The Intestines

Question 1

What are the differences between the jejunum and the ilium?

Answer 1

Jejunum: 
-Upper left quadrant 
-Thick intestinal wall 
-Long vasa recta 
Less arcades 

Ilium:

• Lower right quadrant
• Thin intestinal wall
• Shorter vasa recta
• More arcades

Question 2

What is the blood supply to ilium and jejunum?

Answer 2

Superior Mesenteric artery.

This comes off the abdominal gives of branches that form a plexus.

Question 3

What is the venous drainage of the ileum and jejunum?

Answer 3

Superior mesenteric vein

It eventually drains into the portal vein which enters the liver and supplies 70-80% fall blood going into the liver. (hepatic arteries supply the rest).

Question 4

What are placate circulares?

Answer 4

The numerous permanent crescentic folds of mucous membrane found in the small intestine especially in the lower part of the duodenum and the jejunum.

Question 5

What are the types of intestinal epithelia?

Answer 5

Enterocytes (most of the cells in the small intestine) -absorptive tall columnar cells.
Goblet cells -mucus producing
Enteroendocrine cells -produce hormones

Question 6

What are the crypts of Lieberkuhn?

Answer 6

Intestinal glands

High turnover of cells - every 3-6 days.

Contain stem cells at the base which migrate to the surface and mature as they migrate into a variety of cell types.

Paneth cells at base (innate mucosal defence cells) produce antimicrobial peptides.

Question 7

How do you absorb carbs?

Answer 7

As monosacchides with Na+.

Question 8

What does starch consist of?

Answer 8

Straight chain (amylose - alpha 1-4 bonds) and branched chains (amylopectin- alpha 1-6 bonds) of glucose

Question 9

How is starch first broken down?

Answer 9

Salivary and pancreatic amylase breaks the a-1-4 bonds in amylose producing maltose.

Question 10

What are alpha dextrin?

Answer 10

Shorter but still branched chains of glucose.

Question 11

What is isomaltase used for?

Answer 11

Break the branched alpha 1,6 bonds.

Question 12

What enzymes are found in the brush border that help with the digestion of starch

Answer 12

Maltese

Isomaltase

Question 13

How are monosaccharides absorbed?

Answer 13

Na+/K+ ATPase on basolateral membrane. which maintains low intracellular Na+.

SGLT-1 binds Na+ which allows glucose so Na+ and glucose moves into cell.

GLUT2 transports glucose out of enterocyte. This diffuses down gradient into capillary blood.

Fructose uses GLUT5 transporter to enter enterocyte via facilitated diffusion.

Question 14

Where does protein digestion begin?

Answer 14

In stomach - pepsinogen released from chief cells gets converted to pepsin by HCl.
Pepsin acts on proteins to covert them to oligopeptides / amino acids so they can move to the small intestine.

Question 15

Why is trypsinogen important?

Answer 15

Once trypsinogen is converted to trypsin, it catalyses the conversion of zymogens

Trypsinogen to trypsin is catalysed by enteropeptidase (enterokinase).

Question 16

Give some examples of endopeptidases

Answer 16

Trypsin
Chymotrypsin
Elastase

-Cut in middle of chain

Question 17

Give some examples of exopeptidases

Answer 17

Carboxypeptidases

-chop off end of chain

Question 18

How does the brush border of SI help to digest proteins?

Answer 18

Contain proteases

Sometimes cannot completely digest proteins down to amino acids. But, Intestine can absorb short peptides as well as amino acids by PepT1.

Amino acids are transported into cell (similar to glucose) via Na+AA co-transporters.

Question 19

How does the cytosol of enterocytes contribute to protein digestion?

Answer 19

Small peptides are acted on by cytosolic peptidases (broken down into amino acids)

Certain di- and tri- peptides can also be absorbed into blood.

Question 20

Was is the difference between water uptake in the small and large intestine.

Answer 20

Both have NaKATPase on basolateral membrane
Apical membrane:
SI : Na+ is co-transported with glucose, amino acids ect..
LI: Na+ channels induced by aldosterone.

Question 21

How does oral rehydration fluid work?

Answer 21

Mixture of glucose and salt will stimulate maximum water uptake.
Uptake of Na+ generates osmotic gradient - water follows.
Glucose uptake also stimulates Na+ uptake via NaGlucose cotransporters.

Question 22

What drives water secretion?

Answer 22

Chloride ions

Question 23

What can B12 deficiency lead to?

Answer 23

Megaloblastic anaemia and neurological symptoms.

Question 24

What can cause B12 deficiency?

Answer 24

Lack of intrinsic factor mean B12 cannot bind in the stomach - pernicious anaemia

Hypochlorhydra (inadequate stomach acid) -caused by Gastrin atrophy, PPIs

Inadequate intake in food (strict vegetarians)

Inflammatory disorders of ileum (where it is absorbed) - Crohns disease

Question 25

What causes lactose intolerance?

Answer 25

Caused by deficiency in the enzyme lactase (brush border enzyme).

After age of 2, enzyme is expressed less.

When lactose is consumed in quantity, it cannot be absorbed.

• Remains in gut lumen creating a high osmotic effect.
• Water is not absorbed resulting in diarrhoea
• Lactose is fermented in gut causing flatus / bloating

Question 26

What are the symptoms of IBS?

Answer 26

Abdominal pain 
Bloating 
Flatulence 
Diarrhoea / constipation 
Rectal urgency

Question 27

Causes of IBS?

Answer 27

More common in females than males (2:1)
20s-40s most affected
More common association with psychological disorders

Question 28

What is coeliac disease?

Answer 28

Coeliac disease arises from an immunological response to the gliadin fraction of gluten.

Found in wheat, rye and barley.

Damage mucosa of intestines:

• Absence of intestinal villi
• Lengthening of intestinal crypts
• Lymphocytes infiltrate epithelium-Impaired digestion / malabsorption

Question 29

What are the symptoms of coeliac disease?

Answer 29

Majority related to malabsorption (diarrhoea, weight loss, flatulence, abdominal pain)
Anaemia (impared iron absorption), neurological symptoms (hypocalcaemia)

Question 30

What investigations can be done for coeliac disease?

Answer 30

Bloods -IgA antibodies to smooth muscle endomysium and tissue transglutaminase.

Upper GI endoscopy + biopsy (duodenum)

• Mucosal pathology
• Villi are reduced or absent.

Question 31

What is the treatment for coeliac disease?

Answer 31

Diet - strict gluten free diet

• Clinical improvement quite quick (days / weeks)
• Histological improvements (weeks / months)