Pathology of the small intestine

Question 1

Both the small and large bowel have lots of immune cells within them. True/ False?

Answer 1

False

Only the small intestine has lots of immune cells

Question 2

from which artery does the small intestine get its blood supply?

Answer 2

the superior mesenteric artery

Question 3

what are the 2 main causes of ischaemia of the small bowel?

Answer 3

1. mesenteric artery occlusion (e.g. due to atherosclerosis or thromboembolism from heart)
2. non-occlusive perfusion insufficiency (e.g. in shock, strangulation obstructing venous return - such as a hernia/ adhesion, due to drugs e.g. cocaine, hyperviscosity)

Question 4

which layer of the small bowel is most sensitive to hypoxia and why?

Answer 4

the mucosa
because it is the most metabolically active part of the bowel wall. the longer the hypoxia duration, the greater the damage

Question 5

in non-occlusive ischaemia, when does much of the tissue damage occur?

Answer 5

after reperfusion
(due to reperfusion injury - which is when the restoration of blood flow allows for increased formation of free radicals - which damage tissue)

Question 6

what is the sequence (as duration of ischaemia increases) of outcomes of small intestine ischaemia?

Answer 6

• mucosal infarct (which can be regenerated)
• mural infarct (which regenerates to form a fibrous stricture - so narrows the lumen)
• transmural infarct (which is gangrene - a type of necrosis caused by critically insufficient blood supply) (death will occur if gangrene is not resected)

Question 7

list some possible outcomes of ischaemia of the small intestines

Answer 7

resolution (complete healing)
mesenteric angina (pain after eating due to ongoing poor blood supply)
fibrosis
stricture (narrowing of lumen)
gangrene (transmural infarct)
perforation (hole in the wall of part of the GI tract)
sepsis
death

Question 8

what is Meckel’s diverticulum?

Answer 8

a true (involves all 4 layers of the wall) congenital diverticulum. It's a slight bulge in the small intestine, and is present at birth (it's a now functionless remnant of the vitelline duct - which joined the yolk sac to the midgut lumen of the foetus). 
Meckel's diverticulum may cause bleeding, perforation or diverticulitis (which mimicks appendicitis)

Question 9

what is a diverticulum?

Answer 9

outpouching of a hollow (or fluid-filled) structure in the body. Either true or false, depending on which layers of the structure are involved. True diverticulum = when all 4 layers of the wall are included in the outpouching.
False diverticulum = when only the mucosa and submucosa are included in the outpouching, and are covered only by serosa

Question 10

describe features of Meckel’s diverticulum? Hint: the number 2

Answer 10

this diverticulum is a tubular structure which is:

• 2 inches long
• within 2 feet of the ileocaecal valve
• 2 times as common in males
• present in 2% of the population

Question 11

what is diverticulitis?

Answer 11

digestive disease in which pouches within the large bowel wall (diverticula) become inflamed. Often results in lower abdominal pain of sudden onset. (Having diverticula that are NOT inflamed is known as having “diverticulosis”)

Question 12

Primary/ secondary tumours of the small intestine are common?

Answer 12

secondary e.g. from ovary, stomach, colon

primary e.g. lymphomas, carcinoid tumours, carcinomas are rare

Question 13

which type of lymphoma (Hodgkins or Non Hodgkins) are lymphomas of the small bowel?

Answer 13

non-Hodgkins
Specifically, they are MALTomas (MALT lymphomas) - which is a form of lymphoma involving the mucosa-associated lymphoid tissue, often of the stomach. It’s a cancer originating from B cells in the marginal zone of the MALT.

Question 14

what is enteropathy-associated T cell lymphoma?

Answer 14

a type of T cell lymphoma that affects the small intestine. These cancerous T cells are a possible consequence of refractory cases of coeliac disease or in chronic, untreated cases of Coeliac disease.

Question 15

give some information about carcinoid tumours of the small bowel?

Answer 15

rare, commonest site is appendix
small, yello, slow-growing tumours
locally invasive]
can cause obstruction
produces hormones so can cause paraneoplastic syndrome

Question 16

give some information about carcinoma of the small bowel?

Answer 16

rare
associated with Crohn’s disease and Coeliac disease
identical appearance to colorectal carcinoma
presents late
metastases to lymph nodes and liver can occur

Question 17

what is appendicitis?

Answer 17

inflammation of the appendix, commoner in children

Causes vomiting, abdominal pain, RIF tenderness, increased WCC

Question 18

what are some causes of appendicitis?

Answer 18

• idiopathic (most cases)
• faecoliths (faecal impaction due to dehydration)
• lymphoid hyperplasia
• parasites
• tumours (rare)

Question 19

outline the pathology of acute appendicitis?

Answer 19

-acute inflammation (neutrophilic infiltrate of the muscularis propria)
-mucosal ulceration
-serosal congestion, exudate
-pus in lumen
(acute inflammation must involve the muscle coat)

Question 20

what are complications of appendicitis?

Answer 20

• peritonitis (spread of infection)
• rupture (pus extrudes out)
• abscess (body tries to wall off infection)
• fistula (an abnormal anastomosis)
• sepsis (rare in developed world)

Question 21

what is coeliac disease?

Answer 21

an autoimmune disorder affecting mainly the small intestine. Occurs in those who are genetically predisposed. Upon exposure to gluten, an abnormal immune response may lead to the production of several different autoantibodies that can affect a number of different organs. In small bowel, this shortens and flattens the villi (damages the enterocytes) - affecting nutrient absorption and often leading to anaemia. Strong association with childhood diabetes (another autoimmune disease).

Question 22

what causes coeliac disease?

Answer 22

exposure to the gliadin peptide (component of gluten) in those who are sensitive to it. Reaction is mediated by T cells (IELs).

Question 23

In coeliac disease, is there a change in the number of IELs in the small intestinal wall?

Answer 23

Yes, there are more IELs

Question 24

pathology of coeliac disease?

Answer 24

gliadin peptide presented to CD4 cells by macrophages in the small intestine
CD4 cells release inflammatory cytokines e.g. IFNg and TNF - which directly damage and destroy epithelial cells in the small intestine, and also stimulate B cells to produce antibodies (IgA, anti-tTG and anti-EMA), also causes killer T cells (CD8) to come and destroy cells undergoing inflammation

Question 25

Coeliac disease begins proximally/ distally in the small intestine?

Answer 25

proximally (so duodenal biopsy very sensitive)

The disease extends if untreated

Question 26

metabolic effects of Coeliac disease?

Answer 26

malabsorption of sugars, fats (leads to steatohhoea), amino acids, water, electrolytes, reduced intestinal hormone production leads to reduced pancreatic secretion and bile flow (CCK) leading to gallstones
Effects: weight loss, anaemia, abdominal bloating, failure to thrive, vitamin deficiencies
Other complications: T cell lymphomas of the GI tract (nearly always fatal), increased risk of small bowel carcinoma, gallstones, ulcerative-jejenoilleitis