The Intestines

Question 1

Compare and contrast the features of the jejunum and ileum

Answer 1

Question 2

Identify the branches of the superior mesenteric artery that supplies the midgut

Answer 2

Jejunal and ileal - supply the jejunum and ileum

Ileocolic - supplies ileum leading the colon and the appendix area

Right colic - supplies the ascending colon

Middle colic - supplies the transverse colon

Question 3

Identify the veins that drain the midgut

Answer 3

Question 4

Which veins make up the Portal Vein?

Answer 4

Superior mesenteric Vein and Splenic vein

Question 5

When the terminal branches of the middle colic, right colic and ileocolic anastamose they form which artery?

Answer 5

The Marginal Artery

Question 6

What features of the small intestine allow for increased surface area for absorption?

Answer 6

Villi and microvilli

Plica circularis (permanent folds)

Question 7

How fast or slow do contents move through the small intestine and why?

Answer 7

Slow movement allows for precise control of what is/ isn’t absorbed

Question 8

How often is mucosa of the intestinal epithelia shed?

Answer 8

Every 3-6 days

Question 9

Which cells make up the epithelia of the small intestine and what is the function of each?

Answer 9

• Enterocytes - absorption cells
• Goblet cells - mucus producing
• Enteroendocrine cells - produce hormones

Question 10

Which cells line the intestinal glands (Cryps of Lieberkuhn) and what is the function of each?

Answer 10

• Stem cells - migrate to surface to replace lost cells
• Paneth cells - produce antimicrobial peptids to defend stem cells

Question 11

Which size of carbohydrate can be absorbed in the small intestine?

Answer 11

Monosaccharides only

(Glucose, Galactose, Fructose)

Question 12

How is starch digested?

Answer 12

• Amylase breaks alpha 1-4 glycocydic bonds
• Isomaltase breaks alpha 1-6 glycocydic bonds

Question 13

What are short unbranched and short but branched chains of glucose called?

Answer 13

• Short and unbranches = maltose
• Short and branched = alpha dextrins

Question 14

Which 2 monosaccharides make up lactose?

Answer 14

Glucose and Galactose

Question 15

Which two monosaccharides make up sucrose

Answer 15

Glucose and Fructose

Question 16

How are monosaccharides absorbed across the enterocyte?

Answer 16

• SGLT1 co-transports Na⁺ and glucose (or Galactose) across the brush border
• GLUT5 transports fructose across the brush border
• Monosaccharides transported across basolateral membrane by GLUT 2 transporter
• Na⁺/ K⁺ ATPase maintains the gradient

Question 17

How are proteins digested in the stomach?

Answer 17

Pepsinogen released from chief cells in the stomach

Pepsinogen activated to pepsin by HCl which digests proteins to oligopeptides/ amino acids

Question 18

Which protease released by the pancreas activates other proteases once activated? Which enzyme activates it?

Answer 18

Trypsin

Activated from trypsinogen by enterokinase on epithelial cells

Question 19

What’s the difference between endopeptidases and exopeptidases?

Answer 19

Endopeptidases→ break bonds in middle of polypeptide

Exopeptidases → break bonds at the end to give individual amino acids

Question 20

Name some main endopeptidases and exopeptidases?

Answer 20

endopeptidases:

• Trypsin
• Chymotrypsin
• Elastase

exopeptidases:

• Carboxypeptidase (A & B)

Question 21

Which transporter can asborb short peptides across the brush border into the enterocyte?

Answer 21

PepT1

Question 22

How are amino acids transported into the enterocyte?

Answer 22

Co-transported with Na⁺

Question 23

What is the final step of protein digestion?

Answer 23

cytosolic peptidases in the cytosol of the enterocyte breaks down small peptides so they can be absorbed into blood

Question 24

How is water absorbed in the small intestine?

Answer 24

Water follows the movemenent of Na⁺ into the enterocyte

Either moves transcellularly or paracellularly

Question 25

What is the key difference between Na⁺ absorption in the small and large intestine?

Answer 25

**Small intestine:** Na+ transported with glucose/ amino acids **Large intestine:** Na⁺ channels which are induced by **aldsoterone** when blood pressure gets low (Increased Na⁺ absorption → water follows)

Question 26

What components make up oral rehydration solution?

Answer 26

Mixture of **glucose and salt** (NaCl) Allows for maximal water uptake as water follows Na⁺ which is absorbed with glucose

Question 27

What drives water movement **out** of enterocytes and into the gut?

Answer 27

Driven by **chloride movement** 1. Chloride co-transported with Na and K into epithelial cell 2. Levels of cAMP rise and activates CFTR channel 3. Cl^- ions are secreted 4. Na⁺ driven into lumen by tight junctions 5. Water follows NaCl secretion and moves down the osmotic gradient

Question 28

What 4 reasons pertaining to the GI system can lead to a **vitamin B12 deficiency**?

Answer 28

1. Lack of intrinsic factor released by parietal cells 2. Hypocholorhydria (inadequate stomach acid) 3. Inadequate **intake** seen in _strict vegetarians_ 4. Inflammaotry disorders of the **ileum** where B₁₂ is absorbed e.g. crohn's

Question 29

What is the basic defect in lactose intolerance?

Answer 29

A deficiency in the enzyme **lactase** as the brush border of enterocytes meaning lactose **cannot be digested**

Question 30

What is the consequence of not being able to breakdown lactose?

Answer 30

1. Lactose cannot be absorbed and remains in the gut lumen 2. Lactose is **osmotically active** drawing water into the lumen 3. This leads to **diarrhoea** 4. Lactose in the gut it **fermented** causing **bloating and flatulence**

Question 31

What are some of the symptoms of irritable bowel syndrome?

Answer 31

* Abdominal pain (often cramping, sometimes relieved by defaecation) * Bloating * Flatulence * Diarrhoea/ constipation * Rectal Urgency

Question 32

What is the incidence of irritable bowel syndrome?

Answer 32

* Affects 10-15% of adults * More common in **females** vs males (2:1) * 20s-40s the most affected age range * Associated with psychological disorders

Question 33

What is the pathology in coeliac disease?

Answer 33

An **immunological response** to the **gliadin** component of **gluten** found in wheat, rye and barley

Question 34

What damage to the intestinal mucosa occur in coeliac disease?

Answer 34

* **absence** of intestinal villi * **hypertrophy/ legnthening** of intestinal crypts * **lymphocytes** infiltrate epithelium and lamina propria * Impaired digestion/ malabsorption

Question 35

What are some of the symptoms of coelic disease?

Answer 35

* Majority related to **malabsorption** * diarrhoea * weight loss * flatulence * abdo pain * **Anemia** by impaired Fe²⁺ absorption * **Neurological symptoms** (hypocalcaemia)

Question 36

What investigations would you do if you suspected someone has coeliac disease?

Answer 36

* **Bloods** - looking for **IgA** antibodies to **smooth muscle** endomysium and tissue **transgluataminase** * **Upper GI endoscopy** + biopsy is the **gold standard** * looking for mucosal pathology and reduced/ absent villi

Question 37

How do you treat coeliac disease?

Answer 37

**Strict gluten free diet** Will see clinical improvement very quickly and histological improvement in weeks/ months