Respiratory Physiology Lecture 1.3: The Alveoli Flashcards
What are alveoli?
Tiny, thin-walled, capillary rich sac in the lungs where the exchange of oxygen and carbon dioxide takes place
Where does the exchange of gases take place in the lungs?
Alveoli
Approximately how many alveoli are in the human lung?
~ 500 million
Diameter of alveoli
~⅓ mm
How many capillaries are in the lungs?
~280 billion capillaries
What volume of blood does the lung capillaries have?
- At rest they contain 70 mL of blood
- 200 mL during physical activity
What are the two types of alveolar cells?
- Type I alveolar cells
- Type II alveolar cells
What type of alveolar cell is most abundant?
Type I
Type I alveolar cells
- Most of the surface of the alveolar walls are lined by a continuous mono-layer of flat epithelial cells
- Do not divide
- Susceptible to inhaled or aspirated toxins
Type II alveolar cells
- produce surfactant
- act as progenitor cells
How much of alveolar cells is made up of Type II?
7% of alveolar surface
What is the surfactant produced by Type II alveolar cells?
Detergent-like substance made of lipoproteins
What does surfactant do?
reduces surface tension of alveolar fluid
How do type II alveolar cells act as progenitor cells?
When there is injury to Type I cells, Type II cells can multiply and eventually differentiate into Type I cells
size of capillaries
Capillaries are small (7 to 10 μM in diameter)
What can pass through capillaries?
just enough space for a red blood cell to pass
How long does it take for a RBC to pass through capillaries?
Each red blood cell spends about 0.75 seconds in the capillary network and during this time probably traverses 2 or 3 alveoli
What network do the alveolar walls contain?
The alveolar walls also contain a dense network of capillaries and a small interstitial space (Connective tissue and interstitial fluids)
How does gas exchange occur?
Transfer of O2 and CO2 occurs by diffusion through the respiratory membrane
diameter of respiratory membrane
0.2 - 0.5 uM thick
Another term for type I and type II alveolar cells?
Type I pneumocyte and Type II neumocyte
What makes up the epthelium avelolar wall?
Type I and Type II pneumocytes`
What are the layers of the respiratory membrane?
- Alveolar fluid (With surfactant)
- Alveolar epithelium
- Basement membrane of alveolar epithelium
- Interstitial space
- Basement membrane of capillary endothelium
- Capillary endothelium
What are the layers of the respiratory membrane?
- Alveolar fluid (With surfactant)
- Alveolar epithelium
- Basement membrane of alveolar epithelium
- Interstitial space
- Basement membrane of capillary endothelium
- Capillary endothelium
