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GI Physiology > Intestinal Transport 1: Fluid and Electrolytes > Flashcards

Intestinal Transport 1: Fluid and Electrolytes Flashcards

1
Q

what are the order and lengths of the different small intestine portions?

A

duodenum (11 in)
jejunum (8 ft)
ileum (12 ft)

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2
Q

what is the surface area of the jejunum compared to the ileum? what causes this increase?

A

three times greater

caused by successive folding of the mucosal surface

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3
Q

what are the three amplifications of surface area of the small intestine?

A

macroscopic plica circularis (folds of kerckring), microscopic villi and crypts of Lieberkuhn and submicroscopic microvilli

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4
Q

how does the structure of the colon mucosa differ from the small intestine

A

there are crypts but no villi

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5
Q

how much of the intestines can be removed without compromising absorptive function?

A

half

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6
Q

what is celiac disease? what is another name for it?

A

gluten destroys absorbtive cells and decreases the number of functional villi. dehydration and malnutrition result
sprue

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7
Q

what is tropical sprue?

A

infectious disease associated with diarrhea, malabsorption and nutritional deficiencies

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8
Q

how long does it take for a enterocyte to differentiate and move to the tip of a villus? how long does it take to replace the intestinal epithelium normally?

A

5 days

a week

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9
Q

what do goblet cells do?

A

secret mucous in response to acetylcholine

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10
Q

which two cells have the same stem cell at the base of the crypt?

A

goblet cells and enterocytes

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11
Q

what do the undifferentiated cells at the base of the crypt do? how does this change as they mature?

A

they secrete NaCl from the blood into the lumen

take on absorptive function as they move up the villus

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12
Q

why does the intestinal mucosa have a great radiation sensitivity?

A

because there is a high turnover of the mucosa

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13
Q

what is the shunt pathway? what is it permeable to?

A

paracellular pathway through the tight junctions between enterocytes
permeable to H2O and cations (low permeability to anions)

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14
Q

what matrix is associated with the brush border? what is associated with it?

A

glycoprotein matrix

ectoenzymes are associated with it (enterokinase, disaccharidases and peptidases)

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15
Q

what is contained within the lamina propria of enterocytes?

A

lacteals and capillaries

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16
Q

which parts of the intestines have leakier tight junctions?

A

jejunum> ileum> colon

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17
Q

when are water and most nutrients absorbed by? what are the exceptions?

A

the end of the jejunum

vitamin B12 and bile salts- absorbed in distal ileum

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18
Q

how are bile salts removed from the lumen?

A

sodium dependent cotransport in the distal ileum

19
Q

how is vitamin B12 absorbed?

A

it is absorbed bound to intrinsic factor (secreted by gastric parietal cells) in the distal ilium

20
Q

what does the jejunal enterocyte absorb to prevent diarrhea? what happens to it

A

NaHCO3- transported out of the enterocyte into the blood

21
Q

how does Na enter the jejunal enterocyte across the apical membrane? how does it travel across the basolateral membrane?

A

Na/ glucose and Na/AA cotransport & NA/H antiport

Na/K pump coupled with a K channel to dissapate the gradient

22
Q

what is caused by the increase of the Na/K pump after a meal?

A

electrogenicity of the pump causes a potential to form across the serosal side of the cell

23
Q

what are the 4 mechanisms of sodium absorption and where are they most active?

A

AA and glucose cotransport (jejunum)
Na/H exchanger (jejunum)
Na/H and Cl/CHO3 parallel exchange (ileum and colon)-Cl flows down concentration gradient into blood
epithelial Na channel (distal colon)

24
Q

how is NaCl absorption controlled in the ileum and proximal colon?

A

cAMP inhibits absorption (stimulated by E coli and Vibriocholera toxin)
ACh stimulates cAMP along with VIP in vipomas

25
Q

what is the function of CFTR in crypt cells? how is it influenced by cAMP

A

located on the apical membrane- allows Cl secretion into the lumen
activated by cAMP

26
Q

what ion movement exists at the crypt cell basolateral membrane? what does this do?

A

Na/2Cl/K symporter from blood, K channel out and Na/K pump

creates a concentration gradient for K and Na to move out into the lumen

27
Q

how does ACh stimulate NaCl excretion?

A

by increasing intracellular Ca- increasing K conductance

membrane hyperpolarization drives Cl out of cell

28
Q

what does cholera toxin do to enterocytes? what causes worse diarrhea than cholera?

A

increases cAMP in cells
inhibits absorption of NaCl in ileum
increases secretion of NaCl by jejunal crypt cells
vipomas increase cAMP more–worse diarrhea

29
Q

what is an oral rehydration solution?

A

a mixture of saline and glucose to enhance Na reabsorption (Na/glucose symporter)

30
Q

what 8 endogenous factors promote intestinal secretion?

A

ACh, histamine, CCK, secretin, gastrin, GIP, motilin and VIP

31
Q

what 5 endogenous factors promote intestinal absorption?

A

epinephrine and NE, dopamine, enkephalins, somatostatin and mineralcorticoids

32
Q

how do absorptive and secretory factors relate?

A

substances that promote one tend to inhibit the other

33
Q

what percentage of iron is absorbed from the diet? why not more?

A

5%

because most of ingested iron is ferric and cannot be absorbed

34
Q

what happens at the brush border when body Fe is low?

A

number of transporters increases

35
Q

what type of iron is most efficiently absorbed?

A

heme iron- absorbed as heme and released in cell

ferric iron is released and turned to ferrous

36
Q

what transfers iron around the cell?

A

mobilferrin

37
Q

how is Fe2+ released from food? how is its transformation to ferric iron prevented?

A

acidic pH of stomach releases it

ascorbate and citrate in stomach help reduce to ferrous

38
Q

what is the intracellular storage of iron? how is it transported in the blood?

A

ferritin

transferrin

39
Q

how is non heme iron absorbed in the cell?

A

it is absorbed by DMT1 in the duodenum, driven by H+ gradient (cotransport) formed by Na/H exchanger

40
Q

in what oxidation state is iron carried by transferrin? what enzyme accomplishes this?

A

ferric (3+)

hephaestin

41
Q

how is Ca transported in the blood?

A

half is free, the other half is bound to albumin

42
Q

what transporter promotes calcium absorption?

A

a Ca ATPase that is activated by calmodulin- transports Ca from cell into bloodstream

43
Q

what are the two mechanisms of calcium absorption?

A 
paracellular absorption (unaffected by Vit D)
channel absorption
44
Q

once calcium enters an enterocyte, what happens?

A

it is bound to calbindin and taken up into organelles
extruded by Ca/Na exchanger and Ca pump
(affected by Vit D)

GI Physiology (7 decks)

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