PHYSIOLOGY
EXTERNAL AND INTERNAL
RESPIRATION
EXTERNAL RESPIRATION
Respiration

Movement of gases between the environment and
the body’s cells
– The exchange of air between the atmosphere and the
lungs


Known as ventilation or breathing
Inspiration and Expiration
– The exchanges of O2 and CO2 between the lungs and
the blood
– Transport of O2 and CO2 by the blood
– The exchange of gases between blood and the cells
RESPIRATION
Anatomy of the Respiratory
System

Nasal Concha
– Air eddies
 Air is cleaned
 Warmed
 Humidified

Tonsils and Adenoids
– Lymph nodes that filter the air
– Located in the nose, back of the throat, below
the tongue
Larynx

Contains Vocal Cords
– Connective tissue bands that tighten to create
sound when air moves past them

Thyroid Cartilage
– Sensitive to Testosterone levels
Trachea

Conducts Air
– Lined with pseudostratified ciliated columnar
epithelium
– Cilia can be paralyzed by cigarette smoke

Surrounded by C-shaped Cartilagenous
rings and the trachealis muscle
– Esophagus is dorsal to the trachea

Approximately 4 inches long
The nose serves all the following
functions except
A. As a passageway for air movement
B. As the initiator of the cough reflex
C. Warming and humidifying the air
D. Cleansing the air
Conducting System or
Respiratory Tree

Primary Bronchi
– Surrounded by O-shaped cartilagenous rings
– Bifurcates to Secondary Bronchi in the lungs
– Respiratory Bronchioles
 Surrounded by smooth muscles
 Diameter of the airways becomes progressively
smaller from the trachea to the bronchioles
 The total cross-sectional area increases with each
division of the airways
Pleural Membranes

Visceral Pleura
– Attached directly to the lungs

Parietal Pleura
– Attaches to the visceral pleura
– Also attaches to the thoracic cavity

Serous Fluid
– Separates the two pleura and lubricates in order to decrease friction
– Consistency of egg whites
– Pleurisy occurs when the fluid decreases

The Function of the Pleural Membranes is to hold the
lungs open
Alveoli

Clustered at the ends of the terminal
bronchioles
 Makes up the bulk of lung tissue
 Primary function is the exchange of gases
between themselves and the blood
 Surrounded by elastic fibers
– Creates Elastic Recoil
Capillaries

The alveoli are closely associated with an
extensive network of capillaries
– Blood vessels cover 80-90% of the alveolar
surface forming a continuous “sheet” of blood
in close contact with the air-filled alveoli
Respiratory Membrane

Consists of
– The Wall of the Alveoli
– The Respiratory Space
 This is a fluid filled space
 Pneumonia may cause the space to fill with more
fluid than normal
– This decreases the ability to exchange gases
– The Wall of the Capillary
Surfactant helps to prevent the alveoli
from collapsing by
A. Humidifying the air before it enters
B. Warming the air before it enters
C. Interfering with the cohesiveness of water
molecules, thereby reducing the surface
tension of alveolar fluid
D. Protecting the surface of alveoli from
dehydration and other environment variations
The respiratory membrane is a
combination of
A. Respiratory bronchioles and alveolar ducts
B. Alveolar walls, alveolar space and capillary
walls
C. Atria and alveolar sacs
D. None of the above
Gas Laws

At sea level normal atmospheric pressure is
760mmHg
– On top of Mt. Everest Patm = 153mmHg
Dalton’s Law

The total pressure exerted by a mixture of
gases is the sum of the pressures exerted by
the individual gases
– 78% N2
– 21% O2
– 1% CO2

Partial Pressure of gases
– The pressure of a single gas in a mixture
Gas Law

The total pressure of a mixture of gases, is the sum
of the pressures of the individual gases (Dalton’s
Law)
 Gases, singly or in a mixture, move from areas of
higher pressure to areas of lower pressure
 If the volume of a container of gas changes, the
pressure of the gas will change in an inverse
manner (Boyle’s Law)
Dalton’s Law

To find the partial pressure of any one gas
in a sample of air, multiply the atmospheric
Pressure (Patm) by the gas’s relative
contribution (%) to Patm.
– Partial pressure of an atmospheric gas =
 Patm X % of gas in atmosphere
– Partial pressure of oxygen = 760mmHg X 21%
 PO2 = 760 X 0.21 = 160mmHg
Gases Move from High Pressure
to Low Pressure

Air flow occurs whenever there is a
pressure gradient
Boyle’s Law

The pressure exerted by a gas or mixture of
gases in a sealed container is created by the
collisions of moving gas molecules with the
walls of the container and with each other.
– P1V1 = P2V2

An increase in volume will create a decrease in
pressure and a decrease in volume will create an
increase in pressure
Boyle’s Law

Changes in the volume of the chest cavity during
ventilation cause pressure gradients that create air
flow
– When the chest volume increases, the alveolar pressure
falls, and air flows into the respiratory system

When the chest volume decreases, the alveolar
pressure rises, and air flows out into the
atmosphere
Alveoli

Composed of a single layer of epithelium called
Type I cells
 Type II alveolar cells
– Secretes surfactant
– Surfactant decreases the surface tension of the water
within the alveoli
– Coats the inside of the alveoli
– Cortisol causes the maturation of the type II cells in the
fetal stage of development

Dust Cells
– Phagocytes
Law of LaPlace

The pressure inside a bubble formed by a fluid
film is a function of two factors
– Surface tension of the fluid (T)
– Radius of the bubble (r)


P = 2T/r
Surfactant decreases the surface tension of water
in the alveoli
 Newborn Respiratory Distress Syndrome (RDS)
Air Flow

Flow = changes in P / R
– P = Pressure
– R = Resistance to Flow

Air flow in response to a pressure gradient
 The flow decreases as the resistance to flow
increases
Pressure in the System

Alveolar Pressure
– Pressure in the air spaces of the lungs

Intrapleural Pressure
– Pressure in the pleural fluid

Intrapulmonary Pressure
– Pressure within the lungs as a whole

Atmospheric Pressure
– Pressure in the atmosphere due to a column of air up to
the stratosphere
The pleurae are vital to the integrity of the
lungs because they
A. Contain cilia that protect the lungs
B. control the volume of the lungs
C. Secrete a lubricating serous fluid, allowing
the lungs to glide over the thoracic wall
during breathing
D. Maintain the proper temperature of the lungs
during sleep
The factor(s) responsible for holding the
lungs to the thoracic wall is/are
A. The smooth muscles of the lung
B. The diaphragm and the intercostals muscles
C. The visceral pleurae and the changing volume
of the lungs
D. Surface tension from pleural fluid, positive
pressure, and atmospheric pressure on the
thorax
Inspiration

Time 0.
– In the brief pause between breathes, alveolar pressure is equal to
atmospheric pressure
– When pressures are equal, there is no air flow

Time 0-2 sec
– Oxygen levels fall and Carbon Dioxide levels rise
– Peripheral Chemoreceptors are stimulated
 Located in the carotid arteries
 Sensitive to oxygen levels
– Central Chemoreceptors are stimulated
 Located in the Medulla Oblongata of the brain
 Sensitive ot carbon dioxide levels
Inspiration

Chemoreceptors stimulate the Medulla
Oblongata
 The MO stimulates the Phrenic Nerve
 The Phrenic Nerve stimulates the
respiratory muscles of the thoracic cage and
the diaphragm
 The muscles contract and the thoracic
volume increases
Inspiration

When thoracic volume increases then
alveolar pressure fall approximately
4mmHg below atmospheric pressure
 Air flows from high pressure to low
pressure until the pressures reach
equilibrium
Exhalation

Time 2-4 sec:
– As lung and thoracic volumes decrease air pressure in the lungs
increases until the pressures equal equilibrium
– Stretch receptors in the lung tissue are stimulated
– Stretch receptors send information to the MO and this stops the
phrenic nerve stimulation
– Respiratory muscles relax

Time 4 sec:
– Elastic Recoil occurs
– Alveolar pressure is now higher than atmospheric pressure due to a
decrease in lung volume
– Air leaves the lungs until pressures reach equilibrium
Intrapleural Pressure Changes
During Ventilation
The lungs are “stuck” to the thoracic cage
by the cohesive forces exerted by the fluid
between the two pleural membranes
 If the thoracic cage moves, the lungs move
with it

Intrapleural Pressure

The pressure between the pleural
membranes is normally subatmospheric
 The combination of the outward pull of the
thoracic cage and in inward recoil of the
elastic lungs creates a subatmospheric
intrapleural pressure of about -3mmHg
What happens to subatmospheric
intrapleural pressure if an opening is
made between the sealed pleural cavity
and the atmosphere?
A knifing?

Air in the pleural cavity breaks the fluid bond
holding the lung to the chest wall
 The chest wall expands outward while the elastic
lung collapses to an unstretched state
– Like a deflated balloon
– Pneumothorax

Results in a collapsed lung that is unable to function normally
– Correction of a Pneumothorax


Removing as much air from the pleural cavity as possible with
a suction pum
Sealing the hole
Emphysema

Loss of elastic fibers for elastic recoil
during expiration
– Elastin is destroyed by elastase
 An enzyme released by immune cells

Have more difficulty exhaling than inhaling
Select the incorrect statement about
external respiration
A. Carbon dioxide is exchanged in the alveoli.
B. Cells produce nitrogen by their
metabolism.
C. Diffusion accounts for the transport of
gases.
D. Oxygen is exchanged in the alveoli.
E. The pulmonary capillaries are involved.
The intra-alveolar pressure
A. Is the pressure within the air sacs of the
lung.
B. Never equilibrates with atmospheric
pressure.
C. Is always less than intrapleural pressure.
D. All of the above are correct.
Ventilation

Lung Volumes
– Use a spirometer to measure pulmonary
function

Tidal Volume
 Inspiratory Reserve Volume
 Expiratory Reserve Volume
 Residual Volume
Tidal Volume

Breathing Quietly
– The volume of air that moves during a single
inspiration or expiration (VT).
 Average tidal volume during quiet breathing is
about 350 – 500ml of air
Inspiratory Reserve Volume
(IRV)

At the end of a quiet inspiration, take in as
much additional air as you possibly can
– About 3000ml in a 70kg male
Expiratory Reserve Volume
(ERV)

Stop at the end of a normal exhalation, then
exhale as much air as you possibly can
 This is a forceful exhalation
– Average is about 1100ml
Residual Volume
(RV)

Cannot be measured direction
 Even if you blow out as much air as you
can, air still remains in the lungs and the
airways
– About 1200ml
Lung Capacities

The sum of two or more lung volumes
– Vital capacity (VC)
 The sum of the inspiratory reserve volume,
expiratory reserve volume and tidal volume
 This represents the maximum amount of air that can
be voluntarily moved into or out of the respiratory
system with one breath
Total Lung Capacity

Total Lung Capacity
– Vital capacity + residual volume

Functional Residual Capacity
– Expiratory reserve volume + residual volume
Airway Resistance

Bronchioles are collapsible tubes
 Bronchoconstriction
– Increases resistance to air flow and decreases
the amount of fresh air that reaches the alveoli

Histamine
– Bronchoconstrictor

Bronchodilators
– Decreases resistance to air flow
PARASYMPATHIC INPUT

PNS is the primary neural control of
bronchioles and causes bronchoconstriction
 Smooth muscle in the bronchioles have β-2
receptors that respond to epinephrine and
norepinephrine
– Stimulation of β-2 receptors relaxes airway
smooth muscle and results in bronchodilation

Used to treat asthma or allergies
Chronic Obstructive Pulmonary
Disease (COPD)

Asthma, emphysema, chronic bronchitis
INTERNAL RESPIRATION
Pressure Gradients

Arterial Pressures
– PO2 = 100mmHg
– PCO2 = 40mmHg

Alveolar Pressures
– PO2 = 100mmHg
– PCO2 = 40mmHg

Venous Pressures
– PO2 = 40mmHg
– PCO2 = 45mmHg

Tissue Pressures
– PO2 = 40mmHg
– PCO2 = 45mmHg
Hemoglobin

Oxygen is transported two ways in the
blood
– Dissolved in the plasma
– Bound to hemoglobin

Mean Corpuscular Hemoglobin
– Counting the RBC’s and quantifying the
amount of hemoglobin per RBC

Hemoglobin Concentration or %
Hemoglobin

One hemoglobin molecule binds up to four
oxygen molecules
– Percent oxygen saturation

Globin
– Proteins in the hemoglobin
 Alpha, beta, gamma and delta types
 Adults have 2 alpha and 2 bets
 Fetal Hb
– Two gamma and two alpha
Affects of Oxygen-Hemoglobin
Binding

Any factor that changes the conformation of
the hemoglobin protein can affects its
ability to bind oxygen
 Changes in plasma pH, PCO2, 2,3DPG and
temperature alters oxygen-binding affinity
of hemoglobin
– 2,3DPG = 2,3 Diphosphoglycerate
Carbon Dioxide Transportation

7% of the CO2 is carried by venous blood
dissolved in the blood
 93% diffuses into red blood cells,
– 70% is converted to bicarbonate ions HCO3– 23% binds to hemoglobin as
carbaminohemoglobin
Hydrogen Ion Transportation

Hemoglobin binds hydrogen ions
– Prevents large shifts in the body’s pH
– Too many hydrogen ions in the blood may
cause respiratory acidosis

This is caused by an increase in CO2 levels in the
blood

H2O + CO2 = H2CO3 = H+ + HCO3-
Carbonic
Anyhydrase
Death from carbon monoxide poisoning
would be due to
A. The body’s destruction of hemoglobin
B. The strong affinity of carbon monoxide to
hemoglobin
C. Formation of cellular toxins
D. Inability of form hemoglobin
The entire sequence of events involved in the
exchange of O2 and CO2 between the body
and the external environment is known as
A. Internal respiration
B. External respiration
C. Ventilation
D. Breathing
E. All of the above are correct
The majority of the carbon dioxide
in the blood is found in which
chemical form?
A. Carboxyhemoglobin
B. Bicarbonate
C. Dissolved carbon dioxide gas
D. Carbonic anhydrase
Which of the following factors is (are)
essential to hemoglobin saturation and
the release of oxygen from the heme?
A. Hydrogen concentration
B. Partial pressure of carbon dioxide
C. The amount of 2,3 DPG in the blood
D. All of the above
What happens to plasma pH
during hyperventilation?
How does this change in pH
affect oxygen binding at the lungs
when PO2 is decreased?
How does it affect unloading of
oxygen at the cells?