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GI II > HECKdigestion and absorption of fluids and electrolytes > Flashcards

HECKdigestion and absorption of fluids and electrolytes Flashcards

1
Q

Which part of GI absorbs the most

A

SI

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2
Q

What part of GI ares most electrolytes reabsorbed

A

Jejunum(all) and then in distal colon (except for K)

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3
Q

What is segmental heterogeneity

A

differences of cell expression of the transporters along the length of intestines

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4
Q

What is surface herterogeneity

A

differences in the trasport from top of villus to bottom of crypt

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5
Q

What is cellular heterogeneity

A

differences in transport mechanisms in different cells within sam villus or crypt

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6
Q

What is the net absorption and net secretion in SI?

Large I?

A

SI: absorb NaCl and K, secrete HCO3
LI: absorp NaCl, secrete K HCO3

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7
Q

What does it mean by saying epithelial cells in intestine are polar

A

apical side and basolateral

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8
Q

Mucosal resistnace depends on what type of movement

A

paracellular Resistance from tight junctions

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9
Q

How does resistance of epithelium change as you move away from mouth, change as you move down crypt?

A

increases as move away from mouth

increases as move down crypt

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10
Q

What are secretagogues

A

induce secretion, agonists that also increase second messengers.

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11
Q

What natural substance can act as a laxative

A

bile acid

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12
Q

What are absorptagogoues

A

Induce absorption (neural, endocrine and paracrine)

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13
Q

What are types of absorptagogues

A

mineralcorticoids, glucocorticoids, somatostatin and Norepinephrine

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14
Q

What is osmotic diarrhea

A

dietary component that is pulling H2O into the lumen because it is not being absorbed

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15
Q

What is Secretory diarrhea

A

secretion of fluid and electrolytes from intestine induced by secretagogues

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16
Q

What are secretagogues from bacteria

A

enterotoxins that increase second messengers

does not affect Na absorption

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17
Q

What will reverse secretory diarrhea

A

Na and Glucose solution

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18
Q

Where is most of Na absorbed

A

villous epithelium of SI

surface epithelium of LI

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19
Q

Describe the Na, K ATPase

A

low intracell Na because pumping into interstitial

gradient then used as driving force

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20
Q

What are the 4 types of apical Na transport

A

Nutrient-coupled
Na/H exchanger
Electroneutral NaCl absorption
Electrogenic Na absorption

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21
Q

Describe path and energy for nutrient coupled Na transport

A

secondary active transport running on Na gradient

transports 1 Na in along with glucose or glactose

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22
Q

What is significant about the nutrient-coupled Na transport that is not like the other

A

not inhibited by cAMP of gAMP

so can still work in cholera or E coli enterotoxin from bacteria which increase cAMP

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23
Q

What is the name of the glucose.Na cotransporter

A

SGLT1

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24
Q

What is the other type of Nutrient coupled Na transport

A

Na/aa co-transport

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25
Q

Describe the mech of Na/H exchanger

A

couples Na uptake to H extrusion into intestinal lumen
stimulated by secretion of HCO3 in duodenum
driven by Na gradient

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26
Q

Where in the intestine are the Na/H exchanger

A

throughout intestine, mainly jejunum

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27
Q

What is the effect on pH from Na/pH

A

increase intracell pH

decrease luminal pH

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28
Q

What would pancreatitis have as an effect on NaH exchanger

A

wouldnt run because needs HCO3 to stimulate. so luminal pH would not decrease

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29
Q

In the proximal small intestine why is there the Na/H exchanger without Cl-HCO3

A

runs on HCO3 alone

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30
Q

Describe the mech of the electroneutral NaCl absorption

A

Na-H and Cl-HCO3 apical membrane coupled through pH neutrality

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31
Q

Where and when is the electroneutral NaCl absorption most important

A

ileum and large intestine, primary method of Na absorption between meals

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32
Q

Describe the effects of travelers diarrhea on the electroneutral NaCl

A

inhibited NaCl absorption because of increased cAMP and cGMP because of increased Ca

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33
Q

describe mech of electrogenic Na absorption

A

epithelial Na channels on apical surface

depends on gradient from NaK pump

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34
Q

Where are the electrogenic Na absorption channels very important

A

in the distal colon because is a rescue mechanism for Na conservation

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35
Q

What enhances the electrogenic Na absorption

A

aldosterone(absorptagogue)

36
Q

Describe chloride absorption

A

passive voltage dependent

neg lumen charge from Na leaving causes Cl to enter cell paracellularly

37
Q

Descirbe the active transport of Cl

A

Cl-HCO3 exchanger, does not run with Na/H pump

38
Q

where are the Cl-HCO3 exchangers present

A

surface epithelium of large intestin, villous cells on the ileum

39
Q

What is the other name for the Cl-HCO3 exchanger and why

A

DRA exchanger because down regulated with adenomas (colon cancers)

40
Q

How does Cl cross the basolateral side

A

ClC-2 voltage gated

41
Q

What causes congenital Cl diarrhea

A

absence of Cl-HCO3

42
Q

How is absence of DRA specific to colon

A

the gene is different for Cl exchangers in RBC and renal tubules

43
Q

What are signs of congenital Cl diarrhea

A

extremely high [ ] Cl in stool

high plasma [ ] HCO3 (alkalotic)

44
Q

Describe Cl secretion mechanism

A

requires activation by secretagogues

the NaK pump drives the NaKCl pump to increase intracell Cl levels

45
Q

What is the importance of leaky K channels on apical side

A

needed so that K [ ] in the cell does not get too hight with the NaKCl and NaK pumps

46
Q

What is the name of the main Cl channel on apical side

A

CFTR

47
Q

Where does K absorption take place

A

small intestine and distal colon

48
Q

how does K get absorbed in small intestine

A

paracellular, passive transport, pulled through tight junctions with movement of water

49
Q

how does K get absorbed in distal colon

A

active transport transcellularly
apical H/K pump which pumps H into lumen
basolateral NaK pump

50
Q

Where does K secretion take place

A

only in the large intestine

51
Q

Describe passive K secretion

A

predominant route
driven by negative lumen
paracellular

52
Q

What increases the passive secretion of K

A

dehydration because aldosterone is secreted so Na absorbed so Cl leaves lumen making it more negative and then passive K secretion
high levels of K in stool when dehydrated

53
Q

Describe active K secretion

A

throughout colon, activated by aldosterone and cAMP

pump/leak so the drive is from the NaK and NaClK pump

54
Q

Describe the active Ca absorption

A

only in duodenum, speed of flow reduceds uptake

active transcellular and under the control of vitamin D

55
Q

Why is vitamin D needed for ca uptake

A

because Ca is potent second messenger needs to be bound to Calbindin
Vit D induces synthesis of Calbindin

56
Q

Before Ca-Calbinding cross the basolateral side what must happen

A

separate and then Ca leaves via Na Ca exchanger

57
Q

Describe the passive Ca absorption

A

paracellular

depends on [ ] in interstitium (which reflects plasma levels)

58
Q

Where does passive Ca absorption take place and is Vit D needed

A

not influenced by vit D

talkes place throughout SI (jejunum and ileum)

59
Q

What natural process enhances passive Ca absorption

A

lactation

60
Q

Describe the active uptake of Mg

A

only in ileum

Independent of vit D and Ca- mech not known

61
Q

describe the passive uptake of Mg

A

paracellular throughout duodenum and jejunum

based on Mg [ ]

62
Q

What is Mg [ ] necessary for

A

Parathyroid hormone

63
Q

Whcih form of iron precipitaes more

A

ferric Fe3+

64
Q

which form does iron have to be to be taken up by cells

A

Ferrous Fe2+

65
Q

Where does most of our Fe2+ come from

A

Vit C, asorbic acid reduces Fe3+ to Fe2+ and thus increases absorption

66
Q

What 2 major pathologies arise from iron dysregulation

A

anemia (depletion)

hemochromatosis (iron overload)

67
Q

Why are women less susceptible to hereditary hemochromatosis

A

because during menstruation release excess Fe so it does not build up

68
Q

What can excess iron result in

A

cirrhosis, hepatomas, pancreatic damage, bronze pigmentation, pituitary and gonadal failure, arthritis, cardiomyopathy

69
Q

How do we detect iron dysregulation

A

elevated iron and transferrin saturation, elevated ferritin, liver biopsy

70
Q

What is the Tx for iron dysregulation

A

phlebotomize, blood letting every few months to normalize levels

71
Q

What are the two forms of iron

A

heme iron and nonheme

72
Q

what type of iron is absorbed more efficiently heme or nonheme

A

heme

73
Q

how is heme iron absorbed

A

active transcellular transport in duodenum

binds brush border protein then transported to cytoplasm via endocytotic mech

74
Q

What cleaves heme and Fe3+

A

heme oxygenase

75
Q

What cell reduces Fe3+

A

enterocyte

76
Q

How is nonheme absorbed

A

active transcell transport in duodenum

77
Q

What is the Iron transporter on apical side

A

divalent metal transporter DMT1

cotransports Fe2+ and H (not specific for iron)

78
Q

Which tranporter is responsible for lead poisoning

A

the DMT1

79
Q

What is the name of the reducer for ferric and what is important about its location

A

Ferric reductase Dcytb

located on apical extracell surface because has to reduce Fe3+ before can be taken up by DMT1

80
Q

What protein carries Fe to the basolateral membrane

A

mobilferrin

81
Q

What is the transporter for Fe on the basolateral side

A

Ferroportin transporter FP1

82
Q

When is Fe2+ oxidized

A

when reaches the intersitial fluid.

83
Q

Why must Fe2+ be oxidized in interstitium

A

transferrin can then carry it to the plasma

84
Q

how is Fe3+ stored

A

bound to transferrin and stored in liver and reticuloendothelial system

85
Q

Diarrhea from cholera has what appearance

A

rice water from the mucous

86
Q

What is unique about diarrhea from E coli

A

has blood in it

87
Q

cAMP has what affect on CFTP

A

phosphorylates it

GI II (12 decks)

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