6.4 Gas Exchange Flashcards
What is ventilation?
The replacement of older air in the lungs with fresh air from the body’s external environment
What is ventilation essential for?
Ventilation is essential for the effective exchange of gases in the lungs
Where does gas exchange occur?
The exchange of oxygen and carbon dioxide occurs between the alveoli and the capillaries in the lungs
By what process are gases exchanged and what does this require?
Gases are exchanged by simple diffusion which requires a concentration gradient
What maintains the concentration gradient in the lungs?
This gradient is maintained by
Ventilation
The continuous flow of blood in the capillaries
What is the role of ventilation in terms of aiding gas exchange?
Ventilation maintains concentration gradients of oxygen and carbon dioxide between air in the alveoli and blood flowing in adjacent capillaries
What does breathing in cause in terms of ventilation?
Breathing in fresh air from the surrounding environment increases the concentration of oxygen in the air inside the alveoli
What does breathing out cause in terms of ventilation?
Breathing out removes carbon dioxide
How does ventilation affect the levels of gases in the body?
This means that after ventilation, compared to the blood found in adjacent capillaries, the alveoli have
Higher oxygen levels
Lower carbon dioxide levels
Why is a concentration gradient in the alveoli necessary?
This ensures that oxygen continues to diffuse from the alveoli into the capillaries, while carbon dioxide continues to diffuse from the capillaries into the alveoli
Both gases move down their concentration gradient
How are alveoli (basic) adapted to gas exchange?
The alveoli are specifically adapted for gas exchange as they collectively have a very large surface area and the alveolar walls are only one cell thick which provides a short diffusion distance
What is another name for the alveolar wall?
The alveolar walls are also known as the alveolar epithelium
What are type 1 pneumocytes?
Type I pneumocytes are extremely thin alveolar cells which make up the majority of the alveolar epithelium
How are type 1 pneumocytes adapted?
They are adapted to maximise the rate of gas exchange by providing a short diffusion distance
How are capillaries adapted for gas exchange?
The capillary walls are also only one cell thick which means there is usually less than 0.5μm between the air in the alveoli and the blood, this maximises the rate of diffusion
What are type II pneumocytes?
Type II pneumocytes are rounded cells which secrete a solution that coats the epithelium of the alveoli
Which type of pneumocyte is more abundant?
TYPE 1
They occupy a much smaller proportion of the alveolar epithelium than the type I pneumocytes; around 5% (type II)
What do pneumocytes release?
The solution released by type II pneumocytes is pulmonary surfactant
What is pulmonary surfactant composed of?
Pulmonary surfactant contains molecules that have hydrophobic tails and hydrophilic heads
What is the structure of the pulmonayry surfactant?
The molecules form a monolayer with the hydrophobic tails facing the alveolar air
What is the role of surfactant?
Pulmonary surfactant reduces surface tension, maintaining alveolar shape and preventing the sacs sticking together
This prevents the lungs collapsing
How does surfactant aid gas exchange? both in terms of o2 and co2
The solution also aids gas exchange
The layer of moisture provided by the solution allows oxygen to dissolve before it diffuses into the blood
Carbon dioxide evaporates from the moist surface before it is removed in exhalation
Where does air enter?
Air moves in through the nose and mouth before it is carried to the lungs through the trachea
What is the trachea?
The trachea is a tube supported by rings of cartilage which help to support its shape and ensure it stays open, while allowing it to move and flex with the body