lecture 25

Question 1

what does surfactant do?

Answer 1

• decreases surface tension inside the alveoli and inward pressure
• preventing alveoli from collapsing
• making alveoli easier to expand

Question 2

surfactant

Answer 2

• is secreted by type 2 alveolar cells and lines the inside of the alveoli

Question 3

how does surfactant act as an equalizer

Answer 3

smaller alveoli have greater surface tension which means the greater it wants to collapse on it self, but surfactant make small and big alveoli equal so they can be equal

Question 4

Why do small alveoli tend to collapse on itself

Answer 4

• at an air filled-fluid interface we have surface tension due to the nature of water being polar and is adhesive and cohesive that causes an inwardly directed pressure that promotes collapsibility
• so we’ll pump in a little more surfactant to account for the extra surface tension and since surfactant is lipidy and watery the lipids will break up cohesion between water molecules and less cohesion of water molecules means decrease in surface tension

Question 5

Law of laplace

Answer 5

P (collapsibility) = 2T (surface tension)/r

Question 6

alveolar pressure at rest is

Answer 6

0mm Hg meaning it’s equal to atmospheric pressure

Question 7

intrapleural pressure

Answer 7

is -4mm Hg it is sub atmospheric

Question 8

transpulmonary pressure

Answer 8

• is the force inflating the lungs
  alveolar pressure - intrapleural pressure = 4 mm Hg

Question 9

why is intrapleural pressure sub-atmospheric?

Answer 9

• because the 2 membranes are stuck together so where one goes the other goes, but they are drawn in different directions
• the elastic recoils of lungs is inwards and elastic recoil of chest is outwards

Question 10

Lung compliance and elastance

Answer 10

1. Compliance: ability for lungs to stretch
   Loss of compliance: fibrosis (exposure to asbestos)
2. elastance: ability for lung to snap back after being stretched
   loss of elastance: emphysema (smoking a lot)

Question 11

the volume that moves into and out of lungs

Answer 11

tidal volume (500ml)

Question 12

Boyles Law

Answer 12

P1V1=P2V2
- if volume increase pressure decreases

Question 13

Tidal volume

Answer 13

• volume of air into and out of lungs
• 500mL

Question 14

inspiratory reserve volume

Answer 14

everything you can breath in

Question 15

expiratory reserve volume

Answer 15

everything you can breath out

Question 16

residual volume

Answer 16

• everything that’s left inside that can’t be pushed out

Question 17

inspiratory capacity

Answer 17

= tidal volume + inspiratory reserve volume

Question 18

vital capacity

Answer 18

= TD + IRV + ERV

Question 19

total lung capacity

Answer 19

= TD + IRV + ERV + RV

Question 20

functional residual capacity

Answer 20

= ERV + RV

Question 21

total pulmonary ventilation

Answer 21

air in and air out of respiratory system per minute
= ventilation rate (breath/min) x tidal volume
= 12 breaths/min x 500mL = 6L/min

Question 22

what is anatomical dead space and what is it’s value

Answer 22

• it is everywhere gas exchange is not occurring like conducting airways
• 150 mL

Question 23

alveolar ventilation

Answer 23

• how much air is in alveoli available for gas exchange
  alveolar ventilation = ventilation rate x (tidal volume-anatomical dead space)= 4.2L/min
  Better indicator of ventilation efficiency