Digestion and Absorption of Carbs and Vitamins Flashcards
What are the water soluble vitamins?
Cs and Bs
- Folic Acid (B9)
- Cobalamin (B-12)
What are the fat soluble vitamins?
A,D,E,K
Most of our dietary carbohydrates come from what 3 sources and, in general, how are these broken down?
Starch –> pancreatic digestive enzymes and enzymes in saliva
Sucrose –> brush border enzymes
Lactose –> brush border enzymes
Amylose
- What is the repeating disaccharide unit?
- What are the bonds that link them?
- Maltose
- Alpha-1,4 glycosidic bonds
What are the linkages in amylopectin?
Alpha 1,4 glyosidic with alpha 1,6 glycosidic every 20-30 glucose molecules
What enzyme is secreted in saliva to help digest carbs?
Amylase
Fill in the blanks in this table for carbohydrate digestion.
The result of amylase acting on starches is what?
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
Once the starches are digested into monosacchardies, describe how they are absorbed in the gut wall.
Coupled to Na+ absorption
Describe the role of carbs in osmotic diarrhea.
True/false: Some vitamins can be synthesized by the body.
False - vitains cannot be synthesized by body
How are vitamins absorbed?
Uptaken at apical membrane via simple diffusion or carrier mediated transport. Transport across basolateral membrane is unknown.
Where is iron absorbed?
Duodenum
Where is folate (B9) absorbed?
By what mechanism?
Jejunum
Facilitated diffusion
Where is cobalamin (B12) absorbed?
By what mechanism?
Ileum
Mediated by intrinsic factor
What is the role of gut microbiome in vitamin absorption?
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.
- 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?
- Meat and eggs
- 10-15 years
- 3-5 years
- Anemia with peripheral nerve dysfuction (pernicious anemia)
Describe how B12 is absorbed.
- 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.
A - Ach from vagus
C
D
E
