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The Respiratory System
The Respiratory System
Functions:
– To provide the body with means of taking in(O2) for
the production of ATP and eliminating (CO2) a
byproduct of aerobic respiration.
– To help maintain the body’s pH, by regulating the
blood CO2 levels in the body.
– Work in conjunction with the cardiovascular system
to move these gases from the lungs to the cells
and from the cells to the lungs.
Organs of Respiratory System
Conducting Zone
• Conducting zone
– Provides rigid
conduits for air to
reach the sites of gas
exchange
– Respiratory
structures include
(nose, nasal cavity,
pharynx, trachea,
primary, secondary
and tertiary bronchi)
– No Gas exchange
Respiratory Zone
• Respiratory zone:
– begins as terminal
bronchioles →
respiratory
bronchioles →
alveolar ducts, →
alveolar sacs
composed of alveoli
– This is where gas
exchange occurs!
Nose
• Functions
– Nasal choanae creates turbulent air flow that
allows air to contact mucus membranes and
superficial nasal sinuses.
• The result is cleaner, warmer more humidified
inhaled air.
– detects odors via the olfactory cranial nerve
which also enhances our sense of taste.
– Resonating chamber that amplifies the voice
Pharynx
Larynx
• Larynx (“voice box”)
– contains vocal cords allowing speech production
• Glottis – vocal cords
• Epiglottis
– flap of tissue that guards glottis, directs food and drink to esophagus
Trachea
• Flexible and mobile tube extending from the larynx to
the carina (split into primary bronchi)
• Composed of three layers
– Mucosa – made up of pseudostratified ciliated
epithelium that contain goblet cells that secrete
mucus to trap dirt.
• Mucociliary escalator: cilia beats in an upward
fashion toward the pharynx where debris can be
swallowed.
– Submucosa – connective tissue deep to the mucosa
– Adventitia – outermost layer made of C-shaped rings
of hyaline cartilage which prevent the airway from
collapsing.
Trachea
Respiratory Zone
• Approximately 300
million alveoli:
– Account for most
of the lungs’
volume
– Provide
tremendous
surface area for
gas exchange
– Equivalent to 2
tennis courts in
surface area.
Respiratory Membrane
Respiratory Membrane
Air-blood barrier is composed of alveolar and capillary
walls.
– Alveolar walls: contain 2 main types of cells
1. Type I epithelial cells (simple squamous epithelium)
that permit gas exchange by simple diffusion
2. Type II cells (cuboidal epithelium ) secrete
surfactant which enables the lungs to expand.
3. White blood cells are found in the lumen of the
alveoli.
1. Function to protect against infections from inhaled
pathogens
4 Processes of Respiration
1. Pulmonary ventilation – air moving into and out of the
lungs along their pressure gradients.
•
•
Inspiration – air(O2)flows into the lungs
Expiration – air (CO2) exit the lungs
2. External respiration – gas exchange between the lungs
(alveolus) and the blood (pulmonary capillaries)
3. Transport – transport of oxygen and carbon dioxide
between the lungs and tissues via the circulatory system.
4. Internal respiration – gas exchange between systemic
blood vessels (capillaries) and the tissues (cells)
•
Gases must diffuse into interstitial fluid prior to any exchange
between the tissue and the cell.
Pulmonary Ventilation
• Taking of air into and out of the lungs.
• A mechanical process that depends on
respiratory muscles changing the size of the
thoracic cavity
– Because this cavity is connected to the lungs
via the parietal membranes it may also
influence the lung (alveolar )volume.
• A increase in alveolar volume will move air into the
lungs down it concentration gradient.
• A decrease in alveolus volume will move air out of
the lungs.
Boyle’s Law
• The changes in thoracic volume is necessary to
move air in and out of the lungs. The movement
of air in dependant of:
– Boyle’s law – Pressure and Volume are
inversely proportional.
• P ×V= Constant
• If pressure increases volume decreases
• If pressure decreases volume increases
and vise versa
• This mechanism is dependent on a doublelayered membrane system called (Pleurae)
Pleurae
Parietal
pleurae
Visceral
pleurae
Intrapleural
space
Pleurae
• Parietal pleura
– Covers the thoracic wall and superior face of the
diaphragm
– Continues around heart and between lungs
Visceral pleura
– Covers the external lung surface
• Intrapleural Space
– Space between the parietal and visceral pleurae.
– There is a small amount of fluid (pleural fluid) within
the space that hold the 2 pleurae together
• This will reduce friction between the lungs and the thoracic
cavity.
– Similar to a small amount of water between 2 plains
of glass.
• Slides easily but difficult to separate.
Pulmonary Pressures
• Intrapulmonary pressure and intrapleural pressure
fluctuate with the phases of respiration.
– Intrapulmonary pressure aka. alveolar is the pressure
with in the alveolus
– Intrapleural pressure is the pressure within the pleural
space
• created by many hydrogen bonds between the water
molecules of the pleural fluid.
• Intrapleural pressure must always less than
intrapulmonary pressure and atmospheric
pressure
Pulmonary Pressures
Intrapulmonary
pressure
Atmospheric
pressure
intrapleural
pressure
Lung Collapse
• Caused by equalization of the intrapleural
pressure with the intrapulmonary pressure
• Transpulmonary pressure keeps the airways
open
– Transpulmonary pressure – difference
between the intrapulmonary and intrapleural
pressures
(Ppul – Pip)
Muscles of Respiration
Inspiration
Expiration
Figure 22.13.2
Respiratory muscles
• The muscles collectively work to change the
volume of the thorax during ventilation.
• Inspiration
– Diaphragm via the phrenic nerve flattens out increasing
thoracic volume depth
– External intercostals via intercostal nerves pull the ribs
up and out.
• This collectively increase the size (volume) of the thorax and the
lungs via its attachment to the pleura.
• Expiration
– Normal expiration is a passive process that involves the
relaxation of the inspiratory muscles.
– Forced expiration is an active process involving the
internal intercostals and abdominals contracting forcing
the ribs down decreasing the size (volume) of the thorax.
• coughing
• What is the mechanism of action for the
Heimlich Maneuver?
Lung Compliance
• The lungs ability to expand despite the lungs
tendency to collapse.
• Determined by two main factors:
– Distensibility of the lung tissue and
surrounding thoracic cage
– Reducing surface tension of the alveoli: as the
lungs expand it stretches the type II cell to
produce more surfactant.
• Surfactant is a detergent-like complex, reduces
surface tension by breaking H-bonds allowing the
lungs to expand.
Factors That Diminish Lung Compliance
• Scar tissue or fibrosis that reduces the natural
resilience of the lungs preventing them to expand
during inhalation.
• Blockage of the smaller respiratory passages with
mucus or fluid
• Reduced production of surfactant
• Decreased flexibility of the thoracic cage or its
decreased ability to expand
• Examples include:
– Deformities of thorax
– Ossification of the costal cartilage
– Paralysis of intercostal muscles
Deformities of Thorax
• Barrel Chest
Pectus Excavatum
Environmental Influences of Ventilation:
• The amount of gas flowing into and out of
the alveoli is directly proportional to 
Pressure
– The greater the pressure gradient between
the atmosphere and the alveoli the more air
will enter the lungs
• Atmospheric pressure (Patm)
– Pressure exerted by the air surrounding the
body
• Altitude and (Patm) are inversely proportional.
– It is much easier to breath at sea level than it
is a 10,000 ft above. Why?
Airway Resistance
• Gas flow is inversely proportional to resistance
– The resistance increases as vessel diameter
decreases.
• This will lead to less gas reaching the alveoli for exchange.
• As airway resistance rises, breathing movements become
more strenuous
– Severely constricted or obstructed bronchioles:
• Can occur during acute asthma attacks which
stops ventilation .
– Epinephrine released via the sympathetic nervous
system or medically induced dilates bronchioles and
reduces air resistance.
Dalton’s Law of Partial Pressures
•
The air that we breath is made up of 4 main gases
– N2, O2, H2O and CO2
– There is a different % of each of the above gases
in the atmospheric air.
– Each gas therefore makes up a different
proportion of the total mixture.
• The sum of the partial pressures of each individual
gas is equal to the total pressure of the air.
• The partial pressure of the various gases are
important in establishing the gradients which drives
the gases throughout the system.
Partial Pressure Gradients
Partial Pressures Gradients During
Internal Respiration
• PCO2 (45mmHg) in peripheral tissues is higher than
in the arteries returning from the lungs(40mmHG)
because CO2 is a end product of cellular respiration.
• The PO2(40mmHg)is lower in the tissues than the
arterial blood (95mmHg) because O2 is being
continuously being used by the cells.
• O2 and CO2 will diffuse along their concentration
gradients
– O2 from blood to tissues
– CO2 from tissue to blood
Partial Pressure Gradients During External
Respiration
• Following (internal respiration)O2 unloading to
the tissues and CO2 uptake into the blood the
(PO2) in venous blood decreases to 40 mmHg
and the PCO2 increases to 45mmHg
• Following ventilation the PO2 in the alveoli is104
mmHg and PCO2 decreases to 40mmHg
• O2 and CO2 will diffuse along its pressure
gradient from high to low
–
–
–
–
PO2 =lungs → blood
CO2 = blood → lungs
Diffusion will occur until equilibrium is met.
Blood PO2 and PCO2 will = the alveolus partial
pressures.
Gas Transport: Role of Hemoglobin
• Molecular oxygen is carried in the blood:
– Bound to hemoglobin (Hb) within red blood cells (99%)
• The hemoglobin-oxygen combination is called
oxyhemoglobin (HbO2)
– Dissolved in plasma (1%)
• Carbon dioxide is transported in the blood in three forms
– Dissolved in plasma – 7 to 10%
– Chemically bound to hemoglobin – 20% is carried in
RBCs as carbaminohemoglobin
– Bicarbonate ion in plasma – 70% is transported as
bicarbonate (HCO3–)
Internal Respiration
Internal Respiration
CO2
Carbon
dioxide
+
H2O
Water

H2CO3
Carbonic
acid

H+
Hydrogen
ion
+
HCO3–
Bicarbonate
ion
At the tissues:
• Carbon dioxide diffuses into RBCs
• The high concentration of CO2 causes the above equation to shift to
the right.
– combines with water to form carbonic acid (H2CO3)
• (H2CO3), which quickly dissociates into hydrogen ions and
bicarbonate ions
• Hydrogen ions attach to one of 4 heme molecules in the RBC
dislodging on of the O2 (Bohr effect)
– Oxygen travels down its concentration gradient to the tissues
• Bicarbonate levels quickly build up and will quickly diffuses from
RBCs into the blood plasma
• The chloride shift – to counterbalance the out rush of negative
bicarbonate ions from the RBCs, chloride ions (Cl–) move from the
plasma into the erythrocytes
External Respiration
External Respiration
CO2
Carbon
dioxide
+
H2O
Water

H2CO3
Carbonic
acid

H+
Hydrogen
ion
+
HCO3–
Bicarbonate
ion
• When the blood gets to the lungs these processes are
reversed.
– The above reaction will shift to the left.
• Bicarbonate ions move into the RBCs and bind with
hydrogen ions to form carbonic acid
• Carbonic acid is then split by carbonic anhydrase to
release carbon dioxide and water
– CO2 levels quickly rise in the cell
• CO2 diffuses from the blood into the alveoli along its
concentration gradient.
Oxygen-Hemoglobin Dissociation Curve
• The higher the PO2 in the
blood the greater the percent
O2 saturation.
• The percent O2 saturation
plotted against blood PO2
– this tells us the amount of
oxygen that is bound to
hemoglobin at a particular
PO2 in the blood
– We monitor O2 saturation
levels with patients with
pulmonary issues
• Below 90% is termed
hypoxemia
Other Factors Influencing Hemoglobin Saturation
• Increases in Temperature, H+, PCO2, and BPG increase
O2 unloading from the hemoglobin.
– This will result in a shift to the right on the curve
• When the cells are more metabolically active there is a
greater need for O2.
• Temperature increases in metabolically activity, the
tissues because heat is a byproduct of cellular
respiration.
• Active cells will also produce more CO2 and H20 which
ultimately will lead to greater amounts of H+
– Both these byproducts ensure that O2 will be unloaded from the
RBC and delivered to the tissues.
• Decreases in Temperature, H+, PCO2, and BPG will act
in the opposite manner
– This will result in a shift to the left on the curve
Factors Influencing Hemoglobin Saturation
Medullary Respiratory Centers
• Ventral Respiratory Group:
Sets the underline breathing
rate .It activates the
– Diaphragm stimulated via
the Phrenic Nerve
– External Intercostals
stimulated via the Costal
Nerves
• Dorsal Respiratory Group
(DRG): receives input from
multiple areas.
– It modulates the breathing
rate of the VRG so it can
adapt to various
situations.
Pons (Secondary Centers)
• Apneustic Center
• Stimulation of this center causes strong inspirations or
aids in prolong inspiration.
• stimulations the inspiratory center
• Pneumotaxic Center
• inhibits the VRG to end inspiration
– provides for a smooth transition between inspiration and
expiration
• Stimulation of this center inhibits the Apneustic center
• Contributes to expiration
• Cortical control: we can actively effect our respiratory rate
such as
• holding breath under water
• The Limbic system and hypothalamus also stimulate the
respiratory centers.
• Emotional effect on respiration
Depth and Rate of Breathing:
Reflexes
• Inflation reflex (Hering-Breuer) – stretch
receptors in the lungs are stimulated by
lung inflation
– Upon inflation, inhibitory signals are sent to
the medullary inspiration center to end
inhalation and allow expiration
• Pulmonary irritant reflexes – irritants
promote reflexive constriction of air
passages
Central Chemoreceptors
• Changing PCO2 levels are monitored by Central
chemoreceptors of the brain stem
– Carbon dioxide in the blood diffuses into the
cerebrospinal fluid
–  CO2 + H2O  H2CO3  HCO3- + H+
• PCO2 levels rise (hypercapnia) resulting in increase
in H+ ion level concentration in the medulla.
• This stimulations of( DRG) increased depth and
rate of breathing
– CO2 (expired) + H2O  H2CO3  HCO3- + H+
• This will allow the body to blow off more CO2 thus
reducing CO2 levels reestablishing homeostasis.
Depth and Rate of Breathing:
PCO2
Peripheral Chemoreceptors
• Arch of the Aorta
– main vessel originating from the heart
• Carotid sinus
– main artery in the neck
• Elevated arterial P CO2 and H+ ion
concentration or decrease in PO2 will stimulate
DRG to increase respiratory rate.
– CO2 levels are the main driving force behind
respiratory rate.
Depth and Rate of Breathing: PCO2
• Hypoventilation – When PCO2 levels are abnormally low the
body will slow its respiratory rate.
– Holding your breath or breathing slow and shallow will
cause CO2 levels to start to raise in your blood
• As the CO2 levels start to rise again this will trigger
chemoreceptors to stimulate DRG to increase ventilation
causing thus exhaling more CO2 levels in the blood CO2
– Apnea (breathing cessation) may occur until PCO2 levels
rise
Depth and Rate of Breathing: PCO2
• Hyperventilation – increased depth and rate of
breathing that:
– Quickly flushes CO2 from the blood
• CO2 (expired) + H2O  H2CO3  HCO3- + H+
– Occurs in response to hypercapnia( high CO2 in
blood)
• Though a rise CO2 acts as the original stimulus,
control of breathing at rest is regulated by the
hydrogen ion concentration in the brain
• Why do you give someone a bag to breath into if
they are hyperventilating?
Respiratory Acidosis
• pH of CSF (most powerful respiratory stimulus)
• Respiratory acidosis (pH < 7.35) caused by decline in
pulmonary ventilation ( not blowing CO2 off)
• PCO2(Normal 35-45)=>45 Acidic
– hypercapnia: PCO2 > 45 mmHg
• CO2 easily crosses blood-brain barrier
• in CSF the CO2 reacts with water and releases H+
–  CO2 + H2O  H2CO3  HCO3- + H+
• central chemoreceptors strongly stimulate inspiratory
center (DRG) stimulates phrenic and intercostal nerve
which targets inspiratory muscles increasing respiratory
rate.
– “blowing off ” CO2 pushes reaction to the left
CO2 (expired) + H2O  H2CO3  HCO3- + H+
• so hyperventilation reduces H+ (reduces acid)
Respiratory Alkalosis
• Respiratory alkalosis (pH > 7.35)
– hypocapnia: PCO2 < 35 mmHg
• CO2 (expired) + H2O  H2CO3  HCO3- + H+
– Hypoventilation ( CO2), pushes reaction to the right
 CO2 + H2O  H2CO3  HCO3- + H+
–  H+ (increases acid), lowers pH to normal
• pH imbalances can have metabolic causes
– uncontrolled diabetes mellitus
• fat oxidation causes ketoacidosis, may be
compensated for by Kussmaul respiration
(deep rapid breathing)
Hypoxia
• Causes: Reduced levels of oxygen particularly in the blood.
– hypoxemic hypoxia - usually due to inadequate pulmonary
gas exchange
• high altitudes, drowning, aspiration, respiratory arrest,
degenerative lung diseases, CO poisoning
– ischemic hypoxia - inadequate circulation
• DM, Atherosclerosis
– anemic hypoxia – anemia
• Diet and internal bleed
– histotoxic hypoxia - metabolic poison
• cyanide poisoning
• Signs: cyanosis - blueness of skin, finger nail clubbing
• All types of hypoxia can lead to tissue necrosis ( death)
Signs of Cyanosis
Chronic Obstructive Pulmonary
Disease
• Asthma
– Chemical irritants cause the release of
release of histamine which activates the PNS.
This leads to intense bronchoconstriction
(blocks air flow)
– Treatment is Epinephrine. Why?
• Other COPD’s usually associated with smoking
– chronic bronchitis
– emphysema
Chronic Bronchitis
• Chronic Bronchitis typically occurs in the larger
airways.
• Patients have a history of:
– Smoking
– Dyspnea: labored breathing occurs and gets
progressively worse
– Coughing and sputum production leading to
frequent pulmonary infections.
• COPD patients may develop respiratory failure
accompanied by hypoxemia, carbon dioxide
retention resulting in respiratory acidosis
Chronic Obstructive Pulmonary
Disease
• Emphysema
– An inflammatory response destroys the
alveolar walls ( respiratory membrane)
reducing the surface area for gas exchange
– Lungs become more fibrotic and less elastic
– Air passages collapse with exhalation
trapping CO2 in lungs.
Effects of COPD
•  pulmonary compliance and vital capacity
• Hypoxemia, hypercapnia, respiratory
acidosis
– hypoxemia stimulates erythropoietin release
and leads to polycythemia
• cor pulmonale
– hypertrophy and potential failure of right heart
due to obstruction of pulmonary circulation
Smoking and Lung Cancer
• Lung cancer accounts for
more deaths than any other
form of cancer
– most important cause is
smoking (15
carcinogens)
– If you smoke the
equivalent of 50 pack
years your chance of
getting lung cancer is
100%
• 50% of smokers die
from smoke related
illness.