HECKdigestion and absorption of fluids and electrolytes

Question 1

Which part of GI absorbs the most

Answer 1

SI

Question 2

What part of GI ares most electrolytes reabsorbed

Answer 2

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

Question 3

What is segmental heterogeneity

Answer 3

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

Question 4

What is surface herterogeneity

Answer 4

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

Question 5

What is cellular heterogeneity

Answer 5

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

Question 6

What is the net absorption and net secretion in SI?

Large I?

Answer 6

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

Question 7

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

Answer 7

apical side and basolateral

Question 8

Mucosal resistnace depends on what type of movement

Answer 8

paracellular Resistance from tight junctions

Question 9

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

Answer 9

increases as move away from mouth

increases as move down crypt

Question 10

What are secretagogues

Answer 10

induce secretion, agonists that also increase second messengers.

Question 11

What natural substance can act as a laxative

Answer 11

bile acid

Question 12

What are absorptagogoues

Answer 12

Induce absorption (neural, endocrine and paracrine)

Question 13

What are types of absorptagogues

Answer 13

mineralcorticoids, glucocorticoids, somatostatin and Norepinephrine

Question 14

What is osmotic diarrhea

Answer 14

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

Question 15

What is Secretory diarrhea

Answer 15

secretion of fluid and electrolytes from intestine induced by secretagogues

Question 16

What are secretagogues from bacteria

Answer 16

enterotoxins that increase second messengers

does not affect Na absorption

Question 17

What will reverse secretory diarrhea

Answer 17

Na and Glucose solution

Question 18

Where is most of Na absorbed

Answer 18

villous epithelium of SI

surface epithelium of LI

Question 19

Describe the Na, K ATPase

Answer 19

low intracell Na because pumping into interstitial

gradient then used as driving force

Question 20

What are the 4 types of apical Na transport

Answer 20

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

Question 21

Describe path and energy for nutrient coupled Na transport

Answer 21

secondary active transport running on Na gradient

transports 1 Na in along with glucose or glactose

Question 22

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

Answer 22

not inhibited by cAMP of gAMP

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

Question 23

What is the name of the glucose.Na cotransporter

Answer 23

SGLT1

Question 24

What is the other type of Nutrient coupled Na transport

Answer 24

Na/aa co-transport

Question 25

Describe the mech of Na/H exchanger

Answer 25

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

Question 26

Where in the intestine are the Na/H exchanger

Answer 26

throughout intestine, mainly jejunum

Question 27

What is the effect on pH from Na/pH

Answer 27

increase intracell pH | decrease luminal pH

Question 28

What would pancreatitis have as an effect on NaH exchanger

Answer 28

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

Question 29

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

Answer 29

runs on HCO3 alone

Question 30

Describe the mech of the electroneutral NaCl absorption

Answer 30

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

Question 31

Where and when is the electroneutral NaCl absorption most important

Answer 31

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

Question 32

Describe the effects of travelers diarrhea on the electroneutral NaCl

Answer 32

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

Question 33

describe mech of electrogenic Na absorption

Answer 33

epithelial Na channels on apical surface | depends on gradient from NaK pump

Question 34

Where are the electrogenic Na absorption channels very important

Answer 34

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

Question 35

What enhances the electrogenic Na absorption

Answer 35

aldosterone(absorptagogue)

Question 36

Describe chloride absorption

Answer 36

passive voltage dependent | neg lumen charge from Na leaving causes Cl to enter cell paracellularly

Question 37

Descirbe the active transport of Cl

Answer 37

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

Question 38

where are the Cl-HCO3 exchangers present

Answer 38

surface epithelium of large intestin, villous cells on the ileum

Question 39

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

Answer 39

DRA exchanger because down regulated with adenomas (colon cancers)

Question 40

How does Cl cross the basolateral side

Answer 40

ClC-2 voltage gated

Question 41

What causes congenital Cl diarrhea

Answer 41

absence of Cl-HCO3

Question 42

How is absence of DRA specific to colon

Answer 42

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

Question 43

What are signs of congenital Cl diarrhea

Answer 43

extremely high [ ] Cl in stool | high plasma [ ] HCO3 (alkalotic)

Question 44

Describe Cl secretion mechanism

Answer 44

requires activation by secretagogues | the NaK pump drives the NaKCl pump to increase intracell Cl levels

Question 45

What is the importance of leaky K channels on apical side

Answer 45

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

Question 46

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

Answer 46

CFTR

Question 47

Where does K absorption take place

Answer 47

small intestine and distal colon

Question 48

how does K get absorbed in small intestine

Answer 48

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

Question 49

how does K get absorbed in distal colon

Answer 49

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

Question 50

Where does K secretion take place

Answer 50

only in the large intestine

Question 51

Describe passive K secretion

Answer 51

predominant route driven by negative lumen paracellular

Question 52

What increases the passive secretion of K

Answer 52

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

Question 53

Describe active K secretion

Answer 53

throughout colon, activated by aldosterone and cAMP | pump/leak so the drive is from the NaK and NaClK pump

Question 54

Describe the active Ca absorption

Answer 54

only in duodenum, speed of flow reduceds uptake | active transcellular and under the control of vitamin D

Question 55

Why is vitamin D needed for ca uptake

Answer 55

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

Question 56

Before Ca-Calbinding cross the basolateral side what must happen

Answer 56

separate and then Ca leaves via Na Ca exchanger

Question 57

Describe the passive Ca absorption

Answer 57

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

Question 58

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

Answer 58

not influenced by vit D | talkes place throughout SI (jejunum and ileum)

Question 59

What natural process enhances passive Ca absorption

Answer 59

lactation

Question 60

Describe the active uptake of Mg

Answer 60

only in ileum | Independent of vit D and Ca- mech not known

Question 61

describe the passive uptake of Mg

Answer 61

paracellular throughout duodenum and jejunum | based on Mg [ ]

Question 62

What is Mg [ ] necessary for

Answer 62

Parathyroid hormone

Question 63

Whcih form of iron precipitaes more

Answer 63

ferric Fe3+

Question 64

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

Answer 64

Ferrous Fe2+

Question 65

Where does most of our Fe2+ come from

Answer 65

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

Question 66

What 2 major pathologies arise from iron dysregulation

Answer 66

anemia (depletion) | hemochromatosis (iron overload)

Question 67

Why are women less susceptible to hereditary hemochromatosis

Answer 67

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

Question 68

What can excess iron result in

Answer 68

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

Question 69

How do we detect iron dysregulation

Answer 69

elevated iron and transferrin saturation, elevated ferritin, liver biopsy

Question 70

What is the Tx for iron dysregulation

Answer 70

phlebotomize, blood letting every few months to normalize levels

Question 71

What are the two forms of iron

Answer 71

heme iron and nonheme

Question 72

what type of iron is absorbed more efficiently heme or nonheme

Answer 72

heme

Question 73

how is heme iron absorbed

Answer 73

active transcellular transport in duodenum | binds brush border protein then transported to cytoplasm via endocytotic mech

Question 74

What cleaves heme and Fe3+

Answer 74

heme oxygenase

Question 75

What cell reduces Fe3+

Answer 75

enterocyte

Question 76

How is nonheme absorbed

Answer 76

active transcell transport in duodenum

Question 77

What is the Iron transporter on apical side

Answer 77

divalent metal transporter DMT1 | cotransports Fe2+ and H (not specific for iron)

Question 78

Which tranporter is responsible for lead poisoning

Answer 78

the DMT1

Question 79

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

Answer 79

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

Question 80

What protein carries Fe to the basolateral membrane

Answer 80

mobilferrin

Question 81

What is the transporter for Fe on the basolateral side

Answer 81

Ferroportin transporter FP1

Question 82

When is Fe2+ oxidized

Answer 82

when reaches the intersitial fluid.

Question 83

Why must Fe2+ be oxidized in interstitium

Answer 83

transferrin can then carry it to the plasma

Question 84

how is Fe3+ stored

Answer 84

bound to transferrin and stored in liver and reticuloendothelial system

Question 85

Diarrhea from cholera has what appearance

Answer 85

rice water from the mucous

Question 86

What is unique about diarrhea from E coli

Answer 86

has blood in it

Question 87

cAMP has what affect on CFTP

Answer 87

phosphorylates it