Respiratory System II: Breathing and Gas Exchange
 Respiratory Volumes and
Capacities
 Partial Pressure and Gas
Exchange
 Gas Transport and Hb
Cooperativity
 Neural Control of Respiration
 Respiratory Disorders
Respiratory Volumes and Capacities
 Normal breathing moves about 500
ml of air with each breath (tidal
volume [TV])
 Inspiratory reserve volume (IRV)
•
Amount of air that can be taken
in forcibly beyond the tidal
volume
•
Usually 2100-3200 ml
 Expiratory reserve volume (ERV)
•
Amount of air that can be
forcibly exhaled
•
Approximately 1200 ml
 Factors Affecting Respiratory
Capacity: Size, Gender, Age,
Condition
spirometer
Respiratory Volumes and Capacities
 Residual volume
•
Air remaining in lung after expiration
•
About 1200 ml
 Respiratory Rate
•
Number of cycles/minute
•
Based on one inspiration and expiration
•
Normally about 15 cycles/min
 Minute Ventilation
•
Tidal volume x respiratory rate
(breaths/min)
•
Volume of air inhaled/exhaled per minute
•
Normally 5-8 liters
Respiratory System II: Breathing and Gas Exchange
 Respiratory Volumes and
Capacities
 Partial Pressure and Gas
Exchange
 Gas Transport and Hb
Cooperativity
 Neural Control of Respiration
 Respiratory Disorders
Gas Exchanges Between Blood, Lungs, and Tissues
 External respiration (between lungs and
outside)
 Internal respiration (between bloodstream and
tissues)
 To understand the above processes, first
consider
• Physical properties of gases
• Composition of alveolar gas
Basic Properties of Gases: Dalton’s Law of Partial Pressures
 Total pressure exerted by a mixture of gases is the
sum of the pressures exerted by each gas
 (TP = PPN2 + PPO2 + PPCO2 + PPH2O)
 The partial pressure of each gas is directly
proportional to its percentage in the mixture
Basic Properties of Gases: Henry’s Law
 When a mixture of gases is in contact with a
liquid, each gas will dissolve in the liquid in
proportion to its partial pressure
 At equilibrium, the partial pressures in the two
phases will be equal
 The amount of gas that will dissolve in a liquid
also depends upon its solubility
• CO2 is 20 times more soluble in water than O2
• Very little N2 dissolves in water
Composition of Alveolar Gas
 Alveoli contain more CO2 and water vapor
than atmospheric air, due to
• Gas exchanges in the lungs
• Humidification of air
• Mixing of alveolar gas that occurs with
each breath
Table 22.4
External Respiration Defined
 Exchange of O2 and CO2 across the
respiratory membrane in the lungs
 Influenced by
• Partial pressure gradients and gas
solubilities
• Ventilation-perfusion coupling
• Structural characteristics of the respiratory
membrane
Partial Pressure Gradients and Gas Solubilities
 Partial pressure gradient for O2 in the lungs is
steep
• Venous blood PO2 = 40 mm Hg
• Alveolar PO2 = 104 mm Hg
 O2 quickly diffuses from alveoli to bloodstream
 Aided also by ventilation-perfusion* coupling:
Where alveolar O2 is high, arterioles dilate; where
alveolar O2 is low, arterioles constrict
 Partial pressure gradient for CO2 in the lungs is
less steep:
• Venous blood Pco2 = 45 mm Hg
• Alveolar Pco2 = 40 mm Hg
 CO2 is 20 times more soluble in plasma than
oxygen
 Aided also by ventilation-perfusion coupling: where
alveolar CO2 is high, bronchioles dilate; where
alveolar CO2 is low, bronchioles constrict
*Perfusion is the ability of blood to flow through tissues.
Respiratory System II: Breathing and Gas Exchange
 Respiratory Volumes and
Capacities
 Partial Pressure and Gas
Exchange
 Gas Transport and Hb
Cooperativity
 Neural Control of Respiration
 Respiratory Disorders
Gas Transport in the Blood
 Oxygen transport in the blood
•
Inside red blood cells attached to hemoglobin
(oxyhemoglobin [HbO2])
•
A small amount (< 2%) is carried dissolved in the plasma
 Loading and unloading of O2 is facilitated by change in
shape of Hb
• As O2 binds, Hb affinity for O2 increases
• As O2 is released, Hb affinity for O2 decreases
 Change in binding affinity known as positive
cooperativity
 Fully (100%) saturated if all four heme groups carry O2
 Rate of loading and unloading of O2 is regulated by
many factors
 Sigmoidal relationship seen on binding graph
Increasingly
steeper line (more
saturation) as more
oxygen present.
Other Factors Influencing Hemoglobin Saturation
 Increases in temperature, H+, PCO2, and BPG
(bisphosphoglycerate).
• They modify the structure of hemoglobin and
decrease its affinity for O2 [binding with H ( pH), P
+
CO2,BPG]
• Enhanced O2 unloading in the capillaries where
higher CO2 concentration lowers pH (increases
H+)and facilitates more O2 unloading
• Decreases in temp, H+, PCO2, and BPG
• Modify Hb structure and increase O2 affinity
• Enhanced loading of O2 at the lungs
•
[ binding with  H+ ( pH),  PCO2,  BPG]
Changes in O2 Binding Curve with Difft Temps and pHs
Decreased carbon dioxide
(PCO2 20 mm Hg) or H+ (pH 7.6)
10°C
20°C
38°C
43°C
Normal arterial
carbon dioxide
(PCO2 40 mm Hg)
or H+ (pH 7.4)
Normal body
temperature
Increased carbon dioxide
(PCO2 80 mm Hg)
or H+ (pH 7.2)
Decreased binding
Increased binding
Decreased binding
(a)
Increased binding
p O2 in Hg
(b)
PO (mm Hg)
2
Figure 22.21
Homeostatic Imbalance
 Hypoxia (leading to cyanosis)
• Inadequate O2 delivery to tissues
• A variety of causes
o Too few RBCs
o Abnormal or too little Hb
o Blocked circulation
o Metabolic poisons
o Pulmonary disease
o Carbon monoxide
Hypoxia, Cyanosis, and CO Poisioning
Cyanosis of the face
Cyanotic nail beds
Cherry red skin from carbon monoxide poisoning
External Vs Internal Respiration
• In the lungs, plasma HCO3- and H+ are converted by carbonic anhydrase in the RBC to form
carbonic acid which breaks down into CO2 and H2O; CO2 unloaded into alveoli, blood pH rises
as H+ removed.
•Oxygen diffuses from blood into tissue (acidic conditions favor oxygen off-loading known as
the Bohr Effect)
• An opposite reaction to what occurs in the lungs
• Carbon dioxide diffuses out of tissue into blood plasma as CO2 and water; tese coverted
to carbonic acid (in the RBC) and thence into plasma H+ and HCO3- , dropping pH
•
External respiration
Internal respiration
Respiratory System II: Breathing and Gas Exchange
 Respiratory Volumes and
Capacities
 Partial Pressure and Gas
Exchange
 Gas Transport and Hb
Cooperativity
 Neural Control of Respiration
 Respiratory Disorders
Neural Regulation of Respiration
1. Respiratory rate and depth is the major
regulator of blood pH through retention or
loss of CO2.
2. Phrenic and intercostal nerves enervate
intercostals and the diaphragm
3. Neural centers that control rate and depth are
located in the medulla, especially the ventral
respiratory group (VRG).
4. Suppression of respiratory centers in brain stem
(from sleeping pills, morphine, or alcohol) halts
respiration, and is fatal
5. Hyperventilation (rapid breathing) drives off
CO2 (hypocapnea)and causes blood pH
increase; rebreathing into paper bag acidifies
blood; hyperventilation before a dive
6. Hypoventilation (slow, shallow breathing)
causes CO2 retention (hypercapnia), decreasing
blood pH, H+ triggers faster breathing rate in
brain central chemoreceptors
7. Peripheral chemoreceptors in the aortic and
carotid arteries are O2 sensors; low PO2 causes
increase in ventilation rate
Respiratory Disorders: Chronic
Obstructive Pulmonary Disease (COPD)
 Common Features of Bronchitis
and Emphysema
• Patients almost always have a
history of smoking
• Labored breathing (dyspnea)
becomes progressively more
severe
• Coughing and frequent
pulmonary infections are
common
• Most victims retain carbon
dioxide, are hypoxic and have
respiratory acidosis
• Those infected will ultimately
develop respiratory failure
COPDs are a leading cause of death in the USA