Nutrient digestion

Question 1

Describe the digestive process for conversion of complex carbohydrates to disaccharides

Answer 1

• Starch (α-1,4-glycosidic bonds): amylase (saliva and pancreas)
  
  • Glycogen (α-1,4-gylcocidic bonds): amylase
  • Cellulose (β-1,4-glycosidic bonds): we can’t break these don’t as we do not have cellulase but bacteria can

Question 2

Describe the digestive process for conversion of disaccharides to monosaccharides

Answer 2

• Maltose is broken down by maltase to produce two glucose
  
  • Sucrose is broken down by sucrase to a glucose and a fructose
    
    • Lactose is broken down by lactase into a glucose and a galactose

Question 3

Describe the mechanisms whereby monosaccharides are absorbed across epithelial cells

Answer 3

• Glucose and galactose
- SGLT 1 (coupled with Na) to get into the cell
- GLUT-2 to get out
- To keep the gradient up sodium exits via the sodium potassium pump
• Fructose
- GLUT-5 into cell
- GLUT-2 out

Question 4

Describe the digestive process for converting proteins into small peptides and amino acids

Answer 4

• Proteins are converted into peptides by proteases
• Peptides are converted into amino aides by peptidases
• Peptidases
- Endopeptidase: snip in the middle
- Exopeptidase: trim the ends

Question 5

Describe the mechanisms of absorption for amino acids and small peptides

Answer 5

• Amino acids
	- SAAT 1(coupled with Na) into cell
	- Diffuse out of the cell (amino acids are water soluble)
	• Dipeptides
	- PepT1: into cell (coupled with H)
	- Don't know how they get out

Question 6

Describe the digestive process for conversions of fat to triglycerols and monoglycerols

Answer 6

• Triglycerols= glycerol + 3 steric acids
• Triglycerols are converted to monoglycerols by lipase
• Triglycerols are fat soluble
* Lipases are water soluble

Question 7

what is needed for emulsification

Answer 7

• Mechanical disruption (smooth muscles contract)

* Emulsification agent: keeps droplets from reforming (needs to be amphipathic)

Question 8

What are emulsification droplets?

Answer 8

Bile salts + Phospholipids

Question 9

What are micelles?

Answer 9

• Micelles= Bile salts + Phospholipids + Monoglycerides + Fatty acids

- Fat taxi
- Fat soluble inside and water soluble outside
- The acid microclimate gives the micelles direction, but starts taking hydrogen molecules which makes the micelles unstable and it breaks up
- Micelles are not absorbed

Question 10

Describe the absorption of fat soluble and water soluble vitamins

Answer 10

• Fat soluble: A,D,E,K
	- Same route as fat
	• Water soluble: B, C and folic acid
	- Passive diffusion
	- Carrier mediated
	• Vitamin B12
	- Binds to intrinsic factor to form a complex in the stomach
	- Absorbed in the distal Ilium

Question 11

Describe the absorption of important minerals (iron)

Answer 11

• Iron

- DMT1 (duodenal enterocytes) 
- Ferratin (protein-iron complex that can hold up to 12 irons and it is like iron jail)
- Ferritin is the intracellular iron store that exits the body via faeces
- Iron that doesn't bind leaves the cell (serosa membrane) and binds to transferrin in the blood