6.4 Gas exchange Flashcards
Structure of the respiratory system
- Trachea
- Bronchi
- Bronchioles
- Alveoli
- Intercostal muscles
- Diaphragm
3 main processes involved in physiological respiration (breathing)
- Ventilation: The exchange of air between the atmosphere and the lungs – achieved by the physical act of breathing
- Gas Exchange: The exchange of oxygen and carbon dioxide between the alveoli and bloodstream (via passive diffusion)
- Cell Respiration: The release of energy (ATP) from organic molecules – it is enhanced by the presence of oxygen (aerobic)
What is the purpose of ventilation?
Ventilation maintains concentration gradients of oxygen and carbon dioxide between air in alveoli and blood flowing in adjacent capillaries.
- The inspired air has a higher concentration of oxygen than the air in the alveoli of lungs
- Therefore, oxygen will move into the caplillaries surrounding the alveoli and carbon dioxide will move into the outside air through diffusion (no energy required)
- This reoxygenated blood leaves the lungs through the pulmonary vains which bring it back to the left atrium.
The respiratory system
Where does air enter? Where does it move?
- Air enters the respiratory system through the nose or mouth and passes through the pharynx to the trachea
- The air travels down the trachea until it divides into two bronchi (singular: bronchus) which connect to the lungs
- The right lung is composed of three lobes, while the left lung is only comprised of two (smaller due to position of heart)
- Inside each lung, the bronchi divide into many smaller airways called bronchioles, greatly increasing surface area
- Each bronchiole terminates with a cluster of air sacs called alveoli, where gas exchange with the bloodstream occurs
Structure of an alveolus
Alveoli function as the site of gas exchange, and hence have specialised structural features to help fulfil this role:
- They have a very thin epithelial layer (one cell thick) to minimise diffusion distances for respiratory gases
- They are surrounded by a rich capillary network to increase the capacity for gas exchange with the blood
- They are roughly spherical in shape, in order to maximise the available surface area for gas exchange
- Their internal surface is covered with a layer of fluid, as dissolved gases are better able to diffuse into the bloodstream
What are pneumocytes?
Pneumocytes (or alveolar cells) are the cells that line the alveoli and comprise of the majority of the inner surface of the lungs
- There are two types of alveolar cells – type I pneumocytes and type II pneumocytes
Type I pneumocytes structure and function
- Type I pneumocytes are involved in the process of gas exchange between the alveoli and the capillaries
- They are squamous (flattened) in shape and extremely thin – minimising diffusion distance for respiratory gases
- Type I pneumocytes are connected by occluding junctions, which prevents the leakage of tissue fluid into the alveolar air space
- Type I pneumocytes are amitotic and unable to replicate, however type II cells can differentiate into type I cells if required
Type II pneumocytes structure and function
- Type II pneumocytes are responsible for the secretion of pulmonary surfactant, which creates moist surface within the alveoli.
- This prevents the sides of the alveolus adhering to each other by reducing surface tension (of the water lining the pneomocytes).
- Equalizes the pressure of each alveolus even if they are different sizes. A greater amount of surfactant will be secreted in smaller alveoli compared to larger alveoli..
- Giving different sizes of alveolus the same pressure ensures that each alveolus inflates equally
What happens to the lungs during inspiration?
- External intercoastal muscles contract
- The diaphragm contracts - flattens
- The volume increases
- The pressure decreases
What happens to the lungs during expiration?
- Internal intercoastal muscles contract
- Abdominal muscles are flexed
- The diaphragm relaxes - dome
- The volume decreases
- The pressure increases
How does air travel into the respiratory system via pressure gradients created by muscles?
- When your chest is not moving, air pressure in the lungs is equal to atmospheric pressure, meaning air won’t move
- In order to bring air into your lungs, you have to increase the inside pressure compared to the atmosphere: this is done by contracting the external intercoastal muscles and lowering the diaphragm. Once this pressure difference is created. Air will naturally move from a high pressure to a low pressure, meaning air will move into the lungs.
- With this air in our lungs, we can now decrease the volume of our lungs by flexing our abdominal muscles and contracting our internal intercoastal muscles which greately increase the pressure. At this point the pressure inside out lungs becomes greater than the pressure in the atmosphere meaning air will move out.
Antagonistic muscle action in inspiration and expiration
External and internal intercostal muscles, and diaphragm and abdominal muscles are examples of antagonistic muscle action because they work opposite of one another.
Inspiration: external intercoastal muscles contract and diaphragm contracts
Expiration: internal intercoastal muscles contract and abdominal muscles flex
Lung cancer
Causes and consequences
Lung cancer describes uncontrolled growth of lung cells.
Causes:
- Smoking
- Disease
- Family genetic history
- Ageing
- Exposure to radiation
- Second hand smoke
Consequences:
- Reduced oxygen intake to the body
- It can spread to other organs
Emphysema
Causes and consequences
Another common lung condition, patients who suffer form this condition have damaged their alveoral cells which leads to the development of large holes in the lungs where the healthy cells used to be.
Causes:
- Smoking
Consequences:
- Large holes in the lungs
- Lowers the amount of surface area available for gas exchange
- Shortness of breath
- Greatly increased susceptibility to chest infections
