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DRS > L9 - absorption of water and ions > Flashcards

L9 - absorption of water and ions Flashcards

1
Q

function of small intestine (SI)

A

-absorption of dietary nutrirents

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2
Q

cells in SI

A
  • absorptive cell
  • goblet cells
  • enteric endocrine for secreting hormones
  • stem/progenitor cell - important for crypt-villous axis and division into intestinal cells
  • paneth cell- defences against pathogens
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3
Q

function of villous and crypt enterocytes

A

villous - nutrients and electrolyte absorption

crypt - released secretion

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4
Q

adaptation fo SI for absorption

A
  • folds of the SI
  • villi and microvilli to
  • both increase SA
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5
Q

two movements of solutes being absorbed

A

-transcellular and paracellular

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6
Q

how is water absorbed

A

the chyme is isotonic so no worries about the water diffusing into the lumen of the SI

  • Na ions actively transported into the lateral intercellular cells of SI
  • then Cl- ions are passively absorbed down the electrochemical gradient due to Na ions
  • this causes the space to be hypertonic so water diffuses by osmosis intoo the spaces via TJs
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7
Q

what ions are absorbed or secreted in jejenum

A

-Na actively absorbed
-K+ passively absorbed
-Cl- absorbed
HCO- absorbed

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8
Q

what ions are absorbed or secreted in ileum

A

-Na actively absorbed
-K+ passively absorbed
-Cl- absorbed
HCO- secreted

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9
Q

what ions are absorbed or secreted in colon

A

-Na actively absorbed
-K+ net secretion
-Cl- absorbed
HCO- secreted

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10
Q

how many routes can Na ions can be absorbed

A

-4

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11
Q

how can Na be absorbed through Na/glucose transport

A
  • called SGLT1
  • Na ions actively transported out of the SI cells by ATPase in basal membrane
  • this reduces the conc of NA in the cells
  • so the NA diffuses in with glucose or AA on apical membrane
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12
Q

how can Na be absorbed through Na/H

+ transport

A
  • Na taken in for exchange for H into the lumen
  • Na also transported out to create a conc gradient
  • the pH increases so the HCO3 is secreted to neutralise
  • occur in jejejum and less in duodenumn
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13
Q

how can Na be absorbed through parallel Na/H and Cl/HCO3

A
  • NA actively transported out for low [NA]i
  • water diffuses into the cell and joins with CO2 > carbonic acid> dissociation
  • NA in exchange for H out
  • Cl in for HCO3 out for neutralisation
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14
Q

in what state can parallel Na/H and Cl/HCO3 happen

A
  • fasted
  • because it doesnt require any nutrients
  • doesnt depend on pH
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15
Q

where does parallel Na/H and Cl/HCO3 occur in

A

-ileum and large intestine

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16
Q

how is parallel Na/H and Cl/HCO3 regulated

A
  • by cAMP and cGMP, [Ca2+]i

- this reduces NaCl absorption

17
Q

what happens if the cAMP levels is too high

A
  • the ions arent absorbed so they remain in the lumen
  • the contents in the lumen becomes hyper tonic so the water move into the lumen
  • causes diarhhoa
18
Q

how can Na be absorbed through epithelial Na channels

A
  • enters through the channels

- v.effecient - absorb against large conc gradient

19
Q

what molecule increase Na absorption and how

A

-mineralcorticoids and they increase
-the opening of the apical
channels
-insertion of channels
-synthesis of NA/K pumps

20
Q

where does CL get absobred

A

SI and LI and linked with Na absorption

21
Q

ways that Cl gets absorbed

A
  • parallel Na-H and Cl-HCO
  • passive Cl absorption
  • Cl and HCO3 exchnage
22
Q

how does Cl passive absorption occur

A

driven by electrochemical gradient

-driving force from the SGLT1 transport or Na channels

23
Q

chemical mediators that regulates intestinal electrolyte transport

A
  • absorptagogues

- secretagogues

24
Q

what are absorptagogues and how are they involved in removal of dehydration

A
  • promotes absorption
  • when dehyrdation occurs, this molecule is released
  • stimulates Na absorption and water moves in too
25
Q

what are secretagogues

A

-promotes secretion diarrhoea

26
Q

4 categories of secretagogues

A

-bacterial eneterotoxins
-hormones and NTs
-immunitic cells
laxatives

27
Q

how does enterotoxin induce diarrhoea and treatment for it

A
  • induces cAMP so inhibits Na -Cl absorption

- taking oral medicine containing glucose to increase the action of SGT1 since it’s not affected to absorb Na

28
Q

how can Ca ions be absorbed

A

passively via paracellular pathway

-actively in duodenum under control of VDR

29
Q

steps of active Ca absorption

A
  1. uptake of Ca via Ca channels
  2. the Ca binds to calbindin which acts as a buffer
  3. Ca goes into Ca pump and also exchanged for Na by Na-Ca exchanger . the Ca move from the cell into the interstitial fluid

DRS (18 decks)

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