Digestion of Carbohydrates and Proteins

Question 1

What is the functional unit of the exocrine pancreas made up of?

Answer 1

an acinus and its draining ductule

Question 2

What does the exocrine pancreas contain?

Answer 2

• enzymes (acinus)
• electrolytes (ductule)
• mucin (goblet)

Question 3

What does the endocrine pancreas produce?

Answer 3

• insulin
• glucagon
• somatostatin
• pancreatic polypeptide

Question 4

What do acinar cells in the pancreas secrete?

Answer 4

peptidases, lipases, alpha-amylases and nucleases

Question 5

What do ductal cells secrete?

Answer 5

1.2-1.5L/day of pancreatic juice

Question 6

Why does pancreatic juice have a high HCO3- concentration?

Answer 6

to regulate the pH of the upper intestine

Question 7

What can failure to produce pancreatic juice lead to?

Answer 7

duodenal ulcers

Question 8

What does the aqueous component of pancreatic juice contain?

Answer 8

• same amount of sodium and potassium as the ECF
• more HCO3- than ECF

Question 9

How is an acid tide formed in the plasma?

Answer 9

the HCO3- concentration increases as the rate of secretion increases so there is less time for HCO3-/Cl- exchange

Question 10

What are the 3 enzymatic components of the pancreatic juice?

Answer 10

• pancreatic α-amylase
• pancreatic lipases secreted in their active forms
• pancreatic proteases secreted in inactive zymogen forms

Question 11

What does pancreatic α-amylase do?

Answer 11

• hydrolyse glycogen and starch
• complex carbohydrates (except cellulose) into disaccharides

Question 12

Give examples of pancreatic proteases

Answer 12

trypsin, chymotrypsin and carboxypeptidase A and B

Question 13

What do water-insoluble esters require?

Answer 13

bile salts

Question 14

What is pancreatic secretion stimulated and inhibited by respectively?

Answer 14

• stimulated by parasympathetic system
• inhibited by sympathetic system

Question 15

What is the cephalic phase of pancreatic secretion activated and enhanced by?

Answer 15

activated by thought, sight, smell or taste of food and enhanced by vagal stimulation

Question 16

What happens in the cephalic phase?

Answer 16

secretion of pancreatic juice

Question 17

How is the gastric phase of pancreatic secretion enhanced?

Answer 17

by gastric distention and food breakdown products to release gastrin which produces low-volume high-enzyme pancreatic secretion

Question 18

What is the most important phase of pancreatic secretion?

Answer 18

intestinal phase (responsible for 70% of total secretion)

Question 19

What is the intestinal phase of pancreatic secretion stimulated by?

Answer 19

CCK and secretin released from endocrine cells in the duodenum and upper jejunum

Question 20

What is secretin used for?

Answer 20

to increase HCO3- secretion by the pancreas

Question 21

How does ACh affect pancreatic secretion?

Answer 21

it potentiates the effects of both CCK and secretin

Question 22

When is vagal stimulation more potent in stimulating pancreatic secretion?

Answer 22

when CCK and secretin are present in plasma

Question 23

When are CCK and secretin secreted?

Answer 23

in response to the entrance of chyme into the small intestine and a decrease in pH (<4.5)

Question 24

What are the major stimulants for CCK secretion?

Answer 24

amino acids (mainly phenylalanine and tryptophan), fatty acids and monoglycerides

Question 25

What must happen to CH2O before absorption?

Answer 25

it must be digested into monosaccharides

Question 26

Where does almost all digestion occur?

Answer 26

within the small intestine

Question 27

Where is pancreatic α-amylase most concentrated and what does it do?

Answer 27

in the duodenum and digests carbohydrates into a variety of oligosaccharides

Question 28

How are oligosaccharides converted to monosaccharides?

Answer 28

by brush border disaccharidases

Question 29

What is the rate limiting step in carbohydrate absorption?

Answer 29

the conversion of oligosaccharides to monosaccharides

Question 30

What are the end products of carbohydrate digestion?

Answer 30

fructose, glucose and galactose

Question 31

What parts of the GIT hasve the highest capacity to absorb sugars?

Answer 31

duodenum and upper jejunum

Question 32

What are glucose, galactose and xylose absorbed by?

Answer 32

a common Na+-dependent transport system

Question 33

What is fructose absorbed by?

Answer 33

facilitated transport – most of the fructose is rapidly converted into glucose and lactic acid within epithelial cells to maintain a gradient for diffusion

Question 34

How are monosaccharides transported across the basolateral membrane?

Answer 34

by facilitated transport

Question 35

What does failure to absorb carbohydrates result in?

Answer 35

diarrhoea and intestinal gas

Question 36

What is lactase sensitive to?

Answer 36

infectious and inflammatory diseases that affect the intestine

Question 37

What happens to proteins before they are absorbed?

Answer 37

they are digested into small polypeptides and amino acids

Question 38

What are the 3 enzymes involved in protein digestion?

Answer 38

- gastric pepsin - pancreatic proteases - enterocytes peptidases

Question 39

How much protein is digested and absorbed by the duodenum and jejunum?

Answer 39

50%

Question 40

How much protein reaches the ileum and colon respectively?

Answer 40

- 20-50% reaches ileum - 10% reaches colon

Question 41

What is the protein in stool from?

Answer 41

bacterial and cellular debris

Question 42

What are Na+-dependent transport systems for?

Answer 42

tripeptides, dipeptides and L-amino acids