The Gas Exchange System: Structure & Functions
- Ciliated epithelial cells, goblet cells and mucous glands play vital roles in maintaining the health of the gas exchange system
- Cartilage, smooth muscle, elastic fibres and squamous epithelial tissue all play important structural roles in maintaining the gas exchange system
Structures & functions in the gas exchange system table
| Structure | Function |
| Ciliated epithelial cells | These cells line the trachea to the bronchi. Each cell has tiny projections called cilia, which sweep mucus, dust, bacteria and other microorganisms up and away from the lungs to the mouth, where they are swallowed and digested by stomach acid |
| Goblet cells | Goblet cells are embedded throughout the ciliated epithelium and are mucus-producing cells. The mucus they produce traps dust, bacteria and microorganisms as mentioned above |
| Mucous glands | The mucous glands work with goblet cells in the trachea and bronchi to produce mucus |
| Cartilage | Rings of cartilage line the trachea, or windpipe. Cartilage is a strong but flexible tissue and is essential for keeping the trachea open. Because of its flexibility, the cartilage can move and flex as we breathe |
| Smooth muscle | Smooth muscle is muscle not under conscious control and is found in the walls of the bronchi and bronchioles. It helps to regulate the flow of air into and out of the lungs by dilating and widening when more air is needed |
| Elastic fibres | Elastic fibres are found in the squamous epithelium of the alveolar walls. Elastic fibres are a critical component of alveoli because they allow the tiny alveoli to stretch as they fill with air and recoil to help force air out. It is the elastic abilities of alveoli which enable them to have such a large surface area. In serious cases of COPD, such as advanced emphysema, the alveoli lose these elastic properties |
Worked example
Describe the cause of cystic fibrosis and explain how cystic fibrosis affects the function of the lungs.
Cystic fibrosis is caused by a recessive allele of the CFTR gene. Cystic fibrosis affects the lungs by goblet cells producing thick, sticky and dehydrated mucus. This mucus is much harder for cilia to sweep up the trachea and to the mouth and so mucus accumulates in the airways. As the mucus traps bacteria but the mucus can’t be removed, this leads to frequent infections and eventually scar tissue in the lungs. The fact that mucus obstructs the airways means that gas exchange is less efficient as it is harder for oxygen to reach the lungs and harder for carbon dioxide to be exhaled, causing breathing problems.
Exam Tip
Make sure that you don’t confuse the cilia in the respiratory system for microvilli in the small intestine. At first glance they appear similar, but they have very different functions! Cilia are for sweeping mucus while microvilli are for the absorption of nutrients.
