Midgut and Hindgut Flashcards
Describe midgut generally
Starts in 2nd portion duo
Part of gi tract forming ost of intestines
What supplies midgut
Superior mesenteric a = 2nd unpaired branch aorta
Describe content midgut
Duo - distal 1/2
Jejunum
Ileum
Cecum and appendix
Ascending colon
Transverse colon - prox 2/3
Describe hind gut Gen
Distal portion gi
Shortest portion
What supplies hindgut
Inferior mesenteric a
Describe contents hindgut
Transverse colon = distal 1/3
Descending colon
Sigmoid colon
Recto
Anal canal (upper part)
Describe transition to midgut
In 2nd portion duo = blood supply changes
Describe transition from duo to jejunum
Duodenal flexure
Si = intra
Describe arterial supply duodenum - anastomoses
Superior pancreaticoduodenal (gastroduodenal - common hepatic - celiac trunk) and inferior pancreaticoduodenal (sma) arteries anatomose
Describe jejunum
2nd portion si
Makes proximal 2/5 si
Specialized in nutrient absorption
What is location of jejunum
From duo at duodenojejunal flexure
(Made by suspensory muscle/lig of duo = treitz)
To ileum
Is there a clear anatomical distinction between duo and jejunum
No
What is treitz
Extension so do not regurgitate in mouth, Smooth muscle fibers to help contract
What is purpose of suspensory ligament of jejunum
Jejunum heavy
When Breathe in = increased pressure produced by diaphragm, contract les and pull on treitz = reduce this increased pressure
What is found in jejunum - folds
Plicae circulares = numerous circular folds in its lumen
Increased surface area for absorption
Rugged wall, 1st portion received a much richer bolus
Describe arterial supply distribution jejunum
Less prominent arterial arcades
Long vasa recta (straight arteries)
Compare jejunum and ileum - muscle
Ileum = Less plicae, more smooth, peyers patches
Describe ileum
Final section si
Makes distal 3/5 of si
Longer than jejunum
Describe location of ileum
From jejunum (suspended in mesentery) to ileocecal junction - forms sphincter like end
Describe anatomical distinction of ileum
Contains lymphoid nodules = peyers patches
Plicae circulares = low and sparse
Denser arterial arcades and shorter vasa recta
Compare arterial supplies of jejunum and ileum
Jejnum = long vasa recta, proximal
Ileum = short vasa recta, many of arterial arcades, distal, I LOVE ARCADE FIRE
Describe mesentery of si
Ileum and Jejunum suspended in mesentery = peritoneal fold that carries blood vessels, lymphatics and nerve fibers
Link post abd wall to organ
Describe arterial supply midgut - Gen
From sma
Gives jejunal and ileal arteries
Ends in arterial arcades and vasa recta
What is root of mesentery
Entry/exit vasculature
Describe large intestine
1.5m long and large diameter
Extends from cecum to anal canal
Converters liquid feces to semi solid state
Absorbs water, salt and electrolytes
Describe parts of li
Cecum, appendix, colon (ascending, transverse, descending, sigmoid), rectum, anal canal
Transition to hind gut = in transverse colon
Describe flexures of li
Right colic flexure - hepatic
Left colic flexure - splenic
(Hits organ and changes direction)
Describe Taenia coli of li
Longitudinal band Smooth muscle fibers - helps contract - peristalsis
3 of them = ribbon smooth muscle, organized each side li, converge onto appendix
When contract = makes colon fold on itself
Describe omental appendices of li
Peritoneal covered fat lobules
NOT ON RECTUM
Fat storage?
Depends on bmi
Describe haustra of colon
Pouches like sacculations
Give Segmented appearance to colon
Due to contractions of Tenia coli
Describe cecum
1st part li
Inf to ileocecal opening
Removes water and salts, secreted mucus to lube stool
Describe location of cecum
Right iliac fossa
Is cecum retro
NOOOOOOOOOOOOOO
INTRA
But not suspended in mesentery
Tenia coli = from appendix up
Continuous with ascending colon
Describe appendix
Mobile
Narrow, hollow, blind ended tube connected to cecum
Contains large aggregation of lymphoid tissue
Location highly variable = retrocecal or subcecal
Describe Clinical- mcburney’s point
1/3 of from Asis to umbilicus
Tenderness at this point = acute appendicitis
Surgery needed, if burst = infection would spread in abd region, not contained, could lead to peritonitis
Describe iliocecal opening
Passage of si to li, sphincter= ileocecal
Gastrointestinal reflex = activates peristalsis
Describe ascending colon
Behind liver
Describe location of ascending colon
From cecum to hepatic flexure
Under right lobe of liver
Is ascending colon retro
YES
Creates paracolic gutters
Describe paracolic gutters - ascending colon
Folding of peritoneum forms paracolic gutters
Between colon and posterolateral abdominal wall
Allows passage and accumulation of fluids from diff abd regions
If infection = would accumulate here
*serous fluid, peritoneum
Describe transverse colon
Longest and move movable part of colon
Jump form right side to other
Intra, fixed where spleen is and where liver is but then suspended by mesentery
Is transverse colon in midgut or hindgut
Marks transition between 2
Describe location of transverse colon
Crosses abdomen from hepatic flexure to splenic Flexure
Is transverse colon Intra or retro
INTRA
Completely invested by peritoneum
Connected to post abd wall (over pancreas) by transverse mesocolon
Ant layer of mesocolon adherent to post layer of greater omentum
Describe midgut blood supply - Gen
Branches named by region they supply
Series of branches along sma
Describe midgut blood supply - branches
Jejunal arteries
Ileal arteries
Ileocolic artery (terminal branch sma) = ileocecal junction
Right colic artery = ascending colon
Middle colic artery = midgut section of transverse colon
Describe marginal artery - midgut blood supply
runs along mesenteric border of large intestine: Connects iliocolic, right, middle from SMA & left colic from inferior mesenteric artery (IMA)
Where is descending colon
From splenic flexure to sigmoid colon
Attached to diaphgram through phrenicocolic ligament
What is splenic flexure - descending colon
More acute bend, higher and more posterior than hepatic flexure
Is descending colon Intra
NO retro
Folding of peritoneum forms paracolic gutters
Between colon and posterolateral abdominal wall
Describe clinical case - right and left paracolic gutters
Possible to mobilize colon by cutting peritoneum along peritoneal reflection - white line of toldt
Cut and move it over, so can get to abd aorta first
Describe sigmoid colon
S shaped portion colon
Last portion
When hits iliac bone on left
Describe sigmoid colon Location
Crosses iliac fossa to join rectum in pelvis
Describe sigmoid colon - INTRA OR RETRO
INTRAAAAA
Suspended in sigmoid mesocolon
Quite mobile since suspended in mesocolon
Contains inferior mesenteric vessels
DESCRIBE RECTUM
12 cm long
NO TENIA coli, just smooth muscle
Accumulates feces, not much absorption
Describe rectum location
From sigmoid colon at rectosigmoid junction (level s3) to anal canal as it passed through pelvic floor (ends at anorectal ring)
Describe rectum - Dilations/diameter
First portion is extension of sigmoid colon = same diameter
Rectal ampulla = dilated portion near its end, stores feces before release via anal canal
Is sigmoid colon retro or intra
RETRO - needs to be stable, accumulates Weight
Describe anal canal
2.5-4cm long
Terminal part li
Differentiated from rectum by transition of its internal surface = from endodermal to skin like ectodermal
Where is location anal canal
Below pelvic diaphragm
From anorectal junction (more constricted here) to anus (external opening of rectum)
Surrounded by inner involuntary and outer
voluntary sphincters
Describe clinical - cancers, hemorrhoids
Internal hemorrhoids = no sensory info (simple columnar epi)
External hemorrhoids = can feel (stratified squamous epi)
Cancers will be diff if on inside or outside
Describe hind gut blood supply - Gen
Branches named according to region
All from inferior mesenteric artery
Describe branches of Hindgut blood supply
Left colic = descending colon
Sigmoid arteries = sigmoid colon (in sigmoid mesocolon)
Superior rectal artery = terminal branch for superior rectum
Describe marginal artery - hind gut
runs along mesenteric border of large intestine: Connects iliocolic, right, middle from SMA & left colic from inferior mesenteric artery (IMA)
Describe what blood supply is to rectum
Superior rectal (inf mesenteric artery)
Middle rectal (internal iliac artery)
Inferior rectal (internal pudenal artery)
