Anatomy: Midgut Flashcards
location of the small intestine
gastrointestinal tract
extends from pylorus to ileocaecal junction to the large intestine at the ileocaecal valve
3 parts of the small intestine
duodenum
jejunum
ileum
general overview duodenum
most proximal portion
derived from duodenum digitorum= twelve fingers length
runs from pylorus to the duodenojejunal junction
what are the 4 parts of the duodenum
D1= superior
D2=descending
D3=inferior
D4=ascending
superior D1
first section, spinal level L1
known as the cap
ascends upwards from pylorus of the stomach
connected to liver by the hepatoduodenal ligament
most common site for duodenal ulceration
3cm covered anteriorly and posteriorly by visceral peritoneum and remainder is retroperitoneal
descending D2
L1-L3
curves inferiorly around head of the pancreas
lies posteriorly to the transverse colon and anterior to the right kidney
internally marked by the major duodenal papilla
what is the major duodenal papilla
opening at which bile and pancreatic secretions enter from the ampulla of Vater (hepatopancreatic ampulla)
Inferior D3
L3
travels laterally to the left
crosses over the inferior vena cava and aorta
located inferiorly to the pancreas
posteriorly to the superior mesenteric artery and vein
Ascending
L3-L2
after duodenum crosses aorta it ascends and curves anteriorly to join the jejunum at the duodenojejunal flexure
duodenojejunal flexure
located here is a muscle called the suspensory muscle of the duodenum
contraction of the muscle widens the angle of the flexure
aids movement of the intestinal contents into the jejunum
duodenal ulcers
most likely to occur in the superior portion
common causes are helicobacter pylori infection and chronic NSAID therapy
perforation may be complicated by:
-inflammation of the peritoneum (peritonitis): damages surrounding viscera
-erosion of the gasproduodenal artery: causes haemorrhage and potential hypovolaemia shock
contrasting the jejunum and the ileum to the duodenum
they’re intraperitoneal
what attaches the jejunum and ileum to the posterior abdominal wall
mesentery
jejunum
begins are the duodenojejunal flexure
ileum ends at ileocaecal junction
what occurs at the ileocaecal junction
the ileum invaginate into the cecum to form the ileocecal valve
can prevent reflux of material back into the ileum
characteristic features of the jejunum
located in the upper left quadrant
thick intestinal wall
longer vasa recta (straight arteries)
less arcades (arterial loops)
red in colour
characteristic features of the ileum
located in the lower right quadrant
thin intestinal wall
shorter vasa recta
more arcades
pink colour
arterial supply of the duodenum
proximal to the major duodenal papilla: supplied by the gastroduodenal artery
distal to the major duodenal papilla: supplied by the inferior pancreaticoduodenal artery
marks the change form foregut to midgut
veins of duodenum follow major arteries and drain into hepatic portal vein
lymphatic drainage of the duodenum
pancreatoduodenal
superior mesenteric nodes
arterial and venous supply of jejunum and ileum
from the superior mesenteric artery
venous drainage is from the superior mesenteric vein
lymphatic drainage of the jejunum and ileum
superior mesenteric nodes
where is the cecum located
most proximal part of the large intestine
located between the ileum and ascending colon
when can the cecum be palpated
if enlarged due to faeces, inflammation or malignancy
structure of the cecum
continuous with the ascending colon
is intraperitoneal
has a variable mesentery
ileocecal valve function
prevents reflux of large bowel contents into the ileum during peristalsis
thought to function passively rather than a defined muscular sphincter
cecum arterial supply
ileocolic artery- branch of the superior mesenteric
divides into anterior and posterior cecal arteries
cecum venous supply
ileocolic vein
then empties into the superior mesenteric plexus
lymphatic drainage of the cecum
drains into the ileocolic lymph nodes
what is the appendix
narrow blind-ended tube
attached to the posteromedial end of the cecum
large amount of lymphoid tissue
no vital functions
what is the appendix supported by
the mesoappendix
fold of mesentery which suspends the appendix from the terminal ileum
position of the free end of the appendix is highly variable and categorised into 7 main locations depending on relationship to the ileum, caecum or pelvis
what is the most common position of the appendix
retrocecal
positions of the appendix
pre-ileac
post-ileac
sub-ileal
pelvic
subecal
paracecal
retrocecal
pre-ileal
anterior to the terminal ileum
1 or 2 o clock
post-ileal
posterior to the terminal ileum
1 or 2 o clock
sub-ileal
parallel with the terminal ileum
3 o clock
pelvic
descending over the pelvic brim
5 o clock
subcecal
below the cecum
6 o clock
paracecal
alongside the lateral border of the cecum
10 o clock
retrocecal
behind the cecum
11 o clock
arterial supply to the appendix
from the appendicular artery
venous drainage of the appendix
via the corresponding appendicular vein
where are the arteries and veins associated with the appendix located
in the mesoappendix
innveration of the appendix
ileocolic branch of the superior mesenteric plexus
colon general information
distal part of the gastrointestinal tract
extends from the cecum to the anal canal
receives digested food from the small intestine, absorbs water and electrolytes to form faces
4 parts of the large intestine
ascending
transverse
descending
sigmoid
ascending colon
retroperitoneal
ascends superiorly from the cecum
meets right lobe of the liver to form the colic/hepatic flexure
transverse colon
extends from the right colic flexure to the spleen
turns inferiorly to form the left colic/splenic flexure
attached to the diaphragm by the phrenicocolic ligament
intraperitoneal and enclosed by transverse mesocolon
descending colon
after left colic flexure moves inferiorly towards the pelvis
retroperitoneal in most individuals
located anteriorly to the left kidney
passes over its lateral border
turns medially and becomes sigmoid
sigmoid
40cm long
left lower quadrant
left iliac fossa to level of S3 vertebrae
attached to posterior pelvic wall by mesentery: sigmoid mesocolon
mobile due to length of the mesentery
parabolic gutters
two spaces between the ascending/descending colon and the posterolateral abdominal wall
anatomical structure of the large intestine
attached to the surface of the large intestine are omental appendices
runs longitudinally along surface of the large bowel are 3 strips of muscle teniae coli
teniae coli contract to shorten the wall of the bowel, produces sacculations called haustra
wider diameter Than the small intestine
features cease at the rebtosigmoid junction
what are omental appendices
small pouches of peritoneum, filled with fat
rectosigmoid junction
where the smooth muscle of the teniae coli broken to form a complete layer within the rectum
teniae coli
mesocolic
free
omental coli
structures anterior and posterior to the ascending colon
anterior: small intestine, greater momentum, anterior abdominal wall
posterior: iliacus and quadrates lumborum, right kidney, iliohypogastric and ilioinguinal nerves
transverse colon structures anterior and posterior
anterior: greater omentum, anterior abdominal wall
posterior: duodenum, head of pancreas, jejunum and ileum
descending colon structures anterior and posterior
anterior: small intestine, greater omentum, anterior abdominal wall
posterior: iliacus and quadratus lumborum, left kidney, iliohypogastric and ilioinguinal nerves
sigmoid colon structures anterior and posterior
anterior: urinary bladder, uterus and upper vagina
posterior: rectum,sacrum,ileum
general rule midgut arterial supply
supplied by the superior mesenteric artery
general rule hiindgut arterial supply
by the inferior mesenteric artery
ascending colon arterial supply
from ileocolic and right colic arteries
ileocolic arises the anterior cecal, posterior cecal and colic branches which also supply
transverse colon arterial supply
right colic artery, from superior mesenteric
middle colic artery, from superior mesenteric
left colic artery, from inferior mesenteric
descending colon arterial supply q
left colic artery
sigmoid colon arterial supply
sigmoid arteries
venous drainage of the ascending colon
ileocolic and right colic veins
empty into the superior mesenteric
venous drainage of the transverse colon
middle colic vein
empties into the superior mesenteric
venous drainage of the descending colon
left colic vein
drains into the inferior mesenteric
venous drainage of the sigmoid colon
drained by the sigmoid veins into the inferior mesenteric
where do the superior and inferior mesenteric veins empty into
the hepatic portal vein
innervation of the midgut-derived structures
ascending colon and proximal 2/3 of the transverse
receive their sympathetic, parasympathetic and sensory supply via nerves from the superior mesenteric plexus
innervation of the hangout-dervied structures
distal 1/3 of the transverse colon, descending colon and sigmoid colon
receive from the inferior mesenteric plexus
parasympathetic: pelvic splanchnic nerves
sympathetic: lumbar splanchnic
functions of the mesentery in the abdomen
suspends the small and large intestine from the posterior abdominal wall, allows slight movement
provides a conduit for blood vessels, nerves and lymphatic vessels
postulated to play a pathological role in inflammatory disease such as crohns
how is the mesentery formed
double layered fold of peritoneum
root of the mesentery
point where the mesentery attaches to the posterior abdominal wall
bare area
root is long and narrow and has an oblique orientation
left side of the L2 vertebra to the right sacroiliac junction
6 flexures in the gastrointestinal tract
duodenaljejunal
ileocaecal
hepatic
splenic
those between descending and sigmoid colon
and between the sigmoid and the rectum
mesentery of the small intestine
connects the loops of jejunum and ileum to the posterior abdominal wall and is a mobile structure
right mesocolon
flattened against the posterior abdominal wall
transverse mesocolon
mobile structure and leis between colic flexures
left mesocolon
flattened against the posterior abdominal wall
mesosigmoid
has a medial portion which is flattened against the posterior abdominal wall
region of mesentery associated with the colon itself is mobile
mesorectum
assits in anchoring the rectum through the pelvis
arterial supply to the mesentery
superior mesenteric to the organs of the midgut
inferior mesenteric to the hingut
venous drainage of the mesentery
via the superior mesenertic vein
and inferior mesenteric vein
innervation of the mesentery
superior mesenteric plexus
divides into many secondary plexuses containing parasympathetic and sympathetic innervation to mesentery
lymphatics of the mesentery
inferior mesenteric lymph nodes receive lymph from hindgut organs and drain to the superior mesenteric
superior mesenteric receive lymph from midgut and inferior mesenteric and drain to pre-aortic
superior mesenteric artery
arises from the abdominal aorta
supplies arterial blood to the organs of the midgut
level L1 vertebrae
immediately inferior to the origin of the coeliac trunk
anatomical position of the superior mesenteric artery
anterior to the SMA- pyloric part of the stomach, splenic vein and neck of the pancreas
posterior to the SMA- left renal vein, uncinate process of the pancreas and inferior part of the duodenum
uncinate process
only part of the pancreas that hooks around the back of the SMA
major branches of the superior mesenteric artery
inferior pancreaticduodenal artery
jejunal and ileac arteries
middle and right colic arteries
ileocolic artery
inferior pancreaticoduodenal artery
first branch of the SMA
forms anterior and posterior vessels
anastomose with branches of the superior pancreaticdudenal artery
supplies inferior region of the head of the pancreas, uncinate process and duodenum
jejunal and ileac arteries
pass between layers of the mesentery
form anastamotic arcades which form smaller straight arteries: vasa recta arise to supply the organs
middle colic artery
supplies the transverse colon
right colic artery
supplies the ascending colon
