Small Intestines

Question 1

Describe the differences between the jejunum and the ileum. (4)

Answer 1

Jejunum: upper left quadrant, thick wall, long vasa recta, less arcades (arterial loops)
Ileum: lower right quadrant, thin walls, shorter vasa recta, more arcades.

Question 2

Describe the blood supply to the intestines. (4)

Answer 2

SMA - jejunal and ileal branches.

SMV - joins splenic and IMV to drain into portal vein.

Question 3

Describe what the small intestine has to increase surface area. (3)

Answer 3

Plicae circularis
Villi
Microvilli

Question 4

Describe the epithelial of the small intestine. (5)

Answer 4

Enterocytes - microvilli columnar cells
Goblet cells - mucus producing
Enteroendocrine cells - hormone producing
Has Crypts of Lieberkuhns which has stem cells and paneth cells at the base which produce antimicrobials.

Question 5

Describe lipid digestion in the duodenum. (2)

Answer 5

Pancreatic enzymes and bile emulsify and digest fats.

Question 6

Describe the issues with carbohydrate digestion in the small intestine. (2)

Answer 6

Only monosaccharides can be absorbed and glucose can only enter with Na+.

Question 7

Describe starch digestion in the small intestine (7)

Answer 7

Salivary and pancreatic amylase break 1-4 bonds in amylose producing glucose or maltose.
When they act on the 1-4 bonds in amylopectin, you get alpha dextrins held together by 1-6 bonds.
Isomaltase can break these 1-6 bonds.

Question 8

Describe lactose digestion in the small intestine. (3)

Answer 8

Lactase is a brush border enzyme breaking lactose into galactose and glucose. Can be deficient leading to lactose intolerance.

Question 9

Describe sucrose digestion in the small intestine. (2)

Answer 9

Sucrase is a brush border enzyme that breaks sucrose into glucose and fructose.

Question 10

Describe the transporters in the small intestine for absorption of carbohydrate monomers. (4)

Answer 10

Luminal side:
SGLT1 - glucose or galactose and Na+
GLUT5 - fructose

Basolateral side:
Na+/K+ ATPase to maintain low [Na+]i
GLUT2 - glucose, galactose or fructose.

Question 11

Describe the two methods of releasing and activating proteases. (4)

Answer 11

Pepsinogen release from the stomach gets converted to pepsin by HCl from parietal cells.
Pancreas releases proteases as zygomens which are activated by trypsin.

Question 12

Describe the differences between endo- and exppeptidases. (2)

Answer 12

Endo - cut the middle of protein

Exo - cuts ends of chain.

Question 13

Describe the proteases present in the brush border. (2)

Answer 13

PepT1 - absorbs small peptides and amino acids.

AA/Na+ co-transporter: amino acids only.

Question 14

Explain how oral rehydration fluid works. (2)

Answer 14

Contains water, glucose and Na+.

Uptake of the glucose moves Na+ with it, which moves the water.

Question 15

Describe the pathophysiology of lactose intolerance. (4)

Answer 15

Lactose remains in the lumen because it cannot be broken download, creating osmotic diarrhoea. Lactose is fermented in the gut leading to bloating/flattus.

Question 16

Describe the symptoms of irritable bowel syndrome. (4)

Answer 16

A diagnosis of exclusion with symptoms of abdominal pain, bloating, flatulence, diarrhoea, constipation. Often associated with psychological disorders.

Question 17

Describe the pathophysiology of coeliac disease. (4)
Symptoms (1)
Investigations(2)
Treatment (2)

Answer 17

An autoimmune attack leading to inappropriate T cell activation against gluten that can cause damage to the mucosa of the intestines, leading to swelling of the villi and malabsorption due to decreased surface area.
Symptoms mostly related to malabsorption: diarrhoea, weight loss.
Investigations: IgA blood test (tissue transglutaminase), upper GI endoscopy.
Treatments: strict gluten free diet - clinical improvement in days, histological improvement in months.