Topic 9 Gaseous Exchange. Flashcards
What is the gaseous exchange surface?
A gaseous exchange surface is a specialized structure in organisms that facilitates the exchange of gases, primarily oxygen and carbon dioxide, between the internal environment (such as blood or cells) and the external environment (such as air or water).
What are the 4 features of gas exchange surfaces in humans?
- Large surface area to allow faster diffusion of gases across the surface.
- Thin walls to ensure diffusion distances remain short.
- Good ventilation with air so that diffusion gradients can be maintained.
- Good blood supply to maintain a high concentration gradient so diffusion occurs faster.
- Moist environment to facilitate gas diffusion because gases, like oxygen, need to dissolve in water for efficient transfer into cells.
Describe the pathway of air from the nasal cavity/mouth to the alveoli and back.
When air is inhaled, it enters through the nasal cavity or mouth, passes through the pharynx (throat) and larynx (voicebox), and moves into the trachea. The trachea divides into two primary bronchi, each entering a lung. These further divide into smaller bronchioles, which continue to branch until they become terminal bronchioles. Terminal bronchioles subdivide into respiratory bronchioles, leading to alveolar ducts, which supply air to the alveoli where gas exchange occurs.
During exhalation, this pathway reverses, expelling carbon dioxide-rich air from the alveoli through the alveolar ducts, respiratory bronchioles, terminal bronchioles, bronchioles, tertiary and secondary bronchi, primary bronchi, trachea, larynx, pharynx, and finally out through the nasal cavity or mouth.
Describe the structure of the human gas exchange system, limited to:
- Lungs.
The lungs are two large, spongy organs located in the thoracic (chest) cavity, protected by the rib cage. They are responsible for gas exchange and are divided into lobes; the right lung has three lobes (upper, middle, and lower), while the left lung has two lobes (upper and lower) to accommodate the heart’s position. The surface area of the lungs is significantly increased by tiny air sacs called alveoli, which are clustered at the ends of bronchioles. The lungs are surrounded by a pleural membrane that creates a pressure gradient necessary for inhalation and exhalation.
Describe the structure of the human gas exchange system, limited to:
- Trachea.
The trachea, commonly known as the windpipe, is a tube that connects the larynx (voice box) to the bronchi. The trachea is reinforced with C-shaped rings of cartilage that prevent it from collapsing during breathing. Lined with ciliated epithelium and mucus-secreting goblet cells, it serves to trap dust, pathogens, and other particles from inhaled air before they reach the lungs.
Describe the structure of the human gas exchange system, limited to:
- Bronchi.
Describe the structure of the human gas exchange system, limited to:
- Bronchioles.
As bronchi branch out within each lung, they become smaller tubes known as bronchioles. These structures lack supportive cartilage and can collapse. Bronchioles further divide into terminal bronchioles and respiratory bronchioles that lead directly to alveolar ducts that open into clusters of alveoli where gas exchange occurs.
Describe the purpose of smooth muscle and the absence of cartilage in the bronchioles.
Bronchioles are surrounded by smooth muscle, which can contract or relax to adjust the diameter of the airways. During exercise, the muscles relax to allow a greater flow of air to the alveoli. The absence of cartilage make these adjustments possible.
Describe the structure of the human gas exchange system, limited to:
- Alveoli.
Alveoli (singular: alveolus) are tiny air sacs located at the end of respiratory bronchioles that provide a large surface area for gas exchange. Each alveolus is surrounded by a network of capillaries where oxygen diffuses into blood while carbon dioxide diffuses out into alveolar air to be exhaled. Alveolar walls are very thin and consist of a single layer of squamous epithelial cells for efficient gas diffusion.
Alveolar walls contain elastic fibres and collagen fibres. What is the purpose of these fibres in the alveoli?
Alveolar walls contain elastic fibres which stretch during inspiration and recoil during expiration to help force out air. This elasticity allows alveoli to expand depending on the volume of air breathed in. When the alveoli are fully expanded, the surface area to available for diffusion increases and the air is expelled efficiently when the elastic fibres recoil during expiration.
The walls also contain some collagen fibres to provide support and prevent alveoli from bursting.
Describe the structure of the human gas exchange system, limited to:
- Capillary network.
Surrounding each alveolus is an extensive capillary network composed of thin-walled blood vessels that facilitate rapid gas exchange between air in alveoli and blood in capillaries. The close proximity between alveolar air spaces and capillary walls allows oxygen molecules to diffuse from areas of higher concentration (inhaled air) to lower concentration (blood), while carbon dioxide moves from blood (higher concentration) to alveolar air (lower concentration).
This process is driven by partial pressure gradients.
Where is the cartilage found and what is the purpose of the cartilage?
Cartilage in the trachea and bronchi keeps these airways open and air resistance low; it prevents them from collapsing or bursting as the air pressure changes during breathing. In the trachea, there is regular arrangement of C-shaped rings of cartilage; in the bronchi, there are irregular blocks of cartilage.
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What happens directly after air flows through the nose and the trachea?
As air flows through the nose and the trachea, it is warmed to body temperature and moistened by evaporation from the lining, so protecting the delicate surfaces inside the lungs from desiccation (drying out)
