Ventilation and diffusion

Question 1

The conducting airways

Answer 1

– Cartilage, few smooth muscles

– Collapse rare

Question 2

Dalton’s Law of Partial Pressures

Answer 2

• States that Total pressure (PTotal) of a mixture of gases is the sum of their individual partial pressures (Px)

Question 3

Atmospheric Pressure (PB)

Answer 3

at sea level is 760mmHg or 101.325 kPa

Question 4

relationship between atmospheric pressure and partial pressure

Answer 4

• If atmospheric pressure changes then partial pressure changes
• If proportion of gas changes its partial pressure changes

Question 5

Henry’s Law

Answer 5

• States that the concentration of O2 dissolved in water ([O2]dis) is proportional to the Partial pressure (PO2) in the gas phase

Question 6

Gas exchange between alveolar and blood: • O2 has to:

Answer 6

– dissolve in an aqueous layer
– diffuse across the membranes
– enter the blood

Question 7

Gas exchange between alveolar and blood: Rate of diffusion is proportional to

Answer 7

– Partial pressure difference (∆P)
– Surface area (A)
– Solubility (D, diffusion coefficient)
– molecular mass (D, diffusion coefficient)
– Inversely proportional to tissue thickness (T)

Question 8

Diffusion Limitations of Gas Exchange

Answer 8

• In oedema, T (thickness of barrier) increases
• Transit time through capillary may not be sufficient to complete full gas exchange
– gas exchange reduced
– More marked effect on O2 than CO2, due to greater solubility of CO2

Question 9

Diffusion Limitations of Gas Exchange Emphysema

Answer 9

A reduced (breakdown of tissue and alveolar sacs)
– Gas exchange reduced

Question 10

Diffusion Limitations of Gas Exchange

pulmonary fibrosis

Answer 10

T increased (deposition of fibrotic tissue) – Gas exchange reduced

Question 11

Diffusion Limitations of Gas Exchange

mucus

Answer 11

inflammation of airway, tumours, reduce gas entry – Gas exchange reduced

Question 12

Altitude

Answer 12

• At altitude, atmospheric pressure is reduced

* Hence, PO2 is reduced

Question 13

acute hysiological Adaptations to Altitude

Answer 13

– Hypoxia sensed by peripheral
chemoreceptors
– Ventilatory drive increases initially but blunted by central chemoreceptors that respond to decreased PaCO2 due to increased ventilation
– CO increases due to suppression of cardioinhibitory centre

Question 14

adaptive Physiological Adaptations to Altitude

Answer 14

– Central chemoreceptors adapt so
ventilation rate continues to increase
– PaCO2 drops leading to respiratory alkalosis, kidneys compensate by reducing acid secretion blood pH normalises
– Alkalosis stimulates 2,3 DPG production – leads to rightward sift of O2 dissociation curve

Question 15

• Acclimation blood

Answer 15

– Erythropoietin release stimulated

– Hb conc. increases to 200 g/L from 150 g/L

Question 16

• Acclimation vasculature

Answer 16

– Hypoxia stimulates angiogenesis

– Capillary density increases throughout body

Question 17

• Acclimation cardiopulmonary system

Answer 17

– Vascular and ventricular remodelling
– Smooth muscle growth increase vascular wall thickness
– Right ventricle hypertrophies