial inguinal nodes
What are the two anal sphincters?
What is the difference between their innervation?
Internal and external
- Internal
- Smooth muscle
- Involuntary
- Pelvic splanchnic nerves (parasymp)= relaxes muscle (autonomic)
External
- Skeletal
- Voluntary
- Inferior rectal branch of pudendal nerve (somatic)
What are the branches of the inferior mesenteric artery?
(comes off abdominal aorta at L3)
Left colic
Sigmoidal
Superior rectal
(also marginal artery of drummond as connection between SMA and IMA)
What is the arterial supply of the anal canal?
Clue: Rectal arteries
Superior rectal artery (branch of IMF)
Middle rectal = (Branch of Internal iliac)
Anastamoses with Superior and inferior rectal
Inferior rectal
(Branch of internal pudendal)
which artery supply of rectum is below pectinate line?
1 sup rectal is above
2,3 middle anf inferior rectal arteries are below pectinate line
What is the venous drainage of the anal canal?
What is special about the site of the venous drainage?
Venous drainage of anal canal is a site of porto-venous anastamoses
Superior rectal vein -> Inferior mesentaric –> Hepatic portal (processed by liver)
Middle and Inferior (systemic)
Middle –> Internal iliac vein
Inferior –> Internal pudendal –> Internal iliac
What are haemorrhoids?
Why are haemorrhoids be more painful below the pectinate line?
Enlarged venous plexuses
Very painful if prolapse (bulges out anus) or occur below the pectinate line
Innervation of the anal canal changes from autonomic (inferior hypogastric plexus) to somatic (inferior rectal nerves)
What happens after the lymph has drained from the cisterna chyli into the thoracic duct?
Thoracic duct will drain into the junction of the left subclavian vein and left internal jugular vein
Note the thoracic duct will drain everything below the diaphragm and the right side of the body
How do the paraaortic and pre aortic nodes drain?
Where is pain from foregut, midgut and hindgut referred to?
Foregut T5-T9 = epigastric
Midgut T9-T10/11 = Umbilical
Hindgut (L1-L2) = Hypogastric
