Digestion of Carbohydrates and Proteins Flashcards

1
Q

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

A

an acinus and its draining ductule

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2
Q

What does the exocrine pancreas contain?

A
  • enzymes (acinus)
  • electrolytes (ductule)
  • mucin (goblet)
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3
Q

What does the endocrine pancreas produce?

A
  • insulin
  • glucagon
  • somatostatin
  • pancreatic polypeptide
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4
Q

What do acinar cells in the pancreas secrete?

A

peptidases, lipases, alpha-amylases and nucleases

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5
Q

What do ductal cells secrete?

A

1.2-1.5L/day of pancreatic juice

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6
Q

Why does pancreatic juice have a high HCO3- concentration?

A

to regulate the pH of the upper intestine

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7
Q

What can failure to produce pancreatic juice lead to?

A

duodenal ulcers

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8
Q

What does the aqueous component of pancreatic juice contain?

A
  • same amount of sodium and potassium as the ECF
  • more HCO3- than ECF
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9
Q

How is an acid tide formed in the plasma?

A

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

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10
Q

What are the 3 enzymatic components of the pancreatic juice?

A
  • pancreatic α-amylase
  • pancreatic lipases secreted in their active forms
  • pancreatic proteases secreted in inactive zymogen forms
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11
Q

What does pancreatic α-amylase do?

A
  • hydrolyse glycogen and starch
  • complex carbohydrates (except cellulose) into disaccharides
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12
Q

Give examples of pancreatic proteases

A

trypsin, chymotrypsin and carboxypeptidase A and B

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13
Q

What do water-insoluble esters require?

A

bile salts

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14
Q

What is pancreatic secretion stimulated and inhibited by respectively?

A
  • stimulated by parasympathetic system
  • inhibited by sympathetic system
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15
Q

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

A

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

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16
Q

What happens in the cephalic phase?

A

secretion of pancreatic juice

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17
Q

How is the gastric phase of pancreatic secretion enhanced?

A

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

18
Q

What is the most important phase of pancreatic secretion?

A

intestinal phase (responsible for 70% of total secretion)

19
Q

What is the intestinal phase of pancreatic secretion stimulated by?

A

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

20
Q

What is secretin used for?

A

to increase HCO3- secretion by the pancreas

21
Q

How does ACh affect pancreatic secretion?

A

it potentiates the effects of both CCK and secretin

22
Q

When is vagal stimulation more potent in stimulating pancreatic secretion?

A

when CCK and secretin are present in plasma

23
Q

When are CCK and secretin secreted?

A

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

24
Q

What are the major stimulants for CCK secretion?

A

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

25
Q

What must happen to CH2O before absorption?

A

it must be digested into monosaccharides

26
Q

Where does almost all digestion occur?

A

within the small intestine

27
Q

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

A

in the duodenum and digests carbohydrates into a variety of oligosaccharides

28
Q

How are oligosaccharides converted to monosaccharides?

A

by brush border disaccharidases

29
Q

What is the rate limiting step in carbohydrate absorption?

A

the conversion of oligosaccharides to monosaccharides

30
Q

What are the end products of carbohydrate digestion?

A

fructose, glucose and galactose

31
Q

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

A

duodenum and upper jejunum

32
Q

What are glucose, galactose and xylose absorbed by?

A

a common Na+-dependent transport system

33
Q

What is fructose absorbed by?

A

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

34
Q

How are monosaccharides transported across the basolateral membrane?

A

by facilitated transport

35
Q

What does failure to absorb carbohydrates result in?

A

diarrhoea and intestinal gas

36
Q

What is lactase sensitive to?

A

infectious and inflammatory diseases that affect the intestine

37
Q

What happens to proteins before they are absorbed?

A

they are digested into small polypeptides and amino acids

38
Q

What are the 3 enzymes involved in protein digestion?

A
  • gastric pepsin
  • pancreatic proteases
  • enterocytes peptidases
39
Q

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

A

50%

40
Q

How much protein reaches the ileum and colon respectively?

A
  • 20-50% reaches ileum
  • 10% reaches colon
41
Q

What is the protein in stool from?

A

bacterial and cellular debris

42
Q

What are Na+-dependent transport systems for?

A

tripeptides, dipeptides and L-amino acids