13. Large intestine and Inflammatory Bowel Disease Flashcards
What are the functions of the large intestine?
- 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 defaecation (distal)
What type of epithelium does the large intestine have?
Simple columnar
In which part of the colon is the faeces stored?
Transverse and descending colon
Where does the colonic mucosa derive fatty acids from and what are the by-products?
not from blood
Short chain fatty acids derived from the fermentation of dietary fibre
- The by-products of this fermentation process include CO2, methane and hydrogen gas
What is the relation of different parts of the colon to the peritoneum?
- Ascending and descending colon are secondary retro peritoneal
- Transverse colon has its own mesentery (transverse mesocolon)
- Sigmoid colon has its own mesentery
- Rectum:
- Upper 1/3- intra-peritoneal
- Middle 1/3 - retroperitoneal
- Lower 1/3- no peritoneum
What is the arterial supply to the midgut component of the colon?
Superior Mesenteric Artery:
- ilio-colic: caecum
- right colic: ascending colon
- middle colic: most transverse colon
What is the arterial supply to the hindgut component of the colon?
Inferior Mesenteric Artery:
- left colic: transverse colon and descending colon
- sigmoid: descending colon and sigmoid colon
- superior rectal: Upper 1/3 rectum
At which vertebral level are the SMA and IMA given off?
L1 (trans-pyloric plane) and L3 respectively
- IMA given off slightly to the left
Which arteires supply the lower 2/3rds of the rectum?
- Middle rectal artery (from internal iliac)
- Inferior rectal artery (from internal pudendal artery from internal iliac)
What is the venous drainage of the midgut component of the colon?
- Midgut drains into superior mesenteric vein
What is the venous drainage of the hindgut component of the colon?
- Hindgut drains into inferior mesenteric vein
What is the venous drainage of the rectal component of the colon?
- Upper 1/3 rectum drains into superior rectal vein
- Lower 2/3 rectum drains into system circulation via middle and inferior rectal veins
What is the difference in length between large and small intestine?
- Large intestine much shorter (6 feet vs 20 feet)
* Large intestine is much wider (average 6cm vs 3cm)
Describe the longitudinal muscle layer of the colon?
External longitudinal muscle is incomplete
• Three distinct bands (teniae coli)
What are haustra and what are they due to?
Haustra are sacculations caused by contraction of teniae coli
How much water is absorbed in the colon each day and what is absorption facilitated by?
Approx 1500 mls of water enter colon/day
• <100 mls excreted in faeces
•Facilitated by ENaC
where does most of the water absorption occur in the colon and why?
proximal colon
Much tighter tight junctions
• Allows bigger gradient to form
• Less back diffusion of ions
What is inflammatory bowel disease and what are 2 common examples?
Group of conditions characterised by idiopathic inflammation of the GI tact
- Crohn’s disease and ulcerative colitis
Describe the pattern in Crohn’s disease.
- Affects anywhere in GI tract
- terminal Ileum involved in most cases
- Transmural
- Skip lesions
Describe the pattern in Ulcerative colitis.
- Begins in rectum
- Can extend to involve entire colon (pancolitis)
- Continuous pattern
- Mucosal inflammation - not transmural
What are some extra-intestinal problems of Inflammatory bowel diseases?
- MSK pain (up to 50%) e.g. Arthritis
- Skin (up to 30%) e.g. Erythema nodosum /pyoderma gangrenosum /psoriasis
- Liver/biliary tree e.g. Primary Sclerosing Cholangitis (PSC)
- Eye problems (up to 5%)
What are the causes of inflammatory bowel disease?
- Genetic
- Gut organisms (altered interaction)
- Immune response
What are 2 genetic correlation with inflammatory bowel disease?
- 1st degree relative increased risk
* Identical twins concordance 70%
What are some possible triggers for immunological causes of IBD?
Antibiotics, Infections, Smoking, Diet
What age range do Crohn’s and UC typically affect?
2 peaks for each, about 20-25 and 50
- more common in 20s
What are the signs and symptoms of Crohn’s?
- loose, non-bloody stools
- RLQ pain
- some joint pains (lower limbs)
- weight loss - reduced nutrient absorption
- Tender mass (RLQ)
- Mild perianal inflammation/ulceration
- Low grade fever
- Mildly anaemic
What is the typical patient that will present with Crohn’s disease?
- 22 year old female
- 6/52 hx of 5x loose stools/day
- Non bloody stools
- Weight loss
- Right lower quadrant pain
- Some joint pains (lower limbs)
- Smoker
What is the more likely explanation for mild anaemia in Crohn’s disease?
More likely due to the inflammation rather than any bleeding
- anaemia of chronic inflammation (MEH)
What type of oedema develops in Crohns?
Mucosal oedema
What is the gross appearance in Crohn’s?
skip lesion - Cobblestone appearance:
Inflammed mucosa with ulceration between
what can form in Crohn’s?
- fistulas - inflammation go through transmural wall and connect with other parts of body
- discrete superficial ulcers
- deeper ulcers
- strictures- transmural inflammation lead to fibrosis and narrowing of lumen