L27: Absorption

Question 1

what are the 5 factors that affect absorption

Answer 1

1. reduction in nutrient size by chemical absorption
2. motility
3. transport across the GIT epithelium
4. surface area available for absorption
5. removal via the blood or lymph

Question 2

what does the rate that chyme travels through the GIT depend on

Answer 2

the balance between
1. storage from relaxation = stomach and large intestine
2. movement from peristalsis = stomach, SI and LI

Question 3

what happens when the rate that chyme travels through the GIT is too fast

Answer 3

not enough time for absorption = diarrhea

Question 4

what happens when the rate that chyme travels through the GIT is too slow

Answer 4

too much time for absorption = constipation

Question 5

what does motility affect when it comes to absorption

Answer 5

motility affects the exposure of the products of digestion to absorptive surfaces

Question 6

what does movement in and out of a cell require

Answer 6

1. pathway
2. driving force

Question 7

what are the 2 pathways of absorption

Answer 7

1. transcellular
2. paracellular

Question 8

what are the driving forces of absorption

Answer 8

1. energy
2. electrochemical gradient
3. osmotic gradient

Question 9

what type of absorption if paracellular transport

Answer 9

passive transport

Question 10

how many layers do you cross in paracellular pathway

Answer 10

just one = tight junction

Question 11

what driving force does paracellular pathway require

Answer 11

• osmotic gradient
• electrical/chemical or both

Question 12

what type of transport is transcellular pathway

Answer 12

passive for water or lipids
or active absorption

Question 13

how many layers does the transcellular pathway cross

Answer 13

crosses the cell membrane twice

Question 14

how do lipid soluble nutrients use the transcellular pathway

Answer 14

• through the membrane
• concentration gradient is the driving force

Question 15

how do water soluble nutrients use the transcellular pathway

Answer 15

• need a channel or transporter
• need a driving force
  1. ATP
  2. osmotic gradient
  3. electrical/chemical or both

Question 16

what is the relationship between surface are and absorption

Answer 16

greater surface area = faster rate of absorption

Question 17

how does the small intestine maximize its surface are

Answer 17

1. length = 6m
2. folding
   - plicae circulares
   - villi
   - microvilli

Question 18

what prevents the build up of nutrients in the intestinal fluid after absorption

Answer 18

the removal via the blood and lymph

Question 19

how does the blood and lymph prevent build up of nutrients

Answer 19

• high blood flow to intestines
• blood vessels and lacteals close to the basolateral side of epithelial cells
• maintains the gradient needed for movement across the basolateral membrane

Question 20

how are carbohydrates absorbed

Answer 20

passive and active

Question 21

how are proteins absorbed

Answer 21

passive and active

Question 22

how are water soluble vitamins absorbed

Answer 22

active transport

Question 23

how is sodium absorbed

Answer 23

passive and active transport

Question 24

how are lipids and fat soluble vitamins absorbed

Answer 24

passive absorption only

Question 25

how is water absorbed

Answer 25

passive absorption only

Question 26

what is the driving force fore passive transport

Answer 26

molecules diffuse down their concentration gradient across the leaky tight junctions

Question 27

what is the overall driving force for glucose absorption in active transport

Answer 27

sodium gradient generated by Na/K ATPase

Question 28

how does glucose transport across the apical membrane

Answer 28

- sodium-glucose cotransporter - sodium gradient = secondary active transport

Question 29

how does glucose transport across the basolateral membrane

Answer 29

- glucose transporter - glucose gradient = facilitated diffusion

Question 30

what is the overall driving force for protein active transport

Answer 30

sodium gradient generate by Na/K ATPase

Question 31

how do amino acids transport across the apical membrane

Answer 31

- sodium-amino acid transporter - sodium gradient = secondary active transport

Question 32

how do amino acids transport across the basolateral membrane

Answer 32

- amino acid transporter - amino acid gradient = facilitated diffusion

Question 33

which vitamins are water soluble

Answer 33

C and most of the B group

Question 34

what is the overall driving force for water soluble vitamin transportation

Answer 34

sodium gradient generated by Na/K ATPase

Question 35

how do water soluble vitamins transport across the apical membrane

Answer 35

- sodium-amino acid transporter - sodium gradient = secondary active transport

Question 36

how do water soluble vitamins transport across the basolateral membrane

Answer 36

- vitamin C transporter - vitamin C gradient = facilitated diffusion

Question 37

where is 90% of sodium absorbed

Answer 37

in the small intestine

Question 38

what is the overall driving force if sodium transportation

Answer 38

sodium gradient generated by Na/K ATPase

Question 39

how does sodium transport across the apical membrane

Answer 39

2nd active transport coupled with - monosaccharides - amino acids

Question 40

how does sodium transport across the basolateral membrane

Answer 40

pumped out by Na/K ATPase

Question 41

what are some mechanism on how we lose water

Answer 41

- sweat - urine - feces - breathing

Question 42

where is water secreted from into the GIT

Answer 42

- saliva, stomach, pancreas, liver, enterocytes - approx. 8L total per day

Question 43

what is the passive transport of water called

Answer 43

osmosis

Question 44

how does the small intestine absorb water

Answer 44

- leaky epithelium with leaky tight junctions - mostly absorbed via paracellular - some absorbed via transcellular = aquaporins

Question 45

how does the large intestine absorb water

Answer 45

- tight epithelia with tight junctions - all water reabsorbed via transcellular = aquaporins

Question 46

how are fatty acids and monoglycerides absorbed through the apical membrane

Answer 46

through passive absorption - FFA and monoglycerides diffuse from micelle into cell - the rest of micelle is not absorbed

Question 47

what happens to the fatty acids in the intracellular space after it has been absorbed through the apical membrane

Answer 47

- resynthesized into TAGs - packaged into chylomicrons

Question 48

how are fat soluble vitamins absorbed

Answer 48

they are absorbed passively with lipids

Question 48

how do the fatty acids cross the basolateral membrane to enter the lymph system

Answer 48

- the TAGS are exocytosis in chylomicrons - they then enter the lymph via lacteals of villi

Question 49

what is the driving force for fat soluble vitamin absorption

Answer 49

the concentration gradient

Question 50

how do fat soluble vit cross the apical membrane after being dissolved in micelles with fat

Answer 50

they diffuse the cell membrane because they are lipid soluble

Question 51

how do fat soluble vit cross the basolateral membrane

Answer 51

- packaged into chylomicrons with TAGs and exocytosis - enters the lymph via lacteals of villi