First 418 words of the document:
Air is drawn in through the trachea due to low pressure in the lungs.
Low pressure caused by increase in volume of the thorax as the
diaphragm moves down.
Diaphragm and intercostal muscles relax, pressure increases and air
is forced out of the lungs.
Trachea divides into two bronchi , into bronchioles , into alveoli.
Alveoli are the site of gas exchange.
Mucus lines the tubs in the lungs to trap dust and other microorganisms.
Mucus is removed by cilia that cover epithelial cells by wavelike beating.
People with cystic fibrosis have stickier mucus so is harder to remove
increases chance of lung infection and makes gas exchange less efficient .
Squamous flatter, thin cells, apical membrane faces lumen, cells can
be less than 0.2µm thick.
Columnar taller cells, nucleus at base of the cell, surface facing
lumen usually covered in microvilli (increase the surface area).
Cells work together as a tissue , consists of one or more layers of cells
sitting on a basement membrane (made of protein fibres in a jellylike
proteincarbohydrate matrix) to anchor the epithelium to the
Apical membrane faces the lumen.
Basal membrane faces the basement membrane.
Ciliated epithelial cells line the trachea, bronchus and bronchioles,
have cilia (hairlike structures) to remove mucus from the airways,
nucleus of cells in bottom and centre pseudostratified .
Pathogens can enter the body in the airways, and the mucus traps them, to
be swallowed or coughed out. Swallowing lets the stomach acid kill most of
the microorganisms. In CF , the mucus is so sticky it is hard to remove and
mucus production still continues excess mucus . Harmful bacteria thrive in
the mucus as there are low levels of oxygenanaerobic conditions.
Surface area and diffusion the larger the organism, more exchange has to
happen to meet the organism's metabolic needs. Small surface area to
volume ratio good. Relying on only the outer surface of the organism not
Provide a large surface area for exchange.
Have numerous capillaries surrounding them.
Thin walls reduce the distance of diffusion.
The sticky mucus layer in the bronchioles of a person with CF block the
narrow airways, preventing movement of air. This means the person cannot
get enough oxygen all of the time.