Large Intestine and IBD Flashcards
What epithelial is in the large intestine?
Columnar epithelium -Colonocytes
What does the large intestine do?
Removes water from all the indigestible gut contents (proximal) - turns chyme into a semi solid
Production of certain vitamins
Microbiome - contains lots of commensal bacteria
Acts as temporary storage until defaection (distal)
Colonic mucosa does not get majority of nutrients from blood.
Short chain fatty acids derived from the fermentation of dietary fibre is where most nutrients comes from.
The by-product of this fermentation process includes CO2, methane and hydrogen gas.
Where is the large intestine in relation to the peritoneum?
Ascending and descending colon - retroperitoneal
Transverse and sigmoid colon -intraperitoneal (as it has its own mesentry)
Rectum:
Upper 1/3 - intra-peritoneal
Middle 1/3 - retroperitoneal
Lower 1/3 - no peritoneum
What is the arterial supply to the large large intestine?
Midgut component - superior mesenteric artery
Ileocolic - caecum
Right colic - ascending colon
Middle colic - transverse colon
Hindgut component - inferior mesenteric artery
Left colic - descending colon
Sigmoid - descending colon
Superior rectal artery - upper 1/3 rectum (continuation of IMA)
What is the venous drainage of the large intestine?
Portal vein - 70% of all blood from liver comes from portal vein. Portal vein formed behind neck of pancreas by unification of SMV and splenic vein.
Midgut drains into SMV.
Hindgut drains into IMV which drain into the splenic vein.
Rectum:
Upper 1/3 drains into superior rectal artery (then into IMV).
Middle and lower 1/3s drain into systemic venous system -This is the site of portosystemic anastomosis.
What is the difference between the structure of the small and large intestine?
Large intestine is much shorter and wider.
Large intestine also has crypts but not villi
The external longitudinal muscle is incomplete - Split into three bands (teniae coli). Haustra are sacculations caused by contractions of the teniae coli.
How is water absorbed in the colon?
Facilitated by ENaC
Like principle cells of the late distal convoluted tubule - induced by aldosterone.
Approx 1500mls of water enter colon each day - <100mls excreted in faeces
Most absorbed in proximal colon
Much tighter tight junctions
- Allows bigger gradient to form
- Less back diffusion of ion
What are the two IBDs?
Crohns and Ulcerative Colitis (UC)
Where is Crohn’s found?
Affects anywhere in GI tract Ileum involved in most cases Transmural Skip lesions Deep
Where is ulcerative colitis found?
Begins in rectum Can extend to involve the entire colon Continuous pattern Mucosal inflammation Superficial It is called pancolitis if it goes all the way around.
What other Symptoms can people with IBDs get?
Extra-intestinal problems
-MSK problems (up to 50%) -Arthritis
Skin (up to 30%)
-Erythema nodosum /pyoderma gangrenous / psoriasis
Liver / biliary - primary sclerosing cholangitis
Eye problems - up to 5%
What causes IBDs?
Idiopathic
Genetic - 1st degree relative increased risk -Identical twins concordance 70%.
Gut organisms (altered interaction)
Immune response
Could be triggered by:
- Antibiotics
- Infections
- Smoking
- Diet
What are the signs and symptoms of crohns?
Young people Lots of loose stools -non bloody Weight loss Right lower quadrant pain Some joint pains (Lower limbs) Smoker
Tender mass (RLQ)
Mild perianal inflammation / ulceration
Low grade fever
Mildly anaemia
What is the gross pathology of Crohn’s?
Skip lesions Hyperaemia Mucosal oedema Discrete superficial ulcers Deeper ulcers Transmural inflammation - why get fistula’s (bowel, bladder, vagina, skin) -Thickening of bowel wall -Narrowing of lumen Cobblestone appearance
What is the microscopic appearance of Crohn’s?
Granuloma formation (pathognomonic) -Organised collection of epithelioid macrophages -form when can't get rid of what is deemed as foreign.
