GI 9

Question 1

2 Important Reasons for a Fluid Environment

Answer 1

1. Protect the intestinal lining
2. Needed for enzymatic digestion and diffusion to site of absorption

Question 2

Does the majority of fluid come from the diet or from secretion?

Answer 2

secretion

Question 3

What % of fluid is absorbed by the small intestine?

Answer 3

80%

Question 4

What % of fluids are excreted in the feces?

Answer 4

1%

Question 5

Can absorption and secretion occur simultaneously?

Answer 5

yes

Question 6

Of villus and crypt cells in the intestinal epithelium, which are responsible for absorption and which are responsible for secretion?

Answer 6

Absorption = Villus
Secretion = Crypt

Question 7

2 Paths for Fluid Transport

Answer 7

1. Transcellular path (electrolytes, mainly)
2. Paracellular path (water, some ions like Cl-, Na+, K+)

Question 8

2 Types of Tight Junctions

Answer 8

1. Leaky epithelia
2. Tight epithelia

Question 9

Leaky epithelia location

Answer 9

small intestine

Question 10

Tight epithelia location

Answer 10

colon

Question 11

How does fluid decide what transport mechanism to use? (2)

Answer 11

1. Does it need energy?
2. Does it cause net movement of charge across the membrane?

Question 12

Passive transcellular transport

Answer 12

ion channels responding to an electrochemical gradient

Question 13

Site for major Na+ absorption?

Answer 13

small intestine (specifically jejunum)

Question 14

Two Methods of Na+ absorption in the Jejunum?

Answer 14

1. Sodium cotransporters (electrogenic)
2. Na+/H+ Exchanger (electroneutral)

Question 15

What compound is absorbed in the ileum?

Answer 15

sodium chloride (NaCl)

Question 16

Is Na+ absorption in the ileum electrogenic or electroneutral?

Answer 16

electroneutral (Na+/H+ exchanger and Cl-/bicarbonate exchanger)

Question 17

Is bicarbonate positive or negative charged?

Answer 17

negative

Question 18

During what phase of digestion does sodium absorption in the ileum occur?

Answer 18

interdigestive phase

Question 19

What is there a net absorption of in the small intestine?

Answer 19

Na+, K+,Cl-, and water

Question 20

What is there a net absorption of in the large intestine?

Answer 20

Na+, Cl-, and water

Question 21

What is there a net secretion of in the large intestine?

Answer 21

bicarbonate and potassium

Question 22

What hormone enhances sodium absorption in the colon?

Answer 22

aldosterone (helps increase efficiency during dehydration)

Question 23

Does sodium use a transporter in the colon?

Answer 23

nope, just a channel and an electrochemical gradient generated by primary active transport (restricted diffusion)

Question 24

3 Mechanisms of Chloride Absorption in the Intestine

Answer 24

1. Passive
2. Bicarbonate/Cl- exchangers
3. Coupled/parallel Na+/H+ and Bicarbonate/Cl- exchangers

Question 25

Passive chloride absorption and main location(s)

Answer 25

either via the electrochmeical gradient to follow sodium into cell, or paracellular pathway in the jejunum (electrogenic); jejunum and distal colon

Question 26

Chloride Absorption via Bicarbonate/Cl- exchanger and main location

Answer 26

high conc. of bicarbonate in the cell, bicarbonate is pumped out to lumen so chloride can enter cell (electroneutral); proximal colon

Question 27

Chloride Absorption via parallel exchangers and location

Answer 27

both exchangers on apical side, allows for add'l absoprtion in ileum and proximal colon

Question 28

Mechanism of K+ absorption

Answer 28

passive via tight junctions (with water in small intestine)

Question 29

Is potassium being absorbed in the colon?

Answer 29

Yes, just less than what is being secreted, via channels in the epithelium

Question 30

What does intestinal secretion center on?

Answer 30

active transport of Cl-

Question 31

2 Types of Secretions in the Crypt

Answer 31

1. Chloride 2. Bicarbonate

Question 32

Bicarbonate is secreted in response to what?

Answer 32

acid in the duodenum

Question 33

Chloride Secretion in Crypt Cells

Answer 33

1. Hormones/NTs bind 2. Ca2+/cAMP increase 3. More CFTR on luminal surface 4. Chloride channels open 5. Chloride secreted into lumen, followed by sodium and water (Na+ and H2O via paracellular pathway)

Question 34

Osmotic Forces

Answer 34

generated by transport of solutes/ions and will cause water absorption and secretion

Question 35

Is water transcellular or paracellular?

Answer 35

paracellular (mainly)