Digestion and absorption

What are the 2 enzymes used in carbohydrate digestion?

• Amylase

• Membrane bound disaccharidases

What bonds are hydrolysed in carbohydrate digestion?

Glycosidic

What 2 locations is amylase produced and released?

• Pancreas → Small intestine

• Salivary glands → Mouth

Where is membrane bound disaccharides located?

Attached to cell membranes of epithelial cells lining the ileum

What bonds are hydrolysed in protein digestion?

Peptide

What 3 locations does protein digestion occur?

1. Stomach

2. Duodenum

3. Ileum

What 3 enzymes are used in protein digestion?

• Endopeptidases

• Exopeptidases

• Dipeptidases

What bonds are hydrolysed in lipid digestion?

Ester

What enzyme is used in lipid digestion?

Lipase

How are glucose and galactose absorbed into the epithelial cells (6 steps)?

1. Na⁺ ions are actively transported out of epithelial cells into blood

2. This creates an Na⁺ ion concentration gradient

3. Na⁺ ions diffuse from the lumen of ileum into epithelial cells

4. Using Na⁺ ion dependent transporter proteins

5. Na⁺ ions carry glucose/galactose with them

6. Glucose/galactose is co-transported

How is fructose absorbed into the ileum?

• Facilitated diffusion

• Uses transporter protein

Describe in 6 steps how amino acids are absorbed into epithelial cells

1. Na⁺ ions are actively transported out of epithelial cells into blood

2. This creates an Na⁺ ion concentration gradient

3. Na⁺ ions diffuse from the lumen of ileum into epithelial cells

4. Using Na⁺ ion dependent transporter proteins

5. Na⁺ ions carry amino acids with them

6. Amino acids are co-transported

Describe in 10 steps how monoglycerides and fatty acids are absorbed into the ileum

1. Micelles constantly break up and reform, so release monoglycerides and fatty acids

2. Monoglycerides and fatty acids simply diffuse across the epithelial cell membrane

3. They move into the smooth ER of the epithelial cell

4. A condensation reaction takes place to form triglycerides 

5. Triglycerides are transported to the golgi body via vesicles

6. Within the golgi triglycerides are modified by being combined with proteins and cholesterol to form chylomicrons

7. Vesicles containing chylomicrons form and move to the surface of the small intestine epithelial cell

8. Vesicles fuse with the cell membrane and release the chylomicrons via exocytosis

9. The chylomicrons enter the lacteal of a villi and are transported through the lymphatic system

10. The lymphatic system drains into the subclavian vein located in the neck, so chylomicrons carrying triglycerides enter the blood at this point

What does the hydrolysis of a triglyceride produce?

2 fatty acids + 1 monoglyceride

Where is bile made, stored and released?

• Made: Liver

• Stored: Gallbladder

• Released: Duodenum

What does bile being alkaline do?

Neutralises stomach acid to provide optimum pH for lipase to act

What 4 things do bile salts do?

• Emulsification → Attach to emulsified fat droplets to prevent re-joining via the negatively charged heads

• Form micelles → Increases concentration gradient for diffusion of fatty acids and monoglycerides

• Give greater solubility

• Increase the rate of lipid digestion and absorption

Chylomicron

transport vesicle carrying triglycerides