CFTR and the Causes of CF

7/28/2019 CFTR and the Causes of CF

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CFTR and the causes of

CFWhat goes wrong in cystic fibrosis


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Role of the CFTR proteinThe normal situation

NB: Chloride- ions always move the same way as the sodium+ ions to maintain

electrical neutrality.

Addition of extra ions effectively reduces the concentration of free water (or makes the

solution more concentrated)


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Too little water; mucus too sticky


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In Cystic Fibrosis


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Activity 2.9.

CFTR protein and

membrane

transport

The diagram illustrates

the transport

mechanisms and the

movement of ions into

and out of the epithelial

cells which line the

airways.

An example of the role

of proteins in transport.


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Sodium ions are pumped out of the cell by

active transport at the base of the cell;

this lowers the concentration of sodium

ions in the cell;Sodium ions diffuse into the cell at the

apical end

down the concentration gradient.

The pumping out of the sodium ions at the

base increases the concentration of ions

there(so decreases the concentration of free

water)

so water diffuses by osmosis out of the

cell

this decreases the free water

concentration in the cellso water diffuses by osmosis into the cell

at the apical end from the mucus.

NB: whichever way sodium+ ions are

transported, chloride- ions are moved the

same way to maintain electrical neutrality

The normal si tuat ion.


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The CF situat ion Sodium ions are pumped out of the cell by

active transport at the base of the cell;

this lowers the concentration of sodium

ions in the cell;

The CFTR channel protein normallyregulates the opening (when there is plenty

of water in the mucus) and closing (when

there is not enough water in the mucus) of

the sodium ion channels

In CF the CFTR protein is not present or

not functioningthis causes the sodium channels to

remain open and chloride ions cannot

leave the cell

so sodium ions continue to diffuse into the

cell which, with the chloride ions which

cannot leave, increasing the saltconcentration in the cell and decreasing

the water potential

which causes more water to diffuse by

osmosis from the mucus into the cell

which causes the mucus to become

increasingly viscous (sticky)hence the s m toms of CF.


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Checkpoint 2.5

For each of a) to c) write FIVE BULLETPOINT STATEMENTS to describe theeffect CF has on

a) Gas exchange

b) The digestive system

c) The reproductive system


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Effect of CF in the gas exchangesystem

Sticky mucus;

builds up in lungs

cannot be cleared by cilia

traps dust microorganisms risk of lung infections

blocks airways so breathing more difficult

gas exchange in the alveoli less efficient sincemucus fills alveoli and makes diffusion pathwaylonger and so slower so less oxygen gets intothe blood


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Effect of CF in the digestive system

Sticky mucus blocks pancreatic duct reduces release of digestive enzymes into small

intestine reduces digestion of carbohydrates, proteins and

lipids in food food not fully digested so reducing amount of

essential nutrients absorbed makes diffusion pathway longer for cells to

absorb what nutrient molecules there are furtherreducing uptake


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CFTR and the Causes of CF