Principles of Anatomy and Physiology
Fifteenth Edition
Gerard Tortora and Bryan Derrickson
Chapter 23
The Respiratory System
Principles of Anatomy and Physiology
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Introduction
The purpose of this chapter is to:
1. Describe the anatomy of the respiratory system
2. Explain the physiology of the respiratory system
3. Describe the events that cause inhalation,
exhalation, and gas exchange
4. Explain how oxygen and carbon dioxide are
transported in the blood
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Breathing and Respiration
• Respiration is the exchange of gases between the
atmosphere, blood, and cells
• The combination of 3 processes is required for
respiration to occur
❑ Ventilation (breathing)
❑ External (pulmonary) respiration
❑ Internal (tissue) respiration
• The cardiovascular system assists the respiratory system
by transporting gases
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Pulmonary Ventilation
Interactions Animation:
Pulmonary Ventilation
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Components of the Respiratory System
Structurally, the components of the respiratory system are
divided into 2 parts:
1. Upper respiratory system
2. Lower respiratory system
Functionally, the components of the respiratory system
are divided into 2 zones:
1. Conducting zone
2. Respiratory zone
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Respiratory System Anatomy
Anatomy Overview:
The Respiratory System
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Respiratory System Tissues
Anatomy Overview:
Respiratory System Tissues
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Structures of the Respiratory System (1 of 2)
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Structures of the Respiratory System (2 of 2)
• The upper respiratory system consists of the nose,
pharynx, and associated structures
• The lower respiratory system consists of the larynx,
trachea, bronchi, and lungs
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Overview: Nose, Pharynx, Larynx, and Trachea
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Cartilaginous Framework of the Nose
The external portion of the nose is made of cartilage and
skin, and is lined with mucous membrane
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Internal Anatomy of the Nose
The bony framework of the nose is formed by the frontal,
nasal, and maxillary bones
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Nasal Conchae and Meatuses
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Surface Anatomy of the Nose
1. Root
2. Apex
3. Bridge
4. External naris
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Pharynx
The pharynx functions as a passageway for air and food,
provides a resonating chamber for speech sounds, and
houses the tonsils—which participate in immunological
reactions against foreign invaders
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Larynx (1 of 2)
The larynx (voice box) is a passageway that connects the
pharynx and trachea
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Larynx (2 of 2)
The larynx contains vocal folds, which produce sound when they
vibrate
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Structures of Voice Production
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Trachea
The trachea extends from the larynx to the primary
bronchi
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Bronchi (1 of 3)
At the superior border of the 5th thoracic vertebra, the
trachea branches into a right primary bronchus that
enters the right lung and a left primary bronchus that
enters the left lung
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Bronchi (2 of 3)
Upon entering the lungs,
the primary bronchi further
divide to form smaller and
smaller diameter branches
❑ The terminal
bronchioles are the
end of the conducting
zone
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Bronchi (3 of 3)
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Lungs (1 of 2)
The lungs are paired organs in the thoracic cavity
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Lungs (2 of 2)
The lungs are enclosed and protected by the pleural
membrane
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Lobes and Fissures of the Lungs (1 of 2)
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Lobes and Fissures of the Lungs (2 of 2)
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Alveoli
• When the conducting
zone ends at the terminal
bronchioles, the
respiratory zone begins
• The respiratory zone
terminates at the alveoli,
the “air sacs” found
within the lungs
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Alveoli in a Lobule of a Lung
Alveoli are sac-like structures
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Alveolus
There are 2 kinds of alveolar cells, Type I and Type II
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Respiratory Membrane
The respiratory membrane is composed of:
1. A layer of type I and type II alveolar cells and
associated alveolar macrophages that constitutes
the alveolar wall
2. An epithelial basement membrane underlying the
alveolar wall
3. A capillary basement membrane that is often
fused to the epithelial basement membrane
4. The capillary endothelium
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Blood Supply to the Lungs
• Blood enters the lungs via the pulmonary arteries
(pulmonary circulation) and the bronchial arteries
(systemic circulation)
• Blood exits the lungs via the pulmonary veins and the
bronchial veins
• Ventilation-perfusion coupling
❑ Vasoconstriction in response to hypoxia diverts blood
from poorly ventilated areas to well ventilated areas
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Summary of Structures of the Respiratory
System (1 of 6)
Conducting Structures
Nose
Structure
Vestibule
Respiratory
region
Olfactory
region
Epithelium
Cilia
Nonkeratinized
No.
stratified squamous.
Pseudostratified
Yes.
ciliated columnar.
Olfactory epithelium Yes.
(olfactory receptors).
Goblet Cells
Special Features
No.
Contains
numerous hairs.
Contains conchae
and meatuses.
Functions in
olfaction.
Yes.
No.
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Summary of Structures of the Respiratory
System (2 of 6)
Conducting Structures
Pharynx
Structure
Epithelium
Cilia
Goblet Cells
Special Features
Passageway for air; contains
internal nares, openings for
auditory tubes, and
pharyngeal tonsil.
Passageway for both air and
food and drink; contains
opening from mouth
(fauces).
Passageway for both air and
food and drink.
Nasopharynx
Pseudostratified ciliated Yes.
columnar.
Yes.
Oropharynx
Nonkeratinized
stratified squamous.
No.
No.
Nonkeratinized
stratified squamous.
No.
No.
Laryngopharynx
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Summary of Structures of the Respiratory
System (3 of 6)
Conducting Structures
Structure
Epithelium
Cilia
Larynx
Nonkeratinized stratified
squamous above the vocal
folds; pseudostratified ciliated
columnar below the vocal
folds.
Pseudostratified ciliated
columnar.
No above No above folds;
folds; yes yes below folds.
below folds.
Passageway for air;
contains vocal folds for
voice production.
Yes.
Passageway for air;
contains C-shaped rings
of cartilage to keep
trachea open.
Trachea
Goblet Cells
Yes.
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Special Features
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Summary of Structures of the Respiratory
System (4 of 6)
Conducting Structures
Goblet
Cells
Yes.
Structure
Epithelium
Cilia
Main bronchi
Pseudostratified ciliated
columnar.
Yes.
Lobar bronchi
Pseudostratified ciliated Yes.
columnar.
Pseudostratified ciliated Yes.
columnar.
Ciliated simple columnar. Yes.
Yes.
Ciliated simple columnar. Yes.
No.
Segmental
bronchi
Larger
bronchioles
Smaller
bronchioles
Yes.
Yes.
Special Features
Passageway for air; contain C-shaped
rings of cartilage to maintain
patency.
Passageway for air; contain plates of
cartilage to maintain patency.
Passageway for air; contain plates of
cartilage to maintain patency.
Passageway for air; contain more
smooth muscle than in the bronchi.
Passageway for air; contain more
smooth muscle than in the larger
bronchioles.
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Summary of Structures of the
Respiratory System (5 of 6)
Conducting Structures
Structure
Epithelium
Cilia
Terminal
bronchioles
Nonciliated simple No.
columnar.
Goblet Cells
Special Features
No.
Passageway for air; contain more
smooth muscle than in the
smaller bronchioles.
Gas Exchange Structures Lungs
Structure
Respiratory
bronchioles
Alveolar ducts
Epithelium
Cilia
Simple cuboidal to No.
simple squamous.
Simple squamous. No.
Goblet Cells
No.
No.
Special Features
Passageway for air; gas
exchange.
Passageway for air; gas
exchange; produce surfactant.
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Summary of Structures of the Respiratory
System (6 of 6)
Gas Exchange Structures
Structure
Epithelium
Cilia
Goblet Cells
Special Features
Alveoli
Simple squamous.
No.
No.
Passageway for air; gas exchange;
produce surfactant to maintain
patency.
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The 3 Basic Steps Involved in Respiration
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Pulmonary Ventilation
In pulmonary ventilation, air flows between the
atmosphere and the alveoli of the lungs because of
alternating pressure differences created by contraction
and relaxation of respiratory muscles
❑ Inhalation
❑ Exhalation
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Mechanics of Ventilation – Gas Laws
✓Boyle’s law: Pressure varies inversely with volume
P1·V1 = P2·V2 (at a given T °K)
✓Charles’ law: Volume varies directly with temperature
V1/T1 = V2/T2 (at a given P)
✓Dalton’s law partial pressures: all pressures added up
equals to the total pressure
P = P1 + P2 + P3 +…… + Pn
✓Henry’s law: for gases dissolving in liquids
Concentration ∝ Solubilty & Partial pressure
✓Law of Laplace: Surface tension & alveolar radius:
P = 2T/r
Boyle’s Law
Pressure changes that drive inhalation and exhalation are
governed, in part, by Boyle’s Law
❑ The volume of a gas varies inversely with its pressure
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Muscles of Inhalation and Exhalation
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Position of the Diaphragm During
Inhalation and Exhalation
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Pressure Changes in Pulmonary
Ventilation
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Pressure and Flow
• Atmospheric pressure drives respiration
• 1 atmosphere (atm) = 760 mmHg
• Intra-pulmonary pressure and lung volume
• pressure is inversely proportional to volume
• for a given amount of gas, as volume ↑, pressure ↓ and as volume
↓, pressure ↑
• Pressure gradients
• difference between atmospheric and intrapulmonary
pressure
• created by changes in volume of thoracic cavity
Other Factors Affecting Pulmonary Ventilation
Surface tension
❑ Inwardly directed force in the alveoli which must be
overcome to expand the lungs during each inspiration
Elastic recoil
❑ Decreases the size of the alveoli during expiration
Compliance
❑ Ease with which the lungs and thoracic wall can be
expanded
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Breathing Patterns and Respiratory
Movements
•
•
•
•
•
Eupnea – normal breathing
Apnea – cessation of breathing
Dyspnea – shortness of breath
Tachypnea – increased breathing rate
Costal breathing – shallow breathing, intercostal muscles
used
• Diaphragmatic breathing – ‘belly’ breathing, diaphragm
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Modified Breathing Movements (1 of 3)
Movement
Description
Coughing
A long-drawn and deep inhalation followed by a complete closure of the
rima glottidis , which results in a strong exhalation that suddenly pushes
the rima glottides open and sends a blast of air through the upper
respiratory passages. Stimulus for this reflex act may be a foreign body
lodged in the larynx, trachea, or epiglottis.
Sneezing
Spasmodic contraction of muscles of exhalation that forcefully expels air
through the nose and mouth: Stimulus may be an irritation of the nasal
mucosa.
Sighing
A long-drawn and deep inhalation immediately followed by a shorter but
forceful exhalation.
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Modified Breathing Movements (2 of 3)
Movement
Description
Yawning
A deep inhalation through the widely opened mouth producing an
exaggerated depression of the mandible. It may be stimulated by
drowsiness, or someone else's yawning, but the precise cause is unknown.
Sobbing
A series of convulsive inhalations followed by a single prolonged
exhalation. The rima glottidis closes earlier than normal after each
inhalation so only a little air enters the lungs with each inhalation.
Crying
Laughing
An inhalation followed by many short convulsive exhalations, during which
the rima glottidis remains open and the vocal folds vibrate; accompanied
by characteristic facial expressions and tears.
The same basic movements as crying, but the rhythm of the movements
and the facial expressions usually differ from those of crying. Laughing and
crying are sometimes indistinguishable
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Modified Breathing Movements (3 of 3)
Movement
Description
Hiccupping
Spasmodic contraction of the diaphragrm followed by a spasmodic closure
of the rima glottidis ,which produces a sharp sound on inhalation. Stimulus
is usually irritation of the sensory nerve endings of the gastrointestinal
tract.
Forced exhalation against a closed rima glottidis as may occur during
periods of straining while defecating.
Valsalva (valSAL-va)
maneuver
Pressurizing
The nose and mouth are held closed and air from the lungs is forced
the middle ear through the auditory tube into the middle ear. Employed by those
snorkeling or scuba diving during descent to equalize the pressure of the
ear with that of the external environment.
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Lung Volumes and Capacities (1 of 2)
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Respiratory Capacities
• Vital capacity
• amount of air that an be exhaled with maximum effort after
maximum inspiration; assess strength of thoracic muscles
and pulmonary function
• Inspiratory capacity
• maximum amount of air that can be inhaled after a normal
tidal expiration
• Functional residual capacity
• amount of air in lungs after a normal tidal expiration
• Total lung capacity
• maximum amount of air lungs can contain
Respiratory Volumes and Capacities
• Age: lungs less compliant, respiratory muscles weaken
• Exercise: maintains strength of respiratory muscles
• Body size: proportional, big body has large lungs
• Restrictive disorders: ↓compliance and vital capacity
• Obstructive disorders: interfere with airflow, expiration
more effort or less complete
• Forced expiratory volume: % of vital capacity exhaled/
time; healthy adult - 75 to 85% in 1 sec
• Minute respiratory volume: TV x respiratory rate,
at rest 500 x 12 = 6 L/min; maximum: 125 to 170 L/min
Lung Volumes and Capacities (2 of 2)
Anatomy Overview:
Respiratory Volumes and Capacities
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External and Internal Respiration
• During external respiration, oxygen will diffuse from the
alveoli into the pulmonary capillaries
❑ CO2 moves in the opposite direction
• During internal respiration, oxygen will diffuse from the
systemic capillaries into the tissue
❑ CO2 moves in the opposite direction
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Exchange of Oxygen and Carbon Dioxide
Dalton’s law
❑ Each gas in a mixture of gases exerts its own pressure
as if no other gases were present
Henry’s law
❑ The quantity of a gas that will dissolve in a liquid is
proportional to the partial pressure of the gas and its
solubility coefficient when the temperature remains
constant
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Composition of Air
• Mixture of gases, each contributes its partial pressure,
(at sea level 1 atm. of pressure = 760 mmHg)
• nitrogen constitutes 78.6% of the atmosphere,
PN = 78.6% x 760 mmHg = 597 mmHg
2
• PO2 = 159, PH2O = 3.7, PCO2 = 0.3 mmHg (597 + 159 + 3.7 + 0.3 = 760)
• Partial pressures determine rate of diffusion of gas and
gas exchange between blood and alveolus
• Alveolar air
• humidified, exchanges gases with blood, mixes with residual
air
• contains: PN = 569, PO = 104, PH O = 47, PCO = 40 mmHg
2
2
2
2
Air-Water Interface (Gas Exchange)
• Gases diffuse down their concentration gradients
• Henry’s law: amount of gas that dissolves in water is
determined by its solubility in water and its partial
pressure in air
Alveolar Gas Exchange
• Time required for gases to equilibrate = 0.25 sec
• RBC transit time at rest = 0.75 sec to pass through
alveolar capillary
• RBC transit time with vigorous exercise = 0.3 sec
Factors Affecting Gas Exchange
• Concentration gradients of gases
• PO2 = 104 in alveolar air versus 40 in blood
• PCO = 46 in blood arriving at the lungs vs. 40 in alveolar air
2
• Gas solubility
• CO2 is 20 times as soluble as O2
• equal amounts of CO2 and O2 are exchanged, O2 has ↑ concentration
gradient, CO2 has ↑ solubility
• Membrane thickness - only 0.5 µm thick
• Membrane surface area - 100 ml blood in alveolar capillaries,
spread over 70 m2 (size of tennis court)
• Ventilation-perfusion coupling - areas of good ventilation
need good perfusion (vasodilation)
Concentration Gradients of Gases
Gas Exchange (1 of 2)
Interactions Animation:
Gas Exchange
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Gas Exchange (2 of 2)
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Transport of O2 and CO2 in the Blood
Oxygen:
❑ 1.5% of the O2 is dissolved in the plasma
❑
98.5% of the O2 is carried by hemoglobin (Hb)
Carbon dioxide:
❑ 7% of the CO2 is dissolved in the plasma
23% of the CO2 is carried by Hb inside red blood cells as
carbaminohemoglobin
❑ 70% of the CO2 is transported as bicarbonate ions (HCO3)
❑
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Transport of Oxygen and Carbon Dioxide (1 of 2)
Interactions Animation:
Gas Transport
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Transport of Oxygen and Carbon
Dioxide (2 of 2)
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Ambient Pressure Affects Concentration Gradients
Factors Affecting the Affinity of Hb for
O2 (1 of 5)
• PO2
•
•
•
•
pH
Temperature
BPG (2,3-bisphosphoglycerate)
Type of Hb
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Factors Affecting the Affinity of Hb for O2
(2 of 5)
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Factors Affecting the Affinity of Hb for O2
(3 of 5)
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Factors Affecting the Affinity of Hb for O2
(4 of 5)
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Factors Affecting the Affinity of Hb for O2
(5 of 5)
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Lung Disease Affects Gas Exchange
↑ membrane thickness
↓ surface area
Perfusion Adjusts to Changes in Ventilation
Ventilation Adjusts to Changes in Perfusion
Summary of Chemical Reactions During
Gas Exchange
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Adjustment to Metabolic Needs of Tissues
• Factors affecting CO2 loading
• Haldane effect: low level of HbO2 (as in active tissue)
enables blood to transport more CO2
• HbO2 does not bind CO2 as well as reduced
hemoglobin (HHb)
• HHb binds more H+ than HbO2, shifts the
CO2 + H2O → HCO3- + H+ reaction to the right
Effect of CO2 on O2 dissociation – Haldane Effect
Control of Respiration (1 of 8)
Locations of areas of the respiratory center
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Control of Respiration (2 of 8)
Interactions Animation:
Locations
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Control of Respiration (3 of 8)
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Control of Respiration (4 of 8)
Cortical influences
❑ Allow conscious control of respiration that may be
needed to avoid inhaling noxious gases or water
Chemoreceptor
❑ Central and peripheral chemoreceptors monitor
levels of O2 and CO2 and provide input to the
respiratory center
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Control of Respiration (5 of 8)
Interactions Animation:
Regulation of Ventilation
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Control of Respiration (6 of 8)
Anatomy Overview:
Structures That Control Respiration
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Control of Respiration (7 of 8)
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Control of Respiration (8 of 8)
Hypercapnia
+
❑ A slight increase in PCO (and thus H )
2
❑
Stimulates central chemoreceptors
Hypoxia
❑ Oxygen deficiency at the tissue level
❑ Caused by a low PO2 in arterial blood due to high altitude,
airway obstruction or fluid in the lungs
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Regulation of Blood pH (1 of 2)
Interactions Animation:
Role of the Respiratory System in pH Regulation
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Regulation of Blood pH (2 of 2)
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Effects of Hydrogen Ions
• pH of CSF (most powerful respiratory stimulus)
• Respiratory acidosis (pH < 7.35) caused by failure of
pulmonary ventilation
• hypercapnia (PCO2) > 43 mmHg
• CO2 easily crosses blood-brain barrier, in CSF the CO2 reacts
with water and releases H+, central chemoreceptors
strongly stimulate inspiratory center
• corrected by hyperventilation, pushes reaction to the left by
“blowing off ” CO2
CO2 (expired) + H2O ← H2CO3 ← HCO3- + H+
Effects of Hydrogen Ions
• Respiratory alkalosis (pH > 7.35)
• hypocapnia (PCO2) < 37 mmHg
• corrected by hypoventilation, pushes reaction to the right
CO2 + H2O → H2CO3 → HCO3- + H+
• ↑ H+, lowers pH to normal
• pH imbalances can have metabolic causes
• diabetes mellitus: fat oxidation causes ketoacidosis, can be
compensated for by Kussmaul respiration, (deep rapid
breathing)
Carbon Dioxide & Oxygen
• (CO2) Indirect effects
• through pH as seen previously
• Direct effects
• ↑ CO2 may directly stimulate peripheral and trigger ↑
ventilation more quickly than central chemoreceptors
• (O2) Usually little effect
• Chronic hypoxemia, PO < 60 mmHg, can significantly stimulate
ventilation
– emphysema, pneumonia
– high altitudes after several days
Summary of Stimuli that Affect
Breathing Rate and Depth (1 of 2)
Stimuli that Increase Breathing Rate and
Depth
Stimuli that Decrease Breathing Rate and
Depth
Voluntary hyperventilation controlled by
cerebral cortex and anticipation of activity
by stimulation of limbic system.
Voluntary hypoventilation controlled by
cerebral cortex
Increase in arterial blood Pco2 above 40
mmHg (causes an increase in H+)
detected by peripheral and central
chemoreceptors.
Decrease in arterial blood Pco2 below 40
mmHg (causes a decrease
in H+) detected by peripheral and central
chemoreceptors.
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Summary of Stimuli that Affect
Breathing Rate and Depth (2 of 2)
Stimuli that Increase Breathing Rate
and Depth
Stimuli that Decrease Breathing Rate and Depth
Decrease in arterial blood PO2 from 105 Decrease in arterial blood PO2 below 50 mmHg.
mmHg to 50 mmHg.
Increased activity of proprioceptors.
Decreased activity of proprioceptors.
Increase in body temperature
Decrease in body temperature (decreases
respiration rate), sudden cold stimulus (causes
apnea).
Prolonged pain.
Severe pain (causes apnea)
Decrease in blood pressure
Increase in blood pressure.
Stretching of anal sphincter.
Irritation of pharynx or larynx by touch or
chemicals (causes brief apnea followed by
coughing or sneezing).
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Exercise and the Respiratory System
The respiratory and cardiovascular systems make
adjustments in response to both the intensity and
duration of exercise
❑ As cardiac output rises, the blood flow to the lungs,
termed pulmonary perfusion, increases as well
❑ The O2 diffusing capacity may increase threefold
during maximal exercise so there is a greater surface
area available for O2 diffusion
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Development of the Respiratory System
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Aging and the Respiratory System
Aging results in decreased:
❑ Vital capacity
❑ Blood O2 level
❑
❑
Alveolar macrophage activity
Ciliary action of respiratory epithelia
Consequently, elderly people are more susceptible to
pneumonia, bronchitis, emphysema, and other issues
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The Respiratory System and Homeostasis
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Disorders: Homeostatic Imbalances
• Asthma
• Chronic obstructive
pulmonary disease
• Lung cancer
• Pneumonia
• Tuberculosis
• Common cold
• Pulmonary edema
• Cystic fibrosis
• Asbestos-related
diseases
• Sudden infant death
syndrome
• Acute respiratory
distress
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