Biology 221
Anatomy & Physiology II
TOPIC 7
Respiratory System
Chapter 23
pp. 834-879
E. Lathrop-Davis / E. Gorski / S. Kabrhel
1
Functions
• The main function of the respiratory system is
exchange gases, especially O2 and CO2.
• Other functions of the respiratory system include:
– maintaining acid-base (pH) balance (CO2 + H2O 
H2CO3);
– sound production (vocalizations);
– neurotransmitter removal;
– conversion of angiotensin I to angiotensin II;
– housing olfactory receptors for smell; and
– trapping and dissolving small clots before they reach
the systemic circulation.
2
Basic Processes of Respiration
The four basic processes of respiration are:
• ventilation, which moves air into and out of the lungs;
• external respiration, which is the exchange of gases
between blood and air in lungs;
• blood gas transport, which is the transport of gases
between lungs and body tissues; and
• internal respiration, which is the exchange of gases
between blood and body tissues.
Fig. 23.17, p. 860
3
Basic Airway Organization
There are two major groups of passageways.
• Conducting passageways move air into and out of body
but are not involved in actual gas exchange
– Conducting passageways include the nose, pharynx,
trachea, larynx, bronchi, bronchioles, and terminal
bronchioles.
• Respiratory passageways are involved in the exchange
of gases between air and blood.
– Respiratory passageways include the respiratory
bronchioles, alveolar ducts, and alveoli.
Fig. 23.1, p. 836
4
Lung Anatomy
• The lungs are located in the thoracic cavity lateral to
mediastinum.
• Each lungs consists of lobes. There are 3 on the right
and 2 on left. Lobes are served by secondary bronchi.
• Each lobe consists of several bronchopulmonary
segments, sections of lobes separated by connective
tissue.
– Each bronchopulmonary segment is served by its
own tertiary (segmental) bronchus.
– Each bronchopulmonary segment is supplied by its
own artery, vein, and lymphatics.
– Each segment can be removed surgically with
limited affects on the surrounding segments.
See Fig. 23.10, p. 848
5
Lung Anatomy
• Bronchopulmonary segment are divided into lobules,
which are the smallest visible subdivisions of lung
tissue. Lobules are served by large bronchioles.
• Lung tissue consists of air passageways and respiratory
surfaces embedded in elastic connective tissue.
• The hilus is an indentation on the medial surface of the
lung through which bronchi, blood vessels, lymphatics
and nerves pass.
See Fig. 23.10, p. 848
6
Lung Anatomy (con’t)
• Serous membranes cover the lungs and line the thoracic
cavity.
– The visceral (= pulmonary) pleura covers lungs.
– The parietal pleura lines the thoracic cavity.
– The “space” between them is pleural cavity. This
space is filled with serous fluid.
° Think About It: What is one important function of
this fluid? (See A&P I Unit 2 – Tissues)
See Fig. 23.10, p. 848
7
Conducting Passageways:
Nose and Nasal Cavity
• The functions of the nose and nasal cavity include:
– serving as airways for ventilation;
– moistening, warming, and filtering air;
– resonance of sounds produced for speech;
– housing olfactory receptors for smell.
Fig. 23.3, p. 838
8
Conducting Passageways:
Nose and Nasal Cavity
• Several special structures are associated with the
nasal cavity.
– The paranasal sinuses aid resonance of sound
and lighten the skull. (Covered in lab)
– The nasal conchae are covered with mucous
membranes and increase the surface area for
warming and moistening the air.
– The nasal septum separates right and left and
helps keep an open passage even when one side
is blocked.
Fig. 23.3, p. 838
9
Conducting Passageways:
Nose and Nasal Cavity
– The palate separates the nasal cavity from the
oral cavity. This permits breathing while eating.
° The hard palate consists of the palatine
process of the maxilla and the palatine bones
and is useful during chewing.
° The soft palate consists of muscle and closes
the opening to the nasopharynx during
swallowing.
Fig. 23.3, p. 838
10
Conducting Passageways: Pharynx
• The pharynx connects the nose and mouth to the
larynx.
• The three “parts” of the pharynx are distinguished by
landmarks.
– The nasopharynx carries air only.
° It is located posterior to the nasal cavity, superior
to soft palate.
° It contains the pharyngeal tonsils (adenoids; see
Topic 5).
° The auditory tubes (also called the
pharyngotympanic or eustachian tubes) open into
the nasopharynx. (See A&P I Unit 10)
Fig. 23.3, p. 838
11
Conducting Passageways: Pharynx
– The oropharynx is a passage for air and food.
° It is posterior to oral cavity, inferior to soft palate.
° It is lined with stratified squamous epithelium,
which protects against abrasion.
° The lingual and palatine tonsils protect against
food and air borne particles. (See Topic 5)
– The laryngopharynx is a passage for air and food
° It is inferior to oropharynx and posterior to the
larynx.
° It is also lined with stratified squamous
epithelium.
Fig. 23.3, p. 838
12
Conducting Passageways: Larynx
• The opening into larynx is called the glottis.
• The epiglottis is a piece of mucosa-covered elastic
cartilage.
– It covers the glottis and keeps food out of larynx
during swallowing.
• The walls of the larynx are formed by pieces of hyaline
cartilage including:
– the thyroid cartilage, which is the largest,
– the cricoid cartilage, and
– the arytenoid cartilages, which are important to
sound production.
13
Larynx: Sound Production
• The true vocal cords (folds) are folds of mucosa
containing elastic vocal ligaments that vibrate to
produce sound.
– Tension is controlled by arytenoid cartilages
– The vocal cords tighten during exhalation and air
movement causes vibration of cords.
° Pitch (frequency) is controlled by changing
length and tension of cords.
- Tighter stretch produces higher frequency.
° Loudness depends on force of vibration.
• Vestibular folds, located superior to the vocal folds,
protect the vocal folds.
14
Conducting Passageways: Trachea
• The airways from from the larynx to the level of the T5
vertebra in the chest are patent. That is, they are kept
open to allow free flow of air.
• The trachea contains 16-20 hyaline cartilage rings.
– These rings are incomplete in back, which makes for
easier passage of food through the esophagus.
Fig. 23.5, p. 843
15
Conducting Passageways: Trachea
There are 3 layers in trachea wall.
• The mucosa consists of ciliated pseudostratified
columnar epithelium with goblet cells and an
underlying lamina propria of areolar connective
tissue.
– Goblet cells in the epithelium produce mucus that
helps trap airborne particles.
– Cilia form ciliary escalator, which moves the
particle-laden mucus upwards.
• The submucosa consists of connective tissue layer.
– Seromucous glands secrete additional mucus.
16
Conducting Passageways: Trachea
• The adventitia consists of elastic connective tissue
and hyaline cartilage rings.
– The rings are incomplete posteriorly.
– The trachealis muscle consists of smooth muscle
and bridges the rings posteriorly.
17
Bronchial Tree
• The bronchial tree includes both conducting and
respiratory passageways.
– Conducting passageways include the primary
bronchi through the terminal bronchioles.
– Respiratory passageways include the respiratory
bronchioles, which lead to the alveoli.
• General trends include:
– a decrease in and eventual loss of cartilage rings;
– the gradual addition of smooth muscle to control
airway diameter; and
– flattening of the epithelium, which goes from
pseudostratified columnar to simple squamous.
18
Conducting Passageways:
Primary Bronchi
• One primary bronchus goes to each lung.
• The walls have cartilage with some smooth muscle.
• The bronchi are lined with pseudostratified ciliated
columnar epithelium with numerous goblet cells.
Fig. 23.7, p. 844
19
Conducting Passageways:
Secondary Bronchi
• Secondary bronchi are branches of the primary
bronchi. These serve the lobes of lungs; there are 3 on
right and 2 on left. (See pg. 5)
• Walls have less cartilage and more smooth muscle than
do the primary bronchi.
• The secondary bronchi are lined with pseudostratified
ciliated epithelium in which cell height is smaller than
in the primary bronchi.
http://www.pul.unimaas.nl//respir.htm#lower%20tract
Fig. 23.7, p. 844
20
Conducting Passageways:
Tertiary Bronchi
• Tertiary bronchi are branches of the secondary bronchi
and serve the bronchopulmonary segments.
• The walls have irregular rings of cartilage and much
more smooth muscle.
• Cells of the pseudostratified ciliated epithelium lining
are very short.
Fig. 23.7, p. 844
http://www.pul.unimaas.nl//respir.htm#lower%20tract
21
Conducting Passageways:
Bronchioles
• Bronchioles are small branches of the tertiary bronchi.
– There are many subdivisions and levels of
bronchioles.
• The walls consist mainly of smooth muscle with little
or no cartilage. This muscle will be important to
control of airway diameter.
• Bronchioles are lined with cuboidal epithelium.
Fig. 23.7, p. 844
http://www.pul.unimaas.nl//respir.htm#lower%20tract
22
Conducting Passageways:
Terminal Bronchioles
• Terminal bronchioles are branches deep in the lungs.
• They lack cartilage and smooth muscle is scattered.
• Terminal bronchioles are lined with cuboidal
epithelium.
• Terminal bronchioles are the last of the conducting
passageways and lead to respiratory bronchioles.
Fig. 23.7, p. 844
http://www.pul.unimaas.nl//respir.htm#lower%20tract
23
Respiratory Zone (Passageways)
Respiratory Bronchioles
• Respiratory bronchioles are the smallest and thinnest of
air passageways leading to respiratory surfaces of lung.
• They are lined with low simple cuboidal epithelium.
Fig. 23.8, p. 845
http://www.kumc.edu/instruction/medicine/anatomy/histoweb/resp/resp.htm
24
Respiratory Zone: Alveoli
• Alveolar ducts are passageways from the respiratory
bronchioles to the alveolar sacs and alveoli.
• Alveolar sacs are groups of alveoli with a common
opening.
• Alveoli (singular = alveolus) are the individual air sacs.
http://www.usc.edu/hsc/dental/ghisto/lng/d_28.html
Fig. 23.8, p. 845
25
Respiratory Zone: Alveoli
• Thin-walled structures across which gases are
exchanged
• Barrier to diffusion respiratory gases (CO2 and O2)
• Adjacent alveoli joined by alveolar pores
http://www.usc.edu/hsc/dental/ghisto/lng/d_28.html
Fig. 23.8, p. 845
26
Respiratory Zone:
“Respiratory Membrane”
• The respiratory membrane is the surface across which
gases are exchanged.
– It consists of the alveolar epithelium, the capillary
epithelium, and the basement membrane between
them.
• Alveolar endothelium consists of two types of cells.
– Type I cells are simple squamous epithelium (blue
arrow in the linked image) and function in gas
exchange.
– Type II cells are scattered simple cuboidal cells
(green arrow in the linked image) and secrete
surfactants.
http://www.kumc.edu/instruction/medicine/anatomy/histoweb/resp/resp.htm (#15)
27
Respiratory Zone:
“Respiratory Membrane”
• The basal lamina is the basement membrane that joins
the two epithelial layers.
• Capillary endothelium consists of simple squamous
epithelium.
http://www.kumc.edu/instruction/medicine/anatomy/histoweb/resp/resp.htm
28
Nerve Supply to Lungs
• Nerves enter and leave through the hilus.
• Pulmonary plexuses provide autonomic (ANS)
innervation to smooth muscle of the bronchi and
bronchioles. There are two kinds of plexuses – one for
each division of the ANS.
– The sympathetic pulmonary plexus provides
sympathetic innervation that leads to dilation of
bronchi and bronchioles.
° Think About It: Why would this be important to
the fight or flight response?
Fig. 14.4, p. 519
29
Nerve Supply to Lungs
– Parasympathetic innervation from the pulmonary
plexus of the Vagus (X) nerve causes constriction of
bronchi and bronchioles.
° Think About It: Which division (sympathetic or
parasympathetic) would be involved in responses
to airborne irritants?
- (HINT: The response to irritants is to decrease the size
of the airways.)
Fig. 14.4, p. 517
30
Blood Supply to Lungs
• Vessels enter and leave through the hilus.
• Two systems serve the lungs.
– The pulmonary circulation carries blood to the
respiratory surfaces of the lungs for gas exchange
with air in alveoli.
° Pulmonary arteries bring blood to the lungs.
° Alveolar capillaries are sites of exchange of gases
between air in the alveoli and blood.
° Pulmonary veins carry blood from the lungs to
the heart.
° Recall: Which of these vessels carry oxygenated
blood? Which ventricle pumps into this system?
Which atrium receives blood from it?
31
Blood Supply to Lungs
– The bronchial circulation carries blood to all lung
tissues except the alveoli.
° This circulation goes from the aorta to bronchial
arteries to capillaries to bronchial veins.
° Most blood returns via pulmonary veins due to
numerous anastomoses.
° Recall: Which of these vessels carry oxygenated
blood? Which ventricle pumps into this system?
Which atrium receives blood from it?
32
Ventilation
• Ventilation is the movement of air into or out of lungs.
– Inspiration is movement of air into the lungs.
– Expiration is movement of air into the lungs.
• Air flow is directly related to the pressure gradient; and
inversely related to resistance.
– Air moves from areas of higher pressure to areas of
lower pressure.
– The pressure gradient moves air and gases between
nose (or mouth) and the terminal bronchioles.
– Between the terminal bronchioles and alveoli,
individual gas movement is driven by diffusion.
33
Ventilation: Pressures
3 pressures are involved in ventilation.
• Atmospheric pressure (PA) is the same as air pressure.
– It is the external pressure of the air around the body.
• Intrapleural (intrathoracic) pressure is the pressure
within the pleural cavity.
– Intrapleural pressure is always less than
intrapulmonary pressure (within alveoli) by about 4
mm Hg.
– If intrapleural pressure equals or exceeds
atmospheric pressure, the lungs collapse.
• Intrapulmonary (intra-alveolar) pressure (PL) is the
pressure within the alveoli.
34
Ventilation: Pressures
• Atmospheric pressure normally stays roughly the same
at any given altitude.
• Since atmospheric pressure doesn’t change, ventilation
(breathing) involves changing intrapulmonary pressure.
35
Boyle’s Law
• Boyle’s law states that gas pressure is inversely
proportional to volume (V).
– Increasing volume decreases the pressure on the gas.
– Decreasing volume increases the pressure on the
gas.
• Air moves from higher pressure to lower pressure.
36
Boyle’s Law
• Given the pressures:
– PL = intrapulmonary pressure
– PA = atmospheric pressure
– And that air moves from higher to lower pressure.
• For inspiration: PL < PA
– That is, pressure in the lungs must be less than
atmospheric pressure for air to move into the lungs.
– Volume, V, must increase so that PL can decrease.
• For expiration: PL > PA
– That is, pressure in the lungs must be more than
atmospheric pressure for air to move out of the
lungs.
– V must decrease so that PL can increase
37
Processes of Ventilation
• The process of ventilation involves contraction of
skeletal muscle. (Review notes from A&P I muscle
lab.)
– This allows voluntary control as well as
subconscious control.
• Muscles whose contraction increases the size of the
thoracic cavity will cause inspiration.
– Relaxation of these muscles will cause passive
expiration as they return to their resting state.
• Muscles whose contraction decreases the size of the
thoracic cavity will add to expiration.
38
Processes of Ventilation
Inspiration
1. The diaphragm and/or external intercostal muscles
contract (innervated by phrenic and intercostal
nerves, respectively).
2. Thoracic volume increases.
3. Intrapleural pressure decreases.
4. Lungs expand into the lower pressure thoracic
(pleural) cavity.
5. Intrapulmonary pressure decreases.
6. Air moves in.
39
Processes of Ventilation
Expiration
1. The diaphragm and external intercostal muscles
relax (passive process) and lungs recoil.
2. Thoracic volume decreases.
3. Intrapleural pressure increases.
4. Lungs are compressed by the increased pressure in
thoracic (pleural cavity).
5. Intrapulmonary pressure increases.
6. Air moves out. – Expiration is normally passive
40
“Forced” Air Movements: Expiration
• Forced expiration expels more than the normal amount
of air.
• Forced expiration is accomplished by increasing
intrapleural pressure beyond normal breathing by
making thoracic cavity even smaller.
• The muscles that contribute to forced expiration are:
– abdominal muscles – external and internal obliques,
transversus abdominis; and
– thoracic muscles – internal intercostals, latissimus
dorsi, quadratus lumborum.
41
“Forced” Air Movements: Inspiration
• Forced inspiration involves inhaling more than normal
amount of air.
• This is accomplished by decreasing intrapleural
pressure beyond normal breathing by increasing the
thoracic cavity even more.
• Muscles involved are the:
– pectoralis minor, scalenes, sternocleidomastoid
muscles.
42
Promoting Lung Expansion
• Inspiration (when inspiratory muscles contract) is aided
by two things: compliance and surface tension within
the pleural cavity.
– Compliance is the ability of the lungs to expand.
° Decreased compliance makes it more difficult to
inflate the lungs.
° Causes of reduced compliance include:
- loss of elasticity of lung tissue; and
- increased alveolar surface tension.
43
Promoting Lung Expansion
– Surface tension within the pleural cavity is caused
by pleural fluid.
° Pleural fluid (serous fluid within the pleural
cavity) creates negative intrapleural pressure
between the pleural membranes (not unlike water
between two pieces of glass).
° Excess fluid is normally removed by the
lymphatic system.
° Failure to remove fluid results in a build up of
fluid (pulmonary edema), which increases the
intrapleural pressure (i.e., it becomes less
negative) making it difficult to inflate the lungs.
44
Promoting Lung Compression
• Expiration when inspiratory muscles are relaxing is
aided by alveolar fluid surface tension and elastic
recoil of the lungs.
– Alveolar fluid surface tension causes the lungs to
“want” to collapse by pulling the sides of the
alveoli closer together.
° Surfactant decreases alveolar surface tension,
thus preventing collapse.
- Respiratory distress syndrome (RDS; also known
as hyaline membrane disease of the newborn)
occurs in a premature babies that have insufficient
amounts of surfactant in lung; the lungs collapse
during expiration and must be reinflated.
45
Promoting Lung Compression
– Elasticity is the elastic recoil of lungs due to
elastic tissue in the walls of the lungs.
° Elasticity helps the lungs become smaller like
the deflating of a stretched balloon.
° Emphysema is a disease that decreases
elasticity. This makes exhalation difficult and
instead of being passive, it becomes an active
process.
46
Resistance to Airflow
• Resistance to airflow opposes movement of flow
into/out of lungs.
• Resistance is related to size (radius [r] and length) of
the air passageways and viscosity of the “fluid” (air).
– Resistance  (length of tube x viscosity of fluid) / r4
– Resistance is:
° directly related to tube length;
° directly related to viscosity; and
° indirectly related to radius4 (i.e.,  1/r4).
• Resistance is greatest in medium-sized bronchioles.
Fig. 23.5, p. 854
 Means “is approximately equal to”
47
Factors Increasing Airflow Resistance
Increased airflow resistance decreases flow.
Things that increase resistance include:
• Bronchoconstriction, which makes airways narrower
– Bronchoconstriction is caused by:
° the parasympathetic response to inhaled irritants;
° acetylcholine administration; and
° decreased PCO2 (partial pressure of CO2).
• Other factors that decrease size of airways include:
– solid obstructing tumors;
– mucus accumulation; and
– inflammation.
48
Factors Decreasing Airflow Resistance
Decreased airflow resistance increases flow.
• Bronchodilation makes airways larger. Bronchodilation
is caused by:
– sympathetic innervation;
– epinephrine administration; and
– increased PCO2.
49
Regulation of Ventilation
• Ventilation is controlled by the respiratory center
located in the medulla oblongata (as part of the
reticular formation).
• The respiratory center consists of:
– inspiratory center (dorsal respiratory group or
DRG); and the
– expiratory center (ventral respiratory group or
VRG).
• Under quiet breathing at rest, breathing is controlled
primarily by the DRG.
50
Mechanism of Basic Control
• The active DRG sends impulses to inspiratory
muscles to stimulate contraction (also simultaneously
sends inhibitory impulses to the VRG).
– The phrenic nerve (from the cervical plexus) goes
to the diaphragm.
– Intercostals nerves (from thoracic spinal cord
segments) go to the external intercostals.
• After about 2 seconds, the DRG becomes inactive,
impulses are no longer sent, and expiration occurs as
the inspiratory muscles relax.
• After about 3 more seconds, the DRG becomes active
again.
Fig. 23.24, p. 868
51
Other Coordinating Centers
• The pneumotaxic center located in pons inhibits the
DRG leading to shortened breaths leading to increased
breathing rate (e.g., panting).
• The apneustic center is a hypothetical center in pons
thought to prolong inspiration by stimulating the DRG.
52
Factors Affecting Ventilation Rates
• Pulmonary irritants (air-borne chemicals) are detected
by chemoreceptors in lungs that send impulses via
Vagus nerve.
 The resulting efferent parasympathetic impulses
(also from the Vagus nerve) cause
bronchoconstriction. Efferent somatic impulses
result in coughing or sneezing
See Fig. 23.25, p. 869
53
Factors Affecting Ventilation Rates
• In the Hering-Breuer (inflation) reflex stretch receptors
in the visceral pleura and conducting portions of
airways respond to inflation of lungs and send afferent
impulses via Vagus nerve to the DRG. These impulses
inhibit the DRG, thus preventing over inflation of the
lungs.
See Fig. 23.25, p. 869
54
Factors Affecting Ventilation Rates
• Cortical controls allow conscious control over skeletal
muscles involved in inspiration and expiration.
• The hypothalamus influences the medullary centers in
response to emotions (e.g., pain, fear, anger) or
increased body temperature.
• Chemical controls are based on chemistry of arterial
blood.
– Chemicals are sensed by peripheral chemoreceptors
in the carotid arteries and aorta and by central
chemoreceptors in the medulla oblongata.
See Fig. 23.25, p. 869
55
Chemical Controls: PCO2
• The PCO2 of normal arterial blood is 40 mm Hg + 3
mm Hg.
• Peripheral chemoreceptors located in the carotid
arteries and aorta are not very sensitive to arterial PCO2.
– Sensory (afferent) input is sent to the medulla via
the glossopharyngeal nerves (from carotid arteries)
and vagus nerves (from aorta).
56
See Fig. 23.25, p. 869
Chemical Controls: PCO2
• Central chemoreceptors located in the medulla are
sensitive to changes in PCO2 (as pH changes).
• CO2 diffuses readily across membranes (enters CSF).
– Increased PCO2 in the CSF leads to increased
carbonic acid (H2CO3), which increases H+
concentration and lowers pH.
– Increased H+ stimulates receptors in the medulla
leading to increases in the depth (and/or rate) of
breathing. This increase is hyperventilation.
57
See Fig. 23.25, p. 869
Chemical Controls: PCO2
° Hyperventilation increases CO2 exchange (loss),
thereby returning levels to normal.
° The effect of PCO2 on central receptors works
even when arterial blood pH and PO2 are normal.
– Low PCO2 leads to decreased H+ in the CSF (which
increases pH). The result is slower breathing, or
hypoventilation, which decreases CO2 exchange
(loss), thereby returning levels to normal.
58
See Fig. 23.25, p. 869
Chemical Controls: PO2
• The PO2 of normal arterial blood is around 105 mm Hg.
• The central respiratory center is less sensitive to PO2.
• Peripheral chemoreceptors are sensitive to PO2.
– BUT receptors are only stimulated when PO2 falls
below 60 mm Hg. This is because hemoglobin is still
more than 80% saturated even at a PO2 of 60 mm Hg.
59
Chemical Controls: pH
• The pH of normal arterial blood is around pH 7.4
(slightly alkaline). The normal range is pH 7.35-7.45.
– Decreased arterial pH stimulates peripheral receptors
resulting in increased ventilation even if PCO2 and PO2
are normal.
• Think About It: What would happen to breathing if:
– Arterial pH increased above 7.45?
– Decreased below 7.35?
60
Terms
•
•
•
•
•
Eupnea is normal, quiet breathing.
Dyspnea is difficult, labored breathing.
Apnea is the cessation of breathing (e.g., sleep apnea).
Hypopnea is abnormally slow &/or shallow breathing
Hyperpnea is deep, vigorous breathing (may also be
faster, but main thing is increased depth).
• Tachypnea is rapid breathing.
61
Overview of External and Internal
Respiration and Gas Transport
• External Respiration is the exchange of gases between
air and blood.
• Gas Transport is accomplished by blood (by red blood
cells and plasma).
• Internal Respiration is the exchange of gases between
blood and interstitial fluid (of tissues).
• Important respiratory gases are:
– CO2 (the product of aerobic metabolism) and
– O2 (which is needed for aerobic metabolism).
62
Dalton’s Law of Partial Pressures
• Dalton’s Law of partial pressures states that the
pressure exerted by a single gas in a mixture is directly
proportional to the percentage of that gas in the mixture
– At sea level, the amount O2 accounts for
approximately 20.9% of the gas in air.
– At sea level, total gas pressure is approximately 760
mm Hg.
– Therefore, PO2 is 20.9% x 760 mm Hg = 159 mm
Hg.
See Table 23.4, p. p. 859
63
Dalton’s Law of Partial Pressures
• Approximate Percentages of Gases at Sea Level
N2
79.6%
O2
20.9%
CO2 0.04%
H2O 0.46%
• Total pressure decreases with altitude, therefore, PO2
decreases (see next slide).
See Table 23.4, p. p. 859
64
Oxygen and Altitude
Altitude –
ft above sea
level
0
6000
Atmospheric
pressure
(mmHg)
Partial Pressure of
oxygen (mmHg)
Partial Pressure
of O2 in alveoli
760
609
160
127
105
84
8000
564
118
79
10,000
523
109
74
15,000[1]
430
90
60
18,000[2]
380
~75
~48
24,000
300
~60
~42
29,028[3]
240
~48
~20
[1] ~ Pike’s Peak summit [2] Mt. Everest base camp [3] Mt. Everest summit
http://www.udel.edu/Biology/dion/SicknessComments.html
65
Think-Pair-Share: Altitude Sickness
• What happens to atmospheric oxygen levels as you go
up in altitude?
• If someone were hiking in Colorado on Pike’s Peak
(~14,900 feet above sea level), how much oxygen
would be available in the atmosphere? In the alveoli?
• How would this affect the arterial oxygen levels?
• How would the body respond to the decreased arterial
oxygen? (How does the body normally respond to
hypoxia?)
– What “disorder” of the blood results from this?
• What is pulmonary edema?
66
Henry’s Law
• Henry’s law states that when a mixture of gases comes
into contact with a liquid, individual gases will diffuse
into the liquid in proportion to their partial pressures
• Therefore, Diffusion Rate =
gas solubility X membrane surface area X gradient X oF
membrane thickness X square root of molecular wt.
“gradient” = difference in partial pressures
Which of these would you expect to control?
67
Factors Governing Diffusion Rate
• Gas solubility in liquid depends on temperature, which
is normally held relatively constant.
• Molecular weight of the gas is a constant.
• Temperature of the liquid is body temperature, which
normally stays within narrow range.
• Membrane thickness refers to the capillary and alveolar
walls; this normally stays same but is changed by
diseases such as emphysema and pulmonary edema.
• Membrane surface area normally stays the same, but is
decreased by diseases like lung cancer and emphysema.
http://pathhsw5m54.ucsf.edu/case25/image253.html
http://www-medlib.med.utah.edu/WebPath/LUNGHTML/LUNG059.html
http://www-medlib.med.utah.edu/WebPath/LUNGHTML/LUNG124.html
68
Factors Governing Diffusion Rate
• The partial pressure gradient* is controlled –
maintained by ventilation.
• Partial pressures in the alveoli are different from
atmospheric partial pressures.
Gas Partial
Pressure
Atmospheric
Air, mm Hg
Alveolar Air,
mm Hg
PO2
159
104
PCO2
0.03
40
PH2O
3.5
47
69
Partial Pressure Gradient
• Reasons for difference between atmospheric and
alveolar partial pressures include:
– Humidification (addition of H2O) of inhaled air.
° As H2O is added, its partial pressure increases
and all other partial pressures decrease.
– Gas movements between air and blood.
° Movement of CO2 into the alveoli from the
blood increases alveolar PCO2; and
° Movement of O2 from the alveoli into the
blood decreases alveolar PO2
70
Partial Pressure Gradient
– Mixing of old and new air within the alveoli and
conducting passageways also keeps alveolar air
higher in CO2 and lower in O2.
° Not all alveolar air is exchanged with each
breath.
° Air in the conducting passages is called “dead
air” and does not participate in exchange of
gases between air and blood.
° This air is higher in O2 and lower in CO2 than
alveolar air.
71
External Respiration:
Gas Movements
• O2 is loaded into blood from the alveoli.
• CO2 is unloaded out of blood into the alveoli.
Arteriole
end
Venule
end
72
Ventilation-Perfusion Coupling: PO2
• The circulatory system works in coordination with
respiratory system to maximize effectiveness of gas
exchange.
• PO2 affects the diameter of arterioles (arteriolar
diameter).
– Low airflow in a bronchiole results in decreased PO2
in the airway. This causes vasoconstriction of the
pulmonary arterioles serving the alveoli associated
with that bronchiole.
° Therefore, less blood goes to where alveolar
oxygen will be low.
73
Ventilation-Perfusion Coupling: PO2
– High airflow in a bronchiole results in increased PO2
in the airway leading to alveoli. This causes
vasodilation of the pulmonary arterioles serving that
area.
° Therefore, more blood goes to where alveolar PO2
will be high.
74
Ventilation-Perfusion Coupling: PCO2
• PCO2 affects bronchiolar diameter (diameter of
bronchioles)
– High PCO2 in an airway results in bronchodilation,
which results in increased airflow.
° Increased airflow clears CO2 from the airway.
– Low PCO2 in an airway results in
bronchoconstriction, which results in decreased
airflow.
° Decreased airflow prevents loss of too much CO2,
which would affect pH.
75
Blood Gas Transport: Oxygen
• Most oxygen – around 98.5 % of it – is carried attached
to iron atoms of hemoglobin (Hb).
– Iron (Fe) is part of the heme. There is one Fe per
heme.
– There are 4 heme per hemoglobin molecule.
° Therefore, 4 O2 are carried per molecule.
- Hb with O2 is called oxyhemoglobin [Hb(O2)4]
- Deoxyhemoglobin (HHb) is Hb without oxygen. It
combines with 4 O2 to become Hb(O2)4
• The remaining O2 – around 1.5% – is carried as
dissolved oxygen in plasma. This exerts the partial
pressure of oxygen. http://www.pul.unimaas.nl//respir.htm#lower20%tract
76
Blood Gas Transport: Oxygen
• Because there are 4 chains in Hb, oxygen binding is
cooperative.
– That is, once one molecule of O2 is bound, others
bind more easily.
– It also means that at the tissues, O2 release is
enhanced.
• Oxygen saturation curves demonstrate the effect of PO2
and cooperative binding.
• Systemic venous blood is still at least (>) 70%
saturated with oxygen.
Fig. 23.20, p. 863
77
Oxygen Saturation Curves
Hb saturation depends on:
• PO2 and PCO2;
• temperature;
• pH; and
• blood bis-phosphoglycerate (BPG) levels.
Fig. 23.20, p. 863
Fig. 23.21, p. 864
78
Oxygen Saturation Curves: PO2 & PO2
• The effect of PO2 is due to cooperative binding. As O2
binds, the protein (globin) changes shape, making it
easier for the next O2 to bind.
• CO2 binds to a different part of the Hb molecule. As it
binds, it causes a change in the shape (conformation) of
the Hb molecule. (See Chapter 2 for more on protein
configurations.)
– This shape (conformational) change makes it less
favorable for oxygen binding (i.e., makes it easier
for Hb to give up its oxygen).
Fig. 23.20, p. 863
79
Oxygen Saturation Curves: pH and
Temperature
• pH is due to H+ concentration.
– The Bohr effect refers to effect of pH on affinity of
Hb for O2.
° The more H+, the lower the affinity of Hb for O2.
– H+ results from carbonic acid or lactic acid, both of
which are associated with active tissues.
• Temperature also changes the shape of Hb.
– Higher temperatures reduce the affinity of Hb for
O2, making O2 release easier.
– Higher temperatures are also associated with active
tissues.
Fig. 23.21, p. 864
80
Affect of NO
• NO (nitric oxide) is secreted by endothelial cells of
blood vessels and lungs.
• Although it does not affect oxygen transport directly, it
does affect vessel diameter, and therefore flow.
– NO causes vasodilation of pulmonary and tissue
capillaries and, thus, enhances gas exchange by
increasing blood flow.
81
Metabolism Review
• Aerobic Respiration uses O2 and produces CO2
– Glucose + 6 O2  6 CO2 + 6 H2O + 36 ATP
– Aerobic respiration (also called cellular respiration)
has three stages:
° glycolysis;
° the Kreb’s (citric acid or TCA) cycle;
° and electron transport coupled with
chemiosmosis.
• Anaerobic Respiration occurs in the absence of oxygen.
– Glucose  lactic acid + 2 ATP
82
Metabolism Review
• By-products of glucose catabolism through glycolysis
include:
– BPG (bis-phosphoglycerate), an intermediate of
glycolysis;
– heat because the reactions are inefficient; and
– H+, which lowers pH, from:
° carbonic acid, which is produced when CO2
combines with H2O, or
° lactic acid, which is a result of anaerobic
respiration.
83
Summary of Factors Affecting O2
Transport
Factors Affecting
Association
Favoring Hb-O2
Association
Favoring Hb-O2
Dissociation
Temperature
Low
High
PO2
High
Low
PCO2
Low
High
pH
High
Low
BPG
Low
High
84
Blood Gas Transport: Carbon Dioxide
• 7-10% of CO2 is carried as dissolved carbon dioxide.
• 20-30% is carried attached to the globin part of
hemoglobin to form carbaminohemoglobin.
• About 70% is converted to bicarbonate ions (HCO3-)
for transport in plasma because of the reversible
reaction between CO2 and H2O.
– CO2 + H2O <=> H2CO3 <=> H+ + HCO3– This reaction occurs spontaneously in plasma.
– This reaction occurs much more rapidly in RBCs
due to presence of the enzyme carbonic anhydrase.
85
Carbon Dioxide Transport: Chloride Shift
• CO2 enters RBCs at the body tissues where levels are
relatively high; CO2 leaves RBCs at the lungs where it
is released into the alveoli.
• The chloride shift is the exchange of ions (Cl- and
HCO3-) between plasma and RBCs.
– At body tissues, Cl- enters the RBC and HCO3produced by the carbonic anhydrase reaction
(previous slide) leaves.
– At the lung, HCO3- enters RBCs as the carbonic
anhydrase reaction reverses to produce CO2, Clleaves the RBC. (CO2 also leaves the RBC.)
Fig. 23.22, p. 866
86
Carbon Dioxide Transport:
Haldane effect
• CO2 binds to reduced Hb more efficiently than to
oxyhemoglobin. Therefore,
– more CO2 is carried by Hb when O2 is low; and
– as CO2 increases, O2 dissociation increases.
Fig. 23.23, p. 867
87
Internal Respiration:
Gas Movements
• Internal respiration occurs between tissues and blood.
• O2 enters the tissues from blood.
• CO2 leaves the tissues to enter blood.
88
Factors Affecting Internal
Respiration
Factors affecting internal respiration include:
• the surface area for exchange;
– Surface area depends on the size of the capillary
bed[s] serving the specific tissue;
– The size of the capillary bed varies from tissue to
tissue. For example, red twitch muscle has more
capillaries than white twitch (see A&P I Unit 13 –
Muscle)
89
Factors Affecting Internal
Respiration
• the partial pressure gradient, which is maintained in the
lungs by ventilation;
– hyperpnea and hypopnea change the gradients.
– Think About It: What effect would each have on O2
levels? On CO2 levels?
• the rate of blood flow, which varies with needs of
tissue.
– Blood flow increases during activity when O2
decreases and CO2 increases (see Topic 4).
– Blood flow decreases when tissue is inactive and O2
is not removed nor CO2 produced as quickly.
90
Restrictive Pulmonary Disease
• Restrictive Pulmonary Disease are ones in which total
lung volume is reduced.
• These diseases result in reduced total lung capacity,
vital capacity and resting lung volume.
• Causes of restrictive pulmonary disease include:
– changes to lung tissue that reduce volume (e.g.,
pulmonary fibrosis, tuberculosis, pneumonia,
pulmonary edema); and
– changes to the pleurae, chest wall or respiratory
musculature or nerves that reduce compliance.
91
Chronic Obstructive Pulmonary
Disease (COPD)
• COPDs are chronic diseases in which breathing is
difficult and gets progressively worse; coughing and
pulmonary infection are common.
• Ventilation is impaired and the ability to exhale rapidly
and forcefully is diminished.
• Patient eventually develops respiratory failure.
• COPDs are often (but not always) caused by long-term
smoke inhalation
• COPDs include:
– cystic fibrosis,
– emphysema, and
– chronic bronchitis
92
COPDs
• Cystic fibrosis (CF) is a congenital defect of the Cltransport protein in the plasma membrane.
– The inability to transport Cl- into the lumen of the
airways results in overproduction of thick mucus.
This mucus reduces the usable diameter of the
airways.
– Gene therapy is ineffective because no one knows
exactly what the stem cells are.
http://www.vh.org/Providers/TeachingFiles/ITTR/CysticFibrosis/CFPA.html
93
COPDs
• Emphysema results from the breakdown of intraalveolar walls. This causes permanent enlargement of
the alveoli (which decreases surface area for gas
exchange). The lungs become fibrous and inelastic
• Chronic bronchitis is a chronic irritation and infection
of the bronchi.
• Both are associated with long-term smoking.
http://www-medlib.med.utah.edu/WebPath/LUNGHTML/LUNG059.html
http://pathhsw5m54.ucsf.edu/case25/image253.html
94
Inflammatory Respiratory Disorders
• Pleurisy is an inflammation of pleural membranes
results either in decreased fluid (increases friction) or
fluid build up (increased intrathoracic = intrapleural
pressure)
• Asthma is an inflammation of the airways usually as an
allergic reaction to airborne particles.
– Asthma may be made worse by autonomic factors,
infection (inflammation), exercise, and cold.
– Asthma results in coughing, sneezing, dyspnea,
wheezing, and tightness in the chest.
95
Infant Respiratory Distress
Syndrome (RDS)
• RDS is also known as hyaline membrane disease or
HMD.
• Lack of sufficient surfactants allows surface tension in
the alveoli to increase resulting in collapse of alveoli
on exhalation.
Normal lung: http://www.usc.edu/hsc/dental/ghisto/lng/d_28.html
RDS lung: http://axon.sote.hu/KKK/DESCRIPT/0131/0131001E.HTM
96
Infectious Respiratory Disorders
• Pneumonia is a viral or bacterial infection of the lungs.
• Bronchitis is a viral or bacterial infection of the
bronchi.
• Tuberculosis is a bacterial infection caused by
Mycobacterium tuberculosis
97
Other Respiratory Disorders
• Pneumothorax is presence of air in intrapleural space,
as from a puncture wound. This allows the lung to
collapse. Because the lungs are in separate cavities, one
may collapse while the other stays inflated.
• Lung cancer is a cancerous tumor. Cancer is often
related to inhaled carcinogens (as are found in tobacco
smoke).
http://medicine.creighton.edu/medschool/VideoAtlas/Respiratory/Thoracic%2
0Neoplasia/webstuff/chestcancer1.html
98