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Physiology and Neuroscience > Intestinal Absorption and Secretion > Flashcards

Intestinal Absorption and Secretion Flashcards

1
Q

how many litres is the dietary intake?

A

1.5L

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2
Q

what is the internal secretion formed of and the proportions?

A

saliva - 1.5L
gastric juice - 3L
pancreatic juice - 2L
bile - 0.5L

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3
Q

how many litres is the internal secretion in total?

A

7L

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4
Q

how many litres is the faecal loss?

A

0.2L

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5
Q

how many grams of NaCl have to be retrieved?

A

7L x 9g/L = 63 g of NaCl

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6
Q

are there villi in the colon?

A

no - just deep pits

500mL presented and 300mL recovered

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7
Q

what do crypt cells produce?

A

cells that migrate along villi in 48 hours

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8
Q

when can cells absorb?

A

when they mature

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9
Q

are tip cells mature?

A

yes - they can absorb

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10
Q

what do individual cells on villus have?

A

brush border with enzymes

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11
Q

what is present in the enterocytes

A

lateral spaces and tight junctions

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12
Q

how are the tight junctions at the top of the small intestine (jejunum)

A

leaky

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13
Q

how are the tight junctions at the bottom end of the small intestine (ileum)

A

tight

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14
Q

what do tight junctions allow?

A

permeability - fluid can enter the cell

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15
Q

how much does the surface area expands from simple cylinder

A

600x

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16
Q

how much do the folds of kerckring increase the surface area?

A

3x

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17
Q

how much do the villi increase the surface area?

A

10x

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18
Q

how much do the microvilli increase the surface area?

A

20x

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19
Q

how does this influence absorption

A

it is assumed to enhance absorption - it may be more for a surface for brush border enzymes

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20
Q

what does hydrostatic pressure do?

A

aid or prevent fluid absorption

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21
Q

is there net absorption when pressure is zero?

A

yes

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22
Q

how does the luminal pressure affect the blood pressure

A

if the luminal pressure increases so does the blood pressure

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23
Q

how does the luminal suction pressure affect the fluid absorption

A

it decreases the absorption rate

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24
Q

what does the “standing gradient” explain?

A

the absorption at zero net pressure - NaCl is pumped into the lateral spaces

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25
Q

how many stages are there in the standing gradient

A

2

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26
Q

how does the first stage of the standing gradient work

A

an increase in the osmotic pressure in the lateral spaces pulls fluid in through paracellular and transcellular routes

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27
Q

what happens in the second stage of the standing gradient

A

an increase in the lateral space hydrostatic pressure pushes fluid into the interstitial space and from there into the capillaries

28
Q

what does the biochemical engine for sodium ion transport consist of?

A

a serial membrane sited Na/K ATPase pump that pumps sodium ion out of the cell and takes K ion in

29
Q

how is the concentration of sodium within the cell

A

it is lowered

30
Q

why does the sodium ion diffuses in

A

because of a diffusion gradient for sodium ion

31
Q

what makes the absorbate close to plasma values

A

water dilution and lateral space hypertonicity

32
Q

where does some leakage of Na+ into lumen happen

A

in tight junctions

33
Q

where is the sodium ion from the sodium leakages recycled?

A

in the jejunum

34
Q

how effective is the absorption of the recycled sodium in the jejunum?

A

less efficient

35
Q

what makes the water absorption more effective in the ileum

A

the tight junctions are tight

36
Q

what is linked to the sodium ion gradient

A

the time it takes the solutes to be absorbed

37
Q

what does a sodium ion-glucose transporter (SGLT1) pulls in the brush border membrane?

A

a glucose molecule actively into the cell

38
Q

how does the glucose exits the cell?

A

passively via GLUT2

39
Q

what can glucose force sodium to do?

A

it can force sodium ion entry

40
Q

what is also absorbed by the route

A

many amino acids

41
Q

what makes the transporter PEPT pull peptides into the cell?

A

the proton gradient - pH outside the cell is pH6 through Na/H but inside is pH7.4

42
Q

what kind of ions also facilitate fatty acid absorption?

A

hydrogen ions - sp3 main foodstuffs absorbed by gradients in ions

43
Q

what does sodium ion gradient energises?

A

sugar and some amino acid absorption

44
Q

what does hydrogen ion gradient energises

A

peptides and some amino acid absorption

45
Q

how do fats converted to fatty acids enter the cell?

A

by associating with H+ ions - protonating

46
Q

what type of transport do some essential minerals undergo

A

active transport

47
Q

what type of transport do most essential vitamins undergo if they are nor fat soluble

A

undergo active transport

48
Q

how much liquid can be secreted in an hour by a person infected with cholera?

A

1L per hour

49
Q

what type of infection is cholera

A

intestinal affliction

50
Q

what occurs in cholera?

A

intestinal secretion form the villus cells (enyerocytes) enhanced by enterotoxins

51
Q

what is the normal secretion value per day accepted after 1971

A

1500mls per day – without proof

52
Q

what is the fluid circuit hypothesis

A

separation of secretion and absorption

53
Q

which is the new requirement for new biochemical apparatus

A

chloride to be transported towards the lumen with Na+ passively following

54
Q

what does NKCC1 do

A

it is a co-transporter and powers Cl- entry into the cell down the sodium ion gradient

55
Q

what does CTFR protein do?

A

allows Cl- out into the lumen

56
Q

what is the net effect

A

Cl- is propelled towards the lumen

57
Q

what does the cholera toxin do?

A

enhance the propulsion of Cl- towards the lumen and heat stable STa enterotoxin

58
Q

what attaches to intestinal receptors?

A

STa and cholera toxin (CT)

59
Q

how does STa cause Cl secretion

A

via cGMP guanylate cyclase

60
Q

how does CT cause Cl secretion

A

via cAMP adenylate cyclase

61
Q

how does STa influence fluid absorption

A

it reduces it

62
Q

what should the chloride channel blockers do if the secretion by Cl- channel blockers is ocurring

A

the chloride blockers should restore fluid absorption - but they don’t

63
Q

what does vibrio cholera promote?

A

the production of large amounts of VIP, a neurotransmitter vasoactive intestinal polypeptide), and Bona Occludens Toxin (ZOT)

64
Q

what is the function of ZOT

A

keep lateral spaces open

65
Q

how can we prove that fluid absorption or secretion depends on blood pressure i.e. capillary pressure?

A

using small intestine perfused with zero sodium ion perfusate and a sodium ion transport inhibitor, i.e. a loop that cannot absorb by biochemical means since fluid absorption is inhibited

Physiology and Neuroscience (40 decks)

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