Biology: Cystic Fibrosis

Question 1

Mucus production

Answer 1

Produced in goblet cells lining the walls of the airways. It is continuously secreted and swept away by cilia that cover the epithelial cells lining the airways.

Question 2

Role of mucus

Answer 2

The role of mucus in the lungs is to trap any unwanted dust and microorganisms that are entering the lungs.

Question 3

Mucus with CF

Answer 3

Mucus in individuals with Cystic Fibrosis is thicker and stickier, due to a lack of water and so is harder to sweep away by the cilia, therefore it can reduce the surface area of and even block off entire airways. This means that less gas exchange can occur.

Question 4

Infections

Answer 4

Pathogens become trapped in mucus, causing infections. White blood cells fighting infections break down when they die making the mucus stickier. Lung infections damage gas exchange structures, meaning even less gas exchange will occur.

Question 5

Excess water

Answer 5

Sodium ions are actively pumped across the basal membrane, from cell into tissue.
Sodium ions diffuse through sodium channels in the apical membrane, from mucus into the cell.
Chlorine ions diffuse between cells, down electrical gradient.
Water moves into tissue from cells by osmosis.
Water moves from mucus into cells by osmosis.

Question 6

Water deficit

Answer 6

Chlorine pumped into cell from tissue across basal membrane.
Chlorine diffuses into mucus from cell, through CFTR protein.
Sodium ions diffuse between cells down the electrical gradient into mucus from tissue.
Water moves from cell to mucus by osmosis.
Water moves from tissue into cell by osmosis.

Question 7

With CF

Answer 7

CFTR channel (protein) is absent or non functional.
Sodium channel is permanently open.
Water continually moves out of mucus by osmosis.

Question 8

Malabsorbtion syndrome

Answer 8

Pancreatic duct becomes blocked with sticky mucus. Less digestive enzymes in the gut lead to less nutrients being absorbed. Enzymes trapped in the pancreas cause cysts.

Question 9

Diabetes

Answer 9

Pancreatic duct becomes blocked by sticky mucus. Less insulin gets into blood, leading to high blood glucose levels.

Question 10

Reproduction: Females

Answer 10

Cervix blocked by mucus, less chance of fertilisation.

Question 11

Reproduction: Males

Answer 11

Can lack Vas Deferon (sperm duct), or blocked by sticky mucus. Less sperm in ejaculate.

Question 12

Sweat

Answer 12

Sodium Chloride is not reabsorbed from sweat travelling to the skin, this is because the CFTR protein is faulty. Leads to abnormally salty sweat.

Question 13

DNA

Answer 13

The CF gene codes for the CFTR protein is found on chromosome 7. A common mutation, the DF508 mutation causes the deletion of three nucleotides, meaning there is no phenylalanine, the 508th amino acid within the CFTR protein, so misfolding occurs.

Question 14

Inheritance

Answer 14

CF is caused by monohybrid inheritance, this means that only one gene determines the characteristics displayed.

Question 15

Blood spot trypsinogen test

Answer 15

Individuals with CF have elevated levels of the protein trypsinogen in their blood.

Question 16

Sweat test

Answer 16

Individuals with CF have salty sweat.

Question 17

Genetic screening

Answer 17

Can show both Individuals with CF and carriers. However, does not screen for all known mutations.

Question 18

Amniocentesis

Answer 18

Amniocentesis is carried out whereby a needle is inserted into the amniotic fluid to collect fetal cells. This is usually carried out around 15-17 weeks into pregnancy and has a 1% risk of causing a miscarriage.

Question 19

Chronic villus sampling (CVS)

Answer 19

Chronic Villas Sampling (CVS) can be carried out at around 8-12 weeks, this involves taking some placental tissue for testing, which carries a slightly higher chance of miscarriage than amniocentesis.

Question 20

Non-invasive prenatal diagnosis (NIPD)

Answer 20

A non-invasive prenatal diagnosis (NIPD) can be carried out to eliminate the risk of miscarriage. At around 4-5 weeks into pregnancy, Cell-free fetal DNA (cffDNA) can be detected in the mothers blood. At around 7-9 weeks into pregnancy, there is a sufficient volume of cffDNA in the blood to analyse.

Question 21

Pre-implementation genetic diagnosis (PGD)

Answer 21

This is when IVF is used and the embryo’s are tested for genetic disorders before implanted in the mother, therefore removing the possibility of having an abortion.