The Respiratory System
Chapter 23
(6th edition chapter 22)
Functions of the Respiratory
System
1. Supply oxygen to the circulatory system for delivery to the tissues
2. Remove CO2 (and some other wastes) from blood.
There are 4 processes that we call “respiration”.
1. Pulmonary ventilation - Movement of air into and out of the lungs
(also referred to as “breathing”).
2. External respiration - Gas exchange in the lungs between the blood
of the capillaries and the spaces in the air sacs (alveoli)
3. Transport - The movement of gases by the circulatory system
Strictly speaking, a function of the blood.
4. Internal respiration - Gas exchange between the blood and the
tissues of the body
Overview of respiratory system anatomy
External
Structures
of the nose
Nasal skeletal
structures
Internal anatomy of the upper respiratory tract
The larynx and associated structures
Cross section of the trachea and esophagus
The Lungs
The Lungs
The lower lung
Alveoli and the respiratory membrane
Structure of an alveolar sac
Respiratory Physiology
Boyle’s law: P1V1 = P2V2
Pressure relationships
The negative intrapleural pressure keeps the lungs inflated
Mechanics of Breathing:
Inspiration
Mechanics of Breathing:
Expiration
Changes in
pressure & volume
relationships
Respiratory Physiology
Resistance:
F = P/R
R = resistance
P = change in pressure (the pressure gradient)
Respiratory Volumes
Respiratory Physiology:
Dalton’s Law of Partial Pressures
The total pressure of a mixture of gases is the sum of the partial
pressures exerted independently by each gas in the mixture.
Location
Atmosphere at
sea level
Gas
Approximate %
Partial
pressure in
mmHg
Approximate %
Partial
pressure in
mmHg
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
Total
100.0
760
100.0
760
Alveoli of lungs
Partial pressure
relationships:
Movement of gases
between the lungs
and the tissues
Solubility:
Differential solubility of gases contributes to the
balance of gas exchange
Most soluble
Least soluble
CO2 >>>>>>>>>>>>>>>>> O2 >>>>>>>>>>>>>>>>>>> N2
CO2 is 20 times more soluble than O2
N2 is about half as soluble as O2
Ventilation-Perfusion Coupling
Breathing and blood flow are matched to the partial
pressure of alveolar gases
Respiratory Gas Transport
Oxygen - about 98.5% is bound to
hemoglobin (Hb) and 1.5% in solution.
The affinity of O2 for hemoglobin is influenced by partial pressure
Factors influencing Hb saturation: Temperature
Factors influencing Hb saturation: Pco2 and pH
The Bohr Effect
Decreased pH that results from increased Pco2 lowers the binding
affinity between O2 and Hb. The result is that, under acidosis, Hb
saturates at a lower Po2. This allows more oxygen to be unloaded at the
where it is needed.
BPG (2,3-bisphosphoglycerate)
This compound is produced during glycolysis, anaerobic means of
producing energy from glucose. BPG binds to Hb and decreases O2
affinity. This results in a right-shifted O2 - Hb dissociation curve,
Like we see in the Bohr effect
CO2 Transport
• 7 - 10% dissolved in the plasma
• ~ 20% bound to the amine groups of the Hb molecule as
carbaminohemoglobin
• ~ 70% as bicarbonate ion in the plasma
CO2 Transport & Exchange:
at the tissues
CO2 Transport & Exchange:
in the lungs
The Haldane
Effect
Control of
Respiratory
Rhythm
Medullary
Respiratory
centers
Neural and chemical
influences
Pco2 & pH are the
primary regulators of
ventilation by means
of negative feedback
Pathology and clinical
considerations
Common homeostatic imbalances:
• COPD (chronic obstructive pulmonary disease)
• Asthma
• Tuberculosis
• Lung cancer
COPD:
Emphysema
Results: Loss of lung elasticity, hypoxia, lung fibrosis, cyanosis.
Common causes: Industrial exposure, cigarette smoking.
Tuberculosis
At the beginning of the
20th century a third of
all deaths in people 20 - 45
were from TB.
Antibiotic-resistant strains
of Mycobaterium tuberculosis
are a growing problem at the
beginning of the 21st century.
Lung Cancer
90% of lung cancer patients had one thing in
common…
…they smoked tobacco
Fin