Edexcel Unit 1 Notes Cystic Fibrosis

1 2.4  – In-depth study of a genetic diseases diseases - Cystic fibrosis

Cystic fibrosis is an inherited disorder that mainly affects respiratory, digestive and reproductive systems. It is caused by a recessive allele – so a person will only have the disorder if t hey’re homozygous for the allele they must inherit one recessive allele from each parent. If a person is heterozygous they won’t have CF but they’ll be a carrier. Cystic fibrosis causes the production of thick sticky mucus. 1) Caused by mutation in the gene that codes for CFTR protein ( Cystic Fibrosis Transmembrane Conductance Regulator) 2) CFTR is a carrier protein which transports chloride ions out of cells and into mucus  – causes water to move into the water by osmosis which makes it watery 3) Mutant CFTR is much less efficient at transporting chloride ions out of the cell, so less water moves out by osmosis  – makes the mucus of people with CF abnormally thick and sticky. 4) The thick and sticky mucus causes problems in the respiratory, digestive and reproductive system.

Respiratory system Mucus – Mucus – prevents lung infections by trapping microorganisms. The mucus including microorganisms is then transported towards the throat by cilia (hair like structures that beat to move mucus). In those suffering from CF the mucus is abnormally thick and sticky, which causes some problems.

1) The cilia are unable to move the mucus towards the throat because it becomes thick and sticky 2) The mucus builds up in the airways 3) Some airways can become completely blocked by the mucus- gas exchange cant take place in the area below the blockage 4) This means that the surface area available for gas exchange is reduced, causing breathing difficulties. The digestive system 1) Tube connects the pancreas to small intestine blocked with mucus- preventing digestive enzymes produced by the pancreas from reaching the small intestine. Difficult to digest food - fewer nutrients are absorbed. 2) The mucus can cause cysts (growths) to form in pancreas  – these inhibit the production of enzymes – which also reduces the ability to digest food and absorb nutrients. 3) The mucus lining the small intestine is abnormally thick  – inhibits absorption of  nutrients.

Adam Clarke www.brain-freeze.co.uk

2 Reproductive system Mucus is secreted here to prevent infections / transport sex cells. 1) Men – tubes connecting testicles to penis are absent in some / can be blocked by mucus – sperm cant reach penis 2) Women – thickened cervical mucus – prevent sperm reaching the egg – travel through mucus to reach the egg  – thick mucus reduces the motility of sperm  – reducing chances of it making the journey to the egg. Treating cystic fibrosis Physiotherapy Makes it easier to breathe – take in enough oxygen  – reduce risk of lung infections Devices can change the pressure in the airways and help people to clear their mucus without using more vigorous physiotherapy are being introduced  – flutter, positive expiratory pressure valve and the ThAIRapy bronchial drainage system. Diet and enzymes Mucus – blocks pancreatic duct /lining of the gut  – digesting absorbing food is difficult. Take enzymes with meal – replace missing pancreatic enzymes  – so more food can be digested. More food – make up for what isn’t digested High-energy /fat/carbohydrate foods – twice as much protein Drug therapies Antibiotics – destroy bacteria for lung infections  – aerosols (inhalers) used to breathe them deep into the lungs. Vaccines – childhood vaccines – yearly flu vaccine – pneumonia Mucolytics these are drugs to make mucus runny / easier to move Asthma drugs e.g. salbutamol and steroids  – used to open airways / reduce inflammation in lungs DNAase enzymes – make mucus thinner and easier to cough up Insulin – problems with pancreas  – lead to diabetes – insulin required – control blood concentration Transplant surgery Damage so severe e.g. to heart or lungs – transplant of organ required New organs wont be affected by CF  – rest of body will still have other problems After a transplant the person has to take immunosuppressant drugs  – prevent body reacting against the new tissue and rejecting it. This suppresses the immune system making it harder to fight infections. Infertility treatments IVF – for men – sperm fertilise eggs in vitro  – embryo return to uterus to develop normally.

Adam Clarke www.brain-freeze.co.uk