Lecture 27

Question 1

How does surfactant work?

Answer 1

Surface tension is based on Law of Laplace: P=2T/R where there is an inwards pressure created by the adhesion between molecules. This inwards pressure makes it difficult for alveoli to expand, so surfactant reduces the tension to make the alveoli easier to expand and less likely to collapse.
Smaller alveoli have more surfactant to make up for the lower radius, so this equalizes the pressure in the alveoli and thus the flow of air to the alveoli

Question 2

How does the intrapleural pressure keep the lungs inflated and how do the pressures change during breathing?

Answer 2

Intrapleural pressure is negative, or lower than the atmosphere. This means that there is a force pulling the membranes together. This pulls the membrane and keeps it stuck to the thoracic wall.

When the thoracic cavity expands, the intrapleural pressure decreases, which causes the transpulmonary pressure to increase. to compensate, the alveolar pressure decreases. This causes air to flow into the alveoli.

Question 3

What is a pneumothorax

Answer 3

When there is a puncture in the pleural membranes, there is a loss of the intrapleural pressure (equalizes with atmosphere) so nothing to keep the lungs inflated so they collapse

Question 4

Define lung compliance and elastance

Answer 4

lung compliance: ability of lungs to stretch due to collagen fibers in the interstitial space
lung elastance: ability of lungs to recoil due to elastin fibers

Question 5

How can you measure pulmonary function

Answer 5

spirometer

Question 6

What are the 8 different lung volumes and capacities?

Answer 6

1) tidal volume (how much air inspired/expired during normal breathing)
2) expiratory reserve volume (how much air you can blow out after normal expiration)
3) inspiratory reserve volume (how much air you can breath in after normal inspiration)
4) residual volume (amount of air left after expiratory reserve volume blown out)
5) inspiratory capacity (tidal volume + inspiratory reserve volume)
6) total lung capacity (residual volume + expiratory reserve volume + inspiratory reserve volume + tidal volume)
7) vital capacity (inspiratory reserve volume + expiratory reserve volume + tidal volume)
8) functional residual capacity (expiratory reserve volume + residual volume)