Large intestine and IBD Flashcards
What structures encompass the large intestine?
Caecum to anal canal
What epithelia lines the large intestine?
columnar epithelium
What is the function of the LI?
- removes water from indigestible gut contents turning the chyme into a semi sold (occurs in proximal part)
- produces vitamines
- microbiome
- distal part of LI acts as a temporary storage until defaecation
Where does colonic mucosa get the majority of its nutrients from?
not the blood
- SCAA derived from the fermentation of dietary fibre
- the by product includes CO2, methane and H2(g) which the mucosa uses
What is the LI relationship with the peritoneum?
Ascending and descending colon - retro-peritoneum
Sigmoid and transverse colon - has its own mesentery
rectum
-upper 1/3 is intra-peritoneal
-middle is retro-peritoneum
-lower 1/3 is not peritoneum
How can you get sigmoid volvulus?
- it is twisting of the gut
- the sigmoid colon has its own mesentery and can turn on itelf
Where does the SMA come off the AA?
What does the SMA supply?
L1 - just under the coeliac artery branch
-supplies the midgut component of the large bowel
What are the branches of the SMA and what do they supply?
ileo-colic - caecum
middle colic - transverse colon
right colic - ascending colon
What is the marginal artery?
summation of all the terminal branches anastomosing with each other
What supplies the foregut structures?
coeliac artery branch of the AA
Where does the IMA come off and what does it supply?
- L3
- hindgut
What are the branches of the IMA and what structures do they supply?
- left colic - descending colon
- sigmoid arterires - descending colon
- superior rectal arter - upper 1/3 of rectum
What is significant about the superior rectal artery?
-the IMA becomes this as it enters the pelvis (past the pelvic brim
Foregut venous draining?
blood drains into splenic vein and portal hepatic vein
Mid gut venous drainage?
- SMV
- meets splenic vein splenic vein and both become portal vein (occurs behind the neck of the pancreas
Hind gut venous drainage?
IMV
-meets splenic vein and goes into portal vein
rectum venous drainage?
- upper 1/3 drains into superior rectal vein (IMV)
- middle and lower 1/3 drain into systemic venous drainage (bypass liver)
What are portosystemic anastomosis?
resistance in the portal system (cirrhosis) - increased pressure on veins draining gut through liver
-portosystemic anastomosis - allow the rest of the gut to drain without going through the liver if there is portal hypertension
What can be caused if the portosystemic anastomosis become dilated?
- varices - due to increase pressure
- can cause oesophageal varices
Differences between LI and SI?
- LI shorter
- LI wider
- LI has crypts not villi
- incomplete external longitudinal muscle - teniae coli
- haustra - sacculations caused by contraction of the teniae coli
- tighter tight junctions allowing bigger gradient to form and less back flow of ions
What is the role of the colon and what is it facilitated by?
Water absorption
-faciliatated by ENAC induced by aldosterone
What is IBD?
-group of conditions by idiopathic inflammation of the GI tract than affect function of the gut
What are the 2 common type of IBD?
Chrohn’s disease
UC
What is chrohn’s disease?
- affects anywhere in the GI tract
- mostly involves the ileum
- transmural
- skip lesions
