Digestion And Absorption

Question 1

What are the stages that take place in digestion?

Answer 1

Physical breakdown (via teeth)

Chemical digestion (via enzymes)

Question 2

What is chemical digestion?

Answer 2

The breakdown of large insoluble molecules into smaller soluble ones by enzyme catalyses hydrolysis so they can be absorbed across cell membranes

Question 3

What do carbohydrases do?

Answer 3

Hydrolyse carbohydrates to monosaccharides

Question 4

What do lipases do?

Answer 4

Hydrolyse lipids to glycerol and fatty acids

Question 5

What do proteases do?

Answer 5

Hydrolyse proteins to amino acids

Question 6

How is starch broken down into glucose?

Answer 6

After the physical breakdown in the mouth, salivary enzymes are added to hydrolyse the starch into maltose
This then gets hydrolysed again by pancreatic amylase into glucose
This is then transported to the ileum where co transport takes place absorbing it into the blood.

Question 7

How are lipids broken down into smaller lipid droplets?

Answer 7

Lipids are emulsified by Bile salts which increase their surface area to then be hydrolysed by lipases into fatty acids and glycerol

Question 8

How are proteins digested?

Answer 8

Hydrolysis of the peptide bonds

Endopeptidases hydrolyse peptide bonds in the middle of the polypeptide breaking it down into smaller peptide chains

Exopeptidases hydrolyse peptide bonds between the terminal amino acids and remove them

Dipeptidases hydrolyse peptide bonds in dipeptides to form amino acids

Amino acids are then absorbed into the blood via cotransport in the ileum

Question 9

How are lipids digested?

Answer 9

1. Triglycerides are hydrolysed into fatty acids and glycerol by lipases during digestion
2. They remain associated with the bile salts and have formed miscells
3. Miscells travel to the epithelial cells lining the vile of the ileum
4. The miscells are broken down releasing the glycerol and fatty acids which diffuse across the membrane (non polar) and the bile salts move away
5. These are then transported to the ER where they are recombined to form triglycerides.
6. The triglycerides are then modified in the Golgi and are combined with cholesterol and lipoproteins to form chylomicrons
7. The chylomicrons are moved out of the cell via exocytosis and enter the lymphatic lacteals.
8. The lacteals then transport the chylomicrons to the blood when the triglycerides within are hydrolysed by endothelial cells of blood capillaries and the lipids are absorbed

Question 10

How is the ileum adapted for its function?

Answer 10

Have microvilli to increase surface area for fast diffusion and Active transport

Thin epithelial cells (1 cell thick) so short diffusion pathway

Contain co-transport proteins ( symport proteins

Question 11

What is the ileum?

Answer 11

Part of the small intestine before it joins the large intestine

Question 12

How does glucose co transport work in the ileum?

Answer 12

1. Na+ ions are actively transported into the blood by the sodium potassium pump
2. Now the concentration of Na+ ions is lower in the epithelial cell than the intestinal lumen
3. Na+ ions diffuse into the cell through co transport (symport) proteins which additionally transports glucose form the intestinal lumen.
4. Glucose then diffuse out from the cell and into the blood through carrier proteins (facilitated diffusion)

Question 13

Where is glucose and amino acids absorbed into the blood?

Answer 13

By cotransport of glucose or amino acids in the ileum

Question 14

How is co transport of glucose considered an indirect form of active transport?

Answer 14

ATP is used to generate the Na+ gradient by powering the sodium potassium pump. This is essentially what drives the co transport process and hence is indirectly an active process