What are the 2 kinds of cells that makes up alveolar walls?
Type 1 (gas exhange)
Type 2 (secretes surfactant fluid)
What do type 1 cell of alveoli do?
Allows gas exchange
What do type 2 cells of alveoli do?
Secretes surfactant fluid
What is surfactant?
Detergent like fluid produced by type 2 alveolar cells
What does surfactant do?
Reduces surface tension on alveolar surface membranes, reducing tendancy for alveoli to collapse
What is surface tension?
Attraction between water molecules, occurs wherever there is an air-water interface
What does surfactant do to the compliance of the lung?
What does surfactant do to the lungs tendency to recoil?
Is surfactant more effective in small or large alveoli, and why?
Small because surfactant molecules come closer together and are therefore more concentrated
Why does air spread evenly between small and large alveoli although there would be a pressure difference?
Surfactant reduces surface tension better in small alveoli, making the pressure in small and large equal
When does surfactant production begin and is completed by?
About 25 weeks gestation and is completed by 36 weeks
What is production of surfactant stimulated by?
Thyroid hormones which increase towards the end of pregnancy
What do premature babies often suffer from due to surfactant production being complete at week 36?
Infant respiratory distress syndrome
What is a saline filled lung similar to?
A lung in utero
Why does a lung in utero require a smaller change in pressure to inflate?
Does not need to overcome surface tension (no air-water interface)
What is compliance?
Change in volume relative to change in pressure
What does compliance of the lung represent?
Stretch ability of the lung (not elasticity)
What does a high compliance mean?
Large increase in lung volume for a small increase in ip pressure
What does a low compliance mean?
Small increase in lung volume for a large decrease in ip pressure
What does compliance change with?
Disease and age
Does it require a greater change in pressure from fictional residual capacity to reach a lung volume during inspiration or expiration?
Greater change in pressure is required during inspiration
Why is expiration passive?
Work on inspiration is recovered as elastic recoil during expiration
What is emphysema?
Loss of elastic tissue means expiration requires effort (image c)
What is loss of elastic tissue called?
What is fibrosis?
Inert fibrous tissue means effort of inspiration increases (image d)
What is inert fibrous tissue called?
What does inert mean?
Lacking the ability or strength to move
Does emphysema make inspiration or expiration more difficult?
Expiration (image c)
Does fibrosis make inspiration or expiration more difficult?
Inspiration (image d)
What does the pressure/volume curve vary between?
The apex and the base of the lung