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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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