Week 1 .2 Flashcards
What 2 cells are the alveolar wall made from?
Type 1 alveolar cells - permit gas exchange
Type 2 surfactant cells - secrete surfactant
What is surface tension?
Attraction of water molecules to one another while on a surface. This can cause the alveoli to collapse
What is the benefit of surfactant?
In alveoli, it stops surface tension by stopping attraction of water molecules to one another, so alveoli require less pressure to stay open.
Increases lung compliance (less pressure needed to increase volume)
What is lung compliance? What does it mean to have high compliance?
Stretchability of the lung.
High compliance means less effort to increase volume and small decrease in Intra-pleural pressure
How does lung compliance vary across the lung?
Depending on position. If upright, compliance is higher at the base rather than at the apex, as the alveoli at the base are more compressed due to the weight of the lung, so they have a greater stretching potential. At the apex, alveoli are stretched already so their stretching ability is decreased.
What happens when there is no surfactant?
Surface tension is higher in alveoli. Smaller alveoli collapse as they require more pressure to hold open. Air is thus transferred to larger alveoli, decreasing surface area and rate of gas exchange
What causes IRDS?
Infant respiratory distress syndrome
Babies born prematurely struggle to breathe as surfactant begins to produce at 25 weeks and finishes at 36 weeks. Without this, they have to apply a lot of pressure to breathe
What stimulates production of surfactant?
Thyroid hormones and cortisol
What is the capacity of the anatomical dead space?
150ml
What is pulmonary vs alveolar ventilation?
Pulmonary is air movement into and out of lungs
Alveolar is air movement into and out of alveoli
What is the process of alveolar ventilation?
- Begin with 2200ml air in alveoli and 150ml in anatomical dead space
- Inspire 500ml - of which 350 enters alveoli and 150 from dead space now enters alveoli. Total is now 2700
- Expire 500ml - of which 150 is in dead space and 350 comes from environment . 150ml “stale air” from alvioli stays in dead space - leading 2200ml in alveoli
How does tidal volume vary depending on state?
Decreases when anxious to 300ml and 20 breaths/min
Normal is 500ml and 12 breaths/min
Increases when relaxed to 750ml and 8 breaths/min
When is alveolar ventilation highest vs lowest?
Highest when in rest state - 750-150 = 600ml getting to alveoli. Called hyperventilation
Lowest when in anxious state - 300-150 = 150ml getting to alveoli. Called hypoventilation
What is partial pressure of a gas?
Pressure of a specific gas in a mixture of gasses. Higher conc. of gas in a mixture means it has a higher partial pressur
What happens to partial pressure of O2 and CO2 in different states?
Po2 increases and Pco2 decreases during hyperventilation in anxiety
Po2 decreases and Pco2 increases during hypo-ventilation in sleep
