What causes cystic fibrosis?
A mutation in the cystic fibrosis
transmembrane regulatory protein
What does the CFTR protein do?
It helps control the viscosity (or stickiness) of mucus that lines the
epithelial cells of the airways, digestive and reproductive systems
mucus
cilia
epithelial
cell
If the mucus in airways is…
too sticky: the cilia cannot beat and remove the mucus, which
then clogs up airways
too runny: the mucus can flood the airways
When there is excess water in the mucus
Water is drawn out of the mucus and it thickens
Cl-
Na+
H2O
mucus
2
apical membrane
5
Na+
channel open
1
basal membrane
pump
CFTR
channel
closed
H2O
4
3
Cl-
Na+
H2O
tissue fluid
When there is too little water in the mucus
Water is drawn out of the mucus and it becomes less sticky
Na+
Cl-
Na+
mucus
3
2
4
apical membrane
Na+
channel
closed
CFTR
channel
open
1 Cl-
The CFTR
somehow
blocks the
sodium
channels
H2O
H2O
basal membrane
5
pump
Na+
H2O
tissue fluid
With cystic fibrosis
The mucus becomes very thick and sticky
Cl-
Na+
2
1
H2O
3
X
apical membrane
Na+
channel
open
CFTR
nonfunctional
Water
drawn out
by osmosis
H2O
basal membrane
Cl-
mucus
H2O
The CFTR
protein
cannot block
the sodium
channels so
they are
always open
tissue fluid
How cystic fibrosis affects the lungs
Sticky mucus builds up in the airways, reducing flow of air into alveoli. Lungs
gradually fill up with mucus, making them less effective for gas exchange.
Symptoms:
•
Severe coughing - to remove excess mucus.
•
Breathlessness - shortage of oxygen increases tiredness and lack of
energy
•
Infections - as bacteria are trapped in mucus
How does cystic fibrosis affect the
reproductive systems?
Men
Women
Sperm duct is blocked During the menstrual
and prevents
cycle the levels of
movement of sperm
mucus vary.
Can lack the sperm
ducts
Women with CF have
thick levels of mucus
which can block the
cervix so sperm cannot
reach them.
How cystic fibrosis affects the digestive
system:
Thick, sticky mucus blocks the
pancreatic duct preventing enzymes
from reaching the duodenum.
Food is not digested and absorbed
sufferers fail to put on body mass and
suffer malnutrition.
Trapped digestive enzymes damage
the pancreatic cells affecting cells
producing insulin resulting in diabetes.