Session 7: Large Intestine & Inflammatory Bowel Disease

Question 2

Where does the large intestine extend from?

Answer 2

Caecum to anal canal

Question 3

Epithelium of the LI

Answer 3

Columnar

Question 4

Functions of the LI

Answer 4

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

Question 5

Why are SCFA important in LI?

Answer 5

Because the colonic mucosa doesn’t get its majority of nutrients from blood but from bacteria fermenting dietary fibres.

Question 6

By-products of the fermentation of dietary fibres by the bacteria.

Answer 6

Gases such as CO2, H2 and CH4

Question 7

In relation to the peritoneum what are the ascending and descending colon?

Answer 7

Secondary retroperitoneal

Question 8

Transverse colon

Answer 8

Peritoneal with its own mesentery

Question 9

Sigmoid colon

Answer 9

Peritoneal with its own mesentery

Question 10

Rectum

Answer 10

Upper 1/3 is intra-peritoneal, Middle 1/3 is retroperitoneal and the lower 1/3 has no peritoneum

Question 11

Arterial supply of the caecum

Answer 11

Ileo-colic artery (SMA)

Question 12

Arterial supply of the ascending colon

Answer 12

Right colic artery (SMA)

Question 13

Arterial supply of the transverse colon

Answer 13

Middle colic artery (SMA)

Question 14

Arterial supply of the descending colon

Answer 14

Left colic artery (IMA)

Question 15

Arterial supply of the sigmoid colon

Answer 15

Sigmoid arteries (IMA)

Question 16

Arterial supply of the upper 1/3 of the rectum

Answer 16

Superior rectal artery (IMA)

Question 17

Venous drainage of midgut

Answer 17

SMV

Question 18

Venous drainage of hindgut

Answer 18

IMV

Question 19

Venous drainage of the upper 1/3 of rectum

Answer 19

IMV via superior rectal vein

Question 20

Venous drainage of middle and lower 1/3

Answer 20

Middle and inferior rectal veins draining into systemic venous circulation

Question 21

How does the LI differ from the SI?

Answer 21

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.

Question 22

What are the three distinct bands of the incomplete longitudinal muscle in the LI called?

Answer 22

Teniae coli

Question 23

What separate teniae coli?

Answer 23

Haustra

Question 24

How are haustra formed?

Answer 24

They are sacculations formed by the contraction of teniae coli.

Question 25

Explain the water absorption in the large intestine.

Answer 25

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.

Question 26

How much fluid enters the LI daily?

Answer 26

Around 1.5 litre

Question 27

How much fluid is excreted via faeces of these 1.5 litre?

Answer 27

Around 100 ml. 1.4l is reabsorbed.

Question 28

What are the two main conditions in irritable bowel disease?

Answer 28

Crohn’s disease Ulcerative colitis

Question 29

Age of arising symptoms of Crohn’s disease and Ulcerative colitis.

Answer 29

Young adults around the age of 20. There is also a spike in older adults around the age of 50-60.

Question 30

Give the general presentation of Crohn’s disease and its features.

Answer 30

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.

Question 31

Give the general presentation of Ulcerative colitis and its features.

Answer 31

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.

Question 32

Extra-intestinal problems involving IBD.

Answer 32

MSK pain and arthritis. Skin problems such as erythema nodosum, pyoderma gangrenosum and psoriasis. PSC and in some cases (5%) also eye problems.

Question 33

Causes of IBD

Answer 33

Genetics, Altered interactions of gut organisms, immune response

Question 34

Common symptoms and signs of Crohn’s

Answer 34

Fatigue, weight loss, loose stools without blood, right lower quadrant pain, joint paint, low grade fever, mild anaemia, perianal inflammation/ulceration

Question 35

Gross pathological appearance of Crohn’s disease

Answer 35

Skip lesions, hyperaemia, mucosal oedema, discrete superficial ulcers, deeper ulcers, Transmural inflammation, strictures, narrowing of lumen, fistulae, cobblestone appearance

Question 36

Microscopical pathological appearance of Crohn’s disease.

Answer 36

Granuloma formation with epithelioid macrophages

Question 37

Investigations of Crohn’s

Answer 37

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

Question 38

What might you find on a colonoscopy in Crohn’s?

Answer 38

Cobblestone appearance, skip lesions, strictures, fistulae

Question 39

Common signs and symptoms of Ulcerative colitis

Answer 39

Frequent stools + blood stools. Mucus in stools, weight loss, mild lower abdo pain + cramping. Painful red eye. Normal temp, no perianal inflammation.

Question 40

Microscopical pathological appearance of Ulcerative colitis.

Answer 40

Crypt abscesses, chronic inflammation infiltrating lamina propria, crypt distortion with dysplasia and darkened nuclei. Reduced number of goblet cells.

Question 41

Gross pathological appearance of Ulcerative colitis (generally in severe cases)

Answer 41

Development of non-neoplastic pseudopolyps. Loss of haustra

Question 42

Investigations of Ulcerative colitis.

Answer 42

Bloods to check for anaemia and serum markers. Stool cultures, colonoscopy, X-ray, CT/MRI, Barium enema

Question 43

In the case of difficulty determining whether a patient has UC or Crohn’s what might that suggest? (What category does it fall into?)

Answer 43

Indeterminate colitis

Question 44

In barium enema you may see some long strictures. What is this sign called? In which condition might this be seen?

Answer 44

String sign of kantour. In Crohn's disease

Question 45

Radiological features of ulcerative colitis.

Answer 45

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.

Question 46

Medical treatment of IBD.

Answer 46

A stepwise approach 1 - Aminosalycates for flares and emission 2 - Corticosteroids for flares 3 - Immunomodulators for fistulas and maintenance of remission

Question 47

Surgical treatment of Crohn's.

Answer 47

Not curative To remove fistulas and strictures As little bowel removed as possible.

Question 48

Surgical treatment of UC.

Answer 48

Curable via colectomy as it is constrained to the colon. This is in the case of inflammation not settling. Precancerous changes Toxic megacolon