Download Chapter5 Respiration

Physiology
Chunling Jiang
MD, PhD
Professor of Physiology
Chapter 5
Respiration
Introduction

Concept of Respiration :
gas exchange between body and environment.
This term includes three processes:
1. External respiration
pulmonary ventilaion
atmosphere
O2
alveoli
CO2
gas exchange in lungs
O2
alveoli
blood
CO2
2. Gas transport (in blood)
The blood carries O2 from the lungs to the tissues
and CO2 from the tissues to the lungs
3. Internal respiration
O2
blood
tissue cell
CO2
Fig. 1 The relationship among these three processes
1. Functional Anatomy
 Airways (Fig.2)
1)The nasal cavity, pharynx, trachea, bronchi,
bronchiole and terminal bronchioles.
2)The airways in the lungs contain smooth muscles
which are innervated by efferent autonomic nerve fibers
3)
sympathetic nerve and Parasympathetic nerve
■
Innervation of respiratory tract
Sympathetic n (+)
Parasympathetic n (+)
NE + ß2
smooth
muscles in airways relax
Ach + M
smooth
muscles in airways contract
3. Pulmonary surfactant
=surface active substance
 Synthesized site: Type Ⅱ alveolar cells
 Composition: Dipalmitoyl phosphatidyl eholine,
DPPC
 Physiological Function (Fig.3)
1) to reduce the surface tension, allowing easier
lung expansion
2) to alter surface tension in proportion
to the volume of the alveoli . That is
3) To keep the alveoli dry. The ST tends to suck fluid
into the alveolar space from the capillary. So that the
reduction of the ST also prevents the transudation of
fluid.
4. Motivity of pulmonary ventilation
PLEURA AND INTRAPLEURAL SPACE
 the visceral pleura
 the parietal pleura
 a potential space.
5. Intrapleural pressure(IP)
■
■
■
Concept: pressure in the pleural cavity (Fig.5)
Measure : direct method
indirect method
Normal value:
at the end of inspiration
-5 ~ -10 mmHg
at the end of expiration
-3 ~ -5 mmHg
■
Mechanism
IP = AP - RF
Intrapleural pressure
= alveolar pressure - recoil force
Intrapleural pressure = - recoil force
Significance :
1) attracting the lung to expansion
2) accelerating venous return
6. Pressure in alveoli

Concept: pressure in alveoli
inspiration-------- less than the atmospheric pressure
negative
•
expiration -------- higher than the atmospheric pressure
positive
•
Fig.6
7. Lung capacity and ventilation
1) Lung capacity (Fig.7)
1.
2.
3.
4.
Tidal volume (TV)
Inspiratory reserve volume (IRV)
Expiratory reserve volume (ERV)
Vital capacity (VC)
4. Vital Capacity (VC)
The maximal volume of gas that can be expelled
following a maximal inspiration.
VC = TV + IRV + ERV
Normal value:
Male
-------- 3.5 L
Female -------- 2.5 L
5. Timed vital capacity
The percentage of the vital capacity that an
individual can exhale in a given duration with
maximal effort.
Timed vital capacity = Forced Expiratory Volume
(FEV)
FEV 1.0 ------- 83%
FEV 2.0 ------- 96%
FEV 3.0 ------- 99%
2 ) Lung ventilation
1. Pulmonary ventilation per minute
2. Alveolar ventilation per minute
■physiologic dead space
anatomical dead space
alveolar dead space
§2
Gas Exchange
 A gas diffuses from a region of high partial
pressure to a region of low partial pressure.
The partial pressure of a particular gas is
equal to its percentage concentration times the
total pressure of the gases mixture.
Example PO2
Partial Pressure of O2 and CO2
Table 6-3 Pressure of O2 and CO2 in alveolar air,
venous blood, arterial blood and the tissue
P O2 (mmHg)
P CO2 (mmHg)
Alveolar air
102
40
Venous blood
40
46
Arterial blood
100
40
Tissue
40
46
§3 Transport of oxygen and carbon dioxide
1. Transport of oxygen
(1) Forms of transport
O2 is carried in blood in two forms:
physically dissolved ----- 0.3ml/100ml
Combination with hemoglobin
Hb + O2
HbO2
where Hb is deoxyhemoglobin,
HbO2 is oxyhemoglobin
reversibility of reaction
(2) O2 content, capacity and saturation
a. O2 content
b. O2 capacity
c. O2 saturation
(3) O2 dissociation curve (Fig.9)
Concept: The relation between O2 partial
pressure and O2 saturation.
S shaped
Physiological advantages:
a) PO2 60 ~ 100 mmHg ---- O combined with the Hb
It makes O2 supply safe for body.
2
b) PO2 15 ~ 60mmHg ---- HbO2 released O2
PO2   SO2  
(4) Factors affecting HbO2 dissociation curve
(Fig.10)
Increases in PCO2, H+, T, 2,3-DPG
shift the curve to the right
Significance?
Decreases in PCO2, H+, T, 2,3-DPG
shift the curve to the left
Significance?
§4 Control of Ventilation
1. Respiratory center and respiratory rhythm
Exp.
Methods of investigation---resection
◆Respiratory center:
the upper portion of pons ----- Pneumotaxic center
The lower pons
------ Apneustic center
Medulla
------ Medullary center
inspiratory center
expiratory center
Chemical Regulation of Respiration
The respiratory control system are very sensitive to alterations in
the internal environment of the body. Changes in the body PCO2, pH
and PO2 cause changes in alveolar ventilation designed to restore
these variable to their normal values.
1.Carbon dioxide (CO2)
The most important factor in the control of breathing under normal
conditions
Receptors:
1) Central chemoreceptors
2) Peripheral chemoreceptors
Experiment: PCO2  ventilation 
Pathways:
Mechanism:
CO2 +H2O
H+
H2CO3
HCO3 + H+
stimulate the chemoreceptors
2.O2 :
Pathways:
Po2
R , ventilation
peripheral chemoreceptors
3. [H+]
Pathways:
central chemoreceptors
peripheral chemoreceptors
H+ in blood
the chief site of activity is the
peripheral chemoreceptors
why?
H+ pass across blood-brain barrier too slowly.
H+ in CSF
the chief site of activity is the
central chemoreceptor