Unit 2 - Lungs

Question 1

describe the conducting zone and its respiratory tree

Answer 1

no gas exchange - transfer of gases to & from alveoli/ filtration/ warming & humidifying air
trachea - generation 0/ bronchi (1)/ lobar bronchi (2/3)/ segmental bronchi (4)/ small bronchi (5-11)/ bronchioles (12-15)/ terminal bronchioles (16)

Question 2

describe the cell lining the airways in conducting zone

Answer 2

trachea to small bronchi - pseudostratified columnar ciliated epithelium
bronchioles - simiple ciliated cuboidal epithelium

Question 3

describe the walls lining the airways in conducting zone

Answer 3

trachea/ bronchi - C-shaped rings of hyaline cartilage
smaller bronchi - overlapping cartilage
bronchioles - no cartilage
terminal bronchioles - thick walls due to smooth muscle

Question 4

describe the transitional/ respiratory zones and the respiratory trree

Answer 4

gas exchane - large SA
respiratory bronchioles (17-19)/ alveolar ducts (20-22)/ alveolar sacs (23)

Question 5

what does an alveolar sac contain?

Answer 5

2 or more alveoli enveloped by pulmonary capillaries

Question 6

what are the two types of cell found in alveolar septa?

Answer 6

Type I: squamous epithelial

Tupe 2: thicker cell which synthesis and secrete pulmonary surfactant

Question 7

what is found between alveolar septa and capillaries?

Answer 7

lung parenchyma - connective tissue containing elastic fibres & collagen linking alveoli together
(pores of Kohn interconnect neighbouring alveoli)

Question 8

give the definitions of: TV/ IRV/ ERV/ RV/ FRC/ VC

Answer 8

tidal volume - air taken in/ out in each breath
inspiratory reserve volume = difference in lung volume between normal and maximal inspiration
expiratory reserve volume = difference in lung volume between normal and maximal expiration
residual volume - air remaining after maximal expiration
functional residual capacity - ERV + RV - volume of air left at end of normal expiration
vital capacity - difference in lung volume between maximal inspiration and expiration

Question 9

what is the formula for tidal volume?

Answer 9

dead space + alveolar ventilation

Question 10

what is dead space?

Answer 10

anatomical - air taken in not mixing with air in alveoli
physiological - air taken in not taking part in gas exchange
Vd= Ve (1 -Fe/ Fa) where Ve = minute volume(fVt) and F is fractional content of CO2 in e- air exhaled/ a- alveoli

Question 11

how do you calculate alveolar ventilation rate?

Answer 11

Va = (Vt - Vd) x f
Va = Ve - (Ve x Vd/ Vt)

Question 12

what is the dead space: tidal volume ratio?

Answer 12

Vd/ Vt = (PaCO2 - PeCO2)/ PaCO2

Question 13

why is ventilation uneven?

Answer 13

progressive decrease in intrapleural pressure from apex to base
transpulmonary pressure decreased in lower regions at rest since Patm=Palv so increase more in volume during inspiration
- also lower ribs more curved
- descent of diaphragm expand lower lobes more than upright ones
- peripheral tissue more compliant than deeper tissue

Question 14

describe perfusion at apex, middle and base of lungs

Answer 14

apex - Palv = Pa - high vascular resistance no blood flow
middle - Pa> Palv - blood flow increases down the zones
base - Pa» Palv - arterial pressure exceeds alveolar pressure considerably so increased blood flow

Question 15

what do the dots mean on top of V and Q?

Answer 15

flow in litres per minute

Question 16

what does it mean when Va: Q 
=1
= 0
< 1
> 1

Answer 16

Va: Q - ventilation: perfusion ratio
=1 optimum matching/ optimum gas exchange
= 0 right to left shunt - blood passes through lung without coming into contact with alveolar air
< 1 poorly ventilated alveoli - well perfused
> 1 well ventilated alveoli - poorly perfused

Question 17

what happens in hypoventilation?

Answer 17

ventilation does not meet metabolic demands - increased PCO2/ decreased O2 - chest wall damage -increased dead space

Question 18

what happens in hyperventilation?

Answer 18

ventilation exceeds metabolic demands - decreased PCO2/ increased O2 - asthma attack

Question 19

what are the formulas for work?

Answer 19

mechanical work - force x distance moved

work done by gas - pressure x volume = Nm = J

Question 20

what is the formula for transpulmonary pressure?

Answer 20

Pl= Pa - Ppl (alveolar - intrapleural pressure)

Question 21

what is the behaviour of the curves in pressure-volume loop?

Answer 21

hysteresis - greater pressure change to inhale than to exhale due to static compliance of chest and non-elastic resistances of airways and tissue
difference between curves - cost of ventilation of lung during single respiratory cycle

Question 22

what is compliance?

Answer 22

change in volume / change in pressure

higher compliance = lower resistance = greater elasticity and stretch - reduced work of breathing

Question 23

what two properties determine the elasticity of the lungs?

Answer 23

• elastic fibres of parenchyma

- surface tension of liquid film lining alveoli

Question 24

what is laplace’s law? describe the relevance

Answer 24

P = 2T/r - when lungs inflated with air surface tension and elasticity of parenchyma opposes expansion - this would suggest a higher pressure of 3 kPa to inflate lung when in reality maximum inflation occurs at <2 kPa

Question 25

what accounts for the lower pressure <2kPa than expected to inflate the lungs?

Answer 25

surfactant secreted by Type II cells DECREASE SURFACE TENSION/INCREASE COMPLIANCE - phospholipid hydrophilic head in aqueous phase and hydrophobic tail in air space
during expiration phospholipids become compressed exclude water forming monolayer so decreases tension
during inspiration increase in area leads to slow increase in tension since phospholipid molecules separate slowly

Question 26

describe stages of inspiration

Answer 26

contraction of diaphragm/ intercostal muscles
increase in thorax volume
decrease in intrapleural pressure
expansion of alveoli
reduction in alveolar pressure
flow in air into the lungs

Question 27

describe stages of expiration

Answer 27

relaxation of diaphragm/ intercostal muscles
decrease in thorax volume
increase in intrapleural pressure
reduction of alveoli
increase in alveolar pressure
flow in air out of the lungs

Question 28

what is FEV?

Answer 28

measurement of volume air expelled from lung during first second of a forced breath

Question 29

how does FEV and VC change with a person with fibrosis?

Answer 29

reduced vital capacity

FEV to a lesser extent / unchanged

Question 30

how does FEV and VC change with a person with acute asthma?

Answer 30

reduced FEV

VC to less extent