digestion and absorption

Question 1

What three things can be digested in mammals?

Answer 1

1. carbohydrates
2. proteins
3. Lipids

Question 2

What is the process of the digestion of carbohydrates?

Answer 2

• It begins in the mouth
• Continues in the duodenum
• Completed in the ileum.

Question 3

How many enzymes does carbohydrates need to hydrolyses them into monosaccharides?

Answer 3

Carbohydrates required more than one enzyme to hydrolyze them into monosaccharides such as amylase and membrane - bound disaccharidases.

Question 4

What is the function of amylase in the digestion of carbohydrates?

Answer 4

Amylase is produced by the pancreas and salivary glands. It hydrolyses polysaccharides into the disaccharide maltose by hydrolysing the glycosidic bonds.

Question 5

What are the membrane - bound disaccharides that are involved in the digestion of carbohydrates and what is their function?

Answer 5

Sucrase and lactase are the membrane - bound enzymes that hydrolyse sucrose and lactose into monosaccharides.

Question 6

How many enzymes are involved in the digestion of proteins?

Answer 6

Three enzymes that can be used to hydrolyse proteins ( large polymer molecules) are :
- endopeptidases
- exopeptidases
- membrane -bound dipeptidases

Question 7

What is the function of endopeptidases?

Answer 7

An enzyme that is involved in the digestion of proteins - it hydrolyses peptide bonds between amino acids in the middle of a polymer chain).

Question 8

What is the function of exopeptidases?

Answer 8

An enzyme that is involved in the digestion of proteins - it hydrolyses peptide bonds between amino acids at the end of a polymer chain.

Question 9

What is the function of a membrane - bound dipeptidases?

Answer 9

An enzyme involved in the digestion of proteins - it hydrolyses peptide bonds between two amino acids.

Question 10

What is the process for the digestion of proteins?

Answer 10

Protein digestion starts in the stomach, continues in the duodenum and is fully digested in the ileum.

Question 11

What are lipids digested by?

Answer 11

They are digested by lipase and the action of bile salts.

Question 12

Where is lipase produced and what is its function?

Answer 12

Lipase is produced in the pancreas and it can hydrolyse the ester bond in triglycerides to form the monosaccharides and fatty acids.

Question 13

Where is bile salts are produced and what is its function?

Answer 13

Bile salts are produced in the liver and can emulsify lipids to form tiny droplets, micelles. This increases the surface area for lipase to act on.

Question 14

What 2 stages does digestion lipids involve?

Answer 14

1. Physical ( emulsification and micelle formation )
2. Chemical ( lipase )

Question 15

What is the physical stage that involves the digestion of lipids?

Answer 15

Physical ( emulsification and micelle formation).
- Lipids are coated in bile salts to create an emulsion
- Many small droplets of liquid provides a larger surface area to enable the faster hydrolysis action by lipase

Question 16

What is the chemical stage that involves the digestion of lipids?

Answer 16

Chemical ( lipase )
- Lipase hydrolyses lipids into glycerol and fatty acids ( some monoglycerides ).

Question 17

What are micelles ?

Answer 17

They are water soluble vesicles formed of the fatty acids , glycerol, monoglycerides and bile salts.

Question 18

What do micelles deliver?

Answer 18

Micelles deliver fatty acids, glycerol and monoglycerides to the epitheilal cells of the ileum for absorption.

Question 19

Where are the products of digestion absorbed at?

Answer 19

They are absorbed across the cells lining the ileum.

Question 20

Describe the features of the ileum.

Answer 20

The ileum wall is covered in villi, which have thin walls surrounded by a network of capillaries and epithelial cells have even smaller micro villi.

Question 21

How do the features of ileum maximise absorption.

Answer 21

This happens by increasing surface area, decreasing the diffusion distance and maintaining a concentration gradient.

Question 22

What needs to be required for glucose and amino acids to be absorbed?

Answer 22

• To absorb glucose and amino acids from the lumen to the gut there must be a higher concentration in the lumen compared to the epithelial cells ( for facilitated diffusion ).

Question 23

Why is active transport and co - transport required for the absorption of glucose and amino acids ?

Answer 23

As there is a higher concentration of glucose and amino acids in the epithelial cells rather than in the lumen.

Question 24

Where are lipids digested?

Answer 24

Lipids are digested into monoglycerides and fatty acids by the action of lipase and bile salts.

Question 25

What happens when micelles encounter the ileum epithelial cells?

Answer 25

When they encounter the ileum epithelial cells, they diffuse across the cell-surface membrane to enter the cells of the epithelial cells due to the non-polar nature of the fatty acids and monoglycerides.
once in the cell, these will be modified into triglycerides in the endoplasmic reticulum and Golgi body.