Respiratory Lecture.ppt

HUMAN PHYSIOLOGY
RESPIRATORY SYSTEM
KISII UNIVERSITY
SCHOOL OF HEALTH SCIENCES
DEPARTMENT OF MEDICAL PHYSIOLOGY
(LECTURE SESSION I)
Edwin M. Ruoti BsN., MsP

Sub-Topics
 Respiratory System
 Physical Aspects of Ventilation
2
Physiology of the Respiratory System...Edwin Ruoti BsN; MsP

Specific Learning Objectives
3
By the end of the lecture, you should be able to:
 Describe the structures and functions of the
conducting and respiratory zones of the lungs
 Describe the location and significance of the
pleural membranes
 Explain how intrapleural and intrapulmonary
pressures change during breathing
 Explain how lung compliance, elasticity, and
surface tension affect breathing, and the

Introduction
5
1. Includes:
a. Ventilation (breathing) – mechanical process that
moves air into and out of the lungs
b. Gas exchange between blood and lungs and
between blood and tissues
c. Oxygen utilization by tissues to make ATP –
cellular respiration
2. Ventilation and gas exchange in lungs =
external respiration
3. Oxygen utilization and gas exchange in

Introduction cont…
6
4. Gas exchange in lungs
a. Occurs via diffusion
b. O2 concentration is higher in the lungs than in the
blood, so O2 diffuses into blood.
c. CO2 concentration in the blood is higher than in
the lungs, so CO2 diffuses out of blood.
5. Anatomically divided into:
a. Conduction zone: gets air to the respiratory zone
b. Respiratory zone: site of gas exchange

Structure of the respiratory system
7
 Alveoli
a. Air sacs in the lungs where gas exchange occurs
b. 300 million of them
1)Provide large surface area (760 square feet) to increase
diffusion rate
c. Each alveolus is one-cell layer thick
d. Form clusters at the ends of respiratory
bronchioles

Relationship between lung alveoli &
pulmonary capillaries
Type II alveolar cell
Fluid with surfactant
Type I alveolar cell
Alveolus
Macrophage
White blood cell
Red blood cell
Capillary
8

Micrographs of Alveoli
Capillary within alveolar wall Bronchiole and alveoli
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
From John J. Murray, The Normal Lung, 2nd edition, 1986, © W.B. Saunders
BM
Type I
alveolar cell
RBC
IS
EN
Capillary
endothelium
Air space
in alveolus
Air space
in alveolus
EP
(a)
(b)
(both): Courtesy American Lung Association
9

Alveolar Cells
10
1) Type I: 95−97% total surface area where gas
exchange occurs
2) Type II: secrete pulmonary surfactant and
reabsorb sodium and water, preventing fluid
buildup

2.Pathway of air
Air travels down the nasal cavity 
Pharynx  Larynx (through the
glottis and vocal cords)  Trachea 
Right and left primary bronchi 
Secondary bronchi  Tertiary
bronchi  (more branching) 
Terminal bronchioles  Respiratory
zone (respiratory bronchioles 
Terminal alveolar sacs
11

Conducting and Respiratory
Zones
Conducting zone Respiratory zone
Terminal bronchiole
Air
flow
Respiratory
bronchioles
(500,000)
Alveolar sacs
(8 million)
Alveolus
Terminal
bronchioles
(60,000)
Number of
branches
(1) Trachea
(2) Primary
bronchus
Bronchial
tree
12

Trachea and Respiratory Bronchi
Larynx Thyroid
cartilage
Cricoid
cartilage
Trachea
Left primary
bronchus
Carina
Right
primary
bronchus
(a) (b)
b: © Ralph Hutchings/Visuals Unlimited
13

3.Functions of Conducting Zone
a. Transports air to the lungs: Provide low
resistance to airflow
b. Protect against miscrobes, dust particles
etc
a. Mucus traps small particles, and cilia move it
away from the lungs.
c. Warms, humidifies, filters, and cleans the
air
d. Voice production in the larynx as air
passes over the vocal folds
14

Larynx showing true & false vocal cords
Ventricular fold
(false vocal cord)
Vocal fold
(true vocal cord)
Glottis
© Phototake
15

C.Thoracic Cavity
 Contains the heart, trachea, esophagus, and
thymus within the central mediastinum
 The lungs fill the rest of the cavity.
a. The parietal pleura lines the thoracic wall.
b. The visceral pleura covers the lungs.
c. The parietal and visceral pleura are normally pushed
together, with a potential space between called the
intrapleural space.
 The diaphragm is a dome-shaped skeletal muscle
of respiration that separates the thoracic and
abdominal cavities
16

Thoracic Cavity Cross Section
Anterior
mediastinum
Thoracic wall
Lung
Parietal
pericardium
Visceral
pericardium
Esophagus
Heart (in middle
mediastinum)
Parietal pleura
Visceral pleura
Pleural cavity
Bronchus
Posterior mediastinum
Thoracic vertebra
Pericardial
cavity
Sternum
17

X-ray of the Lungs
(a) (b)
(both): Courtesy of Edward C. Vasquez, R.T.C.R.T., Dept. of Radiologic
Technology, Los Angeles City College
18

Q. Test your knowledge
1. Describe the structures involved in gas
exchange in the lungs and explain how gas
exchange occurs.
2. Describe the structures and functions of the
conducting zone of the respiratory system.
3. Describe how each lung is
compartmentalized by the pleural
membranes. What is the relationship
between the visceral and parietal pleurae?
19

What have we achieved?
 Alveoli are microscopic thin-walled air
sacs that provide an enormous surface
area for gas diffusion.
1. The region of the lungs where gas exchange with
the blood occurs is known as the respiratory zone.
2. The trachea, bronchi, and bronchioles that deliver
air to the respiratory zone constitute the conducting
zone.
20

 The thoracic cavity is delimited by the
chest wall and diaphragm.
1. The structures of the thoracic cavity are
covered by thin, wet pleurae.
2. The lungs are covered by a visceral pleura
that is normally flush against the parietal
pleura that lines the chest wall.
3. The potential space between the visceral
and parietal plurae is called the
intrapleural space.
21

 The respiratory system comprises the lungs,
the airways leading to them, and the chest
structures responsible for moving air into and
out of them.
 The conducting zone of the airways consists of the
trachea,bronchi, and terminal bronchioles.
The respiratory zone of the airways consists of
the alveoli,which are the sites of gas
exchange, and those airways to which
alveoli are attached.
22

 The alveoli are lined by type I cells and some type II cells,
which produce surfactant.
 The lungs and interior of the thorax are covered by pleura;
between the two pleural layers is an extremely thin layer of
intrapleural fluid.
 The lungs are elastic structures whose
volume depends upon the pressure difference
across the lungs—the transpulmonary
pressure—and how stretchable the lungs are.
23

PHYSICALASPECTS OF
VENTILATION

A.Introduction
 Air moves from higher to lower pressure.
 Pressure differences between the two ends of the
conducting zone occur due to changing lung
volumes.
 Compliance, elasticity, and surface tension are
important physical properties of the lungs.
25

B.Intrapulmonary and Intrapleural Pressures
 Types of pressure
a. Atmospheric pressure: pressure of air outside the
body
b. Intrapulmonary or intraalveolar pressure:
pressure in the lungs
c. Intrapleural pressure: pressure within the
intrapleural space (between parietal and visceral
pleura); contains a thin layer of fluid to serve as a
lubricant
26

2.Pressure Differences When
Breathing
a. Inspiration (inhalation): Intrapulmonary
pressure is lower than atmospheric pressure.
1) Pressure below that of the atmosphere is called
subatmospheric or negative pressure
2) Generally about -3mm Hg
b. Expiration (exhalation): Intrapulmonary
pressure is greater than atmospheric pressure.
1) Generally about +3mm Hg
27

Pressure Changes in Normal Breathing
28

3.Intrapleural Pressure
a. Lower than intrapulmonary and atmospheric
pressure in both inspiration and expiration
b. The difference between intrapulmonary and
intrapleural pressure is called the
transpulmonary pressure.
c. Keeps the lungs against the thoracic wall and
allows the lungs to expand during inspiration
29

4.Boyle’s Law
a. States that the pressure of a gas is inversely
proportional to its volume
b. An increase in lung volume during inspiration
decreases intrapulmonary pressure to
subatmospheric levels - Air goes in.
c. A decrease in lung volume during expiration
increases intrapulmonary pressure above
atmospheric levels - Air goes out.
30

C.Physical Properties of the
Lungs
 Lung compliance
a. Lungs can expand when stretched.
b. Defined as the change in lung volume per change
in transpulmonary pressure:
ΔV/ΔP
c. The ease with which the lungs expand under
pressure
d. Reduced by factors that produce a resistance to
distention such as the infiltration of connective
tissue proteins in pulmonary fibrosis
31

2.Elasticity
a. Lungs return to initial size after being stretched
(recoil)
b. Lungs have lots of elastin fibers.
c. Because the lungs are stuck to the thoracic wall,
they are always under elastic tension.
d. Tension increases during inspiration and is
reduced by elastic recoil during expiration
32

3.Surface Tension
a. Resists distension
b. Exerted by fluid secreted on the alveoli
c. Fluid is absorbed by active transport of Na+
and secreted by active transport of Cl-
d. Raises the pressure of the alveolar air as it
acts to collapse the alveolus
e. People with cystic fibrosis have a genetic
defect that causes an imbalance of fluid
absorption and secretion
33

f.Law of Laplace
1) Pressure is directly proportional to surface
tension and inversely proportional to radius of
alveolus.
2) Small alveoli would be at greater risk of
collapse without surfactant.
34

Law of Laplace
r
P =
1
P =
2
Law of Laplace
2 × T
Bronchioles
Alveoli
r = 1
r = 2
2 × T 2 × T
P = T P = 2T
P =
35

D.Surfactant & Respiratory Distress Syndrome
 Surfactant – surface active agent
a. Secreted by type II alveolar cells
b. Consists of hydrophobic protein and phospholipids
c. Reduces surface tension between water molecules by
reducing the number of hydrogen bonds between water
molecules
d. More concentrated as alveoli get smaller during
expiration
e. Prevents collapse
f. Allows a residual volume of air to remain in lungs
36

Production of Pulmonary Surfactant
Basal
lamina Surfactant
Type II
alveolar cell
Alveolus
Macrophage
Type I
alveolar cell
Capillary
endothelium
37

2.Respiratory Distress
Syndrome (RDS)
a. Production of surfactant begins late in fetal life,
so premature babies may be born with a high
risk for alveolar collapse called respiratory
distress syndrome (RDS); treated with
surfactant
b. A similar problem may occur in adults caused
by septic shock, reduced lung compliance and
reduced surfactant – acute respiratory distress
syndrome (ARDS); is not treatable with
surfactant
38

HUMAN PHYSIOLOGY
RESPIRATORY SYSTEM
KISII UNIVERSITY
(LECTURE SESSION II)

Sub-Topics
 Mechanics of Breathing
 Gaseous Exchange in the Lungs
40

41
 Explain how inspiration and expiration are
accomplished
 Describe lung volumes and capacities, and
explain how pulmonary function tests relate to
pulmonary disorders
 Explain how partial gas pressures are
calculated, and their significance in
measurements of arterial blood gases

A. Introduction
 Breathing is also called pulmonary ventilation
a. Inspiration: breathe in
b. Expiration: breathe out
 Accomplished by changing thoracic cavity/ lung
volume
 Thorax must be rigid enough for protection yet
flexible enough to act as bellows for breathing
43

Changes in lung volume during breathing
(b)
(a)
(both): From J.H. Comroe, Jr., Physiology of Respiration: An Introductory Text, 2nd editon, 1974
© Yearbook Medical Publishers, Inc. Chicago
44

B. Inspiration and expiration
 Muscles involved in breathing
a. Diaphragm most important.
1) Contracts in inspiration – lowers, making the thoracic
cavity larger
2) Relaxes in expiration – raises, making the thoracic cavity
smaller
b. External intercostal muscles – raises the rib cage
during inspiration
c. Internal intercostal muscles – lowers the rib cage
during forced expiration
d. Parasternal intercostal muscles – works with the
external intercostals
45

Muscles involved in breathing, cont
e. The scalenes, pectoralis minor, and
sternocleidomastoid are used for forced
inspiration
f. Quiet expiration occurs with the relaxation
of the inspiratory muscles (passive
process)
g. Abdominal muscles are also used for
forced expiration
46

Muscles Involved in Breathing
Muscles of expiration
Muscles of inspiration
Sternocleidomastoid
Scalenes
External
intercostals
Parasternal
intercostals
Diaphragm
Internal
intercostals
External
abdominal
oblique
Internal
abdominal
oblique
Transversus
abdominis
Rectus
abdominis
47

2.Mechanisms of Breathing
a. Inspiration: Volume of thoracic cavity (and
lungs) increases vertically when diaphragm
contracts (flattens) and laterally when
parasternal and external intercostals raise the
ribs.
1) Thoracic & lung volume increase 
intrapulmonary pressure decreases  air in
b. Expiration: Volume of thoracic cavity (and lungs)
decreases vertically when diaphragm relaxes
(dome) and laterally when external and
parasternal intercostals relax for quiet expiration
or internal intercostals contract in forced
48

Quiet (Normal) vs. Forced Ventilation
49

Mechanisms of Pulmonary
Ventilation
(a)
1. At rest 2. Inspiration
757 mmHg
754 mmHg
(b)
763 mmHg
757 mmHg
(c)
Diaphragm
3. Expiration
Atmospheric pressure
(760 mmHg)
Intrapulmonary
pressure
(760 mmHg)
Intrapleural
pressure
(756 mmHg)
50

C.Pulmonary Function Tests
 Spirometry: Subject breathes into and out of a
device that records volume and frequency of
air movement on a spirogram.
a. Measures lung volumes and capacities
b. Can diagnose restrictive and disruptive lung
disorders
51

2.Lung Volume Measurements
a. Tidal volume: amount of air expired or
inspired in quiet breathing
b. Expiratory reserve volume: amount of air that
can be forced out after tidal volume
c. Inspiratory reserve volume: amount of air that
can be forced in after tidal volume
d. Residual volume: amount of air left in lungs
after maximum expiration
52

3.Lung Capacity Measurements
a. Vital capacity: maximum amount of air that
can be forcefully exhaled after a maximum
inhalation
b. Total lung capacity: amount of gas in the lungs
after a maximum inspiration
c. Inspiratory capacity: amount of gas that can
be inspired after a normal expiration
d. Functional residual capacity: amount of gas
left in lungs after a normal expiration
53

4.Relationship between lung volume and capacity
a. Vital capacity = inspiratory reserve volume +
expiratory reserve volume + tidal volume
b. Functional residual capacity = residual volume
+ expiratory reserve volume
c. Total minute volume = tidal volume X breaths
per minute (~ 6L/min)
54

Lung Volumes and Capacities
Spirogram:
0
Lung
volume
in
cubic
centimeters
(cc)
6,000
5,000
4,000
3,000
2,000
1,000
Inspiratory
capacity
Total lung capacity
Vital capacity
Functional
residual capacity
Residual
volume
Expiratory
reserve volume
Inspiratory
reserve volume
Tidal
volume
55

Ventilation Terminology
56

5.Restrictive and Obstructive Disorders
a. Restrictive: Lung tissue is damaged. Vital
capacity is reduced, but forced expiration is
normal.
1) Examples: pulmonary fibrosis and emphysema
b. Obstructive: Lung tissue is normal. Vital capacity
is normal, but forced expiration is reduced.
1) Example: asthma
57

c.Forced Expiratory Volume
(FEV1) Test
1) Obstructive lung disorders are usually
diagnosed by doing forced expiratory volume
tests.
Maximum inspiration = 5 L
1.0
second
2.5 L
(b)
Maximum expiration = 1 L
(a)
1.8 L
(a) FEV1 =
(b) FEV1 =
5 L–1.8 L
5 L–1 L
x 100% = 80%
5 L–2.5 L
5 L–1 L
x 100% = 62.5%
58

D.Pulmonary Disorders
 Asthma
a. Symptoms: dyspnea (shortness of breath) and
wheezing
b. Caused by inflammation, mucus secretion, and
constriction of bronchioles
c. Often called airway hyperresponsiveness
59

Asthma, cont
d. Allergic (atopic) asthma: triggered by
allergens stimulating T lymphocytes to secrete
cytokines and recruit eosinophils and mast
cells, which contribute to inflammation
1) Can also be triggered by cold or dry air, exercise,
or aspirin
2) Causes production of IgE antibodies
3) Reversible with bronchodilator, such as Albuterol
60

2.Emphysema
a. Destruction of alveoli
b. Reduces surface area for gas exchange
c. With fewer alveoli to put pressure on
bronchioles, they collapse during expiration.
d. Smoking is the most common cause. It triggers
inflammation and destruction of alveoli by
immune cells
61

Emphysema destroys lung tissue
(b)
(a)
a: © Robert Calentine/Visuals Unlimited, Inc.; b: © Science VU/Visuals Unlimited, Inc.
62

3.Chronic Obstructive Pulmonary Disease (COPD)
a. Chronic inflammation, narrowing of the
airways, and alveolar destruction
b. Includes emphysema and chronic obstructive
bronchiolitis
c. Accelerated decline in FEV1
d. Inflammation involves macrophages,
neutrophils, and cytotoxic T cells
e. Excessive mucus production and inflammation
triggered by smoking
63

Chronic Obstructive Pulmonary Disease (COPD), cont
f. Most people with COPD smoke.
g. Smoking also promotes the infiltration of
obstructing fibrous tissue and muscle in the
airways and remodeling of blood vessels in the
lungs, leading to pulmonary hypertension.
h. May develop cor pulmonale – pulmonary
hypertension with hypertrophy and eventual failure
of the right ventricle
i. There is no cure.
j. 5th leading cause of death (estimated to move to
3rd by 2020)
64

4.Pulmonary Fibrosis
a. Some people accumulate fibrous tissues in the
lungs when alveoli are damaged.
b. May be due to inhalation of small particles
c. Example: black lung (anthracosis) in miners
65

exchange occurs.
66

 Alveoli are microscopic thin-walled air
sacs that provide an enormous surface
area for gas diffusion.
1. The region of the lungs where gas exchange with
the blood occurs is known as the respiratory zone.
2. The trachea, bronchi, and bronchioles that deliver
air to the respiratory zone constitute the conducting
zone.
67

intrapleural space.
68

A.Introduction
 Measuring pressure
a. Atmospheric pressure can be measured using a
barometer
b. At sea level, the atmospheric pressure is 760 mmHg
or one atmosphere
70

Measurement of Atmospheric Pressure
Vacuum
760 mm
Sea level
Atmospheric
pressure
Hg
71

2. Dalton’s Law
a. The total pressure of a gas mixture is equal to
the sum of the pressures of each gas in it.
b. Partial pressure: the pressure of an individual
gas; can be measured by multiplying the % of
that gas by the total pressure
1) O2 makes up 21% of the atmosphere, so partial
pressure of O2 = 760 X 20% = 159 mmHg.
72

Dalton’s Law, cont
c. Total pressure
1) Nitrogen makes up 78% of the atmosphere, O2 21%,
and CO2 1%.
Pdry = PN2
+ PO2
+ PCO2
= 760 mmHg
d. When air gets to our lungs, it is humid, so the
calculation changes to:
Pwet = PN2
+ PO2
+ PCO2
+ PH2O= 760 mmHg
73

3.Calculation of PO2
a. Addition of water vapor also takes away from the
total atmospheric pressure when calculating
partial pressure O2.
1) Pressure of water at 37°C is a constant 47 mmHg.
2) Partial pressure O2 at sea level:
.21(760 − 47) = 150 mmHg
74

4. Result of Gas Exchange
a. In the alveoli, the percentage of oxygen decreases
and CO2 increases, changing the partial pressure
of each.
75

Partial Pressure of Gases
O2
N2
H2O
CO2
Total
pressure
Inspired air
Variable
000.3 mmHg
159 mmHg
601 mmHg
760 mmHg 760 mmHg
568 mmHg
105 mmHg
40 mmHg
47 mmHg
Alveolar air
76

Partial Pressure Oxygen
Changes with altitude and location
77

B. Partial Pressure of Gases in Blood
 Alveoli and blood capillaries quickly
reach equilibrium for O2 and CO2.
a.This helps maximize the amount of gas
dissolved in fluid.
b.Henry’s Law predicts this.
78

2. Henry’s Law
a. The amount of gas that can dissolve
in liquid depends on:
1)Solubility of the gas in the liquid
(constant)
2)Temperature of the fluid (more gas can
dissolve in cold liquid); doesn’t change
for blood
3)Partial pressure of the gases, the
determining factor
79

Relationship Between Alveoli and Capillaries
Blood
flow Pulmonary venule
Pulmonary
arteriole
Bronchiole
Terminal bronchiole
Capillary network
on surface of alveolus
Pulmonary
venule
Pulmonary
arteriole
Alveolar duct
Alveolar sac
Alveoli
Respiratory bronchiole
80

C. Significance of blood PO2 and PCO2
measurements
 Only measures oxygen dissolved in the
blood plasma. It will not measure oxygen
bound to hemoglobin in red blood cells.
 It does provide a good measurement of
lung function.
 When lungs are functioning properly, PO2
of systemic arterial blood is only 5mm Hg
less than PO2 of alveolar air
a. At normal PO2 of about 100mmHg,
hemoglobin is almost completely filled with O2
81

Significance of blood PO2 and PCO2 measurements,
cont
c. Adding more O2 will not significantly change
the amount of O2 in RBCs, but can increase
the amount of dissolved oxygen
d.Since O2 must dissolve in the plasma
before it can be delivered to tissues, the
rate of O2 diffusion would increase
4. Blood gas measurement of venous
blood is not very useful
82

Blood Gas Measurement
e–
Certified gas cylinder
First step: Calibration of
O2 electrode
Second step: Measurement of
arterial PO2
Dissolved
O2
O2 electrode
Blood-gas machine
Arterial blood
sample
(b)
Calibrate to PO2
of gas
Total pressure = 760 mmHg
% O2 = 20%
PO2
= 152 mmHg
Equilibrium
Dissolved
O2
e–
(a)
83

Partial Pressure of Gas in Blood
Po2
O2
Right
atrium
and
ventricle
To
pulmonary
vein
Systemic
arteries
Body
cells
From
pulmonary
artery
Systemic
veins
Capillaries
CO2
O2
Pco2
= 105
= 40
CO2
Pco2
Po2= 40
= 46
Alveoli
Po2
Pco2
= 100
= 40
Po2 Pco2
= 40 = 46 Po2 Pco2
= 100 = 40
Left
atrium
and
ventricle
84

D. Pulmonary Circulation & Ventilation/Perfusion
 The rate of blood flow through the lungs is
equal to that through the systemic circuit (5.5
L/minute cardiac output).
 Systemic circulation pressure difference is
about 100mm Hg
 The pressure difference between the left
atrium and the pulmonary artery is only 10
mmHg.
 Vascular resistance must be very low.
a. Low pressure/low resistance pathway
b. Reduces possibility of pulmonary edema
85

Pulmonary Circulation & Ventilation/Perfusion, cont
5. Pulmonary arterioles constrict when
alveolar partial pressure O2 is low and
dilate when partial pressure O2 is high.
a. Blood flow to alveoli is increased when they
are full of oxygen and decreased when not.
b. Opposite of systemic arterioles that constrict
when partial pressure O2 in tissues is high.
This ensures that only tissues that need
oxygen are sent blood.
86

6. Arteriole Response to O2
a. Low oxygen depolarizes smooth muscle cells
of the arteriole wall by inhibiting outward flow
of K+.
b. This opens voltage-gated Ca2+ channels,
which stimulate contraction.
c. The response of pulmonary arterioles to low
oxygen levels makes sure that ventilation (O2
into lungs) matches perfusion (blood flow).
87

Lung Ventilation/Perfusion Ratios
Ratio
Blood flow
(L/min)
Ventilation
(L/min)
3.40
0.07
0.24
Apex
Base 0.63
1.29
0.82
88

E. Disorders Caused by High Partial
Pressure of Gases
 Problems for deep-sea divers
 Oxygen toxicity: 100% oxygen is dangerous at
2.5 atmospheres; due to oxidation of enzymes
 Nitrogen narcosis: occurs if nitrogen is inhaled
under pressure; results in dizziness and
drowsiness
 Decompression sickness: When a diver
comes to the surface too fast, nitrogen bubbles
can form in the blood and block small vessels.
 Can also happen if an airplane suddenly loses
pressure
89

exchange occurs.
90

 Alveoli are microscopic thin-walled
air sacs that provide an enormous
surface area for gas diffusion.
1. The region of the lungs where gas
exchange with the blood occurs is known as
the respiratory zone.
2. The trachea, bronchi, and bronchioles that
deliver air to the respiratory zone constitute
the conducting zone.
91

intrapleural space.
92

HUMAN PHYSIOLOGY
RESPIRATORY SYSTEM
KISII UNIVERSITY
(LECTURE SESSION III)

Sub-Topics
 Regulation of breathing
 Hemoglobin and Oxygen
Transport
94

95
 Explain how ventilation is regulated by the
CNS
 Explain how blood gases and pH influence
ventilation
 Describe the changes in percent
oxyhemoglobin as a function of arterial PO2
and explain how this relates to oxygen
transport

A.Introduction
 Contraction and relaxation of breathing
muscles is controlled by motor neurons from
two areas of the brain.
a. Voluntary breathing: from cerebral cortex
b. Involuntary breathing: from respiratory control
centers of the medulla oblongata and pons
97

B.Brain stem Respiratory
Centers
 Motor neurons
a. Those that innervate the diaphragm form the phrenic
nerve and arise from the cervical region of the spinal
cord.
b. Those that innervate the other breathing muscles
arise from the thoracolumbar region of the spinal
cord.
c. Regulated by descending neurons from the brain.
98

2.Medulla Oblongata
a. Rhythmicity center: four types of neurons
identified for different stages of breathing
1) Dorsal respiratory group: made up of inspiratory
neurons (I neurons) that stimulate neurons of the
phrenic nerve
2) Ventral respiratory group: made up of inspiratory
neurons that stimulate spinal respiratory neurons and
expiratory neurons (E neurons) that inhibit the phrenic
nerve
b. Activity of I and E neurons vary in a reciprocal way
to produce the rhythmic pattern of breathing
99

3.Pons
a. Influences medulla activity
b. Apneustic center: promotes inspiration
c. Pneumotaxic center: inhibits inspiration
4. Brainstem respiratory centers control breathing
largely via the phrenic nerve from C3-C6
spinal nuclei
100

Brain Stem Respiratory Centers
Midbrain
Pons
Brain stem
respiratory
centers
Pneumotaxic
area
Apneustic area
Rhythmicity area
Medulla oblongata
Reticular formation
101

5.Chemoreceptors
a. Automatic control of breathing is influenced by
feedback from chemoreceptors, which monitor pH
of fluids in the brain and pH, PCO2 and PO2 of the
blood.
1) Central chemoreceptors in medulla
2) Peripheral chemoreceptors in carotid and aorta
arteries
102

b. Aortic and Carotid Bodies
1) Aortic body sends feedback to medulla along
vagus nerve.
2) Carotid body sends feedback to medulla along
glossopharyngeal nerve.
103

Sensory Input From Aortic and
Carotid Bodies
Sensory nerve fibers
(in glossopharyngeal nerve)
Carotid body
Sensory nerve fibers
(in vagus nerve)
Carotid sinus
Common
carotid artery
Aorta
Heart
Aortic bodies
104

Regulation of Ventilation by the
CNS
Automatic
breathing
Voluntary
breathing
Cerebral cortex
Pneumotaxic
center
Apneustic
center
Pons
Medulla oblongata
Chemoreceptors
Medulla oblongata
Spinal cord
Motoneurons to
respiratory muscles
Chemoreceptors
Aortic and carotid
bodies
105

C.Effects of pH and PCO2
on Ventilation
 When ventilation is inadequate, CO2 levels rise
and pH falls. (hypercapnia)
CO2 + H2O  H2CO3  H+ + HCO3
-
 In hyperventilation, CO2 levels fall and pH
rises. (hypocapnia)
 Oxygen levels do not change as rapidly
because of oxygen reserves in hemoglobin, so
O2 levels are not a good index for control of
breathing.
 Ventilation is controlled to maintain constant
levels of CO2 in the blood. Oxygen levels
106

Effects of PCO2
on Ventilation
Arterial
P
CO
2
(mmHg)
0 2 4 6 8
80
70
60
50
40
30
20
10
Hypoventilation
Normal
ventilation
Hyperventilation
Total minute volume (L/min)
(PCO2
= 40 ± 2)
107

5.Chemoreceptors in the
Medulla
a. When increased CO2 in the fluids of the brain
decrease pH, this is sensed by
chemoreceptors in the medulla, and ventilation
is increased.
b. Senses CO2, not H+ which does not cross the
blood-brain barrier
c. Takes longer, but responsible for 70−80% of
increased ventilation
108

Chemoreceptors in the Medulla
H
+
+
Chemoreceptor
neurons
Medulla
oblongata
Brain
interstitial fluid
Cerebrospinal
fluid (CSF)
Blood-CSF
barrier
Capillary
blood
CO2
CO2
H2O
H2CO3
HCO3
–
109

6.Peripheral Chemoreceptors
a. Aortic and carotid bodies respond to rise in H+
due to increased CO2 levels.
b. Respond much quicker
110

Chemoreceptor Control of Breathing
–
Decreased ventilation
Increased arterial Pco2
Blood pH
Peripheral
chemoreceptors
in aortic and
carotid bodies
Sensory
neurons
Plasma CO2
Blood
Brain
pH of
interstitial fluid
Central
chemoreceptors
in medulla oblongata
Respiratory center
in medulla oblongata
Spinal cord
motor neurons
Respiratory
muscles
Increased ventilation
Negative
feedback
Sensor
Integrating center
Effector
111

D.Effect of Blood PO2
on Ventilation
 Indirectly affects ventilation by affecting
chemoreceptor sensitivity to PCO2
 Low blood O2 makes the carotid bodies more
sensitive to CO2.
 Hypoxic drive – carotid bodies respond directly
to low oxygen dissolved in the plasma (below
70mmHg)
112

Comparing the effects of blood CO2
and O2 on breathing
Total
minute
volume
(liters/min)
8 6 4 2 0
1 2 3 4 5 6 7 8 9
80
60
20
40
10
80
60
40
20
O2 varied
(CO2 constant)
18 16 14 12
%O2
10
CO2 varied
(O2 constant)
%CO2
113

Sensitivity of Chemoreceptors to Changes
in Blood Gases and pH
114

E.Effects of Pulmonary Receptors on Ventilation
 Unmyelinated C fibers in the lungs: affected by
capsaicin; produce rapid shallow breathing
when a person breathes in pepper spray
 Receptors that stimulate coughing:
a. Irritant receptors: in wall of larynx; respond to
smoke, particulates, etc.
b. Rapidly adapting receptors: in lungs; respond to
excess fluid
115

Effects of Pulmonary Receptors on Ventilation, cont
3. Hering-Breuer reflex: stimulated by pulmonary
stretch receptors
a. Inhibits respiratory centers as inhalation proceeds
b. Makes sure you do not inhale too deeply
116

A.Introduction
 Oxygen content of systemic arterial
 1Ltr of blood = 3ml of O2 dissolved (1.5%)
197 ml of O2 bound to Hb (98.5%)
Total = 200ml O2 per 1Ltr of blood
 Cardiac OutPut = 5L/min
O2 carried to tissues = 5L/min x 200ml O2/L
= 200mL O2/Min
 Total O2 content of blood depends on PO2 and
hemoglobin concentration
118

Oxygen Content of Blood
O2
Gas tank
Po2 = 100 mmHg 0.3 ml O2
100 ml 100 ml
20.0 ml O2
Oxyhemoglobin
Po2 = 100 Po2 = 100
Whole blood
Plasma
Oxygen
content
119

B.Hemoglobin
 Most of the oxygen in blood is bound to
hemoglobin.
a. 4 polypeptide globins (2 alpha and 2 beta chains)
and 4 iron-containing hemes
b. Each hemoglobin can carry 4 molecules O2.
c. 280 million hemoglobin/RBC
d. Each RBC can carry over a billion O2 molecules
120

Structure of Hemoglobin
C C
C
C
C C
C C
C C
C
N
N
N
C
C
C C
C
N
Hemoglobin
Beta chain
Heme group
Alpha chain
Alpha chain
Beta chain
CH2
CH
CH3
CH
CH3
HC
CH3
CH2
CH2
COOH
HC
Fe
CH
CH
CH3
CH2
CH2
COOH
Heme
(b)
(a)
CH2
121

2.Forms of Hemoglobin
a. Oxyhemoglobin/reduced (deoxyhemoglobin)
hemoglobin: Iron is in reduced form (Fe2+) and
can bind with O2.
b. Methemoglobin: Oxidized iron (Fe3+) can’t bind
to O2.
1) Abnormal; some drugs cause this.
c. Carboxyhemoglobin: Hemoglobin is bound
with carbon monoxide; has a stronger bond
with CO than with O2
d. Each type has a unique color and absorption
spectrum
122

3.% Oxyhemoglobin Saturation
a. % oxyhemoglobin to total hemoglobin
b. Measured to assess how well lungs have
oxygenated the blood
c. Normal is 97%
d. Measured with a pulse oximeter or blood– gas
machine
123

4.Hemoglobin Concentration
a. Oxygen-carrying capacity of blood is measured
by its hemoglobin concentration.
1) Anemia: below-normal hemoglobin levels
2) Polycythemia: above-normal hemoglobin levels; may
occur due to high altitudes
b. Erythropoietin made in the kidneys stimulates
hemoglobin/RBC production in red bone marrow
when O2 levels are low.
124

5.Loading and Unloading
a. Loading: when hemoglobin binds to oxygen in the
lungs
b. Unloading: when oxyhemoglobin drops off oxygen
in the tissues
deoxyhemoglobin + O2 oxyhemoglobin
c. Direction of reaction depends on PO2
of the
environment and affinity for O2.
1) High PO2
favors loading.
2) Strong bond favors loading and inhibits unloading
125

C.The oxyhemoglobin
dissociation curve
 Oxygen unloading
a. Systemic arteries have a PO2
of 100 mmHg.
1) This makes enough oxygen bind to get 97%
oxyhemoglobin.
2) 20 ml O2/100 ml blood
b. Systemic veins have a PO2
of 40 mmHg.
1) This makes enough oxygen bind to get 75%
oxyhemoglobin.
2) 15.5 ml O2/100 ml blood
c. 22% oxygen is unloaded in tissues
126

PO2
and % Oxyhemoglobin
127

Oxygen Dissociation Curve,
cont
2. Oxygen remaining in veins serves as an
oxygen reserve.
3. The curve is sigmoidal (S-shaped) – at high
PO2, changes in PO2 have little effect on
loading
4. At the steep part of the curve, small changes
produce large changes in % saturation
5. Oxygen unloading during exercise is even
greater:
a. 22% at rest
b. 39% light exercise
128

Oxygen Dissociation Curve
Oxygen
content
(ml
O
2
/100
ml
blood)
0
5
0
0
Percent
oxyhemoglobin
saturation
100
80
60
Amount of O2
unloaded to
tissues
20
15
10
Veins
(at rest) Arteries
100
80
60
40
20
20
40
Po2 (mmHg)
129

D.Effect of pH and Temperature
on Oxygen Transport
 pH and temperature change the affinity of
hemoglobin for O2.
a. This ensures that muscles get more O2 when
exercising.
 Affinity decreases at lower pH and increases at
higher pH = Bohr effect.
a. More unloading occurs at lower pH.
b. Increased metabolism = more CO2 = lower pH
c. More O2 unloading
d. Curve shifts to the right
130

Effect of pH and Temperature
on Oxygen Transport
Percent
oxyhemoglobin
saturation
0
0
100
90
80
70
60
50
40
30
20
10
pH 7.60
7.40
7.20
10 20 30 40 50 140
130
120
110
100
90
80
Po2 (mmHg)
70
60
131

Effect of pH and Temperature
on Oxygen Transport, cont
3. Hemoglobin affinity for O2 is decreased at
increased temperatures.
a. This further enhances the amount of O2 unloaded
to muscles during exercise.
b. Curve shifts to the right
132

E.Effect of 2,3-DPG on Oxygen
Transport
 RBCs obtain energy from the anaerobic
metabolism of glucose (has no nucleus or
mitochondria)
a. During this process, 2,3 diphosphoglyceric acid (2,3-
DPG) is made.
b. Inhibited by oxyhemoglobin
c. 2,3-DPG is produced if a person is anemic or at high
altitude.
d. This increases oxygen unloading.
e. Shifts the oxyhemoglobin dissociation curve to the
right
133

Effect of 2,3-DPG on Oxygen
Transport
–
Less O2
delivery to
the tissues
Negative
feedback
2. Increased O2
unloading to
the tissues
1. Low Po2 at high altitude
Red Blood Cells
Increased 2,3-DPG
Less oxyhemoglobin
Less inhibition of
2,3-DPG production
Lower affinity of
hemoglobin for
oxygen
134

Factors That Affect the Affinity of
Hemoglobin for O2
135

2.Anemia
a. Total blood hemoglobin decrease
b. Adult hemoglobin (hemoglobin A) can bind to
2,3-DPG, but fetal hemoglobin (hemoglobin F)
cannot.
1) Hemoglobin F has 2 gamma chains instead of 2
beta chains
2) Fetal hemoglobin therefore has a higher affinity
for O2 than the mother, so oxygen is transferred
to the fetus.
136

F.Inherited Hemoglobin Defects
 Sickle-cell anemia: found in 8−11% of African
Americans
a. The affected person has hemoglobin S with a single
amino acid difference.
b. Deoxygenated hemoglobin S polymerizes into long
fibers, creating a sickle-shaped RBC.
c. This hinders flexibility and the ability to pass through
small vessels.
137

Sickle-cell anemia, cont
d. Blood flow to organs is restricted, and RBCs
hemolyse.
e. Treated with hydroxyurea; stimulates production
of fetal hemoglobin without the defect
f. This defect imparts a high resistance to malaria
138

Sickle-cell Anemia
(a) (b)
a: © Ingram Publishing/SuperStock; b: CDC/Sickle Cell Foundation of Georgia:
Jackie George, Beverly Sinclair/photo by Janice Haney Carr
139

Inherited Hemoglobin Defects,
cont
2. Thalassemia: found mainly in people of
Mediterranean heritage
a. Production of either alpha or beta chains is
defective.
b. Increased synthesis of gamma chains
c. Many mutations are possible giving a wide range
of symptoms
140

G.Muscle Myoglobin
 Red pigment found in skeletal and cardiac
muscles
 Similar to hemoglobin, but with 1 heme, so it
can only carry 1 oxygen molecule
 Higher affinity to oxygen; oxygen is only
released when PO2 is very low
 Stores oxygen and serves as go-between in
transferring oxygen from blood to mitochondria
141

Myoglobin and Hemoglobin
Dissociation Curves
0
0
Percent
oxygen
saturation
100
Arterial blood
Hemoglobin
20
40
60
80
Myoglobin
Venous blood
120
100
80
Po2 (mmHg)
60
40
20
142

HUMAN PHYSIOLOGY
RESPIRATORY SYSTEM
KISII UNIVERSITY
(LECTURE SESSION IV)

Sub-Topics
 Carbon Dioxide Transport
 Acid Base Balance
144

145
 Explain how carbon dioxide is transported by
the blood
 Explain the relationship between blood levels
of carbon dioxide and the blood pH
 Describe the acid-base balance of the blood,
and how it is influenced by the respiratory
system

A.Introduction
 Carbon dioxide is carried in the blood in three
forms:
a. Dissolved in plasma (more soluble than O2)
b. As carbaminohemoglobin attached to an amino
acid in hemoglobin
c. As bicarbonate ions (accounts for the majority of
transport)
147

Introduction, cont
2. Carbonic anhydrase
a. Carbon dioxide readily reacts with water in the RBC of
the systemic capillaries and plasma
b. Carbonic anhydrase is the enzyme that catalyzes the
reaction to form carbonic acid at high PCO2
H2O + CO2 H2CO3
148

3.Formation of Bicarbonate and H+
a. Carbonic acid is a weak acid that will dissociation
into bicarbonate and hydrogen ions. This reaction
also uses carbonic anhydrase as the catalyst
H2CO3 H+ + HCO3
−
149

B.Chloride Shift
 Once bicarbonate ion is formed in the RBC, it
diffuses into the plasma
 H+ in RBCs attach to hemoglobin and attract
Cl−.
 The exchange of bicarbonate out of and
Cl− into RBCs is called the chloride shift.
150

Carbon Dioxide Transport & the Chloride Shift
1
2
3
CO2
Tissue cells
Plasma
CO2 dissolved
in plasma (10%)
CO2 combined with
hemoglobin to form
carbaminohemoglobin
(20%)
Red blood cells
H
+
+ HCO3
–
H+ combines
with hemoglobin
HCO3
–
(70%)
(Chloride shift)
Cl
–
H2CO3
H2CO3
CO2 + H2O
151

4.Bohr Effect
a. Bonding of H+ to hemoglobin lowers the affinity
for O2 and helps with unloading.
b. This allows more H+ to bind, which helps the
blood carry more carbon dioxide.
152

C.Reverse Chloride Shift
 In pulmonary capillaries, increased PO2 favors the
production of oxyhemoglobin.
 This makes H+ dissociate from hemoglobin and
recombine with bicarbonate to form carbonic acid:
H+ + HCO3
− H2CO3
3. Chloride ion diffuses out of the RBC as
bicarbonate ion enters.
153

Reverse Chloride Shift, cont
4. In low PCO2, carbonic anhydrase converts
carbonic acid back into CO2 + H2O:
H2CO3 CO2 + H2O
5. CO2 is exhaled.
154

Reverse Chloride Shift in the Lungs
1
3
2
Alveoli
CO2 dissolved
in plasma
CO2
Plasma
To pulmonary vein
From pulmonary artery
Red blood cells
HCO3
–
Cl
–
Hemoglobin + CO2
Carbaminohemoglobin H2CO3
H2CO3
CO2 + H2O
HCO3
–
+ H
+
155

ACID-BASE BALANCE OF THE
BLOOD

A.Principles of Acid-Base
Balance
 Maintained within a constant range by the actions
of the lungs and kidneys
a. pH ranges from 7.35 to 7.45.
b. Since carbonic acid can be converted into a gas and
exhaled, it is considered a volatile acid; regulated by
breathing.
c. Nonvolatile acids (lactic, fatty, ketones) are buffered
by bicarbonate; can not be regulated by breathing, but
rather the kidneys
157

2.Bicarbonate as a Buffer
a. Bicarbonate ion is a weak base and is the
major buffer in the blood
excess H+ + HCO3
-  H2CO3
b. Buffering cannot continue forever because
bicarbonate will run out.
c. Kidneys help by releasing H+ in the urine and
by producing more bicarbonate.
158

Bicarbonate as a Blood Buffer
H
+
H
+
HCO3
–
as buffer reserve
HCO3
–
Tissue cells
Capillary
CO2
Red blood cells
Plasma
H2CO3
Bicarbonate
buffer
Anion + H
+
+ HCO3
–
Nonvolatile
(metabolic) acid
pH = 7.40
Cl
–
Hemoglobin
HCO3
–
H
+
H2CO3
CO2 + H2O
159

3.Blood pH: Acidosis
a. Acidosis: when blood pH falls below 7.35
1) Respiratory acidosis: caused by hypoventilation; rise
of CO2 which increases H+ (lowers pH)
2) Metabolic acidosis: caused by excessive production
of acids or loss of bicarbonate (diarrhea)
160

4.Blood pH: Alkalosis
a. Alkalosis: when blood pH rises above 7.45
1) Respiratory alkalosis: caused by hyperventilation;
“blow off” CO2, H+ decreases, pH increases
2) Metabolic alkalosis: caused by inadequate production
of acids or overproduction of bicarbonates, loss of
digestive acids from vomiting
b. Respiratory component of blood pH measured by
plasma CO2
c. Metabolic component measured by bicarbonate
161

Terms Used in Acid Base
Balance
162

Classification of Metabolic & Respiratory
Components of Acidosis & Alkalosis
163

5.Henderson-Hasselbalch
Equation
a. Normal blood pH is maintained when
bicarbonate and CO2 are at a ratio of 20:1.
HCO3
−
pH = 6.1 + log -------------
0.03PCO2
b. Respiratory acidosis or alkalosis occurs with
abnormal CO2 concentration
c. Metabolic acidosis or alkalosis occurs with
abnormal bicarbonate concentration
164

B.Ventilation and Acid-Base Balance
 Ventilation controls the respiratory component
of acid-base balance.
a. Hypoventilation: Ventilation is insufficient to “blow
off” CO2. PCO2 is high, carbonic acid is high, and
respiratory acidosis occurs.
b. Hyperventilation: Rate of ventilation is faster than
CO2 production. Less carbonic acid forms, PCO2 is
low, and respiratory alkalosis occurs.
165

Ventilation and Acid-Base Balance, cont
2. Ventilation can compensate for the metabolic
component.
a. A person with metabolic acidosis will hyperventilate;
“blow off” CO2, H+ decreases, pH rises
b. A person with metabolic alkalosis will hypoventilate;
slow respiration, build up CO2, H+ increases, pH
lowers
166

Effect of Lung Function on Blood Acid-Base Balance
167

HUMAN PHYSIOLOGY
RESPIRATORY SYSTEM
KISII UNIVERSITY
(LECTURE SESSION V)

Sub-Topics
 Effects of Exercise and High
Altitude on Respiratory Functions
 Respiratory Disorders
169

170
 Describe the changes in the respiratory
system that occur in response to exercise
training and high altitude
 Describe the acid-base balance of the blood,
and how it is influenced by the respiratory
system

EFFECTS OF EXERCISE AND
HIGH ALTITUDE ON
RESPIRATORY FUNCTIONS

A.Ventilation During Exercise
 Exercise produces deeper, faster breathing to
match oxygen utilization and CO2 production.
a. Called hyperpnea
 Neurogenic and humoral mechanisms control this.
172

3.Proposed Neurogenic
Mechanisms
a. Sensory nerve activity from exercising
muscles stimulates respiration via spinal
reflexes or brain stem respiratory centers.
b. Cerebral cortex stimulates respiratory centers.
c. Helps explain the immediate increase in
ventilation at the beginning of exercise
173

4.Humoral Mechanisms
a. Rapid and deep breathing continues after
exercise is stopped due to humoral (chemical)
factors.
 PCO2 and pH differences at sensors
 Cyclic variations that are not detected by blood
samples that affect chemoreceptors
174

Effect of exercise on arterial blood gases & pH
pH
Pco
2
(mmHg)
Po
2
(mmHg)
0
Moderate
Heavy
110
40
85
90
95
100
105
35
30
7.45
7.40
7.35
10
Time (min)
50
40
30
20
175

5.Lactate Threshold
a. Ventilation does not deliver enough O2 at the
beginning of exercise.
1) Anaerobic respiration occurs at this time.
2) After a few minutes, muscles receive enough
oxygen.
b. If heavy exercise continues, lactic acid
fermentation will be used again.
1) The lactate threshold is the maximum rate of
oxygen consumption attained before lactic acid
levels rise.
176

Lactate Threshold, cont
c. Occurs when 50−70% maximum oxygen
uptake is reached
1) Due to aerobic limitations of the muscles, not the
cardiovascular system (still at 97% oxygen
saturation)
2) Endurance exercise training increases
mitochondria and Krebs cycle enzymes in the
muscles
177

Changes in Respiratory Function During Exercise
178

B.Acclimation to High Altitude
 Adjustments must be made to compensate for
lower atmospheric PO2.
a. Changes in ventilation
b. Hemoglobin affinity for oxygen
c. Total hemoglobin concentration
179

Blood Gas Measurements at
Different Altitudes
180

2.Changes in Ventilation
a. Hypoxic ventilatory response: Decreases in
PO2 stimulate the carotid bodies to increase
ventilation.
1) Hyperventilation lowers PCO2, causing respiratory
alkalosis.
2) Kidneys increase urinary excretion of bicarbonate
to compensate.
3) Chronically apoxic people produce NO in the
lungs, a vasodilator that increases blood flow.
4) NO bound to sulfur atoms (SNOs) in hemoglobin
may stimulate the rhythmicity center in the
medulla.
181

3.Affinity of Hemoglobin for Oxygen
a. Oxygen affinity decreases, so a higher
proportion of oxygen is unloaded.
b. Occurs due to increased production of 2,3-
DPG
c. At extreme high altitudes, effects of alkalosis
will override this, and affinity for oxygen will
increase.
182

4.Increased Hemoglobin
Production
a. Kidney cells sense decreased PO2 and produce
erythropoietin.
 This stimulates bone marrow to produce more
hemoglobin and RBCs.
 Increased RBCs can lead to polycythemia, which
can produce pulmonary hypertension and more
viscous blood.
183

Changes During Acclimatization to High Altitude
184

Respiratory Adaptations to High
Altitude
1 2 3
Sensor
Integrating center
Effector
Days to weeks
Days
Immediate
High altitude
Low Po2
Carotid bodies 2,3-DPG
in RBCs
Kidneys
Erythropoietin
Pco2
of
arterial blood
Respiratory
alkalosis
Oxygen
unloading
to tissues
Affinity of
hemoglobin
for oxygen
Oxygen
content of
blood
RBC count
and hemoglobin
Bone marrow
Better oxygen
loading in lungs
Proportion
of fresh air
to alveoli
Hyperventilation
Affinity of
hemoglobin
for oxygen
185

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