HUBS192 Lecture 26 - Chemical Digestion

Question 1

what are the 3 main nutrients that undergo chemical digestion?

Answer 1

1) carbohydrates (sugars)
2) proteins
3) lipids (fats)

Question 2

what are carbohydrates?

Answer 2

storage polysaccharides

e.g starch and glycogen

Question 3

what are storage polysaccharides?

Answer 3

large complex chains of monosaccharides

-e.g glucose

Question 4

what are the 3 types of disaccharides ingested from carbohydrates from the human diet?

Answer 4

1) sucrose
- glucose + fructose
2) lactose
- glucose + galactose
3) maltose
- glucose + glucose

Question 5

what is sucrose?

Answer 5

glucose + fructose

Question 6

what is lactose?

Answer 6

glucose + galactose

Question 7

what is maltose?

Answer 7

glucose + glucose

Question 8

are proteins a source of energy and if so/not what are they a source of?

Answer 8

no proteins are a source of amino acids

Question 9

how many amino acids can be synthesised?

Answer 9

12 amino acids

Question 10

what are the amino acids that can not be synthesised called?

Answer 10

essential amino acids

-must be acquired from the diet

Question 11

what are the 2 sources of protein and what is the ratio of these 2 sources out of 100%?

Answer 11

• 50% diet

- 50% endogenous proteins

Question 12

what are endogenous proteins?

Answer 12

proteins secreted into the intestine that are the digestive enzymes and the immunoglobulins

Question 13

are lipids essential?

Answer 13

lipids are not essential

Question 14

are lipids a source of energy?

Answer 14

lipids are an important source of energy

Question 15

what do lipids contain in terms of vitamins?

Answer 15

fat soluble vitamins A,D, E and K

Question 16

what is the function of lipids?

Answer 16

lipids slow down gastric emptying

Question 17

what is the main component of lipids?

Answer 17

mainly triglycerides

Question 18

what is a triglyceride?

Answer 18

glycerol back bone with 3 fatty acids attached

Question 19

how many carbons are in a short fatty acid chain?

Answer 19

< 6 carbons

Question 20

how many carbons are in a medium fatty acid chain?

Answer 20

6-12 carbons

Question 21

how many carbons are in a long chain fatty acid?

Answer 21

12-24 carbons

Question 22

why do we need chemical digestion?

Answer 22

because food is ingested in the form of large complex molecules and the nutrients from food can only be absorbed as small molecules, therefore, chemical digestion is required because it reduces the size of nutrients to allow them to be absorbed

Question 23

where does chemical digestion occur?

Answer 23

occurs at the surface of food particles and utilises digestive enzymes

Question 24

what are the monosaccharides in cellulose joined together by?

Answer 24

long chains of beta 1-4 glycosidic bonds

Question 25

what are the names of the 2 stages of chemical digestion?

Answer 25

stage one = luminal digestion | stage two = contact digestion

Question 26

what occurs in stage one of chemical digestion?

Answer 26

luminal digestion - the initial digestion involving enzymes secreted into the lumen - salivary glands --> salivary amylase - stomach --> pepsin - small intestine --> pancreatic enzymes (pancreatic amylase, trypsin, chymotrypsin, carboxypeptidase, lipase)

Question 27

what occurs in stage two of chemical digestion?

Answer 27

contact digestion - occurs in the small intestine - completes digestion before absorption - involves enzymes produced by enterocytes and attached to the brush border of enterocytes (lining the small intestine) --> sucrase, lactase and maltase - disaccharides converted to monosaccharides

Question 28

where does chemical digestion of proteins occur for luminal digestion?

Answer 28

- pepsin is secreted into the stomach | - trypsin, chymotrypsin , carboxypeptidase in the small intestine are secreted by the pancreas

Question 29

what is the result of chemical digestion of proteins in luminal digestion?

Answer 29

converts proteins into polypeptides

Question 30

what is the result of chemical digestion of proteins in contact digestion?

Answer 30

converts polypeptides into individual amino acids

Question 31

what is the only stage of chemical digestion of lipids (fats)?

Answer 31

only luminal digestion, NO contact digestion

Question 32

what are the enzymes involved with the chemical digestion of lipids?

Answer 32

pancreatic lipase is the main digestive enzyme but lingual lipase and gastric lipase have a minor role

Question 33

why does lipid digestion require a more complex process?

Answer 33

because lipids (fats) are insoluble in water therefore the digestive enzymes can not be dissolved in the luminal fluid

Question 34

what are the 4 stages of the chemical digestion of lipids (fats)?

Answer 34

1) emulsification - motility 2) stabilisation - bile salts 3) digestion (hydrolysis) - enzymes 4) formation of micelles - bile salts

Question 35

what is the function of the emulsification stage of lipid (fat) digestion?

Answer 35

the motility breaks ups big lipid droplets into small droplets (0.5 - 1.0 um) and this increases the surface area for digestion

Question 36

what are the 2 types of emulsification of lipids (fats) and where do each of these occur?

Answer 36

1) simple emulsion - occurs in the stomach where the retropulsion motility pattern takes place 2) more complex emulsion - where the bile salts stabilise the lipid droplets for a long period of time

Question 37

where does stabilisation of lipids (fats) digestion occurs?

Answer 37

occurs in the small intestine

Question 38

where are bile salts secreted by and where are they concentrated?

Answer 38

secreted by the liver and concentrated in the gallbladder

Question 39

where are bile salts released and why?

Answer 39

released into the small intestine with the arrival of food

Question 40

what is the composition of bile salts?

Answer 40

composed of a hydrophobic (water-hating) and a negatively charged hydrophilic side (water-loving)

Question 41

what are the 2 functions of bile salts?

Answer 41

1) stabilise the emulsion in the small intestine | 2) further increase the surface area of the emulsion droplets

Question 42

where does the hydrolysis stage of lipid (fat) digestion occur?

Answer 42

occurs in the small intestine at the surface of emulsion droplets

Question 43

what enzymes does the hydrolysis stage of lipid (fat) digestion) involve and where are these secreted from?

Answer 43

involves lipase and cofactor colipase that are both secreted by the pancreas

Question 44

what is the function of colipase?

Answer 44

collapse anchors lipase to the surface of a emulsion droplet

Question 45

what is the function of lipase?

Answer 45

lipase coverts triglycerides to monoglycerides and free fatty acids

Question 46

what are the products of fat digestion that insoluble in water?

Answer 46

monoglycerides and long chain fatty acids

Question 47

what is the function of the formation of micelles stage in lipid (fat) digestion?

Answer 47

to keep the product of fat digestion in solution through the formation of micelles

Question 48

what are micelles?

Answer 48

micelles are small droplets (4-6 nm diameter) that consist of 20-30 molecules and contain: - bile salts - fatty acids - monoglycerides

Question 49

what does it mean that bile salts are amphipathic?

Answer 49

that the molecule has one side that is hydrophilic and one side that is hydrophobic