CARBS Digestion and Absorption

Question 1

Where digestion begins in earnest

Answer 1

duodenum (first section of small intestine)

Question 2

The mixture for digestion can be any osmolality in these three regions. Where does the luminal contents need to be isosmotic to plasma?

Answer 2

1. oral cavity
2. esophagus
3. stomach

starting in the DUODENUM

Question 3

Which organ contains a larger number of microorganisms?

Answer 3

Large intestine (stomach and small intestinal lumen are relatively free of them)

Question 4

amylose

Answer 4

alpha-1,4 glycosidic linkage

Question 5

amylopectin

Answer 5

alpha-1,4 and alpha-1,6 glycosidic linakeges

Question 6

The human pancreas and salivary glands only secrete which enzyme for digestion and absorption of carbs? What linkages does it cleave? Where is it secreted and specifically where is it NOT secreted?

Answer 6

alpha-amylase, secreted into the lumen of the intestine and NOT into the blood

Question 7

The two components of starch

Answer 7

amylose and amylopectin (70-80% of structure)

Question 8

Where does digestion start?

Answer 8

In the mouth! Salivary gland amylase initiates

Question 9

What in the stomach inactivates salivary gladn amylase?

Answer 9

Acid pH

Question 10

Function of pancreatic amylase

Answer 10

hydrolyzes alpha-1,4 bonds to make small oligos, disacchs, and some monosacchs

Question 11

Enzyme responsible for producing monosaccharides

Answer 11

Brush border glycosidases

Question 12

What absorb monosaccharides? What are the transporters?

Answer 12

Intestinal epithelial cells: SLGT1, GLUT-5

Question 13

What happens to nondigestable complex carbs?

Answer 13

Partially fermented by microorganisms. The short chain free FAs resulting can be used by epithelial cells to make ATP

Question 14

Byproduct of the fermenation process

Answer 14

Methane–gets eliminated along with the non-digestible complex carbs (fiber)

Question 15

What are the two main ectoenzymes the intestinal epithelial cells make and secrete?

Answer 15

Lactase and sucrase

Question 16

What does SLGT1 in the absorptive epithelium transport?

Answer 16

Everything except fructose

Question 17

Glut-5:

1. Transports _____
2. active/not active transporters
3. Absorption capacity

Answer 17

1. fructose (think 5=five=fructose=F)
2. not active
3. incomplete-50%

Question 18

SLGT1

1. Transports ____
2. Active/not active transporter
3. Reabsorption capacity

Answer 18

1. Na-linked glucose/galactose transporter
2. Active transporter: Energy for transportation from Na/K ATPase on basolateral side.
3. High capacity and can absorb ~100%

Question 19

If you ingest equal amounts of glucose and fructose, which will have a higher plasma level?

Answer 19

Glucose will be higher since fructose absorption is not complete.

Question 20

Glut-2

1. Transports ____
2. Location
3. passive/active
4. paracellular reabsorption
5. osmolality

Answer 20

1. galactose/glucose + fructose
2. basolateral side
3. can only transport DOWNHILL (diffusion)
4. Cl
5. isosmotic

Question 21

Role of lactase

Answer 21

Lactose –> Glucose + Galactose

Question 22

Sucrase

Answer 22

Sucrose –> Glucose + Fructose

Question 23

Maltase

Answer 23

Maltose –> Glucose + Glucose

Question 24

If you wanted to lose weight, would you eat fructose or glucose?

Answer 24

Fructose

Question 25

What is the rate of digestion of brown starches? Explain why

Answer 25

The rate of digestion is slow and digestion and absorption occur over a longer distance of GI tract.

Question 26

What is they glycemic index? Compare glycemic index of amylose and oatmeal.

Answer 26

Glycemix index measures plasma glucose (y axis) vs. time. Oatmeal has a LOW index and over time has a much smaller peak than amylose. This is because it remains in the system longer. Feel full longer. Oatmeal rocks!

Question 27

After amylose sharply rises in the glycemix index graph, it drops quickly. What is the cause of this?

Answer 27

Insulin is released due to high blood sugar.

Question 28

What has the lowest glycemic index?

Answer 28

Fructose –30% (oatmeal is 67%)

Question 29

Cellulose, hemicellulose, xylans, pectin, and gums are all examples of what?

Answer 29

Non digestible starches = fiber

-made of plant cell wall materials, we lack enzyme to respond

Question 30

Where do enterocytes in small intestine get nutrition from?

Answer 30

Ingested amino acids

Question 31

3 advantages of eating fiber

Answer 31

1. gut stays full–requires bulk, motility stimulated by contents
2. keeps microflora happy–they digest and yield short chain fatty acids (which feed the colonocytes). methane and hydrogen are eliminated
3. absorbs certain toxins (cholesterol)

Question 32

Why can short (<6C) and medium chain (6-12 C) fatty acids bypass the requirement of bile which is needed for digestion and absorption?

Answer 32

Transporters are in absorptive cells in small and large intestine so these shorter FAs can be absorbed along most of the GI tract and reach the portal vein (to liver).

NB: liver secretes bile which is usually essential for lipid digestion and absorption. The liver screens and filters molecules absorbed by GI tract