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Z MD1 GI block > Digestion and absorption > Flashcards

Digestion and absorption Flashcards

1
Q

what promotes pancreatic alpha-amylase secretion

A

CCK

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1
Q

what emulsifies fat

A

bile salts and lecithin (but need vigorous mixing)

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2
Q

how does pancreatic alpha-amylase get into the duodenum

A

via the pancreatic duct

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2
Q

names of the transporters for glucose and fructose

A

SGLT1 - glucose GLUT5 and GLUT2 - fructose

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2
Q

how is pepsin inactivated

A

neutral pH (in the duodenum)

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2
Q

what happens to lipids when absorbed into epithelial cells

A

the FAs and monoglycerides reform triglycerides in the SER and are then coated with apolipoproteins –> chylomicrons

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4
Q

action of salivary amylase

A

hydrolyses 1:4 alpha linkages between glucose molecules (linear or branched chain)

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4
Q

pepsin is important for

A

breaking down cell-cell adhesion

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6
Q

what is the next carbohydrate digestive enzyme to act after salivary amylase

A

pancreatic alpha-amylase in the duodenal mucosa

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7
Q

what are the 4 main enzymes of the pancreatic proteases after action by enterokinase

A
  • trypsin - elastase - chymotrypsins - carboxypeptidases
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8
Q

how are micelles formed

A

bile salts + lecithin + monoglycerides + FAs + cholesterol

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9
Q

how does digestion of fat start

A

lingual lipase - very minor effect (probably more involved with taste)

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10
Q

where is glucose and fructose absorbed?

A

in the epithelium of duodenum and jejunum - predominatly at the tips of villi

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10
Q

how is pancreatic lipase activated?

A

CCK –> trypsin –> colipase –> lipase

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12
Q

what enzymes are found at the brush border of enterocytes for digestion of carbohydrates

A

isomaltase sucrase maltase

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13
Q

where and how are the FAs absorbed that are made by the microbiota

A

in the distal small bowel and proximal part of the colon via H+ dependent mechanism

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14
Q

what happens to some di and tri-peptides that are transported directly into epithelial cells

A

they are broken down to free amino acids by enterocyte small peptidases

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16
Q

first enzyme of carbohydrate digestion

A

salivary amylase

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17
Q

what size peptides end up at the brush border membrane

A

di and tri peptides and free amino acides

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18
Q

action of pancreatic alpha-amylase

A

hydrolyses 1:4 alpha linkages between glucose molecules (linear or branched)

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19
Q

where do pancreatic carboxypeptidases act? and what are their function

A

at the carboxy terminals of peptides producing free amino acids

21
Q

what is the action of sucrase

A
  • breaks sucrose into glucose and fructose - acts with isomaltase and maltase to break down maltotriose and maltose
21
Q

action of enterokinase

A

activates trypsinogen to trypsin –> positive feedback mechanism –> more trypsin and activates chymotrypsin

21
Q

how is cholesterol esterase activated

A

by bile

22
Q

how are pancreatic pro-enzymes activated

A

first by enterokinase in the epithelial membrane

23
Q

what is the next step in carbohydrate digestion after pancreatic amylase

A

digestion at the brush border membrane of mucosal enterocytes

24
Q

which enzymes act at the brush border for protein digestion

A

mix of: - aminopeptidases - carboxypeptidases - endopeptidases (trypsin, chymotrypsin and elastase) - dipeptidases

25
Q

where do endopeptidases act and what are their function

A
  • act at interior bonds of peptides - produce short polypeptides
26
Q

what is special about maltase and sucrase on the brush border of enterocytes

A

they are synthesised as a single large glycoprotein which is the inserted into the brush border membrane and then separated and activated by separate pancreatic proteases

27
Q

main disacchardies of diet

A

lactose and sucrose

27
Q

major sites of digestion

A

duodenum and upper jejunum

28
Q

what happens to the monosaccharides and amino acids that enter the capillaries from the small intestine

A

go into the circulation –> portal vein –> liver

29
Q

action of cholesterol esterase

A

hydrolysis of: - cholesterol esters - esters of fat - soluble vitamins - phospholipids

31
Q

function of pepsin

A

hydolyses bonds between aromatic amino acids (phenylalanine, tyrosine) and a second amino acid –> producing polypeptides of diverse sizes

33
Q

which enzymes are endopeptidases

A

trypsin elastase chymotrypsin

34
Q

what happens to the chylomicrons formed in epithelial cells

A

they are exocytosed –> enter the lymphatics

35
Q

how is fat absorbed

A

lipids inside micelles bought to apical surface of epithelial cells at tips of villi - when in contact with the membrane, the lipids dissolve in the membrane and enter the cells

37
Q

2 types of pepsinogen and where are they secreted

A
  • pepsinogen 1 - secreted in acid secreting regions - pepsinogen 2 - secreted close to pylorus
38
Q

how are free amino acids transported into capillaries

A

by 7 or more different transport systems

39
Q

what happens to salivary amylase over time

A
  • inactivated at acid pH in the stomach - reactivated at neutral pH in the duodenum after acid neutralization by bicarbonate in pancreatic juice
40
Q

what causes the secretion of pancreatic proteases

A

CCK triggered by amino acids

41
Q

even after salivary and pancreatic amylase acts on carbohydrates, we have a variety of oligosaccharides intact. Why is that?

A

because they are both ineffective at hydrolysing 1:6 alpha linkages

42
Q

how is fructose absorbed

A
  • transported by GLUT5 into epithelial cells - transported by GLUT2 into interstitium
43
Q

action of gastric lipase

A

again - minor role - produces enough FA to activate FA receptors –> release CCK from duodenum

45
Q

dietary monosaccharides

A

glucose and fructose and galactose

46
Q

what is the action of isomaltase

A
  • hydrolyses 1:6alpha linkages - acts with sucrase and maltase to break down maltotriose and maltose
47
Q

what causes the secretion of pancreatic lipolytic enzymes

A

CCK

48
Q

what is the accessory mechanism for the production of FAs

A

fermentation of dietary fibre by microbiota

49
Q

how is glucose absorbed

A

cotransported with Na by a sodium-dependent glucose transporter (SGLT1)

50
Q

how does the digestion of proteins start

A

pepsinogen –> pepsin (from chief cells) in the stomach - activated by gastric acid

Z MD1 GI block (18 decks)

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