GI Absorption

Question 1

The digestion of carbohydrates involves…

Answer 1

The breaking down of large carbohydrate molecules into small ones

Question 2

What are large carbohydrate molecules called?

Answer 2

Polysaccharides (many sugars)

Question 3

Polysaccharides are broken down by enzymes into…

Answer 3

Di and Tri Saccharides

Question 4

Di and Tri Saccharides can be broken down into…

Answer 4

Monosaccharides

Question 5

What are the group of enzymes responsible for breaking Di/TriSacchardies into monosaccharides called?

Answer 5

Brush Border Enzymes (Found in the epithelial layer of gut wall)

Question 6

Provide some examples of Di/Tri Saccharide breakdown?

Answer 6

• Disacchardie Sucrose which is composed of a glucose and fructose molecule is split by enzyme sucrase
• Disaccharide Maltose is composed of two glucose and is broken in two by enzyme maltase
• Disaccharide Lactose composed of one glucose and one galactose is broken into by enzyme lactase

Question 7

Describe how to the carbohydrate monosaccharides Glucose and Galactose are absorbed?

Answer 7

They are co-transported along with sodium ions by secondary active transport using ATP. Both sugar and sodium ion bind to transport protein

Question 8

Describe how the carbohydrate monosaccharide fructose is absorbed.

Answer 8

Fructose is absorbed by facilitated diffusion (carrier mediated)

Question 9

What is involved in the digestion of protein?

Answer 9

The breakdown of Polymers (large) into peptides (small) using the enzyme pepsin.

Question 10

What can protein peptides then be broken into and how?

Answer 10

Peptides can be broken into amino acids by pancreatic enzymes and brush border enzymes

Question 11

How are protein AA’s absorbed?

Answer 11

By secondary active transport along with sodium and hydrogen ions. (this is a different active transport system than that used by carbohydrates)

Question 12

Describe the basic composition of a lipid triglyceride?

Answer 12

One glycerol and three AA’s

Question 13

How are triglycerides broken down?

Answer 13

Triglycerides are broken down into monoglycerides + 2 fatty acids by the lipase enzymes

Question 14

Lipids are hydrophobic. How does this impact on their absorption?

Answer 14

They have a small surface area and so are digested and absorbed and slowly.

Question 15

What happens to lipids when bile salts are added?

Answer 15

Bile salts along with the churning action of the gut work to emulsify lipids breaking up the fat droplets into lots of small droplets thus increasing the surface area and speed of absorption

Question 16

Prior to the arrival of bile salts, what are the three products produced after lipase has acted on fat droplets?

Answer 16

• Short chain fatty acids (less than 12 carbons)
• Long chain fatty acids (more than 12 carbons)
• Monoglycerides

Question 17

How are short chain fatty acids absorbed?

Answer 17

Diffusion

Question 18

How are long chain fatty acids and monoglycerides absorbed?

Answer 18

Using bile salts to form micelles

Question 19

What are micelles?

Answer 19

Fat droplets surrounded by amphipathic bile salts that keep them soluble.

Question 20

How do micelles facilitate absorption?

Answer 20

Micelles once formed move to the brush border where the long chain fatty acids or monoglycerides are released and absorbed

Question 21

Following the absorption of long chain fatty acids and monoglycerides into an epithelial cell what happens next?

Answer 21

• Long chain fatty acids and monoglycerides join together into triglycerides
• Triglycerides combine with cholesterol and proteins to form chylomicrons
• chylomicrons are then expelled from the cell by exocytosis and they enter lacteal vessels in the villi

Question 22

What are lacteals?

Answer 22

Lymphatic vessels associated with the villus which drain into the blood stream.

Question 23

What food products are absorbed by lacteals?

Answer 23

Lipids