RESPIRATORY SYSTEM
Marieb - Chapter 22
Respiratory Processes
•Pulmonary Ventilation
•External Respiration
•Transport of Respiratory Gases
•Internal Respiration
Conducting
Zone
Respiratory
Zone
Larynx
Cartilages of the Larynx
Trachea & Bronchi
Trachea
Bronchi & Bronchioles
Bronchioles and Alveoli
Bronchiole if <1mm diameter
Boyle’s Law
P1V1 = P2V2
Robert Boyle (1627-1691)
Physical Factors Influencing
Pulmonary Ventilation
• Airway Resistance - The major source is
friction encountered in the respiratory
passages.
• Alveolar Surface Tension - force created by
alveolar fluid that resists lung distension.
Surfactant (surface active agent) lowers
surface tension.
• Lung Compliance - The distensibility
(stretchiness) of lung tissue and the thoracic
cage.
ASTHMA
• Bronchiole smooth muscle is
sensitive to neural and chemical
controls.
• In an asthma attack, bronchioles
first become inflamed, then the
muscle constricts causing
airways to narrow.
• Risk factors include exposure to
indoor allergens during infancy,
allergies, and a family history
of asthma.
Respiratory Volumes
M
F
Minute Ventilation
= Tidal Volume X Respiratory Rate
MV = TV x RR
= 500 ml/breath X 12 breaths/min
= 6000 ml/min
Dead volume = 1ml/pound ideal body weight
“Fresh” inspired air is diluted by the left over air
remaining in the lungs from the previous breathing cycle.
Alveolar Ventilation
= (Tidal Volume - Dead Space) X Respiratory Rate
AVR = (TV - ADS) x RR
= (500 ml/breath - 150 ml) X 12 breaths/min
= 350 ml/breath X 12 breaths/min
= 4200 ml/min
Gaseous Exchange
Dalton’s Law
of Partial Pressures
Ptotal = P1 + P2 + . . . Pn
John Dalton (1766-1844)
Gaseous Exchange
Henry’s Law
A gas will dissolve in a liquid in
proportion to its partial pressure
William Henry (1775-1836)
N2
78.6
597
74.9
569
O2
20.9
159
13.7
104
CO2
0.04
0.3
5.2
40
H2O
0.46
3.7
6.2
47
100%
760
100%
760
1 atmosphere= 1 Torr = 760mmHg
N2
78.6
597
74.9
569
O2
20.9
159
13.7
104
CO2
0.04
0.3
5.2
40
H2O
0.46
3.7
6.2
47
100%
760
100%
760
Gas Solubilities
• CO2 is about 20X more soluble in
plasma than O2
• N2 is practically insoluble.
Respiratory Membrane
5 m thick in healthy lungs
thickness
gas diffusion
Total Surface Area
75 m2 in healthy lungs
surface area
gas diffusion
OXYGEN TRANSPORT
1.5% dissolved in plasma
98.5% bound to hemoglobin
HHb + O2
Lungs
tissues
HbO2 + H+
O2 Dissociation Curve
PO2 lung =
104mmHg
PO2
Bohr Effect
CARBON DIOXIDE TRANSPORT
7-10% dissolved in plasma
~20% bound to hemoglobin
CO2 + Hb
HbCO2
~70% as bicarbonate ion (HCO3-)
CO2 + H2O
carbonic
anhydrase
H2CO3
H+ + HCO3-
CO2 Transport: Tissue
Figure 22.22a
• CO2 diffuses into plasma and into the RBC
– RBCs contain carbonic anhydrase which rapidly combine H2O
and CO2 to form H2CO3
– H2CO3 quickly dissociates to H+ and HCO3– H+ ions become associated with protein portion of Hb (triggers
the Bohr effect)
– HCO3- rapidly diffuses out of RBC into plasma
– Cl- moves into RBC to balance ionic charges (chloride shift)
CO2 Transport: Lung
Figure 22.22b
• In the lungs the process reverses
–
–
–
–
–
HCO3- moves into the RBC
Cl- shifts out of RBC
HCO3- binds H+ g H2CO3
Carbonic anhydrase splits H2CO3 g H2O + CO2
CO2 moves down its partial pressure gradient to the alveoli