Session 7: Large Intestine & Inflammatory Bowel Disease Flashcards
Where does the large intestine extend from?
Caecum to anal canal
Epithelium of the LI
Columnar
Functions of the LI
Absorption of ions and water to turn chyme into a solid mass. Production of certain vitamins like K and B12 via bacteria. Gut flora, act as a temporary storage unit for faeces. Supplement of short chain fatty acids via bacteria
Why are SCFA important in LI?
Because the colonic mucosa doesn’t get its majority of nutrients from blood but from bacteria fermenting dietary fibres.
By-products of the fermentation of dietary fibres by the bacteria.
Gases such as CO2, H2 and CH4
In relation to the peritoneum what are the ascending and descending colon?
Secondary retroperitoneal
Transverse colon
Peritoneal with its own mesentery
Sigmoid colon
Peritoneal with its own mesentery
Rectum
Upper 1/3 is intra-peritoneal, Middle 1/3 is retroperitoneal and the lower 1/3 has no peritoneum
Arterial supply of the caecum
Ileo-colic artery (SMA)
Arterial supply of the ascending colon
Right colic artery (SMA)
Arterial supply of the transverse colon
Middle colic artery (SMA)
Arterial supply of the descending colon
Left colic artery (IMA)
Arterial supply of the sigmoid colon
Sigmoid arteries (IMA)
Arterial supply of the upper 1/3 of the rectum
Superior rectal artery (IMA)
Venous drainage of midgut
SMV
Venous drainage of hindgut
IMV
Venous drainage of the upper 1/3 of rectum
IMV via superior rectal vein
Venous drainage of middle and lower 1/3
Middle and inferior rectal veins draining into systemic venous circulation
How does the LI differ from the SI?
It is much shorter (6 feet vs 20 feet) The large intestine is also much wider. The large intestine has crypts and not villi. The LI’s longitudinal muscle is incomplete and come in three distinct bands.
What are the three distinct bands of the incomplete longitudinal muscle in the LI called?
Teniae coli
What separate teniae coli?
Haustra
How are haustra formed?
They are sacculations formed by the contraction of teniae coli.
Explain the water absorption in the large intestine.
By ENaC governed by levels of aldosterone. The movement of sodium and chloride ions leads to water moving with it. There are much tighter tight junctions in the LI as well compared to SI which leads to a bigger gradient forming. There is less back flow of ions and water due to these tight junctions.
How much fluid enters the LI daily?
Around 1.5 litre
How much fluid is excreted via faeces of these 1.5 litre?
Around 100 ml. 1.4l is reabsorbed.
What are the two main conditions in irritable bowel disease?
Crohn’s disease Ulcerative colitis
Age of arising symptoms of Crohn’s disease and Ulcerative colitis.
Young adults around the age of 20. There is also a spike in older adults around the age of 50-60.
Give the general presentation of Crohn’s disease and its features.
Any part of the GI tract can be affected. Ileum is however the most commonly involved. It is a transmural disease which means it will effect the entire wall of the intestines. Appearance of skip lesions.
Give the general presentation of Ulcerative colitis and its features.
Begins in the rectum and can make its way up or remain rectal. Has a continuous pattern compared to the skip lesions in Crohn’s. Also leads to mucosal inflammation.
Extra-intestinal problems involving IBD.
MSK pain and arthritis. Skin problems such as erythema nodosum, pyoderma gangrenosum and psoriasis. PSC and in some cases (5%) also eye problems.
Causes of IBD
Genetics, Altered interactions of gut organisms, immune response
Common symptoms and signs of Crohn’s
Fatigue, weight loss, loose stools without blood, right lower quadrant pain, joint paint, low grade fever, mild anaemia, perianal inflammation/ulceration
Gross pathological appearance of Crohn’s disease
Skip lesions, hyperaemia, mucosal oedema, discrete superficial ulcers, deeper ulcers, Transmural inflammation, strictures, narrowing of lumen, fistulae, cobblestone appearance
Microscopical pathological appearance of Crohn’s disease.
Granuloma formation with epithelioid macrophages
Investigations of Crohn’s
Blood to look for anaemia, CT/MRI scans to look for bowel wall thickening, obstruction and extramural problems. Barium enema to look for strictures and fistulae. Colonoscopy
What might you find on a colonoscopy in Crohn’s?
Cobblestone appearance, skip lesions, strictures, fistulae
Common signs and symptoms of Ulcerative colitis
Frequent stools + blood stools. Mucus in stools, weight loss, mild lower abdo pain + cramping. Painful red eye. Normal temp, no perianal inflammation.
Microscopical pathological appearance of Ulcerative colitis.
Crypt abscesses, chronic inflammation infiltrating lamina propria, crypt distortion with dysplasia and darkened nuclei. Reduced number of goblet cells.
Gross pathological appearance of Ulcerative colitis (generally in severe cases)
Development of non-neoplastic pseudopolyps. Loss of haustra
Investigations of Ulcerative colitis.
Bloods to check for anaemia and serum markers. Stool cultures, colonoscopy, X-ray, CT/MRI, Barium enema
In the case of difficulty determining whether a patient has UC or Crohn’s what might that suggest? (What category does it fall into?)
Indeterminate colitis
In barium enema you may see some long strictures.
What is this sign called?
In which condition might this be seen?
String sign of kantour.
In Crohn’s disease
Radiological features of ulcerative colitis.
Double contrast enema
Featureless descending sigmoid and descending colon with lack of haustra. This is called lead pipe colon.
Continuous lesions without skipping.
Whole colon
Mucosal inflammation causing a granular appearance.
Medical treatment of IBD.
A stepwise approach
1 - Aminosalycates for flares and emission
2 - Corticosteroids for flares
3 - Immunomodulators for fistulas and maintenance of remission
Surgical treatment of Crohn’s.
Not curative
To remove fistulas and strictures
As little bowel removed as possible.
Surgical treatment of UC.
Curable via colectomy as it is constrained to the colon.
This is in the case of inflammation not settling.
Precancerous changes
Toxic megacolon
