This document provides an overview of a university lecture on the respiratory system. It begins with an introduction to the structures and functions of the respiratory system, including ventilation, gas exchange in the lungs and tissues, and the conducting and respiratory zones. It then discusses specifics of lung anatomy like the alveoli, pleural membranes, and thoracic cavity. Finally, it covers physical aspects of ventilation such as pressures, compliance, elasticity, and surfactant. The goal is for students to understand respiration at the organ, tissue, and cellular levels.
3. 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
Physiology of the Respiratory System...Edwin Ruoti BsN; MsP
5. 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
Physiology of the Respiratory System...Edwin Ruoti BsN; MsP
6. 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
Physiology of the Respiratory System...Edwin Ruoti BsN; MsP
7. 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
Physiology of the Respiratory System...Edwin Ruoti BsN; MsP
8. 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
Physiology of the Respiratory System...Edwin Ruoti BsN; MsP
10. 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
Physiology of the Respiratory System...Edwin Ruoti BsN; MsP
11. 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
Physiology of the Respiratory System...Edwin Ruoti BsN; MsP
12. 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
Physiology of the Respiratory System...Edwin Ruoti BsN; MsP
14. 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
Physiology of the Respiratory System...Edwin Ruoti BsN; MsP
16. 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
Physiology of the Respiratory System...Edwin Ruoti BsN; MsP
19. 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
Physiology of the Respiratory System...Edwin Ruoti BsN; MsP
20. 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
Physiology of the Respiratory System...Edwin Ruoti BsN; MsP
21. What have we achieved?
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
Physiology of the Respiratory System...Edwin Ruoti BsN; MsP
22. What have we achieved?
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
Physiology of the Respiratory System...Edwin Ruoti BsN; MsP
23. What have we achieved?
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
Physiology of the Respiratory System...Edwin Ruoti BsN; MsP
25. 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
Physiology of the Respiratory System...Edwin Ruoti BsN; MsP
26. 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
Physiology of the Respiratory System...Edwin Ruoti BsN; MsP
27. 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
Physiology of the Respiratory System...Edwin Ruoti BsN; MsP
28. Pressure Changes in Normal Breathing
28
Physiology of the Respiratory System...Edwin Ruoti BsN; MsP
29. 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
Physiology of the Respiratory System...Edwin Ruoti BsN; MsP
30. 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
Physiology of the Respiratory System...Edwin Ruoti BsN; MsP
31. 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
Physiology of the Respiratory System...Edwin Ruoti BsN; MsP
32. 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
Physiology of the Respiratory System...Edwin Ruoti BsN; MsP
33. 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
Physiology of the Respiratory System...Edwin Ruoti BsN; MsP
34. 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
Physiology of the Respiratory System...Edwin Ruoti BsN; MsP
36. 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
Physiology of the Respiratory System...Edwin Ruoti BsN; MsP
38. 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
Physiology of the Respiratory System...Edwin Ruoti BsN; MsP
40. Sub-Topics
Mechanics of Breathing
Gaseous Exchange in the Lungs
40
Physiology of the Respiratory System...Edwin Ruoti BsN; MsP
41. Specific Learning Objectives
41
By the end of the lecture, you should be able to:
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
Physiology of the Respiratory System...Edwin Ruoti BsN; MsP
43. 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
Physiology of the Respiratory System...Edwin Ruoti BsN; MsP
45. 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
Physiology of the Respiratory System...Edwin Ruoti BsN; MsP
46. 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
Physiology of the Respiratory System...Edwin Ruoti BsN; MsP
48. 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
Physiology of the Respiratory System...Edwin Ruoti BsN; MsP
49. Quiet (Normal) vs. Forced Ventilation
49
Physiology of the Respiratory System...Edwin Ruoti BsN; MsP
51. 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
Physiology of the Respiratory System...Edwin Ruoti BsN; MsP
52. 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
Physiology of the Respiratory System...Edwin Ruoti BsN; MsP
53. 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
Physiology of the Respiratory System...Edwin Ruoti BsN; MsP
54. 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
Physiology of the Respiratory System...Edwin Ruoti BsN; MsP
57. 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
Physiology of the Respiratory System...Edwin Ruoti BsN; MsP
59. 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
Physiology of the Respiratory System...Edwin Ruoti BsN; MsP
60. 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
Physiology of the Respiratory System...Edwin Ruoti BsN; MsP
61. 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
Physiology of the Respiratory System...Edwin Ruoti BsN; MsP
63. 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
Physiology of the Respiratory System...Edwin Ruoti BsN; MsP
64. 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
Physiology of the Respiratory System...Edwin Ruoti BsN; MsP
65. 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
Physiology of the Respiratory System...Edwin Ruoti BsN; MsP
66. 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?
66
Physiology of the Respiratory System...Edwin Ruoti BsN; MsP
67. 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.
67
Physiology of the Respiratory System...Edwin Ruoti BsN; MsP
68. What have we achieved?
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.
68
Physiology of the Respiratory System...Edwin Ruoti BsN; MsP
70. 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
Physiology of the Respiratory System...Edwin Ruoti BsN; MsP
72. 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
Physiology of the Respiratory System...Edwin Ruoti BsN; MsP
73. 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
Physiology of the Respiratory System...Edwin Ruoti BsN; MsP
74. 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
Physiology of the Respiratory System...Edwin Ruoti BsN; MsP
75. 4. Result of Gas Exchange
a. In the alveoli, the percentage of oxygen decreases
and CO2 increases, changing the partial pressure
of each.
75
Physiology of the Respiratory System...Edwin Ruoti BsN; MsP
78. 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
Physiology of the Respiratory System...Edwin Ruoti BsN; MsP
79. 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
Physiology of the Respiratory System...Edwin Ruoti BsN; MsP
81. 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
Physiology of the Respiratory System...Edwin Ruoti BsN; MsP
82. 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
Physiology of the Respiratory System...Edwin Ruoti BsN; MsP
85. 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
Physiology of the Respiratory System...Edwin Ruoti BsN; MsP
86. 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
Physiology of the Respiratory System...Edwin Ruoti BsN; MsP
87. 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
Physiology of the Respiratory System...Edwin Ruoti BsN; MsP
89. 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
Physiology of the Respiratory System...Edwin Ruoti BsN; MsP
90. 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?
90
Physiology of the Respiratory System...Edwin Ruoti BsN; MsP
91. 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.
91
Physiology of the Respiratory System...Edwin Ruoti BsN; MsP
92. What have we achieved?
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.
92
Physiology of the Respiratory System...Edwin Ruoti BsN; MsP
94. Sub-Topics
Regulation of breathing
Hemoglobin and Oxygen
Transport
94
Physiology of the Respiratory System...Edwin Ruoti BsN; MsP
95. Specific Learning Objectives
95
By the end of the lecture, you should be able to:
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
Physiology of the Respiratory System...Edwin Ruoti BsN; MsP
97. 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
Physiology of the Respiratory System...Edwin Ruoti BsN; MsP
98. 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
Physiology of the Respiratory System...Edwin Ruoti BsN; MsP
99. 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
Physiology of the Respiratory System...Edwin Ruoti BsN; MsP
100. 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
Physiology of the Respiratory System...Edwin Ruoti BsN; MsP
102. 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
Physiology of the Respiratory System...Edwin Ruoti BsN; MsP
103. 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.
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Physiology of the Respiratory System...Edwin Ruoti BsN; MsP
106. 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
Physiology of the Respiratory System...Edwin Ruoti BsN; MsP
108. 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
Physiology of the Respiratory System...Edwin Ruoti BsN; MsP
110. 6.Peripheral Chemoreceptors
a. Aortic and carotid bodies respond to rise in H+
due to increased CO2 levels.
b. Respond much quicker
110
Physiology of the Respiratory System...Edwin Ruoti BsN; MsP
112. 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
Physiology of the Respiratory System...Edwin Ruoti BsN; MsP
114. Sensitivity of Chemoreceptors to Changes
in Blood Gases and pH
114
Physiology of the Respiratory System...Edwin Ruoti BsN; MsP
115. 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
Physiology of the Respiratory System...Edwin Ruoti BsN; MsP
116. 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
Physiology of the Respiratory System...Edwin Ruoti BsN; MsP
118. 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
Physiology of the Respiratory System...Edwin Ruoti BsN; MsP
120. 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
Physiology of the Respiratory System...Edwin Ruoti BsN; MsP
122. 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
Physiology of the Respiratory System...Edwin Ruoti BsN; MsP
123. 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
Physiology of the Respiratory System...Edwin Ruoti BsN; MsP
124. 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
Physiology of the Respiratory System...Edwin Ruoti BsN; MsP
125. 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
Physiology of the Respiratory System...Edwin Ruoti BsN; MsP
126. 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
Physiology of the Respiratory System...Edwin Ruoti BsN; MsP
128. 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
Physiology of the Respiratory System...Edwin Ruoti BsN; MsP
130. 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
Physiology of the Respiratory System...Edwin Ruoti BsN; MsP
132. 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
Physiology of the Respiratory System...Edwin Ruoti BsN; MsP
133. 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
Physiology of the Respiratory System...Edwin Ruoti BsN; MsP
135. Factors That Affect the Affinity of
Hemoglobin for O2
135
Physiology of the Respiratory System...Edwin Ruoti BsN; MsP
136. 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
Physiology of the Respiratory System...Edwin Ruoti BsN; MsP
137. 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
Physiology of the Respiratory System...Edwin Ruoti BsN; MsP
138. 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
Physiology of the Respiratory System...Edwin Ruoti BsN; MsP
140. 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
Physiology of the Respiratory System...Edwin Ruoti BsN; MsP
141. 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
Physiology of the Respiratory System...Edwin Ruoti BsN; MsP
144. Sub-Topics
Carbon Dioxide Transport
Acid Base Balance
144
Physiology of the Respiratory System...Edwin Ruoti BsN; MsP
145. Specific Learning Objectives
145
By the end of the lecture, you should be able to:
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
Physiology of the Respiratory System...Edwin Ruoti BsN; MsP
147. 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
Physiology of the Respiratory System...Edwin Ruoti BsN; MsP
148. 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
Physiology of the Respiratory System...Edwin Ruoti BsN; MsP
149. 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
Physiology of the Respiratory System...Edwin Ruoti BsN; MsP
150. 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
Physiology of the Respiratory System...Edwin Ruoti BsN; MsP
152. 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
Physiology of the Respiratory System...Edwin Ruoti BsN; MsP
153. 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
Physiology of the Respiratory System...Edwin Ruoti BsN; MsP
154. 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
Physiology of the Respiratory System...Edwin Ruoti BsN; MsP
157. 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
Physiology of the Respiratory System...Edwin Ruoti BsN; MsP
158. 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
Physiology of the Respiratory System...Edwin Ruoti BsN; MsP
160. 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
Physiology of the Respiratory System...Edwin Ruoti BsN; MsP
161. 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
Physiology of the Respiratory System...Edwin Ruoti BsN; MsP
162. Terms Used in Acid Base
Balance
162
Physiology of the Respiratory System...Edwin Ruoti BsN; MsP
163. Classification of Metabolic & Respiratory
Components of Acidosis & Alkalosis
163
Physiology of the Respiratory System...Edwin Ruoti BsN; MsP
164. 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
Physiology of the Respiratory System...Edwin Ruoti BsN; MsP
165. 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
Physiology of the Respiratory System...Edwin Ruoti BsN; MsP
166. 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
Physiology of the Respiratory System...Edwin Ruoti BsN; MsP
167. Effect of Lung Function on Blood Acid-Base Balance
167
Physiology of the Respiratory System...Edwin Ruoti BsN; MsP
169. Sub-Topics
Effects of Exercise and High
Altitude on Respiratory Functions
Respiratory Disorders
169
Physiology of the Respiratory System...Edwin Ruoti BsN; MsP
170. Specific Learning Objectives
170
By the end of the lecture, you should be able to:
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
Physiology of the Respiratory System...Edwin Ruoti BsN; MsP
172. 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
Physiology of the Respiratory System...Edwin Ruoti BsN; MsP
173. 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
Physiology of the Respiratory System...Edwin Ruoti BsN; MsP
174. 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
Physiology of the Respiratory System...Edwin Ruoti BsN; MsP
176. 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
Physiology of the Respiratory System...Edwin Ruoti BsN; MsP
177. 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
Physiology of the Respiratory System...Edwin Ruoti BsN; MsP
178. Changes in Respiratory Function During Exercise
178
Physiology of the Respiratory System...Edwin Ruoti BsN; MsP
179. 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
Physiology of the Respiratory System...Edwin Ruoti BsN; MsP
180. Blood Gas Measurements at
Different Altitudes
180
Physiology of the Respiratory System...Edwin Ruoti BsN; MsP
181. 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
Physiology of the Respiratory System...Edwin Ruoti BsN; MsP
182. 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
Physiology of the Respiratory System...Edwin Ruoti BsN; MsP
183. 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
Physiology of the Respiratory System...Edwin Ruoti BsN; MsP