Digestion of Carbohydrates, Proteins and Lipids

Question 1

What drives the entire absorption process of carbs and proteins? What is the one exception to this?

Answer 1

• Na+/K+ ATPase
• Fructose is only one not dependent on ATPase, and has it’s own channel

Question 2

Describe glucose absorption.

Answer 2

• Glucose absorption is not directly dependent on energy
• Glucose absorption is secondary to active transport

Question 3

How does insulin affect glucose transport in the stomach and kidney?

Answer 3

It does not

Question 4

What does insulin primarily affect?

Answer 4

Adipose tissue

resting muscles

Question 5

Where is protein digested?

Answer 5

The lumen

Question 6

Does glucose require digestion for absorption?

Answer 6

Nope

Question 7

What digests sucrose prior to absorption?

Answer 7

Brush border enzymes

Question 8

These are directly absorbed by cell then broken down inside cell, what are they?

Answer 8

Oligopeptides

Question 9

These are broken down before absorption cell then resynthesize original molecule. What are they?

Answer 9

TAGs

Question 10

All chemical digestion and nutrient absorption occurs in the small intestine, what developments allow for greater surface area?

Answer 10

1. Circular folds of mucosa
2. Villi
3. Microvilli

Question 11

Juice secreted by small intestine does not contain any digestive enzymes. The synthesized enzymes act within the brush-border membrane of epithelial cells. What are the three enzymes we covered?

Answer 11

1. Enterokinase
2. Disaccharidases
3. Aminopeptidases

Question 12

Peptidase

Answer 12

breaks down peptides into amino acids

Question 13

Sucrase, maltase, lactase

Answer 13

break down disaccharides into monosaccharides

Question 14

Lipase

Answer 14

breaks down fats into fatty acids and glycerol

Question 15

Enterokinase

Answer 15

converts trypsinogen to trypsin

Question 16

Somatostatin

Answer 16

hormone that inhibits acid secretion by stomach

Question 17

Cholescystokinin

Answer 17

hormone that inhibits gastric glands, stimulates pancreas to release enzymes in pancreatic juice, stimulates gallbladder to release bile

Question 18

Secretin

Answer 18

stimulates pancreas to release bicarbonate ions in pancreatic juice

Question 19

What does the small intestine absorb?

Answer 19

• 80 % ingested water
• Electrolytes
• Vitamins
• Minerals
• Carbonates
  • active/facilitated transport
  • monosaccharides

•Proteins

   - di-/tripeptides
    - amino acids

•Lipids

   - monoglycerides
    - fatty acids
    - micelles
    - chylomicrons

Question 20

Fill in the boxes with the appropriate enzymes

Answer 20

Question 21

What are the two steps of carbohydrate digestion?

Answer 21

1. Intraluminal hydrolysis of starch to oligosaccharides by amylases
2. membrane digestion of oligo to mono by brush border disaccharidases

Question 22

What are the four brush border oligosaccharidases?

Answer 22

1. Lactase
2. Glucoamylase
3. Sucrase
4. Isomaltase

Question 23

What are the two steps of carbohydrate absorption?

Answer 23

1. Uptake across apical membrane into epithelial cell
2. coordinated exit across basolateral membrane

Question 24

Where does protein digestion begin?

Answer 24

In the stomach, when pepsin digests proteins to form polypeptides

Question 25

What are the endopeptidases of the duodenum and jejunum? (3)

Answer 25

1. Trypsin 2. Chymotrypsin 3. Elastase

Question 26

What are the exopeptidases of the duodenum and jejunum?

Answer 26

1. Carboxypeptidases 2. Aminopeptidase

Question 27

What are the brush border enzymes responsible for breaking down protein?

Answer 27

1. Carboxypeptidase 2. Aminopeptidase 3. dipeptidase

Question 28

Fill in the boxes with the correct enzymes or compounds.

Answer 28

Question 29

How are aminoacides and polypeptides transported across the basolateral membrane of enterocytes?

Answer 29

Facilitated or simple diffusion

Question 30

What type of transporter is PepT1? What does it move?

Answer 30

H+/oligopeptide cotransporter •dipeptides, tripeptides and tetrapeptides into enterocytes across apical membrane

Question 31

What is the defect responsible for Hartnup disease?

Answer 31

Impaired a.a. transport in the SLC6A19 transporter across the apical brush border membrane of the small intestine. (Also impacts transport in the proximal tubule of the kidney)

Question 32

What are the symptoms of Hartnup disease?

Answer 32

1. Pellagra like skin eruptions 2. cerebellar ataxia 3. gross aminoaciduria

Question 33

How does Hartnup disease manifest in infancy?

Answer 33

1. failure to thrive 2. photosensitivity 3. intermittent ataxia 4. nystagmus 5. tremor

Question 34

PepT1 also plays a major role in supplying what compound to the body?

Answer 34

Nitrogen

Question 35

Fill in the blanks with the appropriate compounds or enzymes.

Answer 35

Question 36

Describe steps 1-7 of the image.

Answer 36

Dietary fat (TGs) emulsified by bile salts into fat droplets 2. Lipase hydrolyses TGs into mono-glycerides & free FAs 3. These water insoluble products are carried in interior of water- soluble micelles to luminal surface of S.I. epithelial cells 4. Micelle in epithelial surface, mono-glycerides & free FAs leave micelles & passively diffuse through luminal membranes 5. Mono-glycerides & free FAs resynthesized into TGs inside epithelial cells 6. TGs aggregate & coated with lipoprotein to form water soluble chylomicrons 7. Chylomicrons enters lacteals

Question 37

What does the large intestine secrete into the colonic lumen?

Answer 37

K+ and HCO3-

Question 38

Hartnup disease can be overcome by a high protein diet. Why is this is possible?

Answer 38

The presence of PepT1 allows for the uptake of dietary di and tripeptides from the small intestinal lumen.