1. GI Part 5

Question 1

what are the most abundant organic molecules in nature

Answer 1

carbohydrates

Question 2

list the functions of carbohydrates (4)

Answer 2

1. energy source
2. storage form of energy
3. cell membrane component (communication)
4. structural component (cell wall of bacteria)

Question 3

what are all carbohydrates made of

Answer 3

monosaccharides

Question 4

what is an example of a 5 carbon monosaccharide and a 6 carbon monosacchraide

Answer 4

5 carbons: pentoses – ribose

6 carbons: hexoses – glucose

Question 5

what are disaccharides

Answer 5

monosaccharides linked by glycosidic bonds

Question 6

what is an oligosaccharide

what is a polysaccharide

Answer 6

3-10 monosaccharides

> 10 monosaccharides (up to 100)

Question 7

what are examples of disaccharides

Answer 7

sucrose
lactose
maltose

Question 8

what is lactose

Answer 8

glucose + galactose connected by B linkage

milk sugar

Question 9

where does carbohydrate digestion start in pigs and humans

Answer 9

begins in mouth – alpha-amylase in salivary glands

Question 10

what are the major dietary carbohydrates (4)

Answer 10

1. starch
2. glycogen
3. saccharose
4. lactose

Question 11

how is further digestion of carbohydrates achieved

how is digestion finished

Answer 11

further digestion achieved by pancreatic enzymes

digestion is finished by enzyme secreted in the intestinal mucosa

Question 12

where does absorption of carbohydrates take place

Answer 12

duodenum and upper jejunum

Question 13

what is the absorption of carbohydrates mediated by

Answer 13

mediated by a Na-dependent transport mechanism (SGLT1) present at apical membrane

mediated by facilitated transport mechanisms at the apical membrane (GLUT5) and the basolateral membrane (GLUT2)

Question 14

where are proteins denatured

Answer 14

in the stomach

Question 15

what are proteins partially hydrolyzed by

what percentage of ingested proteins are hydrolyzed by this

Answer 15

pepsin

12-15%

Question 16

where does final digestion and absorption of proteins take place

Answer 16

small intestine

Question 17

what does pepsin turn proteins into

what does it turn peptides into

Answer 17

pepsin hydrolyzes proteins into oligopeptides

pepsin hydrolyzes peptides into amino acids

Question 18

what type of transport system do most amino acids use

what type of transport system do di and tripeptides use

Answer 18

most amino acids use secondary transport systems

di and tripeptides use tertiary transport systems

Question 19

how do amino acids get into the portal vein

Answer 19

facilitated diffusion

Question 20

what is amphipathic character

what parts of lipids are in each category of amphipathic character

Answer 20

both hydrophobic and hydrophilic

CH3(CH2)n – hydrophobic hydrocarbon chain

COO- – hydrophilic carboxyl group (ionized at pH 7)

Question 21

what are lipids used to synthesize (6)

Answer 21

1. prostaglandins
2. steroid hormones
3. phospholipids
4. platelet activating factor (PAF)
5. sphingomyelin – component of myelin in nerve fibers
6. bile acids produced from cholesterol

Question 22

where does emulsification occur and what does it do and why is it important

Answer 22

emulsification occurs in the duodenum

aims to reduce the surface area of the hydrophobic lipid droplets

crucial for lipase function which binds at the interface droplet/aqueous solution

Question 23

what emulsifies fat droplets

Answer 23

bile acids

Question 24

what do bile acids consist of

Answer 24

sterol ring

side chain of amino acids (taurine or glycine)

Question 25

what character of lipids allows emulsification

Answer 25

amphipathic character

Question 26

what are the main dietary lipids (3)

Answer 26

1. cholesterol esters
2. phospholipids
3. triglycerides

Question 27

where does lipid digestion start

Answer 27

stomach – gastric lipase

Question 28

steps of lipid digestion (6)

Answer 28

1. bile acids emulsify large fat droplets
2. emulsified fat droplets are still too large to enter the spaces of the microvilli
3. pancreas lipases hydrolyze triglycerides into monoglycerides and free fatty acids
4. these are surrounded by bile acids to form micelles
5. micelles can get into cell by diffusion, bile salts remain in the lumen
6. inside the cell monoglycerides and free fatty acids combine to create triglycerides

Question 29

what forms mixed micells

Answer 29

monoglycerides
free fatty acids
cholesterol
liposoluble vitamins

Question 30

what are the liposoluble vitamins

Answer 30

A
D
E
K

Question 31

how are mixed micelles absorbed

Answer 31

mixed micelles approach the brush border membrane of enterocytes where they will be absorbed

Question 32

do short chain fatty acids form mixed micelles

Answer 32

no

they are small enough to be directly absorbed

Question 33

what happens to long chain fatty acids once they are absorbed

Answer 33

long chain fatty acids go into the endoplasmic reticulum for re-esterification (re-synthesis) of more complex lipids – MAG + FFA = TAG

Question 34

what do triglycerides then become after re-esterification

Answer 34

chylomicrons

Question 35

how are chylomicrons release and where to

Answer 35

chylomicrons are released by exocytosis into the lymphatic vessel

Question 36

how do chylomicrons get to the blood

Answer 36

once in the lymphatic vessel they travel through the thoracic duct to the left subclavian vein and into the blood

Question 37

do chylomicrons go through the liver

Answer 37

no they bypass the liver because they go into the lymphatic system instead of the portal vein