The Respiratory System
ANATOMY OF THE RESPIRATORY SYSTEM
TABLE OF CONTENT
The Respiratory Tract:
The Lungs
Alveoli
THE RESPIRATORY SYSTEM CONSISTS OF:
1) Respiratory
Tract:
Nose through
bronchi
2) The lungs.
The respiratory tract
further divided into the upper and lower respiratory tract
The upper respiratory tract
from the nose through the pharynx
The lower respiratory tract
(The Bronchial Tree)
from the larynx to tertiary bronchi
The Bronchial Tree
The Bronchial Tree Extends to
Bronchioles and Alveoli
Alveoli
Bronchioles and Alveoli
Cartilage
Ring
asthma
attack
Cartilage
Plates
Bronchioles
No Cartilage
but Smooth Muscles
Ciliary Lining of the Lower Respiratory Tract
Cilia
Cross Section
Longitudinal Section
Electron Micrograph of Cilia
The cilia beat upward and drive the
debris-laden mucus to the pharynx, where it
is swallowed.
THE LUNGS
The Lungs overlap with the
respiratory tract.
Inside Lungs
Primary
Bronchi
Secondary
Bronchi
Tertiary
Bronchi
Bronchioles
Alveoli
THE LUNGS
- consist of the left and the right lungs
- The left lung is divided into two lobes; the right into three.
- receives the
bronchus, blood
and lymphatic
vessels, and nerves
through its hilum.
- The bronchi
extend into alveoli
ALVEOLI
~700 SF surface area
Alveoli consists of :
1) type I alveolar cells (95%), thin
2) type II alveolar cells (5%), secrete surfactant.
3) macrophages (dust cells), defense
- Each alveolus is surrounded with a basket of
capillaries.
surrounded with capillaries
The respiratory membrane:
1) the wall of the alveolus
2) the endothelial wall of the capillary
3) their fused basement membranes
Alveoli contain elastic fibers which helps expiration.
Low blood pressure keeps alveoli dry.
Gas exchange occurs only in alveoli.
Dead Space
- starts from
nose to terminal
bronchiole
- where there is
no gas exchange
- ~ 150 ml
terminal
bronchiole
SUMMARY
ANATOMY OF THE RESPIRATORY SYSTEM
The Respiratory Tract:
The Lungs
Alveoli
ventilation
gas exchange
transport by blood
gas exchange
MECHANICS OF VENTILATION
TABLE OF CONTENTS
Driving Force for Air Flow
Resistance to Airflow
Measurements of Ventilation
Alveolar Ventilation
Terms:
inspiration or inhalation: breathing in
expiration or exhalation: breathing out
Driving Force for Air Flow
Airflow driven by the pressure difference between
atmosphere (barometric pressure) and inside the
lungs (intrapulmonary pressure).
760 mmHg
atmospheric
pressure = 760 mmHg
Before inspiration
atmospheric
pressure = 760 mmHg
atmospheric
pressure = 760 mmHg
atmospheric
pressure = 760 mmHg
Mechanism for the Change in Intrapulmonary
pressure
Boyle’s Law:
Volume x Pressure = Constant
P
V
gas
Inspiration:
 Volume   Pressure
Expiration:
 Volume   Pressure
Inspiration:
 Volume   Pressure
Expiration:
 Volume   Pressure
Can the lungs expand/shrink by
themselves?
Major Respiratory Muscles
1) The Diaphragm
1)
1) The
TheDiaphragm
Diaphragm
- the
principal
muscleMuscles
of
2)
External
Intercostal
2)
External
2)
External Intercostal
IntercostalMuscles
Muscles
inspiration
3) Internal Intercostal Muscles
3)
The
Muscles
3)
TheAbdominal
Abdominal
Muscles
pulls
the
diaphragm
down,
- Inspiration
muscles
4) The Abdominal Muscles
increasing all three
- increases
4)
Internalthe
Intercostal
Muscles
dimensions
of
the
thoracic
- Expiration muscles
anteroposterior
and
cage.
-transverse
pulls the diaphragm
up,
dimensions
of the
- Extra Expiration muscles
reducing
chest. the vertical
dimension of the thoracic
cage.
Coupling Between
Lungs and Thoracic Cage
- The lungs and thoracic cage are coupled by the pleurae.
Visceral pleura covers the surface of each lung;
parietal pleura lines the chest cavity.
- The two pleurae form the pleural cavity.
- The pleural fluid serves to reduce friction during chest
expansion.
- Intrapleural pressure: The pressure in the pleural cavity
is negative.
pleural cavity
Parietal pleura
visceral pleura
lung
Potential pleural cavity
(negative intrapleural pressure)
Generation of the negative intrapleural pressure
The thoracic cage is larger than the
natural size of the lungs.
Parietal pleura
visceral pleura
lung
Potential pleural cavity
(negative intrapleural pressure)
pneumathorax
air
air
Conclusion
Lungs
pleurae
- pressure
Thoracic Cage
Inspiration
Contraction of
1) diaphragm
2) external intercostal muscles

The lungs are carried along.

 Lung volume

 pressure

Air flows in.
active
Resting Expiration
Relaxation of
1) diaphragm
2) external intercostal muscles

The lungs shrink.

 Lung volume

 pressure

Air flows out.
passive
Forced Expiration
Relaxation of
1) diaphragm 2) external
intercostal muscles
and
Contraction of
abdominal, internal intercostal
and other accessory respiratory
muscles.

 Lung volume

 pressure

Air flows out.
active
SUMMARY
Driving Force for Air Flow
Atmosphere-lung pressure gradient
Major respiratory muscles
Coupling between lungs and thoracic cage
Resistance to Airflow
TABLE OF CONTENTS
Resistance
1) Alveolar Surface Tension
2) Elastic Resistance
3) Airway Resistance
Compliance
1) Alveolar Surface Tension
-
generated by a thin film of
liquid over the surface of
alveolar epithelium,
-
tends to cause a collapse of
the alveoli,
-
Resists against
inspiration.
Alveolar surface tension is a resistance
against inspiration.
Alveoli
-
Surface tension is reduced
by surfactant.
( type II alveolar epithelial
cells)
Pre-term infants don't have
enough surfactant.
type II
surfactant
Resistance
1) Alveolar Surface Tension
2) Elastic Resistance
3) Airway Resistance
- Against inspiration due
to elastic fibers in the
lungs and chest wall,
- Increases in pulmonary
fibrosis.
Resistance
1) Alveolar Surface Tension
2) Elastic Resistance
3) Airway Resistance
- Due to friction, affected
by airway caliber.
- Against inspiration and
expiration!
- Increases during asthma
attack (smooth muscle
contraction in bronchiole.
Resistance
1) Alveolar Surface Tension
2) Elastic Resistance
3) Airway Resistance
Compliance
- The reciprocal of resistance,
- An indicator of ease with which the lungs
expand.
Measurements of Ventilation using Spirometer
Alveolar ventilation rate =
(tidal volume – dead space) x resp freq (/min)
Dead Space
inspiration
expiration
Changes in Spirometric Measures
Restrictive disorders
- (pulmonary fibrosis)
compliance & vital
capacity.
Changes in Spirometric Measures
Obstructive disorders
- No change in respiratory
volumes
-  FEV1.
one-second forced
expiratory volume
SUMMARY
MECHANICS OF VENTILATION
Driving Force for Air Flow
Resistance to Airflow
Measurements of Ventilation
Alveolar Ventilation
NEURAL CONTROL OF VENTILATION
Rhythm?
Center in the medulla oblongata
1) inspiratory center
- stimulates inspiration
muscles.
2) expiratory center
-
inhibits the
inspiratory center,
-
stimulates expiration
muscles.
The pons fine-tunes ventilation.
Afferent Connections to the Respiratory Centers
the limbic system
Hypothalamus
Chemoreceptors
the lungs
Chemoreceptor-initiated Reflexes
Peripheral chemoreceptors
- aortic and carotid bodies,
- monitor O2, CO2 and pH of the
blood.
Central chemoreceptors
- close to the surface of the
medulla oblongata,
- monitor the pH of the
cerebrospinal fluid.
CHEMORECEPTOR-MEDIATED REFLEX
O2, CO2, or pH
stimulate chemoreceptors
reflex
frequency and depth of respiration
Voluntary Control
- the motor cortex,
- bypass the brainstem
respiratory centers,
- limited voluntary control.
GAS EXCHANGE in the LUNGS
ventilation
gas exchange
transport by blood
gas exchange
- The gas exchange between
alveolar air and the blood is via
diffusion of O2 and CO2.
- Diffusion of a gas is driven
by O2 and CO2 partial
pressure gradient.
PO2 = 40 mmHg
PCO2 = 46
mmHg
PO2 = 104 mmHg
PCO2 = 40 mmHg
The partial pressure of a gas refers to the share
of the total pressure generated by a mixture of
gases.
H 2O
104 mmHg
13.6%
O2
N2
Total = 760 mmHg
40 mmHg
CO2 5.3%
Oxygen and carbon dioxide cross the respiratory
membrane and the air-water interface easily.
PO2 = 40 mmHg
PCO2 = 46 mmHg
PO2 = 104 mmHg
PCO2 = 40 mmHg
Overview of Gas Exchange in the Lungs
Factors That Affect the
Efficiency of Alveolar Gas
Exchange
1. partial pressure
2. solubility
3. respiratory membrane
thickness/area
4. ventilation-perfusion
coupling
1) Partial pressure
PO2104 mmHg
PCO2 40 mmHg
a) High altitude
b) Hyperbaric chamber
c) Obstructive disease
H 2O
O2
O2
CO2
Air
N2
Total = 760 mmHg
CO2
N2
Total = 760 mmHg
1) Partial pressure
PO2 40 mmHg
PCO2 46 mmHg
2) Solubility
PO2104 mmHg
PCO2 40 mmHg
CO2 has a higher solubility than O2.
CO2
Pressure Gradient 6 mmHg
O2
64 mmHg
1) Partial pressure
2) Solubility
3) Respiratory membrane
thickness/area
1) Partial pressure
2) Solubility
3) Respiratory membrane
thickness/area
4) Ventilation-perfusion Coupling
- average V-P ratio = 0.8
- autoregulated by:
PO2 and PCO2
causes:
1) vasoconstriction of
pulmonary arterioles
2) dilation of bronchioles
summary
1) Driving force for gas exchange
2) Factors that affect the efficiency of alveolar
gas exchange
Gas transport
by the blood
TABLE OF CONTENT
1) Carbon Dioxide Transport
2) Oxygen Transport
Carbon Dioxide Transport
7% dissolved in the
blood as a gas,
23% as carbaminohemoglobin,
70% as carbonic acid
in the plasma.
Oxygen Transport
- About 98.5% of O2 in the blood
are carried by hemoglobin.
- The rest is physically
dissolved in plasma.
Hypoxemia
Blood Oxygen Content
- average 20 ml/dL
- determined by:
1) saturation of
hemoglobin
Hypoventilation
CO poisoning
2) content of
hemoglobin
anemia
Carbon monoxide competes with oxygen for heme
binding with a much higher affinity.
Problem: deoxygenate hemoglobin
Treatment: hyperbaric oxygen chamber
GAS EXCHANGE in the TISSUES
How to dissociate?
O2
1. Carbon Dioxide Loading
2. Oxygen Unloading
Dissociation of O2 from
hemoglobin (HB) is affected by:
PO2  dissociation
PCO2  dissociation
pH
 dissociation
DPG
 dissociation
(2,3-diphosphoglycerate)
Temperature  dissociation
O2
In Lungs
High PO2, low PCO2
O2
 association with HG
favor the loading of O2
100% saturated
In tissues
High PCO2, low
PO2, low pH, DPG
 dissociation of O2
from HG
favor the unloading
O2
In tissues
High PCO2, low
PO2, low pH, DPG
 dissociation of O2
from HG
favor the unloading
O2
Utilization Coefficient
- The amount of oxygen uptake by tissue
versus the arterial blood oxygen content
20 ml O2/dL
15.6 ml O2/dL
blood
4.4 ml O2/dL
cell
cell
cell
cell
cell
Utilization Coefficient = 4.4 ml / 20 ml = 22%
Function of Oxygen ?
glucose
without oxygen
2 ATP
with oxygen
38 ATP
Can human beings produce oxygen?
Oxygen Toxicity
- Excessive oxygen generates hydrogen
peroxide and free radicals, which destroy
enzymes and damage nervous tissue.
- Oxidative toxicity with aging.
Hypercapnia
-
PCO2 > 43 mmHg
caused by hypoventilation (respiratory diseases)
Hypocapnia
-
PCO2 < 37 mmHg
caused by hyperventilation
Summary
of the Respiratory System
ventilation
gas exchange
transport by blood
gas exchange
Oxyhemoglobin Dissociation Curve
Oxygen Dissociation & Temperature
Active tissue - more O2
released
PO2 (mmHg)
Oxygen Dissociation & pH
Active tissue - more O2
released
Bohr effect: release of O2 in response to low pH