Lecture 11-Intestines

Question 1

What are the roles of the intestines?

Answer 1

Absorb nutrients, water and electrolytes paracellularly or transcellularly

Question 2

What contributes to the large SA of the small intestine?

Answer 2

Villi, microvilli and plicae circulares

Question 3

True or false: monosaccharides and disaccharides are absorbed by the small intestine

Answer 3

FALSE - only monosaccharides

Question 4

Where does final breakdown of sugars occur?

Answer 4

Brush border

Question 5

Which bonds are between glucose molecules in amylose?

Answer 5

Alpha 1, 4

Question 6

Which bonds are between glucose molecules in amylopectin?

Answer 6

Alpha 1, 4 between the straight chains and alpha-1, 6 between the branches

Question 7

Which enzyme breaks alpha-1,4 bonds?

Answer 7

Amylase

Question 8

Which enzyme breaks alpha-1,6 bonds?

Answer 8

Isomaltase

Question 9

Which channel on the apical membrane allows the entry of glucose into the cell?

Answer 9

SGLT-1 (moves with Na+)

Question 10

Which channel transports glucose out of the enterocyte?

Answer 10

GLUT-2

Question 11

Which channel on the apical membrane allows fructose to enter the cell and by which mechanism?

Answer 11

GLUT-5 by facilitated diffusion

Question 12

Complete the sentence: in the stomach, pepsinogen from ______ cells is converted to pepsin by ___

Answer 12

Chief

HCl

Question 13

What converts trypsinogen to trypsin?

Answer 13

Enteropeptidase

Question 14

What does trypsin do?

Answer 14

Activates other proteases

Question 15

What are the two groups of proteases?

Answer 15

• endopeptidases: breaks bonds in the middle of the polypeptide
• exopeptidases: breaks bonds at the end of the polypeptide

Question 16

Give examples of each group of proteases

Answer 16

• endopeptidases: trypsin, chymotrypsin, elastase

- exopeptidases: carboxypeptidase

Question 17

True or false: most protein products are ingested as di/tripeptides

Answer 17

TRUE

Question 18

How are protein products absorbed in the small intestine?

Answer 18

• Na+/AA co-transporter on apical membrane

- di/tripeptides moved by H+ co-transporter (PepT1) and converted to AA by cytosolic peptidases

Question 19

True or false: Na/K ATPase is present on the basolateral membranes of the small and large intestines

Answer 19

TRUE

Question 20

How does Na+ enter the cell in the small intestine?

Answer 20

Na+ co-transporter

Question 21

How does Na+ enter the cell in the large intestine?

Answer 21

Na+ channels induced by aldosterone

Question 22

How is calcium absorbed when Ca2+ intake is low?

Answer 22

Active transcellular absorption:

• Ca2+ enters the cell via facilitated diffusion
• Ca2+ ATPase removes the ion from the basolateral membrane

Question 23

What is required for the active transport of Ca2+?

Answer 23

Vitamin D

Question 24

How is calcium absorbed when intake is high?

Answer 24

Passive paracellular absorption

Question 25

What is needed for iron absorption?

Answer 25

Gastric acid

Question 26

How is iron absorbed when levels are low?

Answer 26

Binds to transferrin and transported to stores (Hb and ferritin complexes in bone marrow, liver and spleen)

Question 27

How is iron absorbed when levels are high?

Answer 27

Iron in ferritin complexes

Question 28

How are water soluble vitamins absorbed?

Answer 28

By Na+ co-transport

Question 29

Where is vitamin B12 absorbed?

Answer 29

Terminal ileum, bound to intrinsic factor

Question 30

What is the basis of oral rehydration therapy?

Answer 30

Uptake of Na+ generates an osmotic gradient for water to follow and glucose uptake stimulates Na+ uptake so a mix of glucose and Na+ stimulates maximum water uptake

Question 31

What is Coeliac disease?

Answer 31

Intolerance to gliadin fraction of gluten found in wheat, rye and barley

Question 32

What are the symptoms of coeliac disease?

Answer 32

- diarrhoea - flatulence - weight loss - sensory loss in hands

Question 33

Describe the pathophysiology of coeliac disease

Answer 33

Immune response, damage to mucosa of intestines: - absence of villi so loss of SA -> diarrhoea - lengthening of crypts - lymphocytes infiltrate epithelium -> malabsorption

Question 34

What are the investigations conducted to confirm coeliac disease?

Answer 34

- upper GI endoscopy - biopsy - bloods

Question 35

How can coeliac disease be treated?

Answer 35

Avoid gluten