Download Module 17 Respiratory System

Module 17
Respiratory System
Objective 1. List the functions of the respiratory system. Name the four respiratory
processes.
Assignment: Tortora, p. 874 or Wiley Plus – 23 Chapter Opener
Functions:
1. Provides for gas
exchange
2. Helps regulate blood pH
3. Contains smell receptors
4. Filters incoming air
5. Produces vocal sounds
6. Excretes water and heat
The four processes carried
out by the respiratory
system are:
1. Pulmonary ventilation:
moving air into and out
of the lungs
2. External respiration:
exchange of gases at the
alveoli of the lungs
3. Transport of respiratory
gases to the tissues
4. Internal respiration:
exchange of gases
between blood and tissue
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Objective 2. Describe functions for each of the structures of the respiratory system: nose
and paranasal sinuses, pharynx, larynx, trachea, bronchi, pleural membranes, ribs and
thoracic wall, diaphragm and intracostal muscles, phrenic nerves and pulmonary plexus. Be
able to identify each of these on a diagram or photograph.
Assignment: Tortora, pp. 550-551, 875-889, 891 or Wiley Plus – 15.2 Anatomy of Autonomic
Motor Pathways & 23.1 Respiratory System Anatomy
Let’s turn our attention to the parts of the respiratory system.
Anatomically, these structures can be divided into the upper and lower respiratory system.
The nose, paranasal sinuses, and pharynx make up the upper respiratory system. The
larynx, or voice box separates the upper from lower respiratory system. The larynx,
trachea, bronchi, and lungs make up the lower respiratory system.
We’ll begin with the
structures of the upper
respiratory system. The
nose is made up of hyaline
cartilage which gives it
flexibility. Air enters
through the external nares
(nostrils). Nose hairs
actually have a function
(besides distinguishing older
men)! The hairs act as a
filter for all of the crap you
might breath in.
In the internal nose are
scroll-like bones that make up the nasal conchae also called turbinates. The conchae
provide a turbulent area that air passes through before reaching the rest of the respiratory
passages. The conchae are lined with a mucous membrane which helps trap foreign
particles and warms and humidifies the air, The olfactory epithelium is near the superior
nasal concha which increases the surface area and mixes the air to help with olfaction.
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Objective 2. Describe functions for each of the structures of the respiratory system: nose
and paranasal sinuses, pharynx, larynx, trachea, bronchi, pleural membranes, ribs and
thoracic wall, diaphragm and intracostal muscles, phrenic nerves and pulmonary plexus. Be
able to identify each of these on a diagram or photograph.
Sinuses are cavities within cranial and facial bones that are lined with a mucous membrane.
These spaces lighten the weight of the head
so we have an easier time carrying our head
around. They also serve as chambers that
resonate sound as we speak or sing.
Remember how funny you sound when
your sinuses are stuffed up with a cold. If
we walked around on all fours our sinuses
would easily drain. Because humans have
evolved to walk on two feet, our sinuses
don’t drain as easily. They may trap
microorganisms and fluid and we find
ourselves with a nasty sinus infection!
The pharynx or throat is a
hollow tube that starts at the
posterior part of the internal
nares and descends to the
opening of the larynx. The
pharynx serves as a
passageway for air and food,
is a resonating chamber for
sound, and houses the
tonsils.
The pharynx can be divided
into three anatomical
regions.
Nasopharynx: Lies behind the internal nares and has a purely respiratory function.
▪ Eustachian tubes (auditory tubes)
▪ Houses the pharyngeal tonsils (adenoids)
Oropharynx: Lies behind the mouth with both reparatory and digestive functions.
▪ Houses the palatine tonsils (removed in a tonsillectomy) and the lingual tonsils
Laryngopharynx: Lies inferior to the oropharynx and opens into the larynx and esophagus
▪ Respiratory and digestive functions
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Objective 2 (continued). Describe functions for each of the structures of the respiratory
system: nose and paranasal sinuses, pharynx, larynx, trachea, bronchi, pleural membranes,
ribs and thoracic wall, diaphragm and intracostal muscles, phrenic nerves and pulmonary
plexus. Be able to identify each of these on a diagram or photograph.
The larynx or voice box connects the
laryngopharynx with the trachea. It sits in
the midline of the neck anterior to the
esophagus and superior to the trachea. The
hyoid bone, an unattached, free-floating Ushaped bone, sits superior to the larynx.
The opening of the larynx is the glottis.
Folds of tissue, the vocal chords, and the
opening between them make up the glottis.
Vibrations caused by air passing the vocal
chords produces sound. The
greater the pressure, the
louder the sound. Tension
on the vocal chords
produces pitch. Men’s vocal
folds become thicker and
longer during puberty under
the influence of male sex
hormones (androgens)
producing a lower pitched
voice.
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Objective 2 (continued). Describe functions for each of the structures of the respiratory
system: nose and paranasal sinuses, pharynx, larynx, trachea, bronchi, pleural membranes,
ribs and thoracic wall, diaphragm and intracostal muscles, phrenic nerves and pulmonary
plexus. Be able to identify each of these on a diagram or photograph.
Nine pieces of cartilage
make up the larynx:
Single cartilage:
▪ Thyroid: (Adam’s apple).
Forms the anterior surface of
the larynx
▪ Epiglottis: Leaf shaped
piece of hyaline cartilage
that closes over the larynx
when food or liquids are
swallowed. The epiglottis
allows gases such as oxygen
through the larynx into the
trachea.
▪ Cricoid: A ring of hyaline cartilage that forms the inferior portion of the larynx.
Paired cartilage:
▪ Arytenoid: Influence changes in position and tension of the vocal folds.
▪ Corniculate and Cuneiform: Support the vocal folds and the epilglottis
The thyroid and cricoid cartilages serve as
landmarks for making an emergency airway.
A tracheostomy tube is inserted between
these two pieces of cartilage. A tracheotomy
is the procedure of cutting (–tomy) the
trachea. A tracheostomy means to form a
mouth or an opening (–stomy) in the
trachea. This is a semi-permanent or
permanent procedure used for patients with
long-term needs such as a patient with oral
cancer.
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Objective 2 (continued). Describe functions for each of the structures of the respiratory
system: nose and paranasal sinuses, pharynx, larynx, trachea, bronchi, pleural membranes,
ribs and thoracic wall, diaphragm and intracostal muscles, phrenic nerves and pulmonary
plexus. Be able to identify each of these on a diagram or photograph.
The trachea or windpipe is a semi-rigid
passageway for air that’s about 12 cm (5
inches) long. Incomplete cartilage rings
resembling the letter C surround the trachea
giving it support and preventing collapse of
the trachea, especially during inhalation.
The trachea is anterior to the esophagus.
The posterior surface of the trachea is shared
with the esophagus.
The trachea divides into the right and left
primary bronchi. The bronchi resemble an
inverted tree, branching into divisions of
secondary bronchi, tertiary bronchi, and
eventually into the tiny bronchioles and
terminal bronchioles. The right primary
bronchus extends more vertically, is wider,
and shorter than the left. Because of this, an
aspirated object is more likely to lodge in
the right bronchus than the left.
The carina is an internal ridge where the
trachea divides into the right and left
bronchus. The carina (Latin for boat prow)
is used as a landmark when performing a
bronchoscopy or visual examination of the
bronchi. The carina is very sensitive area
for triggering the cough reflex.
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Objective 2 (continued). Describe functions for each of the structures of the respiratory
system: nose and paranasal sinuses, pharynx, larynx, trachea, bronchi, pleural membranes,
ribs and thoracic wall, diaphragm and intracostal muscles, phrenic nerves and pulmonary
plexus. Be able to identify each of these on a diagram or photograph.
The right and left lungs are
slightly different. The right
lung contains 3 lobes while
the left contains 2. This is
because the apex of the
heart rests at the medial
portion of the left lung, the
cardiac notch. The apex or
superior part of the lung
rests slightly above the
clavicle. The base of the
lungs rests on the
diaphragm. The anterior,
lateral, and posterior
surfaces of the lungs rest
against the ribs.
The primary bronchi, blood vessels, lymphatic vessels, and nerves enter the lungs at the
hilum, an opening on the medial surface of each lung. The primary bronchi branch to form
secondary bronchi, one for each lobe of the lung. The secondary bronchi further branch to
form bronchioles which divide into several alveolar ducts. These ducts end in grape-like
clusters called alveoli. The alveoli provide a large surface area for the exchange of gases. It’s
estimated that the lungs contain 300 million alveoli, giving a surface area about the size of a
racquetball court for gas exchange!
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Objective 2 (continued). Describe functions for each of the structures of the respiratory
system: nose and paranasal sinuses, pharynx, larynx, trachea, bronchi, pleural membranes,
ribs and thoracic wall, diaphragm and intracostal muscles, phrenic nerves and pulmonary
plexus. Be able to identify each of these on a diagram or photograph.
The lungs, like other visceral
organs, are covered with a
double-walled serous
membrane. Remember that
serous membranes line
organs and body cavities that
do not open to the external
world. A serous membrane
consists of areolar connective
tissue covered by simple
squamous epithelium
(mesothelium). The visceral
pleura adheres to the lung.
The parietal pleura adheres
to the chest wall. Between
the two pleura is a small space, the pleural
cavity which contains pleural fluid. This
fluid reduces friction. We would hate to be
in pain every time we took a breath! The
pleural fluid allows easy movement as the
lungs expand and contract. The fluid also
allows the two layers of the membrane to
adhere to each other because of the surface
tension it creates.
If the membrane becomes inflamed, a
condition called pleurisy occurs which can
be extremely painful because of friction
between the two layers. Excess fluid may
accumulate in the pleural cavity due to
inflammation. This serious condition, called
pleural effusion, makes it difficult to breathe.
The visceral organs of the thoracic cavity are
protected by the ribs and sternum. The
volume of the thoracic cavity changes due to
contractions of muscles expanding this area.
We will learn more about this in Objective 8.
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Objective 2 (continued). Describe functions for each of the structures of the respiratory
system: nose and paranasal sinuses, pharynx, larynx, trachea, bronchi, pleural membranes,
ribs and thoracic wall, diaphragm and intracostal muscles, phrenic nerves and pulmonary
plexus. Be able to identify each of these on a diagram or photograph.
The inferior portion of the
lungs rest on a large, domeshaped muscle, the
diaphragm. This muscle,
which forms the floor of the
thoracic cavity, is the most
important muscle that
powers breathing.
Contraction of this muscle
enlarges the thoracic cavity
enabling inhalation (more
about this to come). The
diaphragm is responsible for
about 75% of the air that
enters the lungs during
normal quiet breathing.
The internal intercostal muscles make up the intermediate layer of the intercostal space.
These muscles help decrease the size of the thoracic cavity during forced exhalation.
The phrenic nerve arises from the cervical plexus at levels C3, C4, and C5. It stimulates the
diaphragm muscle to contract, enabling inspiration. The mnemonic ―C3, 4, 5, keep the
diaphragm alive‖ can help you remember the origin of this important spinal nerve.
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Objective 2 (continued). Describe functions for each of the structures of the respiratory
system: nose and paranasal sinuses, pharynx, larynx, trachea, bronchi, pleural membranes,
ribs and thoracic wall, diaphragm and intracostal muscles, phrenic nerves and pulmonary
plexus. Be able to identify each of these on a diagram or photograph.
The lungs receive both
sympathetic and
parasympathetic
innervations. Remember
that the sympathetic
nervous system enables the
―fight or flight‖ response. If
you were running from a
saber-tooth tiger (or on a
hot date) you would need
more air to your lungs.
Under sympathetic
stimulation, smooth
bronchial muscle dilates.
Sympathetic nervous
outflow arises from the
thoracolumbar region of the
spinal cord. Sympathetic
nerves that innervate the
lungs have cell bodies in the
intermediate horn (sides of
the gray matter) in the T1T4 areas of the spinal cord.
The nerves synapse at the
sympathetic chain ganglia
(along the sides of the spinal
cord). The nerves enter the
lungs at the hilus forming
the pulmonary plexus.
Remember that the
parasympathetic nervous system enables the ―rest and repose‖ response. Think postThanksgiving dinner; breathing is barely necessary when one is semi-comatose digesting on
the couch! Parasympathetic stimulation causes mucus secretion and constriction of
bronchial smooth muscle. The parasympathetic nerve innervating the lungs is Cranial
nerve X, the vagus nerve, using acetylcholine as the neurotransmitter.
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Objective 3. Define conducting zone and respiratory zone. Define upper and lower
respiratory tracts.
Assignment: Tortora, p. 875 or Wiley Plus – 23.1 Respiratory System Anatomy
The respiratory tract is divided into the
conducting zone and the respiratory zone.
The conducting zone consists of all of those
structures that bring the air to the alveoli
where gas exchange will occur. The nose,
pharynx, larynx, trachea., bronchi,
bronchioles and terminal bronchioles are all
part of the conducting zone. The function
of the conducting zone is to filter, warm,
moisten and conduct the air to the lungs.
The respiratory zone is where gas exchange
takes place in the lungs. Respiratory bronchioles, alveolar ducts, alveolar sacs, and alveoli
make up the respiratory zone.
As mentioned previously, the respiratory tract is also divided into the upper and lower
portions. The upper respiratory tract includes the nasal cavity, oral cavity, and the pharynx.
Although views differ as to the proper classification of the larynx, the text classifies it as
part of the upper respiratory
tract. The lower respiratory
tract includes the trachea
and all components of the
lungs.
The upper respiratory tract
is full of endogenous
(normal) flora. The lower
respiratory tract should be
sterile. Sputum, an
abnormal, thick, mucus (spit
mixed with respiratory
secretions) is often cultured
if a physician suspects
pneumonia. As the patient
coughs up the sputum (sorry
for the visual!) it mixes with normal microorganisms of the upper respiratory tract. The
microbiologist must discern between the normal flora and any harmful pathogens.
828
Objective 4. List each of the structures through which air passes during inspiration.
Assignment: Tortora, p. 875 or Wiley Plus – 23.1 Respiratory System Anatomy
Let’s summarize by looking
at the travel itinerary for an
air molecule. Remember
that the molecule must first
travel through cavities and
tubes that make up the
conducting zone. Think of
it as going down a big water
slide before it makes its final
splash in the respiratory
zone. The molecule travels
from the outside world
through the mouth or nose
(depending on your personal
preference). It then must
make it down the pharynx, through the larynx, and down the trachea. From here there’s a
choice involved. The molecule may either make a right or left turn into the right or left
primary bronchus. Now the branching begins and each air molecule can take many
different paths through the secondary bronchi, tertiary bronchi, and the tiny bronchioles.
These bronchioles end in the basic unit of the lung, the lobule. We are now entering the
respiratory zone where oxygen and carbon dioxide will be exchanged. Each lobule contains
a lymphatic vessel, an
arteriole, a venule, and a
branch from a terminal
bronchiole. The terminal
bronchioles subdivide into
tiny respiratory bronchioles.
At the end of the respiratory
bronchioles we find the
grape-like clusters of alveoli
where gas exchange occurs.
The oxygen from our air
molecule diffuses into the
bloodstream, traveling out to
the tissues where it’s needed
for metabolism.
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Objective 5. Describe the histology of the respiratory epithelium. State a function for each
kind of epithelium.
Assignment: Tortora, pp. 177, 888-889 or Wiley Plus – 4.3 Epithelial Tissue & 23.1 Respiratory
System Anatomy
Remember that function
denotes structure. This is
true of the tissues of the
respiratory tract. Tissues
vary throughout the
respiratory tract to meet
specific functions.
Parts of the pharynx and
larynx are lined with
stratified squamous
epithelium for protection
(think tortilla chips!).
Most of the conducting
portion of the respiratory
tract is lined with pseudostratified columnar ciliated cells, also called the respiratory
epithelium. This epithelium also contains goblet cells which produce mucus. The mucus
and the cilia form the mucocillary escalator which transports foreign particles out of the
respiratory tract.
The trachea lies anterior to
the esophagus. The trachea
is supported by C shaped
rings of hyaline cartilage
which prevent the trachea
from collapsing, blocking
the conduction of air.
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Objective 5 (continued). Describe the histology of the respiratory epithelium. State a
function for each kind of epithelium.
Smooth muscle lines the bronchi and
bronchioles. This is important to control
the diameter of the airways. When you’re
exercising and gasping for air, the
sympathetic nervous system stimulates the
bronchi and bronchioles to dilate, allowing
the passage of more air to the lungs. When
you’re sleeping on the couch after your
strenuous workout, the airways constrict
under parasympathetic stimulation and
secretions increase. Inflammatory
conditions such as asthma also cause
constriction of the airways, trapping air
within the lungs.
As we move deeper into the
respiratory zone, the
epithelium changes. Alveoli
are lined with two types of
epithelium. Type I alveolar
cells are simple squamous
epithelium. These cells are
the site of gas exchange.
They are by far the most
numerous cell lining the
alveoli. The capillaries
carrying red blood cells are
also lined with a single layer
of squamous epithelium.
These cells, along with the
type I alveolar cells, form the alveolar-capillary (A-C) membrane, a thin membrane that
gases can easily diffuse across.
Type II alveolar cells, are simple cuboidal epithelium, and secrete surfactant. This is a
soap-like substance that decreases surface tension allowing easier inflation of the alveoli and
preventing the collapse of alveoli after exhalation.
Alveolar macrophages are there for clean up of large particles and invaders.
831
Objective 6. Define pulmonary ventilation, inspiration, and expiration.
Assignment: Tortora, pp. 890-893 or Wiley Plus – 23.2 Pulmonary Ventilation
Respiration: The process of gas exchange in the body.
Pulmonary Ventilation: The inhalation and exhalation of air. This involves the exchange
of air between the atmosphere and the alveoli of the lungs.
Inhalation: Movement of air into the lungs from the atmosphere.
▪ Active process requiring muscle action
Exhalation: Movement of air out of the lungs into the atmosphere.
▪ Passive process during quiet breathing due to the elastic recoil of the lungs
▪ Active (muscle help) during vigorous exercise or certain disease conditions causing
difficult expiration (chronic obstructive pulmonary diseases)
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Objective 7. Define: Boyle’s Law. Explain the application of Boyle’s Law to inspiration and
expiration.
Assignment: Tortora, p. 890 or Wiley Plus – 23.2 Pulmonary Ventilation
Let’s shift our attention to two important physics laws and principles behind these laws that
will help us understand respiration. The idea that a gas is made up of little billiard balls
zipping around and colliding with each other is called by the rather fancy name The Kinetic
Molecular Theory. There are five principles in the theory:
1. There is a lot more space
between gas particles than
the gas particles themselves
occupy.
2. Particles move in a
straight line until they
collide. They move in
different directions and have
different speeds.
3. The particles in a gas
don’t interact with each
other much, if at all.
4. When particles collide,
all the energy goes into
bouncing, and none is
absorbed by the particle.
5. The average speed of the particles is related to the temperature.
In the 19th century, a number of scientists stated Gas Laws. These laws were ―absorbed‖
into the Kinetic Molecular Theory but we still learn them by the name of the person who
stated them first.
833
Objective 7 (continued). Define: Boyle’s Law. Explain the application of Boyle’s Law to
inspiration and expiration.
Boyle’s Law says that pressure (which we can think of as the number of collisions with the
walls of the container) times volume is a constant at constant temperature. Human bodies
are at a constant temperature of 37°C.
If pressure goes up, volume goes down. (If you press on a syringe, its volume decreases).
If volume goes up, pressure goes down. (That is, there is more room between the molecules
and fewer collisions).
http://demonstrations.wolfram.com/AnExperimentWith BoylesLaw/
834
Objective 8. State the pressures in the structures of the respiratory system during
inspiration and expiration.
Assignment: Tortora, pp. 890-893 or Wiley Plus – 23.2 Pulmonary Ventilation
Boyle’s law has a direct
application to the principles
governing inspiration and
expiration. During
inspiration, contraction of
the diaphragm and external
intercostals muscles increase
the volume of the thoracic
cavity. As we just learned,
as the volume increases,
pressure decreases. The
pressure in the thoracic
cavity is now slightly less
than atmospheric pressure.
Following the principle of diffusion, air will flow from high to low pressure into the
thoracic cavity.
During deep, labored
breathing, additional
muscles are used to further
enlarge the thoracic cavity.
The accessory muscles
include the
sternocleidomastoid which
elevates the sternum, the
scalene muscles and
pectoralis minor which
elevate ribs.
During inhalation the lifting
of the sternum acts as the
handle of a pump while the
ribs elevate up and out like
the handles of a bucket.
835
Objective 8 (continued). State the pressures in the structures of the respiratory system
during inspiration and expiration.
Exhalation is a passive process during quiet breathing. Elastic recoil of the chest wall and
lungs causes the volume in the thoracic cavity to decrease. As the volume decreases, the
pressure increases. Pressure is now higher in the thoracic cavity than atmospheric air and
air flows out from high to low pressure.
During forced exhalation, abdominal muscles and the internal intercostals contract further
decreasing the volume of the thoracic cavity and increasing the pressure.
836
Objective 9. Describe the forces which promote collapse of lung and those which oppose
lung collapse. State why pneumothorax leads to atelectasis.
Assignment: Tortora, p. 885 or Wiley Plus – 23.1 Respiratory System Anatomy
Air may leak into the pleural cavity from trauma to the lung or a spontaneous rupture of a
bleb, a weak spot on the lung. The pressure of the air does not allow the lung to fully
inflate and a pneumothorax or collapsed lung may occur. Physicians treat a pneumothorax
by placing a chest tube between the ribs in the wall of the thoracic cavity. This allows the
air to flow out. The tube is then removed or sealed off and the hole in the chest wall
repaired so the lungs can spontaneously re-inflate.
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Objective 10. State the four respiratory volumes and four respiratory capacities. Identify
each of these on a spirogram.
Assignment: Tortora, pp. 894-896 or Wiley Plus – 23.3 Lung Volumes and Capacities
Pulmonary function can be tested using a spirometer, which measures the volume of air
exchanged during breathing and the respiratory rate. The record of this measurement is
called a spirogram. Four respiratory volumes and four respiratory capacities are measured:
Respiratory volumes:
▪ Tidal Volume (VT): Volume of air inspired or expired during normal quiet breathing
▪ Inspiratory Reserve Volume: All of the air that you can breathe in from the top of tidal
volume (during a very deep inhalation).
▪ Expiratory Reserve Volume: All of the air that you can breathe out from the bottom of
tidal volume during a forced exhalation.
▪ Residual Volume: Air still present in lung tissue after the thoracic cavity has been
opened.
838
Objective 10. State the four respiratory volumes and four respiratory capacities. Identify
each of these on a spirogram.
Respiratory capacities are combinations of specific lung volumes:
Inspiratory capacity: The sum of tidal volume and inspiratory reserve volume.
Functional residual capacity: The sum of residual volume and expiratory reserve volume.
Vital capacity: The sum of inspiratory reserve volume, tidal volume, and expiratory reserve
volume.
Total lung capacity: Sum of vital capacity and residual volume
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Objective 11. State Dalton’s Law. State Henry’s Law. Explain how each is relevant to
external and internal respiration. Using these laws, compare and contrast human physiology
at normal atmospheric pressure and at high pressure.
Assignment: Tortora, pp. 896-897, 899 or Wiley Plus – 23.4 Exchange of Oxygen and Carbon
Dioxide
The exchange of gases at the alveoli and the tissues is explained by
2 physical laws: Dalton’s Law and Henry’s Law.
Dalton’s Law says that the particles in a gas don’t care about each
other. In a mixture of different gases (gas A and gas B and gas C),
the pressure due to gas A is exactly equal to its proportion in the
mixture.
For Earth’s atmosphere, 21% of the atmosphere is oxygen, so 21% of the atmospheric
pressure is due to oxygen. We call this the partial pressure of oxygen. We represent the
partial pressure of oxygen as PO2 or pO2; the partial pressure of CO2 as PCO2; and so forth.
The element argon is 1% of the Earth’s atmosphere. What percentage of atmospheric
pressure is contributed by argon?
Henry’s Law says the amount of a gas that is
dissolved in a liquid is directly proportional
to the partial pressure of the gas. In the body
much more CO2 is dissolved in blood plasma
than O2 because it is 24x more soluble than
oxygen. A hyperbaric chamber increase the
atmospheric pressure of oxygen, and more
dissolves in solution (the blood).
840
Objective 11 (continued). State Dalton’s Law. State Henry’s Law. Explain how each is
relevant to external and internal respiration. Using these laws, compare and contrast human
physiology at normal atmospheric pressure and at high pressure.
When Olympians came to Salt Lake City to compete, they had to contend with the high
altitude. Atmospheric pressure decreases as we ascend in altitude. Henry’s Law states that
if the atmospheric pressure of oxygen is lower, less will dissolve in solution. Altitude
sickness may occur because of the lack of oxygen dissolved in the blood. Ultimately
pulmonary vessels may vasoconstrict increasing pulmonary pressure. Fluid may be pushed
out of the vessels leading to the serious condition of pulmonary edema. Lack of oxygen to
the brain may lead to cerebral edema and subsequent death.
The opposite condition may occur with scuba divers. For every 30 feet that a diver
descends, atmospheric pressure increases by 1 atm (760 mmHg). A much larger amount of
nitrogen than normal is now dissolved in the blood because of the high pressure. If a diver
ascends too rapidly, nitrogen may come out of solution leading to joint and lung damage, a
painful condition called ―the bends.‖
841
Objective 12. Describe, in detail, the process of external respiration and movement of gases
across the alveolar-capillary (A-C) membrane.
Assignment: Tortora, pp. 897-899 or Wiley Plus – Exchange of Oxygen and Carbon Dioxide
External respiration occurs at the alveolarcapillary membrane. External respiration is
the diffusion of atmospheric oxygen from
the alveoli of the lungs to blood in the
pulmonary capillaries. In exchange, CO2 in
blood coming from the tissues diffuses into
alveolar capillaries and is exhaled.
While the alveolar-capillary membrane is very thin (about 0.5 µm) an oxygen molecule
must still pass through the alveolar cell membrane, alveolar basement membrane, capillary
basement membrane and capillary endothelial cell membrane. (The two basement
membranes are fused, which makes the journey that much shorter.)
842
Objective 12 (continued). Describe, in detail, the process of external respiration and
movement of gases across the alveolar-capillary (A-C) membrane.
The diagram below gives a step-by-step breakdown of external respiration. Waste-laden
blood from the tissues returns to the heart and then enters the lungs via the pulmonary
arteries and arterioles. CO2 diffuse across the alveolar-capillary membrane and is exhaled.
O2 from the atmosphere diffuses from the alveoli to the blood. This now oxygen-rich blood
returns to the left atrium of the heart via the pulmonary venules and veins. It is then
pumped out to the tissues of the body.
Remember that gases diffuse independently of one another from an area of high pressure to
low pressure. CO2 and O2 are simply diffusing down their concentration gradients.
843
Objective 13. Explain ventilation-perfusion coupling.
Assignment: Tortora, p. 889 or Wiley Plus – 23.4 Exchange of Oxygen and Carbon Dioxide
Pulmonary ventilation ( ) is
the amount of air entering
the lungs each minute. (The
―V‖ is for ventilation; the
dot indicates per minute.)
Alveolar ventilation ( ) is
the amount of air entering
the alveoli each minute. If
air enters your lungs, but
does not enter the alveoli,
then its gases cannot be
absorbed into the blood.
Perfusion ( ) is the amount
of blood that flows through
the capillaries each minute.
Under hypoxic conditions (low amounts of oxygen) pulmonary blood vessels constrict. This
constriction causes blood to move (or shunt) from areas of low oxygen in the lungs to areas
of high oxygen. Blood flow is greatest, therefore, in alveoli that have the greatest amount of
oxygen flow. This matching of blood flow to oxygen is ventilation-perfusion coupling.
A ratio of ventilation to
perfusion ( / ) can be
calculated and is normally
about 1. This means that
ventilation (air flow) and
perfusion (blood flow) are
equally matched. This ratio
is changed in disease states
that affect oxygen flow or
blood flow. For example, if
a patient has difficulty
breathing, oxygen flow
decreases and the ratio is
disrupted. If a patient has a
blood clot in the lung, blood
does not flow and the ratio is again disrupted. If the ventilation/perfusion ratio is disrupted,
inadequate exchange of oxygen and carbon dioxide occurs.
844
Objective 14. Describe the process of internal respiration.
Assignment: Tortora, pp. 900-901 or Wiley Plus – 23.5 Transport of Oxygen and Carbon Dioxide
Internal respiration is the exchange of O2 and CO2 between systemic capillaries and tissue
cells. This exchange occurs in tissues throughout the body. Gases again diffuse from high
to low pressure. The tissues are actively using oxygen for metabolism. The partial pressure
of oxygen is lower in the tissues and higher in the blood and therefore diffuses into the
tissues. CO2 is a waste product of metabolism. Its partial pressure is higher in the tissues
than the blood so it diffuses from high to low, leaving the tissues and entering the
bloodstream.
845
Objective 14 (continued). Describe the process of internal respiration.
Carbon dioxide and oxygen are carried through the bloodstream in different forms:
Oxygen: 98.5% is carried bound to hemoglobin in RBCs
1.5% is dissolved in the plasma
Carbon dioxide: 70% travels through the bloodstream as bicarbonate (HCO3-)
23% is bound to hemoglobin
7% is dissolved in the plasma
846
Objective 15. Compare and contrast the processes of external and internal respiration.
Compare and contrast the partial pressures of oxygen and carbon dioxide during the process
of external and internal respiration.
Assignment: Tortora, pp. 897-901, 905 or Wiley Plus – 23.4 Exchange of Oxygen and Carbon
Dioxide & 23.5 Transport of Oxygen and Carbon Dioxide
In summary, external respiration is the exchange of gases between the pulmonary
capillaries and the alveoli which contain atmospheric air. CO2 diffuses from the capillaries
into the alveoli; O2 diffuses from the alveoli to the pulmonary capillaries.
Internal respiration is the exchange of gases between the tissues and the systemic
capillaries. Oxygen diffuses into the tissues, carbon dioxide diffuses from the tissues into
the bloodstream.
847
Objective 15 (continued). Compare and contrast the processes of external and internal
respiration. Compare and contrast the partial pressures of oxygen and carbon dioxide during
the process of external and internal respiration.
The PO2 is highest in the alveoli where it’s about 105 mm Hg. The pressure drops slightly as
blood enters the left atrium (100 mm Hg). The PO2 in the tissues is only about 40 mmHg.
Thus O2 flows from the higher pressure in the systemic capillaries into the tissues. As
blood leaves the tissues, the PO2 drops to approximate that of the tissues, about 40 mm Hg
CO2 diffuses in the opposite direction. CO2 is highest in the tissues and in the blood
returning to the left atrium and the lungs via the pulmonary arteries (PCO2 45 mm Hg),
hence CO2 diffuses into the alveoli. CO2 leaving the lungs and in the systemic circulation
traveling to the tissues has a partial pressure of 40 mmHg. This is lower than the tissues
(PCO2 45 mm Hg), thus, CO2 diffuses from the tissues to the systemic capillaries
The slide at the right depicts the different
ways CO2 and O2 are carried in the blood.
The mechanisms by which CO2 is carried
are discussed further in Objective 17.
848
Objective 16. Be able to label and explain important features of the oxygen-hemoglobin
saturation curve. Describe how different conditions (oxygen partial pressure, temperature,
carbon dioxide partial pressure) might alter the saturation curve. Compare and contrast the
oxygen saturation curve for fetal and adult hemoglobin.
Assignment: Tortora, pp. 901-903 or Wiley Plus – 23.5 Transport of Oxygen and Carbon Dioxide
The O2-Hemoglobin
saturation curve shows the
proportion of Hb bound to
O2. The higher the PO2 (X
axis) the more oxygen is
bound to Hb (Y axis).
Certain conditions influence
the O2-Hb saturation curve.
During conditions such as
exercise, tissues need more
oxygen. Actively working
tissues generate acids as
waste, lowering the pH. A
drop in pH shifts the curve
to the right, causing more O2
to be released at the tissues
(see the red line).
849
Objective 16 (continued). Be able to label and explain important features of the oxygenhemoglobin saturation curve. Describe how different conditions (oxygen partial pressure,
temperature, carbon dioxide partial pressure) might alter the saturation curve. Compare and
contrast the oxygen saturation curve for fetal and adult hemoglobin.
Actively working tissues also generate more
CO2 as waste. Higher PCO2 levels shift the
curve to the right and more O2 is delivered
to the tissues.
A tissue that is resting generates less CO2.
This shifts the curve to the left and less O2 is
delivered to the tissues.
Actively working tissues also generate heat.
Higher temperatures shift the curve to the
right, and more O2 is delivered. Resting
tissue generates less heat, and less O2 is
delivered.
When we’re sick and have a fever, more O2
is delivered to the tissues helping them fight
infection. Ingenious!
Fetal Hb has a higher affinity for O2 than
adult Hb. When PO2 is low, Fetal Hb can
carry up to 30% more O2 than maternal Hb.
Because of this, oxygen diffuses easily from
maternal to fetal blood.
850
Objective 17. State the ways carbon dioxide is carried in the blood, and rank their relative
importance.
Assignment: Tortora, pp. 903-905 or Wiley Plus – 23.5 Transport of Oxygen and Carbon Dioxide
The conversion of CO2 to
bicarbonate to be carried in
the plasma is a somewhat
complicated process. First,
CO2 combines with H20 in
the red blood cell to form
carbonic acid (H2CO3-).
Carbonic acid dissociates to
HCO3– and H+. The bicarbonate ions leave the RBC,
exchanging for Cl– ions. At
the alveoli the reaction reverses and CO2 is exhaled.
This reaction can be visualized on the graphic below
and on the following page.
851
Objective 18. State the chemical equation which describes the relationship between carbon
dioxide, bicarbonate ion, and carbonic acid in blood. Predict how raising and lowering pH
or carbon dioxide concentration will affect this system.
Assignment: Tortora, pp. 904-905, 1072 or Wiley Plus – 23.5 Transport of Oxygen and Carbon
Dioxide & 27.3 Acid-Base Balance
Buffers prevent rapid, drastic changes in pH of body fluids by converting strong acids and
bases into weak acids and bases. This is a rapid conversion which takes place in fractions of
a second. Most buffer systems in the body consist of a weak acid and a weak base.
Buffer reactions can proceed from left to right or right to left. In the carbonic acidbicarbonate buffer system, excess hydrogen ions can be instantly converted to water and
carbon dioxide. Under alkaline conditions, water and carbon dioxide are converted to
hydrogen and bicarbonate ions.
852
Objective 18 (continued). State the chemical equation which describes the relationship
between carbon dioxide, bicarbonate ion, and carbonic acid in blood. Predict how raising
and lowering pH or carbon dioxide concentration will affect this system.
853
Objective 19. Define: hyperventilation, hypoventilation, panting, eupnea, hyperpnea and
apnea.
Assignment: This page.
Because CO2 easily converts to an acid, the respiratory system can help control blood pH by
either speeding up breathing to get rid of CO2 or slowing down breathing to retain CO2.
Hyperventilation, or excessive ventilation is a mechanism used by the body to lower the
blood pH. Hyperventilation during your favorite exam may also lead to alkalosis. (You
knew exams were bad for your health!). Hypoventilation retains more CO2. The body may
use this mechanism in conditions of alkalosis to increase the pH. Patients with chronic
obstructive pulmonary diseases such as emphysema have difficulty exhaling and often build
up CO2 leading to acidosis.
854
Objective 20. State the location and function of the respiratory control centers in the
brainstem.
Assignment: Tortora, pp. 905-906 or Wiley Plus – 23.6 Control of Respiration
CONTROL OF RESPIRATION
NEURAL REGULATION—Medulla
The function of the medulla rhythmicity area,
which has both an inspiratory and an
expiratory center, is to control the basic
rhythm of respiration.
The inspiratory center stimulates the
diaphragm via the phrenic nerve, and the
external intercostal muscles via intercostal
nerves. [Inspiration normally lasts about 2
seconds.]
Most of exhalation is a passive process caused by the elastic recoil of the lungs. Usually the
expiratory center is inactive during quiet breathing (nerve impulses cease for about 3 seconds).
During forced exhalation, however, impulses from this center stimulate the internal intercostals
and the abdominal muscles to contract.
NEURAL REGUALTION—Pons
Other sites in the pons help the medullary centers manage the transition between inhalation and
exhalation.
The pneumotaxic center limits the duration of inspiration, so the lungs don’t get too full.
The apneustic center coordinates the transition between inhalation and exhalation.
855
Objective 20 (continued). State the location and function of the respiratory control centers
in the brainstem.
OTHER SOURCES OF REGULATION
 The medulla and pons control the basic rhythm of respiration, but inputs from other areas also
have a role.
 Our cerebral cortex has voluntary control when we want it.
 Emotions (limbic system) affect breathing.
 Hypercapnia (hypocarbia) (elevated PCO2), low O2, or acidosis (low pH) stimulate more rapid
breathing.
 Bronchial stretch receptors, sensing overinflation, arrest breathing temporarily (Hering-Breuer
reflex).
 The hypothalamus, sensing a fever, increases breathing.
 Moderate pain increases breathing. Severe pain causes apnea — a temporary cessation of
breathing.
856
Objective 21. Explain homeostatic mechanisms involved in control of blood gases and pH.
Assignment: Tortora, pp. 906-90909or Wiley Plus – 23.6 Control of Respiration
The body has a built in mechanism to regulate CO2, O2, and H+ levels in the blood.
Chemoreceptors send input to the inspiratory center to increase respirations if CO2 and/or
H+ are high or PO2 is low.
CO2, H+ , O2 = Increase in rate and depth of breathing
Can you die by holding your breath?
If the PO2 drops below from a normal level of 100 mm Hg to above 50 mm Hg,
chemoreceptors are stimulated. You are consciously holding your breath through the
influence of the motor cortex. If your PO2 drops below a certain level, fainting (syncope)
follows, and the brainstem will take over the work of breathing while you are unconscious.
Why can you hold your breath longer if you hyperventilate first?
A low PCO2 (below 40 mmHg) does not signal chemoreceptors and will not stimulate the
inspiratory center. (The inspiratory center responds to high CO2, not low CO2). So if you
hyperventilate, blowing off CO2, the inspiratory center slows and you can hold your breath
longer.
Why is it
dangerous to
hyperventilate and
then swim
underwater?
Swimmers were
once encouraged
to hyperventilate
before swimming
to be able to hold
their breath
longer. This is
dangerous because
O2 levels may fall
to a dangerously
low condition
before the chemoreceptor reflex is activated, causing fainting (syncope). Passing out in the
water is usually not a good idea as drowning may occur!
857
Objective 22. Summarize the embryonic development of the respiratory system. Explain the
role of surfactant in care of premature infants.
Assignment: Tortora, pp. 910-911 or Wiley Plus – 23.8 Development of the Respiratory System
The lungs begin to develop
during just the fourth week
of pregnancy. The slide on
the left shows further
development of the fetal
lungs. At 16-26 weeks of
pregnancy the lungs become
highly vascular and
respiratory bronchioles, alveolar ducts, and some primitive alveoli begin to develop. An
infant born at 26 weeks may survive, however death frequently occurs because the
respiratory system is so immature. From 26 weeks to birth, the alveoli develop. At birth,
only about a sixth of the alveoli are present. These continue to develop during the first
eight years of life.
Remember from Module 2 that water has
surface tension. Hydrogen bonding tightly
holds water molecules together. This is why
your little brother can pour water over the
brim of your glass without it spilling over.
Alveoli must overcome this surface tension
to inflate.
858
Objective 22 (continued). Summarize the embryonic development of the respiratory
system. Explain the role of surfactant in care of premature infants.
Remember also from Module 2 that
surfactants act like soap, breaking up
hydrogen bonds and reducing surface
tension. In the lungs, surfactant is
manufactured by type 2 alveolar cells.
Surfactant acts to break up surface tension
caused by water molecules in the air-liquid
interface within the alveoli of the lungs.
Surfactant is necessary to prevent the
collapse of alveoli on exhalation. Amounts
of surfactant sufficient to permit survival of
a premature infant are not produced until
26-28 weeks of gestation.
The important role of surfactant in infant
respiratory distress syndrome was
discovered in the 1950s. After several
decades of research, an artificial surfactant
was developed. This is given into the airway of the infant at, or shortly after, birth.
Immediate improvements in lung function are usually observed. Infant mortality has
greatly decreased since the
advent of exogenous
surfactant therapy.1
1
Rocca et al. In The Pulmonary
Epithelium in Health and Disease.
Proud, D (ed). Wiley:Hoboken,
2008.
859