7a.) Large Intestine/Inflammatory Bowel Disease Flashcards
Where does the large intestine extend from and to?
Caecum to anal canal
State 4 roles of the large intestine
- Removes water from all indigestible gut contents (proximal part) turning chyme into a semi-solid
- Microbiome (healthy, varied microbiome has a role in health)
- Production of vitamins (bacteria produce some vitamins e.g. vitamin k)
- Temporary storage until defaecation (distal)
Where does the colonic mucosa get majority of its nutrients from?
From short chain fatty acids derived from fermentation of dietary fibre- it DOES NOT get the majority of nutrients from blood like you would expect.
Bi-products of fermentation include: CO2, methane and H2 gas
Which parts of the large intestine generally act as temporary storage?
Transverse and descending colon
Describe whether each of the following parts of the large intestine are intra- or retroperitoneal:
- Ascending colon
- Transverse colon
- Descending colon
- Sigmoid colon
- Upper 1/3 rectum
- Middle 1/3 rectum
- Lower 1/3 rectum
- Ascending colon: retro
- Transverse colon: intra (has mesocolon as it’s mesentery)
- Descending colon: retro
- Sigmoid colon: intra
- Upper 1/3 rectum: intra
- Middle 1/3 rectum: retro
- Lower 1/3 rectum: no peritoneum
Describe the arterial supply of the midgut portion large intestine (colon)
Colon= midgut up to 2/3 transverse colon therefore branches of SMA:
- Caecum: ileo-colic
- Ascending colon: right colic
- Transverse colon: middle colic
Describe the arterial supply of the hindgut portion of the large intestine
Becomes hindgut 2/3 along transverse colon; hindgut is supplied by inferior mesenteric artery branches:
- Descending colon: left colic
- Sigmoid colon: sigmoid arteries
- Upper 1/3 rectum: superior rectal artery
What is the marginal artery?
Vessel that extends length of colon and is formed from anastomoses of the branches of IMA and SMA; it provides collateral supply to the colon
The superior rectal artery is a continuation of the IMA; true or false?
True
Describe the venous drainage of the colon
- Midgut structures drain into SMV
- Hindgut structures drain into IMV
- Upper 1/3 of rectum drains into rectal vein which drains into IMV
IMV joins the splenic vein. Splenic vein then meets SMV to become portal vein.
- Middle & lower 1/3 of rectum drains into systemic system
Compare large and small intestine in terms of:
- Length
- Width
- Crypts
- LI shoreter (6ft vs 20ft)
- LI wider (6cm vs 3cm)
- LI has crypts not villi
Describe the arrangement of the longitudinal muscle layer surrounding the large intestine
- Longitudinal muscle layer of muscularis propria is not continuous
- It is in 3 distinct bands called teniae coli
- Contraction of teniae coli cause haustra
What are epiploic appendages and where are they found?
Small puches of peritoneum filled with fat siutated along colon
Describe water absorption in the large intestine
- Water absorption facilitated by ENaC
- Na+ moves into cell
- Water follows down osmotic gradient
- Tigher tight junctions between cells to prevent ions diffusing back into lumen therefore allowing a greater concentration gradient to form
Describe how aldosterone increases water reabsorption in large intestine
- Stimulates basolateral Na+/K+ ATPase to decrease [Na+] in cell
- Increases expression of ENaC in apical membrane
- Both of above increase Na+ reabsorption which increases water reabsorption
Where, in the large intestine, is most water absorbed?
Proximal colon
Approximately 1500mls of water enters colon each day; approximately how much is excreted in faeces?
100mls
What ages is there a high incidence of ulcerative colitis and crohn’s disease?
Describe the inflammation in crohn’s disease, include:
- Where it is in GI tract
- Where in GI tract it is common
- Depth of inflammation
- Skip lesions
- Anywhere in GI tract from mouth to anus
- Terminal ileum, colitis and anorectal inflammation
- Transmural (through wall of GI tract)
- Skip lesions “patchy”
Describe the inflammation in ulcerative colitis, include:
- Where in GI tract it affects
- Pattern of inflammation
- Depth of inflammation
- Only affects colon- starts in rectum
- Continous pattern
- Mucosal inflammation (doesn’t go deeper than lamina propria)
What is pancolitis?
Severe form of UC where inflammatin has spread from rectum to entire colon
Describe the macroscopic pathological appearance of crohn’s disease
- Skip lesions
- Hyperaemia (affected bowel= red & inflammed)
- Mucosal oedema
- Discrete superficial ulcers
- Deeper ulcers
- Thickening of bowel wall
- Narrowing of lumen
- Fistulae
Describe the microscopic pathological appearance of crohn’s disease
Granulomas (bodys attempt to contain an offending agent that it cannot eradicate- has epithelioid macrophages= macrophages that have elongated)
Describe some microscopic pathological changes seen in ulcerative colitis
- Crypt abscesses (neutrophil exudate in crypts)
- Irregular shaped glands (they should be short & straight)
- Dysplasia of glands
- Darker crowded nuclei
- Reduced number of goblet cells
- Increased numbers of paneth cells
Describe some macroscopic pathological changes seen in ulcerative colitis
- Lack of haustra- inflammation reduces appearance on imaging
- Pseudopolyps (areas that are healing after inflammation- more common in UC but can get in CD)
Describe how you could investigate ulcerative colitis
- Bloods
- Anaemia
- CRP
- Stool cultures
- Colonscopy
- Imaging:
- CT/MRI less useful in UC as unlikley to get fistulas like in CD
- Barium enema
It is sometimes very difficult to distinguish between crohn’s and ulcerative colitis; true or false?
True. Sometimes, even after diagnostic investigation, 10% of people have disorders that cannot be classified which we call intermediate colitis.
Just remember symptoms can overlap for each
Compare crohn’s and ulcerative colitis in terms of:
- Location
- Rectal involvement
- Gross bleeding
- Perianal disease
- Fistula formation
- Malnutrition
Compare crohn’s and colitis in terms of:
- Inflammation
- Granulomas
- Fibrosis
- Crypt abcesses
Compare crohns and colitis in terms of:
- Mucosal involvement
- Apthous (mouth) ulcers
- Linear ulcers
- Friable mucosa (delicate- touch will bleed)
- Cobblestone appearance
- Fistula
- Narrowing
What does it indicate if we can see ‘String sign of kantour’ on barium follow through enema in crohn’s?
Strictures
What radiological features might you see on a double contrast enema (barium & air) on a patient with ulcerative colitis?
Lack of haustra on descending and sigmoid colon- call this “lead pipe colon”
