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Transcript
The Respiratory System
Chapter 23
(6th edition chapter 22)
Functions of the Respiratory
System
1. Supply oxygen to the circulatory system for delivery to the tissues
2. Remove CO2 (and some other wastes) from blood.
There are 4 processes that we call “respiration”.
1. Pulmonary ventilation - Movement of air into and out of the lungs
(also referred to as “breathing”).
2. External respiration - Gas exchange in the lungs between the blood
of the capillaries and the spaces in the air sacs (alveoli)
3. Transport - The movement of gases by the circulatory system
Strictly speaking, a function of the blood.
4. Internal respiration - Gas exchange between the blood and the
tissues of the body
Overview of respiratory system anatomy
External
Structures
of the nose
Internal anatomy of the upper respiratory tract
The larynx and associated structures
The Glottis
Figure 23–5
Respiratory epithelium
Anatomy of the Trachea
Figure 23–6
Cross section of the trachea and esophagus
Gross
Anatomy of
the Lungs
Figure 23–7
Bronchi and
Lobules
Figure 23–9
Secondary Bronchi
• Branch to form tertiary bronchi, also called
the segmental bronchi
• Each segmental bronchus:
– supplies air to a single bronchopulmonary
segment
Bronchopulmonary Segments
• The right lung has 10
• The left lung has 8 or 9
Bronchial Structure
• The walls of primary, secondary, and
tertiary bronchi:
– contain progressively less cartilage and more
smooth muscle
– increasing muscular effects on airway
constriction and resistance
The Bronchioles
Figure 23–10
The Bronchioles
• Each tertiary bronchus branches into
multiple bronchioles
• Bronchioles branch into terminal
bronchioles:
– 1 tertiary bronchus forms about 6500 terminal
bronchioles
Bronchiole Structure
• Bronchioles:
– have no cartilage
– are dominated by smooth muscle
Asthma
• Excessive stimulation and
bronchoconstriction
• Stimulation severely restricts airflow
Alveolar
Organization
Figure 23–11
Alveolar Epithelium
• Consists of simple squamous epithelium
• Consists of thin, delicate Type I cells
• Patrolled by alveolar macrophages, also
called dust cells
• Contains septal cells (Type II cells) that
produce surfactant
Surfactant
• Is an oily secretion
• Contains phospholipids and proteins
• Coats alveolar surfaces and reduces surface
tension
Respiratory Distress
• Difficult respiration:
– due to alveolar collapse
– caused when septal cells do not produce enough
surfactant
Respiratory Membrane
• The thin membrane of alveoli where gas
exchange takes place
3 Parts of the
Respiratory Membrane
1. Squamous epithelial lining of alveolus
2. Endothelial cells lining an adjacent
capillary
3. Fused basal laminae between alveolar and
endothelial cells
Alveoli and the respiratory membrane
Structure of an alveolar sac
Pleural Cavities and
Pleural Membranes
• 2 pleural cavities:
– are separated by the mediastinum
• Each pleural cavity:
– holds a lung
– is lined with a serous membrane (the pleura)
Pleural Cavities and
Pleural Membranes
Figure 23–8
The Pleura
• Consists of 2 layers:
– parietal pleura
– visceral pleura
• Pleural fluid:
– lubricates space between 2 layers
Respiratory Physiology
Boyle’s law: P = 1/V or
P1V1 = P2V2
Pressure relationships
The negative intrapleural pressure keeps the lungs inflated
Mechanisms
of
Pulmonary
Ventilation
Figure 23–14
Mechanics of Breathing:
Inspiration
Mechanics of Breathing:
Expiration
Compliance of the Lung
• An indicator of expandability
• Low compliance requires greater force
• High compliance requires less force
Factors That Affect Compliance
1. Connective-tissue structure of the lungs
2. Level of surfactant production
3. Mobility of the thoracic cage
Gas Pressure
• Can be measured inside or outside the lungs
• Normal atmospheric pressure:
– 1 atm or Patm at sea level: 760 mm Hg
Pressure and Volume Changes with Inhalation
and Exhalation
Intrapulmonary Pressure
• Also called intra-alveolar pressure
• Is relative to Patm
• In relaxed breathing, the difference between
Patm and intrapulmonary pressure is small:
– about —1 mm Hg on inhalation or +1 mm Hg
on expiration
Maximum
Intrapulmonary Pressure
• Maximum straining, a dangerous activity,
can increase range:
– from —30 mm Hg to +100 mm Hg
Intrapleural Pressure
• Pressure in space between parietal and
visceral pleura
• Averages —4 mm Hg
• Maximum of —18 mm Hg
• Remains below Patm throughout respiratory
cycle
Injury to the Chest Wall
• Pneumothorax:
– allows air into pleural cavity
• Atelectasis:
– also called a collapsed lung
– result of pneumothorax
Respiratory Physiology
Resistance:
F = P/R
R = resistance
P = change in pressure (the pressure gradient)
Respiratory Volumes
and Capacities
Figure 23–17
Gas Exchange
• Depends on:
– partial pressures of the gases
– diffusion of molecules between gas and liquid
The Gas Laws
• Diffusion occurs in response to
concentration gradients
• Rate of diffusion depends on physical
principles, or gas laws
– e.g., Boyle’s law
Composition of Air
•
•
•
•
Nitrogen (N2) about 78.6%
Oxygen (O2) about 20.9%
Water vapor (H2O) about 0.5%
Carbon dioxide (CO2) about 0.04%
Gas Pressure
• Atmospheric pressure (760 mm Hg):
– produced by air molecules bumping into each
other
• Each gas contributes to the total pressure:
– in proportion to its number of molecules
(Dalton’s law)
Partial Pressure
• The pressure contributed by each gas in the
atmosphere
• All partial pressures together add up to 760
mm Hg
Respiratory Physiology:
Dalton’s Law of Partial Pressures
The total pressure of a mixture of gases is the sum of the partial
pressures exerted independently by each gas in the mixture.
Location
Atmosphere at
sea level
Gas
Approximate %
Partial
pressure in
mmHg
Approximate %
Partial
pressure in
mmHg
N2
78.6
597
74.9
569
O2
20.9
159
13.7
104
CO2
0.04
0.3
5.2
40
H2O
0.46
3.7
6.2
47
Total
100.0
760
100.0
760
Alveoli of lungs
Partial
pressure
relationships:
Movement of
gases between
the lungs and
the tissues
Henry’s Law
• When gas under pressure comes in contact
with liquid:
– gas dissolves in liquid until equilibrium is
reached
• At a given temperature:
– amount of a gas in solution is proportional to
partial pressure of that gas
Henry’s Law
Figure 23–18
Diffusion and the
Respiratory Membrane
• Direction and rate of diffusion of gases
across the respiratory membrane determine
different partial pressures and solubilities
Efficiency of Gas
Exchange
• Due to:
– substantial differences in partial pressure across
the respiratory membrane
– distances involved in gas exchange are small
Efficiency of Gas
Exchange (2 of 2)
– O2 and CO2 are lipid soluble
– total surface area is large
– blood flow and air flow are coordinated
Solubility:
Differential solubility of gases contributes to the
balance of gas exchange
Most soluble
Least soluble
CO2 >>>>>>>>>>>>>>>>> O2 >>>>>>>>>>>>>>>>>>> N2
CO2 is 20 times more soluble than O2
N2 is about half as soluble as O2
Ventilation-Perfusion Coupling
Breathing and blood flow are matched to the partial
pressure of alveolar gases
The Oxyhemoglobin
Saturation Curve
• Is standardized for normal blood (pH 7.4,
37°C)
• When pH drops or temperature rises:
– more oxygen is released
– curve shift to right
• When pH rises or temperature drops:
– less oxygen is released
– curve shifts to left
Oxygen - about 98.5% is bound to
hemoglobin (Hb) and 1.5% in solution.
Respiratory Gas Transport
pH, Temperature, and Hemoglobin
Saturation
Factors influencing Hb saturation: Temperature
Factors influencing Hb saturation: Pco2 and pH
The Bohr Effect (1 of 2)
• Is the effect of pH on hemoglobin saturation
curve
• Caused by CO2:
– CO2 diffuses into RBC
– an enzyme, called carbonic anhydrase,
catalyzes reaction with H2O
– produces carbonic acid (H2CO3)
The Bohr Effect
• Carbonic acid (H2CO3):
– dissociates into hydrogen ion (H+) and
bicarbonate ion (HCO3—)
• Hydrogen ions diffuse out of RBC,
lowering pH
2,3-biphosphoglycerate (BPG)
• RBCs generate ATP by glycolysis:
– forming lactic acid and BPG
• BPG directly affects O2 binding and release:
– more BPG, more oxygen released
BPG Levels
• BPG levels rise:
– when pH increases
– when stimulated by certain hormones
• If BPG levels are too low:
– hemoglobin will not release oxygen
Fetal and Adult Hemoglobin
Figure 23–22
Fetal and Adult Hemoglobin
• The structure of fetal hemoglobin:
– differs from that of adult Hb
• At the same PO :
2
– fetal Hb binds more O2 than adult Hb
– which allows fetus to take O2 from maternal
blood
CO2 Transport
• 7 % dissolved in the plasma
• ~ 23% bound to the amine
groups of the Hb molecule as
carbaminohemoglobin
• ~ 70% as bicarbonate ion in
the plasma
CO2 Transport & Exchange:
at the tissues
CO2 Transport & Exchange:
in the lungs
The Haldane
Effect
Control of Respiration
• Gas diffusion at peripheral and alveolar
capillaries maintain balance by:
– changes in blood flow and oxygen
delivery
– changes in depth and rate of respiration
Quiet Breathing
• Brief activity in the DRG:
– stimulates inspiratory muscles
• DRG neurons become inactive:
– allowing passive exhalation
Quiet Breathing
Figure 23–25a
Forced Breathing
Figure 23–25b
The Apneustic and Pneumotaxic
Centers of the Pons
• Paired nuclei that adjust output of
respiratory rhythmicity centers:
– regulating respiratory rate and depth of
respiration
Respiratory
Centers
and Reflex
Controls
Figure 23–26
5 Sensory Modifiers of
Respiratory Center Activities
• Chemoreceptors are sensitive to:
– PCO , PO , or pH
2
2
– of blood or cerebrospinal fluid
• Baroreceptors in aortic or carotic sinuses:
– sensitive to changes in blood pressure
5 Sensory Modifiers of
Respiratory Center Activities
• Stretch receptors:
– respond to changes in lung volume
• Irritating physical or chemical stimuli:
– in nasal cavity, larynx, or bronchial tree
5 Sensory Modifiers of
Respiratory Center Activities
• Other sensations including:
– pain
– changes in body temperature
– abnormal visceral sensations
Chemoreceptor
Responses to PCO2
Hypercapnia
• An increase in arterial PCO
2
• Stimulates chemoreceptors in the medulla
oblongata:
– to restore homeostasis
Hypoventilation
• A common cause of hypercapnia
• Abnormally low respiration rate:
– allows CO2 build-up in blood
Hyperventilation
• Excessive ventilation
• Results in abnormally low PCO
2
(hypocapnia)
• Stimulates chemoreceptors to decrease
respiratory rate
Baroreceptor Reflexes
• Carotid and aortic baroreceptor stimulation:
– affects blood pressure and respiratory centers
• When blood pressure falls:
– respiration increases
• When blood pressure increases:
– respiration decreases
The Hering–Breuer Reflexes
• 2 baroreceptor reflexes involved in forced
breathing:
– inflation reflex:
• prevents overexpansion of lungs
– deflation reflex:
• inhibits expiratory centers
• stimulates inspiratory centers during lung deflation
Protective Reflexes
• Triggered by receptors in epithelium of
respiratory tract when lungs are exposed to:
– toxic vapors
– chemicals irritants
– mechanical stimulation
• Cause sneezing, coughing, and laryngeal
spasm
Pathology and clinical
considerations
Common homeostatic imbalances:
• COPD (chronic obstructive pulmonary disease)
• Asthma
• Tuberculosis
• Lung cancer
Respiratory Performance and Age
Figure 23–28
COPD:
Emphysema
Results: Loss of lung elasticity, hypoxia, lung fibrosis, cyanosis.
Common causes: Industrial exposure, cigarette smoking.
Tuberculosis
At the beginning of the
20th century a third of
all deaths in people 20 - 45
were from TB.
Antibiotic-resistant strains
of Mycobaterium tuberculosis
are a growing problem at the
beginning of the 21st century.
Lung Cancer
90% of lung cancer patients had one thing in
common…
…they smoked tobacco
Fin