Digestion and Absorption of Carbs and Vitamins

Question 1

What are the water soluble vitamins?

Answer 1

Cs and Bs

• Folic Acid (B9)
• Cobalamin (B-12)

Question 2

What are the fat soluble vitamins?

Answer 2

A,D,E,K

Question 3

Most of our dietary carbohydrates come from what 3 sources and, in general, how are these broken down?

Answer 3

Starch –> pancreatic digestive enzymes and enzymes in saliva

Sucrose –> brush border enzymes

Lactose –> brush border enzymes

Question 4

Amylose

• What is the repeating disaccharide unit?
• What are the bonds that link them?

Answer 4

• Maltose
• Alpha-1,4 glycosidic bonds

Question 5

What are the linkages in amylopectin?

Answer 5

Alpha 1,4 glyosidic with alpha 1,6 glycosidic every 20-30 glucose molecules

Question 6

What enzyme is secreted in saliva to help digest carbs?

Answer 6

Amylase

Question 7

Fill in the blanks in this table for carbohydrate digestion.

Answer 7

Question 8

Answer 8

Question 9

The result of amylase acting on starches is what?

Answer 9

Breaking long polysaccharides into chains of glucose that are 2-9 glucose monomers in length (aka oligosaccharides) so that brush border enzymes in duodenum (SI) can then complete break down into monosaccharides

Question 10

Once the starches are digested into monosacchardies, describe how they are absorbed in the gut wall.

Answer 10

Coupled to Na+ absorption

Question 11

Describe the role of carbs in osmotic diarrhea.

Answer 11

Question 12

True/false: Some vitamins can be synthesized by the body.

Answer 12

False - vitains cannot be synthesized by body

Question 13

How are vitamins absorbed?

Answer 13

Uptaken at apical membrane via simple diffusion or carrier mediated transport. Transport across basolateral membrane is unknown.

Question 14

Where is iron absorbed?

Answer 14

Duodenum

Question 15

Where is folate (B9) absorbed?

By what mechanism?

Answer 15

Jejunum

Facilitated diffusion

Question 16

Where is cobalamin (B12) absorbed?

By what mechanism?

Answer 16

Ileum

Mediated by intrinsic factor

Question 17

Answer 17

Question 18

What is the role of gut microbiome in vitamin absorption?

Answer 18

Microbiota produce a lot of water soluble vitamins. However, they do so in the colon, which is downstream of the places where vitamins are absorbed, so these vitamins largey go un-utilized.

Question 19

• Where do we get vitamin B12 in diet?
• If you are a vegetarian, how long until you develop deficiency?
• If you have impaired absorption, how long until you develop deficiency?
• What do B12 deficiencies lead to?

Answer 19

• Meat and eggs
• 10-15 years
• 3-5 years
• Anemia with peripheral nerve dysfuction (pernicious anemia)

Question 20

Describe how B12 is absorbed.

Answer 20

• Food-bound B12 enters mouth and salivary glands secrete Transcobalamin I (R-binder), both travel to stomach
• Chief cells secrete pepsinogen –> degrades protein and frees B12
• B12 binds to R-binder in stomach once free
• Parietal cells secrete IF, which travels with R-B12 complex into duodenum
• Pancreatic proteases in duodenum degrade R-binder, freeing B12 to complex with IF
• IF-B12 complex binds receptor in ileum and undergoes endocytosis
• B12 enters portal circulation after binding carrier protein Transcobalamin II.

Question 21

Answer 21

A - Ach from vagus

C

Question 22

Answer 22

D

E