nutrient digestion

Question 1

what are monosaccharides

Answer 1

breakdown products of complex carbs that are absorbed in small int

Question 2

what are disaccharides

Answer 2

lactose - glc + galactose

sucrose - glc + fruct

maltose - glc + glc

Question 3

how are polysaccharides digested (starch, glycogen)

Answer 3

hydrolysed by a-amylase

Question 4

how are monosaccharides absorbed across intestinal epithelium cells

Answer 4

Villi and microvilli on apical membrane and tight junctions

Glc need transporter - SGLT1 and Na+, water passes through tight junctions, conformational change, GLUT-2 transporter on basolateral side

Question 5

what are the 2 membranes in the small intestine cells

Answer 5

• apical - brush border w microvilli (go through this first)

- basolateral

Question 6

what transporters does glucose need in SI

Answer 6

SGLT1

GLUT-2

Question 7

what transporters does fructose need in SI

Answer 7

GLUT-5

Question 8

what is blood glucose maintained at?

Answer 8

5 mlmol

Question 9

how are proteins broken down into small peptides + AA

Answer 9

enzymes hydrolyse peptide bonds = proteases or peptidases

Question 10

what does AA absorption require

Answer 10

SAAT1 and Na+

water through

Question 11

what does peptide absorption require

Answer 11

PepT1 and Hion transport

Na and K pump

Question 12

what is the microclimate at the brush border in SI

Answer 12

acidic, pH < 6, lower than the lumen

Question 13

how is insoluble fat in form of triaglycerol digested in SI

Answer 13

digested by pancreatic lipase - water-soluble enzyme, can only digest surface of fat droplet
emulsification
micelles

Question 14

what is ingested fat in the form of

Answer 14

triaglycerol

Question 15

what does emulsification require from the body

Answer 15

mechanical disruption and smooth muscle contraction

Question 16

what is absorption of fat enhanced by

Answer 16

micelles

Question 17

what do micelles do in absorption of fat

Answer 17

keep molecules separated from each other

Micelle breakdown

• release small amount of FA + monogylcerides into solution, diffuse across cell membrane
• micelle not absorbed

Question 18

why do you need emulsifiers for fat absorption

Answer 18

prevents small droplet reforming to large

Question 19

what are some amphiphatic molecules, what do they do

Answer 19

bile salt and phospholipids in bile, production of emulsifiers and micelles for solubilising fats - into FA and monoglycerides

Question 20

what happens to digested fats once they enter SI cell

Answer 20

enter smooth endoplasmic reticulum (sER)
reformed into triacylglycerols
through golgi apparatus and exocytosed into ECF
chylomicrons
pass into lacteals between endothelial cells into lymphatic system

Question 21

how are fat soluble vitamins absorbed into SI

A, D, E, K

Answer 21

same as fat
broken down by pancreatic lipase
emulsified and micelles

Question 22

how are water soluble vitamins absorbed into SI

B, C, folic acid

Answer 22

passive diffusion or carrier-mediated transport

Question 23

how is vitamin B12 absorbed

Answer 23

binds to intrinsic factor in stomach, absorbed in distal ileum

Question 24

what is the result of B12 deficiency

Answer 24

pernicious anaemia (rbc dont mature)

Question 25

how is iron absorbed

Answer 25

across brush border membrane - DMT1 into duodenal enterocytes (cell of intestinal lining)
incorporated into ferritin (intracellular iron store, bound form)
unbound iron across membrane into blood stream

Question 26

what does iron in blood bind to?

Answer 26

transferrin

Question 27

what happens in hyperaemia

Answer 27

too much iron in body. -> inc ferritin levels -> more iron bound in enterocytes

Question 28

what happens in anaemia

Answer 28

not enough iron in body -> dec ferritin levels -> more iron released in blood

Question 29

what is ferrittin

Answer 29

protein-iron, intracellular iron store