The Respiratory System

Review the anatomy of the respiratory system

Functions of the respiratory system

gas exchange

regulation of acid-base balance


Chemistry and physics of respiration

Boyle’s law 1

P1V1 = P2V2

mechanism of inhalation

role of diaphragm

role of intercostal muscles

mechanism of expiration

role of diaphragm

role of intercostal muscles

respiratory volumes

measurable volumes

tidal volume

anatomic dead space

inspiratory reserve volume

expiratory reserve volume

residual volume

calculated capacities

inspiratory capacity

functional residual capacity

vital capacity

total lung capacity

Charles’ law

V1/T1 = V2/T2

molecular basis of gas diffusion

net diffusion of a gas in one direction depends on concentration gradient

gas pressures in a mixture of gases depends on partial pressures

Dalton’s law of partial pressures

Ptotal = P1 + P2 + P3 + ... + Pn

Henry’s law 2

concentration of dissolved gas = pressure × SC

Gas Solubility coefficient
O2 0.024
CO2 0.57
N2 0.012

vapor pressure of water:  47 mm Hg at 37 °C

pressure gradient for diffusion 3

D ∝ (ΔP × A × S)/(d × (MW)0.5)

where D = diffusion rate; A = cross-sectional area; S = solubility

diffusion coefficient = S/(MW)0.5

Gas Relative diffusion coefficient
O2 1.0
CO2 20.3
N2 0.53

Composition of atmospheric, humidified, alveolar, and expired air

Gas Atmospheric air Humidified air Alveolar air Expired air
percent partial
percent partial
percent partial
N2 597.0 78.5 563.4 74.1 569.0 74.9 566.0 74.5
O2 159.0 20.9 149.3 19.6 104.0 13.7 120.0 15.8
CO2 0.3 0.04 0.3 0.04 40.0 5.26 27.0 3.55
H2O 3.7 0.49 47.0 6.18 47.0 6.18 47.0 6.18

Diffusion of gases through the respiratory membrane

factors affecting

thickness of membrane [0.63 µm on average]

surface area of membrane

diffusion coefficient

pressure difference

Types of respiration

internal respiration

external respiration

Transport of oxygen and carbon dioxide

role of hemoglobin in oxygen transport

Hb + 4(O2) ↔ Hb(O2)4


oxygen-hemoglobin dissociation curve

partial pressure of oxygen



BPG (or DPG)

fetal hemoglobin

hypoxia - inadequate oxygenation

anemic hypoxia

stagnant hypoxia

hypoxic hypoxia

histotoxic hypoxia

carbon dioxide transport

in solution

as carbaminoHb

Hb + CO2 ↔ HbCO2

as bicarbonate ion

H2O + CO2 ↔ H2CO3 ↔ H+ + HCO3-

Control of respiration

brainstem centers

medullary respiratory centers

dorsal respiratory group

pacemaker functioning for inspiration

ventral respiratory group

mixed functioning for inspiration and expiration

pontine respiratory group

pneumotaxic area inhibits DRG

apneustic center

prevents inhibition of DRG

chemoreceptors and chemosensitive area

hydrogen ions

aortic bodies

carotid bodies

Questions for thought
1.   Explain the significance of (a) Boyle’s law, (b) Dalton’s law, and (c) Henry’s law to the process of respiration.
2.   What are the differences between pulmonary volumes and respiratory capacities? Make sure you list each, and describe how each is determined.
3.   What is the functional difference between the dorsal respiratory group (DRG) and the ventral respiratory group (VRG) of the brainstem?
4.   Ms Vandross is admitted to the ER after having been rescued from her closed garage where she was working on her auto, but had left the engine running. The physician in charge places her on 100% O2. Shortly thereafter, she stops breathing and dies. What was the error? And what should have been done?
5.   Discuss the effects of hyperventilation on blood oxygen, carbon dioxide, and pH.
6.   Describe how oxygen and carbon dioxide are transported in the blood.