GI PHYSIOLOGY III - DIGESTION

Question 1

TRUE/FALSE: enterocytes in the small intestine make digestive enzymes?

Answer 1

true

Question 2

what are the main nutrients that undergo chemical digestion?

Answer 2

carbohydrates, proteins and lipids

Question 3

what does carbohydrates store?

Answer 3

• polysaccharides
• large complex of monosaccharides

Question 4

what are the ingested carbohydrates?

Answer 4

starch and glycogen
- long chains of glucose

disaccharides
- sucrose (glu + fruc)
- lactose (glu + galac)
- maltose (glu + glu)

limited amount of monosaccharides
glucose

Question 5

what bond joins the chains of glucose in starch and glycogen?

Answer 5

alpha 1-4 glycosidic bond

Question 6

what is the main source of energy for body?

Answer 6

carbohydrates

Question 7

which are the essential amino acids that can not be synthesised?

Answer 7

histidine, leucine, lysine

Question 8

which are the sources of protein?

Answer 8

• 50% from diet
• 50% endogenous proteins like enzymes and immunoglobulins

Question 9

what is an important source of energy but not essential

Answer 9

lipids

Question 10

what are the fat soluble vitamins?

Answer 10

ADEK

Question 10

what are the ingested lipids mainly are?

Answer 10

triglycerides: glycerol back bone with 3 fatty acids attached

Question 11

what are the average amount consume of the nutrients that needed chemical digestion per day?

Answer 11

• carbs: 250-800g
• proteins: 70-100g
• lipids: 100-150g

Question 11

what is the role of chemical digestion?

Answer 11

reduces the size of nutrients allow them to be absorbed

Question 12

what is the role of mechanical digestion that assist chemical digestion?

Answer 12

mechanical digestion breaks up food, increases surface area available for chemical digestion

Question 13

TRUE/FALSE: digestive enzymes are extracellular

Answer 13

true

Question 14

list the optimal pH for each type of digestive enzyme?

Answer 14

• salivary and small intestinal enzymes: alkaline
• gastric: acidic

Question 15

what are the 2 stages of chemical digestion?

Answer 15

• luminal digestion
• contact digestion

Question 15

what is luminal digestion and where does it occur?

Answer 15

• initial digestion involving enzymes secreted into lumen
• salivary glands, stomach, small intestine - pancreatic

Question 16

what is contact digestion and where does it happen?

Answer 16

• completes digestion before absorption, involves enzymes produced by enterocytes and attached to brush border of enterocytes
• in small intestine

Question 17

what happens during luminal digestion of carbs?

Answer 17

• salivary and pancreatic amylase
• polysaccharides converted to oligosaccharides and disaccharides

Question 18

what happens during contact digestion of carbs?

Answer 18

• involves brush border enzymes: disaccharidases
• disaccharides converted to monosaccharides

Question 19

what happens during luminal digestion of proteins?

Answer 19

• pepsin in stomach
• trypsin and chymotrypsin to break down peptide bonds in small intestine
• carboxypeptidase acts as COOH terminus in small intestine
• convert proteins to polypeptides

Question 20

where is pepsin, trypsin, chymotrypsin and carboxypeptidase secreted?

Answer 20

• pepsin: precursors secreted by chief cells in stomach
• trypsin, chymotrypsin, carboxypeptidase: pancreas

Question 21

what occurs during contact digestion of protein?

Answer 21

many types of enzymes attached to brush borders, involved peptidase to convert polypeptides to individual amino acids

Question 22

where does fat digestion happen and does it involves both stage of digestion like carbs and proteins?

Answer 22

- in lumen of small intestine - NO contact digestion

Question 23

what is the main digestive enzyme of lipid digestion? what are the minor ones?

Answer 23

- pancreatic lipase main - lingual lipase and gastric lipase minor

Question 24

why is lipid digestion harder than carbs and proteins'?

Answer 24

because normally, digestive enzymes would dissolve in aqueous luminal fluid, however fat is insoluble in water and being seperated from the aqueous fluid

Question 25

what are the stages of lipids digestion? what does it mean?

Answer 25

- emulsification: motility - stabilisation using bile salts - digestion/hydrolysis using enzymes - formation of micelles using bile salts

Question 26

what does emulsification do to the lipid molecule and how does that assist the digestion?

Answer 26

- motility breaks up lipid droplets into small droplets - increase surface area for digestion

Question 27

where does lipid emulsification occur in?

Answer 27

- stomach: retropulsion as simple emulsion - small intestine: segmentation with bile salt stabilised the droplets

Question 28

where does stabilisation happen in?

Answer 28

small intestine

Question 29

describe structure of bile salt and what does it do to the lipid droplets?

Answer 29

- have a hydrophobic and negative charged hydrophilic side - the hydrophobic site + phospholipid attach to the droplets and stabilise as well as reduce the size of the emulsion droplets to increase the surface area

Question 30

where does hydrolysis occur in?

Answer 30

small intestine at surface of emulsion droplets

Question 31

what are the enzymes involved in hydrolysis stage of lipid digestion? where are they secreted from? what do they do?

Answer 31

- lipase and colipase - colipase anchors lipase to surface of droplet - lipase converts triglycerides to monoglyceride and free fatty acid

Question 32

however, after hydrolysis, monoglyceride and fatty acid are still insoluble inwater, therefore, they needed to be kept in solution through a formatioin of _______________

Answer 32

micelles

Question 33

what is micelles, describe the structure of micelle?

Answer 33

- small droplets around 4-6nm diameter - consist of 20-30 molecules of: bile salts, fatty acids and monoglycerides

Question 34

what does amphipathic means TRUE/FALSE: bile solubilises the products of lipid digestion

Answer 34

- amphipathic = have both hydrophylic and hydrophobic site - true (remember bile is not a lipolytic enzyme, it just assist the enzymes)