Physiology 2

Question 1

What are the two main types of digestion occurring in the small intestine?

Answer 1

Luminal digestion - mediated by pancreatic enzymes secreted into the duodenum

Membrane digestion –> mediated by enzymes situated at the brush border of epithelial cells

Question 2

Which cells control absorption from the lumen in the small intestine and what are heir two membranes/borders?

Answer 2

Enterocytes

• apical membrane (brush border) faces lumen
• basolateral membrane faces interstitium

Question 3

What are they different classes of carbohydrate?

Answer 3

Polysaccharides
Oligosaccharides
Monosaccharides

Question 4

What are the different types of polysaccharides?

Answer 4

Starch (plant)
- amylose: straight chain
- amylopectin: branched chain
Glycogen (more highly branched than amylopectin)

Question 5

What are the different types of oligosaccharides and what are they made up of?

Answer 5

Sucrose = glucose + fructose
Lactose = glucose + galactose

Question 6

What are the different types of monosaccharides?

Answer 6

Glucose
Fructose
Galactose (not from diet)

Question 7

In what form can dietary carbohydrates be absorbed?

Answer 7

As monosaccharides

Question 8

Where and how are polysaccharides converted to oligosaccharides?

Answer 8

Intraluminal hydrolysis

By alpha-amylase (salivary and pancreatic)

Question 9

Where and how are oligosaccharides converted to monosaccharides?

Answer 9

Membrane digestion at the brush border

By lactase, maltase, sucrase-isomaltase

Question 10

Where are carbohydrates absorbed in the small intestine?

Answer 10

Duodenum and jejunum

Question 11

How are the monosaccharides absorbed over the apical membrane (brush border)?

Answer 11

Glucose and galactose –> SGLT1

Fructose –> GLUT5

Question 12

How are the monosaccharides transported through the basolateral membrane?

Answer 12

GLUT2

Question 13

In what form can protein be absorbed from the intestinal lumen?

Answer 13

Oligopeptides

Amino acids

Question 14

How are some proteins digested in the stomach?

Answer 14

HCl denatures proteins
Pepsin cleaves proteins into peptides
(not essential for protein digestions)

Question 15

How does protein digestions occur in the duodenum?

Answer 15

5 pancreatic proteases are secreted as proenzymes from the acinar cells of the exocrine pancreas
(converted into active form in duodenum)

Question 16

What are the 5 pancreatic proteases?

Answer 16

Trypsin
Chymotrypsin
Elastase
Procarboxypeptidase A
Procarboxypeptidase B

Question 17

Where are additional proteases present?

Answer 17

Brush border

Within cytoplasm of the enterocyte

Question 18

In what form can proteins be absorbed over the basolateral membrane?

Answer 18

Amino acids only

Question 19

Why are fats (lipids) more difficult to digest?

Answer 19

They are insoluble/poorly soluble in water

–> must be converted from solid fat to emulsion of fat droplets in order for enzymes to break it down

Question 20

How is fat broken down in the stomach?

Answer 20

Gastric lipase (modest importance in adults)

Question 21

How is fat broken down in the duodenum?

Answer 21

Pancreatic lipase

Question 22

What is the role of bile salts in fat digestion?

Answer 22

Bile salts released into duodenum in response to CCK
Act as detergents to help emulsify large lipid droplets into small droplets
–> increase surface area for attack by pancreatic lipase

Question 23

What happens when there is a failure to secrete bile salts?

Answer 23

Lipid malabsorption - steatorrhoea

Secondary vitamin deficiency due to failure to absorb fat soluble vitamins

Question 24

Which vitamins are fat soluble?

Answer 24

A, D, E and K

Question 25

How are fatty acids and monoglycerides transported across the enterocyte?

Answer 25

Short chain fatty acids –> diffuse across both membranes

Long chain fatty acids and monoglycerides are resynthesised to triglycerides in the enterocyte before crossing the basolateral membrane

Question 26

How is cholesterol absorbed from the intestinal lumen?

Answer 26

Via the NPC1L1 protein

Question 27

Which drugs blocks the NPC1L1 protein in order to reduce absorption of cholesterol?

Answer 27

Ezetimibe

Question 28

What form is dietary iron usually in, and what form can be absorbed by duodenal enterocytes?

Answer 28

Dietary –> Fe3+

Absorbed –> Fe2+

Question 29

Describe the conversion of Fe3+ to absorbable Fe2+

Answer 29

Fe3+ is reduced (accepts an electron) which is promoted by:
- HCl in stomach
- vitamin C
- ferric reductase
Fe2+ then binds to gastroferrin (from gastric parietal cells)

Question 30

How are where is vitamin B12 absorbed?

Answer 30

Intrinsic factor released from gastric parietal cells
B12 binds to intrinsic factor in the small intestine
B12-instrinsic factor complex is absorbed in the terminal ileum

Question 31

Which diet predisposed to B12 deficiency?

Answer 31

Vegan diet –> B12 not present in vegetables

Question 32

Which two hormones are responsible for reporting levels of stored fat to the brain?

Answer 32

Leptin (made and released from fat cells)
Insulin

–> inform hypothalamus to eat less and increase energy burn

This malfunctions in obesity

Question 33

What happens if someone has a genetic deficiency of leptin?

Answer 33

Mimics starvation in brain –> obsessive eating –> obesity

Can give therapeutic leptin injections

Question 34

In normal, diet induced obesity, what happens to leptin levels?

Answer 34

High leptin levels

BUT leptin resistance

Question 35

Which drug is licenced for weight loss and how does it work?

Answer 35

Orlistat

- inhibits pancreatic lipase, decreasing triglyceride absorption

Question 36

What are the side effects of Orlistat?

Answer 36

Cramping, bloating, flatulence, abdominal pain and diarrhoea
Need to take supplements for fat soluble vitamins
Tend to get rebound weight gain

Question 37

What are the effects of bariatric surgery?

Answer 37

Gastric bypass surgery

• -> substantial, sustainable weight loss
• -> significantly reduced mortality
• -> often complete resolution of T2DM