Structure of the lung

1. Ciliated epithelial cells line the airways with goblet cells 

2. Goblet cells produce the mucas

3. Cilia, hair like structures, beat and move the mucas

4. Basement membrane holds it in position

Microorganisms become trapped in the mucus in the lungs. Some of these can cause illness- these are called pathogens. Microorganisms, dust or debris that get stuck in the mucus are continually removed by the wave beating of cilia that cover the epithelial cells lining the tubes of the gas exchange system. The mucas is normally moved by cilia into the back of the mouth cavity where it is either coughed out or swallowed, thus reducing the risk of infection. Acid in the stomach kills most microorganisms that are swallowed. Gases such as oxygen cross the walls of the alveoli into the blood system by diffusion. To supply enough oxygen to all the body’s respiring cells, gas exchange must be rapid. The fine structure of the lungs helps to maximise this.

People with CF have mucus that is drier than usual resulting in a sticky mucus layer that the cilia (hair like structures) find hard to move. Low levels of oxygen are diffusing slowly through it and epithelial cells are using it up. Bacteria thrive in anaerobic conditions. Mucas production still continues, as it would in a normal lung, and the airways build up layers of thickened mucas. White blood cells fight the infections within the mucas but as they die they break down, releasing DNA which makes the mucus even stickier. Repeated infections can eventually weaken the body's ability to fight the pathogens, and cause damage to the structures of the gas exchange systems. 

The sticky mucas layer in the bronchioles of a person with CF tends to block these narrow airways, preventing ventilation of the alveoli below the blockage. This reduces the number of alveoli providing surface area for gas exchange. Blockages are more likely at the narrow ends of the airways. These blockages will often air to pass when the person breathes in but not when they breathe out, resulting in over-inflation of the lung tissue beyond the blockage. This can damage the elasticity of the lungs.

People with CF find it difficult to take part in physical exercise because their gas exchange systems cannot deliver enough oxygen to their muscle cells. The oxygen is needed for the chemical process of anaerobic respiration, which release the energy used to drive the contraction of the muscles during exercise. People with CF become short of breath when taking exercise but exercise is very beneficial to them. 

These cells have cilia surronding them. Cilia are small hair like structures which beat and move mucas, up and out of the lungs. In the trachea, bronchi and bronchiole there are ciliated epithilial cells with cilia on the free surface. These cilia beat and move substances along the tube they line. The ciliated columnar epithelium of the gas exchange airways appears to be stratified (composed of several layers), but in fact each cell is in contact with the basement membrane. It appears to have several layers because some cells have their nucleus at the base of the cell while in others it is in the centre, giving the impression of different layers. This epithelium is therefore known as pseudostratified.