l9: GI salt and water transport Flashcards Preview

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Flashcards in l9: GI salt and water transport Deck (31)
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1
Q

what does the jejunum reabsorb

A

Na+ cl- H20 & K+

2
Q

What does the ileum reabsorb and secrete

A

Na H20 cl k

Secretes- bicarbonate

3
Q

What in total does the colon secrete and absorb

A

Secretes- k+ and bicarbonate

Absorbs- Na cl and H20

4
Q

Describe enterocytes

A

columnar epithelial cells in small intestine
Polarised
Apical side- faces lumen; has microfolds
Basal side: Communicates with bloodstream & lymphatic lacteals
Seperated by tight junctions

5
Q

function of tight junctions

A

Allow passage of water &

Restrict passive flow of solutes after secretion or absorption

6
Q

What are the 2 types of epithelial transport & describe each

A

Paracellular: Forms regulated and restrictive Permeation in both directions through tight junctions: uses electrochemical gradients to move water & solute

Transcellular: Employs membrane transporters to move H20 & molecules through cell-active process
Sets up gradient, via solute movement, for passive transport of H20 & solutes.

7
Q

What are the 3 types of transepithelial channels

A

Channels- gated and ion specific, via electrochemical gradient

Carrier -

pumps

8
Q

What are the 3 types of transport, describe each

A

Passive
active - Primary-uses ATP, against electrochem gradient: ie Na-ATPase channel
Secondary- Cotransport- Na-glucose transporter

solvents drag-water leaks from lumen, through paracellular space to reach osmotic equilibrium on basolateral side. -upper small intestine
- moves/pulls additional solutes

9
Q

For all concepts look at the diagrams from slides 36 to 41

Describe concept 1

A

NA/K ATPase- Basolateral active transport. Creates Na electrochemical gradient, between enterocyte and lumen

10
Q

Concept 2

A

Na coupled transport-AA or glucose-Apical
the NA gradient from C1 allows coupled Na transport from lumen.
secondary transport- couples uphill movement of AA or glucose to downhill movement of NA, helping to set up Na/K-ATPase
Process is electrogenic as lumen becomes more negative

11
Q

Concept 3

A

Apical side: Separate NA and cl antiporters.

Na-H exchanger + HCO3-Cl exchanger, creating NACL

12
Q

Concept 4

A

Apical and Basolateral: CL- secretion occurs in conjunction with basolateral NA K CL absorption
Na-k-ATPase drives NA gradient allowing Apical Cl- secretion through CFTR channel and coupled import of k cl and na from basolateral
Due to high chloride conc CFTR widely expressed in colon

13
Q

concept 5

A

Water will travel through intercellular tight junctions in the setting of NACL absorption
from lumen to blood

14
Q

H20 Absorption in the small intestine

A

Basolateral Na/k-ATPase pumps
Leads to build up of NACL in paracellular spaces between enterocytes
Provides osmotic gradient that draws water into paracelluar spaces

15
Q

Oral rehydration therapy

A

Utilises mechanism of glucose-coupled NA absorption
oral rehydration solutions to promote fluid absorption by coupling Na with glucose in solution
Channel SGT-1 binds 2 Na molecules to 1 glucose, transporting them into cell.

16
Q

How do GI cells secrete water

A

In small intestine cl- secretion draws Na and H20 across tight junctions

17
Q

How does the jejunum absorb water

A

Solvent drag

Highest NA absorption coupled with nutrient absorption

18
Q

How does the ileum absorb water

A

Highest NACL absorption

19
Q

How does the colon absorb water

A

Apical NA and k

Aldosterone increases synthesis of Na channels and increased k secretion

20
Q

What are the effects of the cholera toxin

A
Stimulates excess cAMP in crypt cells 
cAMP activates CFTR channel 
therefore massive influx of cl-
Na follows forming NaCL
Followed by H20 secretion, more than can be reabsorbed 
Result: H20 and electrolyte loss-fatal
21
Q

Large Intestine: regulated by what hormone

A

Aldosterone

22
Q

What is the function of secreting cl- and HCO3- into lumen

A

Buffers for acid produced by bacteria

23
Q

what are the Na channels called

A

Basolateral-NHE1
Apical: NHE 2&3
For Na/H exchanger

24
Q

Na+ and H+ exchangers coupled with cl-/HCO3- result in

A

NaCl absorption

25
Q

CL- through

A

Lc16 channel

CL/HCO3

26
Q

What systems interact with the regulation of ion transport and secretion

A

Hormonal-enteroendocrine cells- Endocrine system
Immune cell- Derived factors-Immune system
Bioactive substances secreted into lumen- neurotransmitters -Enteric Nervous system

27
Q

Pathophysiological changes of transepithelial transport

A

Congenital-genetic
Acquired- via infection, inflammation, hormonal abnormalties

1.Stim of net fluid & electrolyte secretion
increased propulsive muscle contraction
Mucosal destruction & increased permeability
Nutrient malabsorption

28
Q

Gastrointestinal infections

A

Diarrhoea- bacterial enterotoxin- cholera, ecoli

29
Q

How do enterotoxins work?

A

Cause secretory diarrhoea by interacting with receptors & signal transduction pathways in enterocytes

30
Q

Cystic fibrosis

A

Autosomal Recessive disease
Deletion in gene for Transmembrane regulator CFTR channel; and therefore sticky mucus and high viscosity of luminal contents.
As no paracellular Na and H20 as no gradient set up
Presents as intestinal obstruction & meconium in newborns

31
Q

What is lactose intolerance

A

Lactose not digested into glucose and galactose and therefore not absorbed & remains in lumen - causing osmotic diarrhoea