physiology

Question 1

forces keeping alveoli open

Answer 1

transmural gradient

pulmonary surfactant - reduces alveolar surface tension

alveolar interdependence -  If alveolus starts to collapse the surrounding alveoli are stretched then recoil exerting expanding forces in collapsing alveolus to open it

Question 2

elastic forces promoting alveolar collapse

Answer 2

elastic recoil of lungs + chest wall

alveolar surface tension (surfactant REDUCES surface tension - premature babies need to overcome high surface tension to inflate lungs)

Question 3

how does a pneumothorax effect transmural pressure gradient?

Answer 3

abolishes it - by raising intrathoracic pressure -> leading to lung collapse

Question 4

which pressure must decrease to allow air to flow into lungs during inspiration

Answer 4

interalveolar pressure must become less than atmospheric pressure for air to flow into lungs during inspiration

• before inspiration they are equal, expansion of lungs makes intralveolar pressure fall (boyles law)

Question 5

boyles law

Answer 5

at any constant temp the pressure exerted by a gas varies inversely with the volume of the gas

(increase in size of lungs makes intraalveolar pressure fall)

Question 6

muscles of respiration (major, acessory of inspiration, muscles of active respiration)

Answer 6

major = diaphragm + external intercostal muscles

accessory of inspiration (contracts only on forceful inspiration) = sternocleidomastoid, scalenus, pectoral

muscles of active expiration (contracts only during active expiration) = abdominal muscles, internal intercostal muscles

Question 7

what can be measured by spirometry

Answer 7

tidal volume
inspiratory reserve volume
expiratory reserve volume
inspiratory capacity
vital capacity

Question 8

whatlung measurements can NOT be measured by spirometry

Answer 8

residual volume
functional residual capacity
total lung volumes

Question 9

inspiratory / expiratory reserve volumes

Answer 9

IRV = extra volume of air that can be maximally inspired over + above the typical resting tidal volume

ERV = extra volume of air that can be actively expired by maximal contraction beyond the normal volume of air after a resting tidal volume

Question 10

residual volume

Answer 10

minimum volume of air remaining in the lungs even after a maximal expiration

(tidal volume = volume of air entering or leaving lungs during a single breath)

Question 11

inspiratory capacity? how can it be calculated?

Answer 11

max volume of air that can be inspired at the end of a normal quiet expiration

IC = IRV + TV

Question 12

*functional residual capacity? how can it be calculated?

Answer 12

volume of air in lungs at end of normal passive expiration

(FRC = ERV + RV)

Question 13

vital capacity

Answer 13

max volume of air that can be moved out during a single breath following a maximal inspiration

VC = IRV + TV + ERV

Question 14

how does emphysema affect residual volume?

Answer 14

residual volume increases as elastic recoil of lungs is lost

Question 15

affect of airway obstruction on FVC, FEV1 + FEV1/FVC%

Answer 15

FVC - normal

FEV1 = low

FEV1/FVC% = low!

Question 16

affect of lung restriction on FVC, FEV1 + FEV1/FVC%

Answer 16

FVC = low

FEV1 = low

FEV1/FVC% = normal!

Question 17

affect of combination of airway obstruction + restriction on FVC, FEV1 + FEV1/FVC%

Answer 17

all LOW

Question 18

FVC, FEV1 in asthma vs COPD

Answer 18

COPD - smaller FVC + FEV1,
–> FEV1/FVC post bronchodilator - <70%

asthma –> FEV1/FVC = <75%

Question 19

does parasympathetic or sympathetic activation cause bronchodilation

Answer 19

sympathetic -> bronchodilation

para -> bronchoconstriction

Question 20

effect of decreased pulonary compliance

Answer 20

greater change in pressure needed to produce a given change in volume (lungs are stiffer), causes SOB (esp on exertion)

restrictive pattern on spirometry

Question 21

causes of decreased lung compliance

Answer 21

pulmonary fibrosis
pulmonary oedema - **heart failure
lung collapse
pneumonia
absence of surfactant

Question 22

causes of increased pulmonary compliance

Answer 22

if elastic recoil lost -> emphysema, hyperinflation of lungs (have to work harder to get air out)

compliance increases with age

Question 23

when is work of breathing increased

Answer 23

decreased pulmonary compliance
airway resitance increased
elastic recoil decreased

a need for increased ventilation

Question 24

pulmonary ventilation vs alveolar ventilation

Answer 24

Pulmonary ventilation = volume of air breathed in + out per minute
- increase -> increase tidal volume + resp rate
–> more advantageous to increase depth of breathing due to dead space

Alveolar ventilation = volue of air exchanged between atmosphere + alveoli per min

–> Alveolar ventilation is less than pulmonary ventilation due to presence of anatomical dead space

Question 25

ventilation vs perfusion

Answer 25

Ventilation = rate gas passes through lungs
Perfusion = rate blood passes through lungs

Question 26

alveolar dead space

Answer 26

mismatch between air in alveoli + blood in pulmonary capillaries
- Ventilated alveoli not adequately perfused with blood = alveolar dead space
o V small, of little significance in healthy
o Could increase significantly in disease

• Accumulation of CO2 in alveoli as a result of increased perfusion decreases airway resistance leading to increased airflow
• Increased alveolar O2 conc as a result of increased ventilation causes pulmonary vasodilation which increases blood flow to match larger airflow

Question 27

affect of pulmonary arterioles on decreased O2

Answer 27

vasoconstriction
- vasodalite on increased O2

(systemic arterioles do opposite)

Question 28

HbF compared to Hb

Answer 28

interact less with 2,3 biphophoglycerate in RBCs

has a higher affinity for O2 - compared to adult Hb
HbF curve shifted to left compared to Hb

ALLOWs O2 transfer from mother to foetus even if pO2 is low