adaptations of type I and type II pneumocytes Flashcards
What is the function of Type I pneumocytes (AT1 cells) in the lungs?
Type I pneumocytes (AT1 cells) are adapted for the diffusion of oxygen and carbon dioxide across the alveolar wall into the blood.
What structural adaptations do Type I pneumocytes have to facilitate gas exchange?
Type I pneumocytes are very thin (around 15μm thick) and wide, which reduces the diffusion distance between air in the alveolus and blood in the capillaries, increasing the rate of gas exchange.
Why do Type I pneumocytes have a small volume of cytoplasm?
Type I pneumocytes have a small volume of cytoplasm because they are adapted for passive gas exchange, requiring minimal mitochondria and cellular machinery for energy production.
What is the role of the thin wall of capillaries adjacent to Type I pneumocytes?
The thin wall of the adjacent capillaries also facilitates gas exchange. The air in the alveolus and blood in the capillary are less than 0.5μm apart, creating a short diffusion distance for efficient gas exchange.
What is the function of Type II pneumocytes (AT2 cells)?
Type II pneumocytes produce and secrete surfactant, a substance that reduces surface tension in the alveoli, preventing the alveoli from collapsing and facilitating efficient gas exchange.
How are Type II pneumocytes (AT2 cells) structurally adapted for their role in surfactant production?
Type II pneumocytes are smaller (about 10μm across), with dense cytoplasm containing mitochondria, rough endoplasmic reticulum (RER), and lysosomes. These organelles support the synthesis and secretion of surfactant.
Where is surfactant stored in Type II pneumocytes?
Surfactant is stored in lamellar bodies, which are vesicles containing layers of phospholipid and some proteins. These vesicles undergo exocytosis to secrete surfactant into the alveolus.
How does surfactant produced by Type II pneumocytes prevent alveolar collapse?
Surfactant forms a monolayer on the surface of the alveolar moisture, with phospholipid heads facing inward and tails facing outward. This reduces surface tension by preventing hydrogen bonding between water molecules, which could otherwise cause the alveoli to collapse.
Why is the role of surfactant crucial for gas exchange in the lungs?
Without surfactant, the surface tension in the alveoli would be too high, causing them to collapse, making gas exchange difficult. The surfactant lowers surface tension and keeps the alveoli open, ensuring efficient oxygen and carbon dioxide exchange.
