Download 13.Respiratory

Chapter 13
The Respiratory System
Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning
Respiration
• General function is to obtain O2 for use by the
body’s cells and to eliminate the CO2 the body cells
produce
• Encompasses two separate but related processes
– Internal respiration
– External respiration
Chapter 13 The Respiratory System
Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning
Internal Respiration
• Cellular respiration
• Refers to metabolic processes carried out within the
mitochondria, which use O2 and produce CO2, while
deriving energy from nutrient molecules
• Respiratory quotient (RQ)
– Ratio of CO2 produced to O2 consumed
– Varies depending on foodstuff consumed
Chapter 13 The Respiratory System
Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning
External Respiration
• Refers to sequence of events involved in the exchange of O2
and CO2 between the external environment and the cells of
the body
• Four steps
– Ventilation – movement of air into and out of the lungs
– O2 and CO2 are exchanged between air in alveoli and
blood within the pulmonary capillaries by means of
diffusion
– Blood transports O2 and CO2 between lungs and tissues
– O2 and CO2 are exchanged between tissues and blood by
process of diffusion across systemic (tissue) capillaries
Chapter 13 The Respiratory System
Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning
External and Internal Respiration
Chapter 13 The Respiratory System
Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning
Nonrespiratory Functions of Respiratory
System
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•
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•
•
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Route for water loss and heat elimination
Enhances venous return
Helps maintain normal acid-base balance
Enables speech, singing, and other vocalizations
Defends against inhaled foreign matter
Removes, modifies, activates, or inactivates various
materials passing through the pulmonary circulation
• Nose serves as the organ of smell
Chapter 13 The Respiratory System
Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning
Respiratory System
• Consists of
– Respiratory airways leading into the lungs
– Lungs
– Structures of the thorax involved in producing
movement of air through the airways into and out
of the lungs
Chapter 13 The Respiratory System
Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning
Respiratory Airways
• Tubes that carry air between the atmosphere and
the air sacs
– Nasal passages (nose)
– Pharynx (common passageway for respiratory
and digestive systems)
– Trachea (windpipe)
– Larynx (voice box)
– Right and left bronchi
– Bronchioles
• Alveoli (air sacs) are clustered at ends of terminal
bronchioles
Chapter 13 The Respiratory System
Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning
Respiratory Airways
• Trachea and larger bronchi
– Fairly rigid, nonmuscular tubes
– Rings of cartilage prevent collapse
• Bronchioles
– No cartilage to hold them open
– Walls contain smooth muscle innervated by
autonomic nervous system
– Sensitive to certain hormones and local
chemicals
Chapter 13 The Respiratory System
Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning
Alveoli
• Thin-walled inflatable sacs
• Function in gas exchange
• Walls consist of a single layer
of flattened Type I alveolar
cells
• Pulmonary capillaries encircle
each alveolus
• Type II alveolar cells secrete
pulmonary surfactant
• Alveolar macrophages guard
lumen
• Pores of Kohn permit airflow
between adjacent alveoli
(collateral ventilation)
Chapter 13 The Respiratory System
Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning
Lungs
• Occupy much of thoracic cavity
– Heart, associated vessels, esophagus, thymus,
and some nerves also occupy space
• Two lungs
– Each is divided into several lobes
– Tissue consists of highly branched airways, the
alveoli, the pulmonary blood vessels, and large
quantities of elastic connective tissue
• Outer chest wall (thorax)
– Formed by 12 pairs of ribs which join sternum
anteriorly and thoracic vertebrae posteriorly
Chapter 13 The Respiratory System
Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning
Lungs
• Diaphragm
– Dome-shaped sheet of skeletal muscle
– Separates thoracic cavity from the abdominal
cavity
• Pleural sac
– Double-walled, closed sac that separates each
lung from the thoracic wall
– Pleural cavity – interior of plural sac
– Intrapleural fluid
• Secreted by surfaces of the pleura
• Lubricates pleural surfaces
Chapter 13 The Respiratory System
Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning
Pleural Sac
Chapter 13 The Respiratory System
Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning
Respiratory Mechanics
• Interrelationships among pressures inside and
outside the lungs are important in ventilation
• Three different pressure considerations important in
ventilation
– Atmospheric (barometric) pressure
– Intra-alveolar pressure (intrapulmonary pressure)
– Intrapleural pressure (intrathoracic pressure)
Chapter 13 The Respiratory System
Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning
Pressures Important in Ventilation
Chapter 13 The Respiratory System
Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning
Respiratory Mechanics
• Changes in intra-alveolar
pressure produce flow of air
into and out of the lungs
• If this pressure is less than
atmospheric pressure, air
enters the lungs. If the
opposite occurs, air exits
from the lungs.
• Boyle’s law states that at
any constant temperature,
the pressure exerted by a
gas varies inversely with the
volume of a gas.
Boyle’s Law
Chapter 13 The Respiratory System
Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning
Respiratory Mechanics
• Major inspiratory muscles
– Diaphragm
• Major inspiratory muscle
• Innervated by phrenic nerve
– External intercostal muscles
• Activated by intercostal nerves
• 75 % of the enlargement of the thoracic cavity during quiet
respiration is due to the contraction and flattening of the
diaphragm.
• This expansion decreases the intrapleural pressure (down to
754). The lungs are drawn into this area of lower pressure.
They expand. This increase in volume lowers the intraalveolar pressure to a level below atmospheric pressure. By
this difference, air enters the lungs.
• The action of accessory inspiratory muscles can further
enlarge the thoracic cavity.
Chapter 13 The Respiratory System
Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning
Anatomy of the Respiratory Muscles
Chapter 13 The Respiratory System
Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning
Respiratory Mechanics
• Onset of expiration begins with relaxation of inspiratory
muscles
– Relaxation of diaphragm and muscles of chest wall, plus
the elastic recoil of the alveoli, decrease the size of the
chest cavity
– Intrapleural pressure increases and lungs are compressed
– Intra-alveolar pressure increases. When pressure
increases to level above atmospheric pressure, air is
driven out – expiration occurs
– Forced expiration can occur by contraction of expiratory
muscles
• Abdominal wall muscles
• Internal intercostal muscles
Chapter 13 The Respiratory System
Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning
Respiratory Muscle Activity During Inspiration
Chapter 13 The Respiratory System
Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning
Respiratory Muscle Activity During Expiration
Chapter 13 The Respiratory System
Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning
Airway Resistance
• Primary determinant of resistance to airflow is the
radius of the conducting airway
• Autonomic nervous system controls contraction of
smooth muscle in walls of bronchioles (changes the
radii)
• Chronic obstructive pulmonary disease abnormally
increases airway resistance
– Expiration is more difficult than inspiration
– Diseases
• Chronic bronchitis
• Asthma
• Emphysema
Chapter 13 The Respiratory System
Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning
Compliance
• Lungs have elastic recoil – rebound if stretched
• Compliance
– Refers to how much effort is required to stretch or
distend the lungs
– The less compliant the lungs are, the more work
is required to produce a given degree of inflation
– Decreased by factors such as pulmonary fibrosis
Chapter 13 The Respiratory System
Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning
Elastic Recoil
• Refers to how readily the lungs rebound after having
been stretched
• Responsible for lungs returning to their
preinspiratory volume when inspiratory muscles
relax at end of inspiration
• Depends on two factors
– Highly elastic connective tissue in the lungs
– Alveolar surface tension
• Thin liquid film lines each alveolus
• Reduces tendency of alveoli to recoil
• Helps maintain lung stability
– Newborn respiratory distress syndrome
Chapter 13 The Respiratory System
Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning
Work of Breathing
• Normally requires 3% of total energy expenditure for
quiet breathing
• Lungs normally operate at about “half full”
• Work of breathing is increased in the following
situations
– When pulmonary compliance is decreased
– When airway resistance is increased
– When elastic recoil is decreased
– When there is a need for increased ventilation
Chapter 13 The Respiratory System
Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning
Lung Volumes and Capacities
• Can be measured by a spirometer
• Spirogram is a graph that records inspiration and
expiration
Chapter 13 The Respiratory System
Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning
Lung Volumes and Capacities
Description
Average
Value
Tidal volume (TV)
Volume of air entering or leaving lungs
during a single breath
500 ml
Inspiratory reserve
volume (IRV)
Extra volume of air that can be maximally
inspired over and above the typical resting
tidal volume
3000 ml
Inspiratory capacity
(IC)
Maximum volume of air that can be
inspired at the end of a normal quiet
expiration
(IC =IRV + IV)
3500 ml
Expiratory reserve
volume (ERV)
Extra volume of air that can be actively
expired by maximal contraction beyond the
normal volume of air after a resting tidal
volume
1000 ml
Residual volume
(RV)
Minimum volume of air remaining in the
lungs even after a maximal expiration
1200 ml
Chapter 13 The Respiratory System
Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning
Lung Volumes and Capacities
Description
Average Value
Functional residual
capacity (FRC)
Volume of air in lungs at end of
normal passive expiration
(FRC = ERV + RV)
2200 ml
Vital capacity (VC)
Maximum volume of air that can
be moved out during a single
breath following a maximal
inspiration (VC = IRV + TV + ERV)
4500 ml
Total lung capacity (TLC) Maximum volume of air that the
lungs can hold (TLC = VC + RV)
Forced expiratory
volume in one second
(FEV1)
Volume of air that can be expired
during the first second of
expiration in a VC determination
Chapter 13 The Respiratory System
Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning
5700 ml
Variations in Lung Volume
Chapter 13 The Respiratory System
Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning
Respiratory Dysfunction
• Two general categories of dysfunction that yield
abnormal results during spirometry
– Destructive lung disease
– Restrictive lung disease
• Additional conditions affecting respiratory function
– Diseases affecting diffusion of O2 and CO2 across
pulmonary membranes
– Reduced ventilation due to mechanical failure
– Failure of adequate pulmonary blood flow
– Ventilation/perfusion abnormalities involving a
poor matching of air and blood so that efficient
gas exchange does not occur
Chapter 13 The Respiratory System
Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning
Abnormal Spirograms Associated with Obstructive and
Restrictive Lung Diseases
Chapter 13 The Respiratory System
Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning
Pulmonary Ventilation
• Minute ventilation
• Volume of air breathed in and out in one minute
Pulmonary ventilation = tidal volume x respiratory rate
(ml/min)
(ml/breath)
(breaths/min)
Chapter 13 The Respiratory System
Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning
Alveolar Ventilation
• More important than pulmonary ventilation
• Volume of air exchanged between the atmosphere
and the alveoli per minute
• Less than pulmonary ventilation due to anatomic
dead space
– Volume of air in conducting airways that is
useless for exchange
– Averages about 150 ml in adults
Alveolar ventilation = (tidal volume – dead space) x
respiratory rate
Chapter 13 The Respiratory System
Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning
Effect of Different Breathing Patterns on
Alveolar Ventilation
Chapter 13 The Respiratory System
Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning
Alveolar Ventilation
• Alveolar dead space
– Quite small and of little importance in healthy
people
– Can increase even to lethal levels in several
types of pulmonary disease
• Local controls act on smooth muscle of airways and
arterioles to match airflow to blood flow
– Accumulation of carbon dioxide in alveoli
decreases airway resistance leading to increased
airflow
– Increase in alveolar oxygen concentration brings
about pulmonary vasodilation which increases
blood flow to match larger airflow
Chapter 13 The Respiratory System
Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning
Gas Exchange
• At both pulmonary capillary and tissue capillary
levels, gas exchange involves simple diffusion of O2
and CO2 down partial pressure gradients
• Partial pressure exerted
by each gas in a mixture
equals the total pressure
times the fractional
composition of this gas
in the mixture
Chapter 13 The Respiratory System
Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning
Oxygen and Carbon Dioxide Exchange Across Pulmonary and
Systemic Capillaries Caused by Partial Pressure Gradients
Chapter 13 The Respiratory System
Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning
Gas Exchange
• Additional factors that affect the rate of gas transfer
– As surface area increases, the rate increases
– Increase in thickness of barrier separating air and
blood decreases rate of gas transfer
– Rate of gas exchange is directly proportional to
the diffusion coefficient for a gas
Chapter 13 The Respiratory System
Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning
Gas Exchange
• Exchange across systemic capillaries also occurs down
partial pressure gradients
• By equilibration in the alveoli, the oxygen in the systemic
capillaries has a high partial pressure (e.g., 100) compared to
tissue cells (e.g., 40). These cells are using oxygen.
• The partial pressure for carbon dioxide in the systemic
capillaries is low (e.g., 40) compared to the tissue cells (e.g.,
46), which are making this gas through their metabolism.
• By partial pressure gradients, oxygen diffuses from the
systemic capillaries into the tissue cells (100 to 40, higher to
lower). Carbon dioxide diffuses in the opposite direction.
• Having equilibrated with the tissue cells, the blood leaving the
systemic capillaries is low in oxygen and high in carbon
dioxide.
• This blood returns to the right side of the heart and on to the
lungs. At the pulmonary capillaries, the blood acquires
oxygen and releases some of its carbon dioxide.
Chapter 13 The Respiratory System
Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning
Gas Transport
• Most oxygen in the blood is transported bound to
hemoglobin.
Hb + O2 ↔ HbO2
(reduced hemoglobin or
(oxyhemoglobin)
deoxyhemoglobin)
Chapter 13 The Respiratory System
Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning
Gas Transport
• Hemoglobin combines with oxygen to form
oxyhemoglobin. This is a reversible process,
favored to form oxyhemoglobin in the lungs.
• Hemoglobin tends to combine with oxygen as
oxygen diffuses from the alveoli into the pulmonary
capillaries.
• A small percentage of oxygen is dissolved in the
plasma.
• The dissociation of oxyhemoglobin into hemoglobin
and free molecules of oxygen occurs at the tissue
cells. The reaction is favored in this direction as
oxygen leaves the systemic capillaries and enters
tissue cells.
Chapter 13 The Respiratory System
Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning
Gas Transport
Partial pressure of oxygen is main factor determining the percent
of hemoglobin saturation
• The percent saturation is high where the partial pressure of
oxygen is high (lungs).
• The percent saturation is low where the partial pressure of
oxygen is low (tissue cells). At the tissue cells oxygen tends
to dissociate from hemoglobin, the opposite of saturation.
• This relationship is shown in the oxygen-hemoglobin
dissociation curve.
• The plateau part of the curve is where the partial pressure of
oxygen is high (lungs).
• The steep part of the curve exists at the systemic capillaries,
where hemoglobin unloads oxygen to the tissue cells.
Chapter 13 The Respiratory System
Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning
Oxygen Hemoglobin Dissociation Curve
Chapter 13 The Respiratory System
Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning
Gas Transport
Hemoglobin promotes the net transfer of oxygen at both the alveolar and tissue levels.
• There is a net diffusion of oxygen from the alveoli to the blood. This
occurs continuously until hemoglobin is as saturated as possible
(97.5% at 100 mm of Hg).
• At the tissue cells hemoglobin rapidly delivers oxygen into the blood
plasma and on to the tissue cells. Various factors promote this
unloading.
• An increase in carbon dioxide from the tissue cells into the systemic
capillaries increased hemoglobin dissociation from oxygen (shifts
the dissociation curve to the right).
• Increased acidity has the same effect.
• This shift of the curve to the right (more dissociation) is called the
Bohr effect.
• Higher temperatures also produces this shift, as does the production
of BPG.
• Hemoglobin has more affinity for carbon monoxide compared to
oxygen.
Chapter 13 The Respiratory System
Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning
Gas Transport
Most carbon dioxide (about 60%) is transported as the bicarbonate ion.
• Carbon dioxide combines with water to form carbonic acid. The
enzyme carbonic anhydrase facilitates this in the erythrocyte.
Carbonic acid dissociates into hydrogen ions and the bicarbonate
ion.
• This two-step, reversible process is favored at the tissue cells. The
reverse of this process (bicarbonate ions forming free molecules of
carbon dioxide) occurs in the lungs.
• 30% of the carbon dioxide is bound to hemoglobin in the blood. This
is another means of transport.
• About 10% of the transported carbon dioxide is dissolved in the
plasma.
• By the chloride shift, the plasma membrane of the erythrocyte
passively facilitates the diffusion of bicarbonate ions (out of the red
cell) and chloride ions.
• By the Haldane effect the removal of oxygen from hemoglobin at the
tissue cells increases the ability of hemoglobin to bind with carbon
dioxide.
Chapter 13 The Respiratory System
Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning
Abnormalities in Arterial PO2
Hypoxia
• Condition of having insufficient O2 at the cell level
• Categories
– Hypoxic hypoxia
– Anemic hypoxia
– Circulatory hypoxia
– Histotoxic hypoxia
Hyperoxia
• condition of having an above-normal arterial PO2
• Can only occur when breathing supplemental O2
• Can be dangerous
Chapter 13 The Respiratory System
Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning
Abnormalities in Arterial PCO2
• Hypercapnia
– Condition of having excess CO2 in arterial blood
– Caused by hypoventilation
• Hypocapnia
– Below-normal arterial PCO2 levels
– Brought about by hyperventilation which can be
triggered by
• Anxiety states
• Fever
• Aspirin poisoning
Chapter 13 The Respiratory System
Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning
Control of Respiration
• Respiratory centers in brain stem establish a rhythmic
breathing pattern
– Medullary respiratory center
• Dorsal respiratory group (DRG)
– Mostly inspiratory neurons
• Ventral respiratory group (VRG)
– Inspiratory neurons
– Expiratory neurons
– Pre-Bötzinger complex
• Widely believed to generate respiratory rhythm
– Pneumotaxic center
• Sends impulses to DRG that help “switch off” inspiratory
neurons
• Dominates over apneustic center
Chapter 13 The Respiratory System
Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning
Control of Respiration
– Apneustic center
• Prevents inspiratory neurons from being switched off
• Provides extra boost to inspiratory drive
– Hering-Breuer reflex
• Triggered to prevent overinflation of the lungs
– Chemical factors that play role in determining
magnitude of ventilation
• PO2
• PCO2
• H+
Chapter 13 The Respiratory System
Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning
Control of Respiration
Chapter 13 The Respiratory System
Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning
Influence of Chemical Factors on Respiration
Chapter 13 The Respiratory System
Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning
Peripheral Chemoreceptors
• Carotid bodies are located in the carotid sinus
• Aortic bodies are located in the aortic arch
Chapter 13 The Respiratory System
Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning
Factors That May Increase Ventilation During
Exercise
•
•
•
•
Reflexes originating from body movement
Increase in body temperature
Epinephrine release
Impulses from the cerebral cortex
Chapter 13 The Respiratory System
Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning
Factors That Influence Ventilation That Are
Unrelated to Need for Gas Exchange
• Protective reflexes such as sneezing and coughing
• Inhalation of noxious agents which can trigger
immediate cessation of breathing
• Pain originating anywhere in body reflexly stimulates
respiratory center
• Involuntary modification of breathing occurs during
expression of various emotional states
• Respiratory center is reflexly inhibited during
swallowing
Chapter 13 The Respiratory System
Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning
Dead Space
Chapter 13 The Respiratory System
Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning
Respiratory Anatomy
Chapter 13 The Respiratory System
Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning
Respiratory Muscle
Chapter 13 The Respiratory System
Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning
Volume Pressure
Chapter 13 The Respiratory System
Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning