Digestion and absorption

Question 1

what promotes pancreatic alpha-amylase secretion

Answer 1

CCK

Question 1

what emulsifies fat

Answer 1

bile salts and lecithin (but need vigorous mixing)

Question 2

how does pancreatic alpha-amylase get into the duodenum

Answer 2

via the pancreatic duct

Question 2

names of the transporters for glucose and fructose

Answer 2

SGLT1 - glucose GLUT5 and GLUT2 - fructose

Question 2

how is pepsin inactivated

Answer 2

neutral pH (in the duodenum)

Question 2

what happens to lipids when absorbed into epithelial cells

Answer 2

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

Question 4

action of salivary amylase

Answer 4

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

Question 4

pepsin is important for

Answer 4

breaking down cell-cell adhesion

Question 6

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

Answer 6

pancreatic alpha-amylase in the duodenal mucosa

Question 7

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

Answer 7

• trypsin - elastase - chymotrypsins - carboxypeptidases

Question 8

how are micelles formed

Answer 8

bile salts + lecithin + monoglycerides + FAs + cholesterol

Question 9

how does digestion of fat start

Answer 9

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

Question 10

where is glucose and fructose absorbed?

Answer 10

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

Question 10

how is pancreatic lipase activated?

Answer 10

CCK –> trypsin –> colipase –> lipase

Question 12

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

Answer 12

isomaltase sucrase maltase

Question 13

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

Answer 13

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

Question 14

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

Answer 14

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

Question 16

first enzyme of carbohydrate digestion

Answer 16

salivary amylase

Question 17

what size peptides end up at the brush border membrane

Answer 17

di and tri peptides and free amino acides

Question 18

action of pancreatic alpha-amylase

Answer 18

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

Question 19

where do pancreatic carboxypeptidases act? and what are their function

Answer 19

at the carboxy terminals of peptides producing free amino acids

Question 21

what is the action of sucrase

Answer 21

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

Question 21

action of enterokinase

Answer 21

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

Question 21

how is cholesterol esterase activated

Answer 21

by bile

Question 22

how are pancreatic pro-enzymes activated

Answer 22

first by enterokinase in the epithelial membrane

Question 23

what is the next step in carbohydrate digestion after pancreatic amylase

Answer 23

digestion at the brush border membrane of mucosal enterocytes

Question 24

which enzymes act at the brush border for protein digestion

Answer 24

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

Question 25

where do endopeptidases act and what are their function

Answer 25

- act at interior bonds of peptides - produce short polypeptides

Question 26

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

Answer 26

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

Question 27

main disacchardies of diet

Answer 27

lactose and sucrose

Question 27

major sites of digestion

Answer 27

duodenum and upper jejunum

Question 28

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

Answer 28

go into the circulation --\> portal vein --\> liver

Question 29

action of cholesterol esterase

Answer 29

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

Question 31

function of pepsin

Answer 31

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

Question 33

which enzymes are endopeptidases

Answer 33

trypsin elastase chymotrypsin

Question 34

what happens to the chylomicrons formed in epithelial cells

Answer 34

they are exocytosed --\> enter the lymphatics

Question 35

how is fat absorbed

Answer 35

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

Question 37

2 types of pepsinogen and where are they secreted

Answer 37

- pepsinogen 1 - secreted in acid secreting regions - pepsinogen 2 - secreted close to pylorus

Question 38

how are free amino acids transported into capillaries

Answer 38

by 7 or more different transport systems

Question 39

what happens to salivary amylase over time

Answer 39

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

Question 40

what causes the secretion of pancreatic proteases

Answer 40

CCK triggered by amino acids

Question 41

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

Answer 41

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

Question 42

how is fructose absorbed

Answer 42

- transported by GLUT5 into epithelial cells - transported by GLUT2 into interstitium

Question 43

action of gastric lipase

Answer 43

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

Question 45

dietary monosaccharides

Answer 45

glucose and fructose and galactose

Question 46

what is the action of isomaltase

Answer 46

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

Question 47

what causes the secretion of pancreatic lipolytic enzymes

Answer 47

CCK

Question 48

what is the accessory mechanism for the production of FAs

Answer 48

fermentation of dietary fibre by microbiota

Question 49

how is glucose absorbed

Answer 49

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

Question 50

how does the digestion of proteins start

Answer 50

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