Nutrient Digestion and Absorption

Question 1

What are the primary dietary constituents

Answer 1

Carbohydrates
Proteins
Fat
Vitamins
Water
Minerals

Question 2

How many molecules are in a oligosaccharide?

Answer 2

3-9 molecules

Question 3

How many molecules are in a polysaccharide?

Answer 3

10+ molecules

Question 4

What are some carbohydrates?

Answer 4

Monosaccharides
Disaccharides
Oligosaccharides
Polysaccharides

Question 5

What are the 3 main monosaccharides?

Answer 5

Glucose
Galactose
Fructose

Question 6

What is the difference between alpha and beta glucose?

Answer 6

Structural isomers of glucose
The orientation of the OH group on C1 is different
Beta has OH group above ring
Alpha has OH group below ring

Question 7

What is the differences and similarities between D-glucose and L-glucose?

Answer 7

Stereoisomers
In D-glucose the 3 hydroxyl groups are on right side with one hydrogen
In L-glucose, they are on left
D-glucose is mainly used and is narrower

Question 8

What are the 3 disaccharides?

Answer 8

Maltose
Sucrose
Lactose

Question 9

What is maltose made up of?

Answer 9

2 glucose molecules

Question 10

What is sucrose made up of?

Answer 10

1 glucose and 1 fructose

Question 11

What is lactose made up of?

Answer 11

1 galactose and 1 glucose

Question 12

What are the breakdown products of monosaccharides?

Answer 12

Complex CHOs which are absorbed by small intestine

Question 13

What bond is two monosaccharides bonded together by?

Answer 13

Glycosidic bond

Question 14

What are disaccharides are broken down into?

Answer 14

Constituent monomers by brush border enzymes in the small intestine

Question 15

Describe degradation of disaccharides?

Answer 15

Brush border enzymes break down them in small intestine
Degradation by lactase, maltase and sucrase

Question 16

What are 3 main polysaccharides?

Answer 16

Starch
Cellulose
Glycogen

Question 17

What is alpha-amylose?

Answer 17

Glucose linked in straight chains

Question 17

What is amylopectin?

Answer 17

Glucose chains highly branched

Question 17

Describe a starch

Answer 17

Plant storage form of glucose
Glucose monomers linked by alpha 1,4 glycosidic bonds - hydrolysed by amylases

Question 18

Describe cellulose

Answer 18

Constituent of plant cell walls
Dietary fibre - requires bacteria (cellulase)
Unbranched, linear chain of glucose monomers linked by beta 1,4 glycosidic bonds

Question 19

Describe glycogen

Answer 19

Animal storage form of glucose
Linked by alpha 1,4 glycosidic bonds

Question 20

What is the differences of starch, cellulose and glycogen?

Answer 20

Starch and Glycogen have alpha bonds so can be hydrolysed by amylases in saliva and pancreas
Cellulose is beta bonds so requires bacteria/cellulase

Question 21

What are some features of the small intestine?

Answer 21

Apical membrane
Microvilli
Tight junctional complex
Basolateral membrane

Question 22

What is transcellular transport?

Answer 22

Hydrophobic molecules can transport through cell

Question 23

What is vectoral transport?

Answer 23

Needs carriers and energy so is active directional transport

Question 24

What are some glucose transporters?

Answer 24

SGLT1 - need 2 Na and 1 glucose GLUT2 - enables protein facilitated glucose movement across cell membranes Works along with the Na/K pump to create electro chemical gradient

Question 25

Are glucose transporters passive or active?

Answer 25

Active

Question 26

What are some fructose transporters in small intestine?

Answer 26

GLUT5 - facilitated diffusion so passive as no fructose in blood but high glucose

Question 27

Describe proteins

Answer 27

Polymers of amino acids linked together by peptide bonds with variation in chain length Small - 3 to 10 in length = peptides

Question 28

What are the enzymes which hydrolyse proteins and peptide bonds into amino acids?

Answer 28

Proteases and peptidases

Question 29

Describe the breakdown of a protein

Answer 29

Endopeptidases break down the middle of chain into 2 smaller peptides Aminopeptidase and Carboxypeptidases then further break down

Question 30

Describe transport of amino acid across membrane

Answer 30

Through SAAT1 Facilitated transport along by the Na/K pump

Question 31

Describe transport of di and tripeptides across membrane

Answer 31

NHE3 - exchanger PepT1 is a c-transporter Works along with Na/K pump and other pumps to go across into blood

Question 32

What is the acid microclimate?

Answer 32

pH less than 6 near brush border - microvilli pH more than 7 further into small intestine Affects the absorption of weak electrolytes

Question 33

Where does fat digestion take place and by what enzyme?

Answer 33

Small intestine by pancreatic lipase

Question 34

What form is fat most commonly ingested as?

Answer 34

Triacylglycerol

Question 35

What is triacylglycerol broken down into by lipase?

Answer 35

Monoglyceride and 2 fatty acids

Question 36

Describe triacylglycerols

Answer 36

Present as large lipid droplets which are insoluble in water so lipase works on surface of droplet making slow digestion

Question 37

What is the process of emulsification?

Answer 37

Dividing large lipid droplets into smaller droplets which increases surface area and accessibility for lipase action

Question 38

What does emulsification require?

Answer 38

Mechanical disruption of large lipid droplets into small droplets Emulsifying agent - stops small reforming to large droplets

Question 39

What are some emulsifying agents?

Answer 39

Bile salts + phospholipids secreted in bile Amphipathic molecules

Question 40

Explain amphipathic molecules as emulsifying agents

Answer 40

Non polar portions associate with non-polar interior of lipid droplet Polar portions exposed at water surface so repel other small lipid droplets

Question 41

What is absorption enchased by formation of?

Answer 41

Micelles - smaller than emulsion droplets

Question 42

What does a micelle consist of?

Answer 42

Bile salt + monoglycerides + fatty acids + phospholipids

Question 43

Describe the structure of micelles

Answer 43

Polar at micelle surface then non-polar form core Hydrophobic fatty acids and monoacylglycerols in interior Bile salts on exterior

Question 44

What does micelle breakdown cause?

Answer 44

Releases small amounts of free fatty acids and monoglycerides into solution causing diffusion across plasma membrane

Question 45

What is the purpose of dynamic equilibrium between fatty acids and monoglycerides in solution and micelles?

Answer 45

Retains most of fat digestion products in solution while constantly replenishing supply of free molecules for absorption

Question 46

What happens when fatty acids and monoglycerides enter the smooth endoplasmic reticulum (sER)?

Answer 46

Reformed into triacylglycerol by enzymes in sER after entering epithelial cells

Question 47

When inside cells what is triacylglycerol coated in?

Answer 47

Amphipathic protein

Question 48

Explain triacylglycerol leaving epithelial cell

Answer 48

Transported in vesicles formed in sER membrane - processed in golgi apparatus and exocytosed at serosal membrane

Question 49

What are extracellular fat droplets called?

Answer 49

Chylomicrons

Question 50

Where do chylomicrons pass into?

Answer 50

Lacteals between endothelial cells - cant pass through capillary basement membrane

Question 51

What is the difference between fat-soluble and water-soluble vitamins?

Answer 51

Fat soluble follow fat absorption paths Water soluble absorbed by passive diffusion or carrier mediated

Question 52

What does B12 deficiency lead to?

Answer 52

Pernicious anaemia - failure of red blood cell maturation

Question 53

How is Vitamin B12 absorbed?

Answer 53

Binds to intrinsic factor in stomach to form complex then absorbed via specific transport in distal ileum

Question 54

How is iron absorbed?

Answer 54

Across brush border membrane via DMT1 into duodenal enterocytes Either binds to ferritin or unbound

Question 55

What happens to iron bound to ferritin?

Answer 55

Protein iron complex - intracellular iron store

Question 56

What happens to iron that is unbound?

Answer 56

Transported across serosal membrane into blood and binds to transferrin

Question 57

What does hyperaemia cause?

Answer 57

Increased ferritin level so more iron bound in enterocytes

Question 58

What does anaemia cause?

Answer 58

Decreased ferratin levels and more iron released to blood