Gastrointestinal system 7

Question 1

What are the main nutrients that undergo chemical digestion

Answer 1

Carbohydrates (sugars)
Proteins
Lipids (fats)

Question 2

Why are carbohydrates an important source of energy

Answer 2

250-800 mg per day

Storage polysaccharides

Question 3

Describe structure of carbohydrates

Answer 3

Large complex chains of monosaccharides - (like glucose)

Question 4

Describe the composition of starch and glycogen

Answer 4

Long chains of glucose joined by alpha 1-4 glycosidic bonds

Question 5

What are three disaccharides

Answer 5

Sucrose (glucose and fructose)
Lactose (glucose and galactose)
Maltose (2 glucose)

Question 6

How much protein do we ingest a day

Answer 6

70-100g per day

Question 7

Are proteins a source of energy

Answer 7

No

Question 8

Why are proteins important

Answer 8

Required for amino acids

Question 9

How many amino acids can we synthesise

Answer 9

12

Question 10

What essential amino acids need to be ingested

Answer 10

Histidine
Leucine
Lysine

Question 11

Where do our proteins come from

Answer 11

50% diet

50% endogenous proteins - secreted into intestine (enzymes and immunoglobins)

Question 12

How much lipids do we ingest

Answer 12

100-150 per day

Question 13

Why do we need lipids

Answer 13

Source of energy - not essential -
Fat soluble vitamins (A,D, E & K),
Slow gastric emptying

Question 14

What is the main lipid

Answer 14

Gylcerol (backbone with 3 fatty acids attached)

Question 15

What are the viable lengths of fatty acids

Answer 15

Short chain - <6 carbons
Medium chain - 6-12 carbons
Long chain - 12-24 carbons

Question 16

Why do we need chemical digestion

Answer 16

Large complex molecules only absorbed as small molecules - reduces size of nutrients to allow absorption

Question 17

How is chemical and mechanical digestion related

Answer 17

Chemical digestion breaks up food particles to increase surface area for chemical digestion

Question 18

What are general properties of digestive enzymes

Answer 18

Extracellular
Organic catalysts
Very specific
Have optimal pH

Question 19

What is the composition of cellulose

Answer 19

Long chains of beta 1-4 glycosidic bonds

Question 20

What are the optimal pH’s of different enzymes

Answer 20

Salivary enzymes - alkaline
Gastric enzymes - Acidic
Small intestine - Alkaline

Question 21

What are the two stages of chemical digestion called

Answer 21

Luminal digestion

Contact digestion

Question 22

Describe luminal digestion

Answer 22

Enzymes secreted in lumen
Salivary - amylase
Stomach - pepsin
SI - Pancreatic enzymes

Question 23

Describe Contact digestion

Answer 23

In SI - completes digestion before absorption

Involves enzymes produced by enterocytes - attached to brush boarder

Question 24

Describe luminal digestion of carbohydrates

Answer 24

Salivary and pancreatic amylase converts polysaccharides to disaccharides

Question 25

Describe contact digestion of carbohydrates

Answer 25

Disaccharides converted to monosaccharides - Sucrase, lactase, maltase

Question 26

Describe luminal digestion of proteins

Answer 26

Pepsin in stomach | trypsin, Chymotrypsin and carbopeptidase in SI convert proteins into polypeptides

Question 27

Describe contact digestion of proteins

Answer 27

Peptidase attaches to brush boarder and converts polypeptides into amino acids

Question 28

Describe chemical digestion of lipids

Answer 28

Pancreatic lipase - lingual lipase and gastric lipase minor | No contact digestion

Question 29

What is the problem with lipid digestion

Answer 29

Digestive enzymes dissolved in luminal fluid - as lipids are fat soluble requires more complex process

Question 30

Describe the steps in chemical digestion of fats

Answer 30

Emulsification Stabilisation Digestion (Hydrolysis) Formation of micelles

Question 31

What does emulsification do

Answer 31

Breaks up lipid droplets into small droplets (0.5 - 1 um) In stomach - simple In SI - complex - bile salts stabilise

Question 32

Describe Stabilization

Answer 32

In SI | Bile salts - released with arrival of food - stabilize emulsion in small intestine - reduces size further

Question 33

Describe bile salts

Answer 33

Secreted by liver and concentrated in gall bladder | Have a hydrophobic and hydrophilic side

Question 34

Describe hydrolysis

Answer 34

Surface area of emulsion droplets in SI | Lipase converts triglycerides to monoglycerides and free fatty acids

Question 35

What is involved in hydrolysis

Answer 35

Involves Lipase and cofactor colipase - secreted by pancreas | Colipase anchors lipase to surface of droplet

Question 36

Why do we need micelles

Answer 36

Products of fat digestion insoluble in water

Question 37

Describe formation of micelles

Answer 37

Small droplets consisting of 20-30 molecules - Bile salts (amphipathic) surround fatty acids and monoglycerides