B10 Digestion and Absorption

Question 1

What is the definition of digestion?

Answer 1

• When enzymes hydrolyse large insoluble molecules into small soluble molecules so they can be absorbed and assimilated.

Question 2

What does assimilated mean?

Answer 2

• Be used by the body for a function

Question 3

What are the adaptations of the small intestine?

Answer 3

• Microvilli which increase SA
• One cell thick wall which decreases diffusion distance
• ## Lots of mitochondria for active transport

Question 4

Describe the steps of the conversion of starch into glucose.

Answer 4

• Starch is hydrolysed ( the glycosidic bond) into maltose by amylase that is released in the salivary glands, in the mouth
• Amylase gets denatured in the stomach
• The pancreas secretes more amylase
• More maltose is made
• Maltase hydrolyses maltose into glucose which is then absorbed into the blood

Question 5

Where is the enzyme maltase found?

Answer 5

• Embedded in the epithelial cell membrane

Question 6

What are co-transporters ( symports)?

Answer 6

• They are a type of carrier protein which bind two molecules at the same time.

Question 7

What are proteases (peptidases)?

Answer 7

Enzymes that hydrolyse the peptide bond between amino acids in the polypeptide chain to produce amino acids.

Question 8

What are the three types of proteases (in order of when each one is released)?

Answer 8

1. Endopeptidase
2. Exopeptidase
3. Dipeptidase

Question 9

Where is Endopeptidase released and what does it do?

Answer 9

• Released in the stomach
• Hydrolyses SOME internal peptide bonds
• This increases the surface area for exopeptidase
  endo= inside peptide chain

Question 10

Where is Exopeptidase released and what does it do?

Answer 10

• Released in the pancreas
• Hydrolyses peptide bonds at the end of the polypeptide to form amino acids

Question 11

Where is Dipeptidase released and what does it do?

Answer 11

• Embedded in the cell membrane
• Hydrolyses peptide bonds between amino acids of dipeptides to form amino acids for the absorption of amino acids

Question 12

Where does lipid digestion occur?

Answer 12

• Small intestine

Question 13

Describe the steps in lipid digestion.

Answer 13

• A fat globule has a low surface area so it is emulsified using Bile salts which are produced by the liver and stored in the gall bladder.
• Fat droplets are formed which have a higher surface area so lipase can hydrolyse the ester bonds forming fatty acids, glycerol and monoglycerides.
• To prevent the lipid products from forming a fat globule again the products are put in a micelle which is SOLUBLE and made of Bile salts and phospholipids.
• The micelle breaksdown and reforms near the small intestine villi until there is a high enough concentration of fatty acids and monoglycerides and a low concentration inside the cell. The micelle moves from high to low concentration via simple diffusion.

Question 14

Describe the steps in Lipid Absorption.

Answer 14

1. The lipid products enter the epithelial cell (not the micelle structure)
2. The products are resynthesised back into triglycerides by the Smooth Endoplasmic Reticulum
3. The golgi body forms a chylomicron using phospholipids, cholesterol and protein.
4. The protein is produced via the RER
5. The triglycerides are transported in the Chylomicron via exocytosis passed the blood into the lacteal.
6. Lacteal is part of the lymphatic system which eventually leaves to the blood.

Question 15

What is the ileum?

Answer 15

The end of the small intestine

Question 16

How is glucose absorbed into the blood?

Answer 16

• Sodium ions are actively transported out via the Na+/K+ pump creating a concentration gradient
• Glucose moves into the epithelial cell via co-transport with Sodium ions against the concentration gradient.
• Glucose moves into the blood by facilitated diffusion