Cystic Fibrosis

Cystic Fibrosis

Mucus in the lungs

  • Lungs allow rapid gas exchange between the atmosphere and the blood
  • Air drawn into the trachea due to low pressure in the lungs (caused by diaphragm)
  • Trachea – two bronchi – bronchioles – alveoli (sites of gas exchange)
  • Mucus produced by goblet cells
  • Any dust, debris or microorganisms are trapped and removed
  • Removed by cilia, covering the epithelial cells, which beat.
  • CF: stickier mucus which is harder to move
  • Stickier mucus increases chance of lung infection and makes gas exchange less efficient

Epithelial Cells

  • Lining cell
  • Epithelial cells work together as a tissue called epithelium
  • Consists of one or two cells sitting on a basement membrane (made of protein fibres in jelly-like matrix)
  • Squamous epithelium: lines the walls of the alveoli and capillaries (very thin)
  • Columnar epithelium: column shaped found in small intestine
  • Ciliated epithelium: cilia on the free surface – appears stratified due to position of nuclei. This is known as pseudostratified


Sticky Mucus

  • Microorganisms are trapped in the mucus, some cause illness, these are called pathogens
  • CF: mucus production continues although mucus cannot be moved by cilia
  • Low levels of oxygen in the mucus because oxygen diffuses slowly through it, and epithelial cells use more oxygen, causing harmful bacteria to thrive.


Increase of Size on Surface Area

  • Surface area to volume ratio: calculated by dividing an organisms total surface area by its volume


Gas Exchange

  • Alveoli provide a large surface area
  • There are numerous capillaries around the alveoli
  • Thin walls mean a short distance between the alveolar air and blood in the capillaries


Rate of diffusion

– Properties of gas exchange surfaces

  1. Surface Area – rate of diffusion is directly proportional to the surface area
  2. Concentration Gradient – rate of diffusion is directly proportional to the difference in concentration across the gas exchange surface
  3. Thickness of the gas exchange surface – rate of diffusion is inversely proportional to the thickness of the gas exchange surface. Thicker = slower


Fick’s Law: (MISSING)