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BIOLOGY 252
Human Anatomy & Physiology
Chapter 23
The Respiratory System:
Lecture Notes
The Respiratory System
• Cells continually use O2
& release CO2
• Respiratory system
designed for gas
exchange
• Cardiovascular system
transports gases in
blood
• Failure of either system
– rapid cell death from
O2 starvation
See manual; 1.12, 2.5 & 4.1
Respiratory System Anatomy
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•
•
•
•
•
•
Nose
Pharynx = throat
Larynx = voicebox
Trachea = windpipe
Bronchi = airways
Lungs
Locations of infections
– upper respiratory tract is above
vocal cords
– lower respiratory tract is below
vocal cords
Nose - Internal Structures
•
•
•
•
Large chamber within the skull
Roof is made up of ethmoid and floor is hard palate
Nasal septum is composed of bone & cartilage
Exam questions - see manual p. 1.12 – 1.17 (bolded information)
Functions of the Nasal Structures
• Olfactory epithelium for sense of smell
• Pseudostratified ciliated columnar with goblet cells
lines nasal cavity
– warms air due to high vascularity
– mucous moistens air & traps dust (cleanse)
– cilia move mucous towards pharynx
• Paranasal sinuses open into nasal cavity
– found in ethmoid, sphenoid, frontal & maxillary
– lighten skull & resonate voice
Pharynx
• Muscular tube (13 cm - 5 in. long) hanging from skull
– skeletal muscle & mucous membrane
• Extends from internal nares to cricoid cartilage
• Functions
– passageway for food and air
– resonating chamber for speech production
– tonsil (lymphatic tissue) in the walls protects
entryway into body
• Distinct regions -- nasopharynx, oropharynx and
laryngopharynx
Cartilages of the Larynx
• Thyroid cartilage forms Adam’s apple
• Epiglottis - leaf-shaped piece of elastic
cartilage
– during swallowing, larynx moves upward
– epiglottis bends to cover glottis
• Cricoid cartilage - ring of cartilage
attached to top of trachea
• Pair of arytenoid cartilages sit upon cricoid
– many muscles responsible for their
movement
– partially buried in vocal folds (true vocal
cords)
– See manual – p. 1.13 - 1.15
Larynx
• Cartilage & connective tissue tube
• Anterior to C4 to C6
• Constructed of 3 single & 3 paired cartilages
Vocal Cords
• False vocal cords (ventricular folds) found above
vocal folds (true vocal cords)
• True vocal cords attach to arytenoid cartilages
Trachea
• Size is 12 cm (5 in) long & 2.5 cm (1in) in diameter
• Extends from larynx to T5 anterior to the esophagus and
then splits into bronchi
• Layers
– mucosa = pseudostratified columnar with cilia &
goblet cells
– submucosa = loose connective tissue & seromucous
glands
– hyaline cartilage = 16 to 20 incomplete rings
• open side facing esophagus contains trachealis m.
(smooth)
• internal ridge on last ring called carina
– adventitia binds it to other organs
– See lab manual p. 2.5 – 2.7
Trachea and Bronchial Tree
• Full extent of airways is visible starting at the larynx and
trachea
Histology of the Trachea
• Ciliated pseudostratified columnar epithelium
• Hyaline cartilage as C-shaped structure closed by trachealis
muscle
Trachea
The trachea extends from the larynx to the
primary bronchi
Copyright © 2014 John Wiley & Sons, Inc. All rights reserved.
Airway Epithelium
• Ciliated pseudostratified columnar epithelium with goblet
cells produce a moving mass of mucus.
Tracheostomy and Intubation
Tracheotomy, syn. = Tracheostomy
• Reestablishing airflow past an airway obstruction
– crushing injury to larynx or chest
– swelling that closes airway
– vomit or foreign object
• Tracheostomy is incision in trachea below cricoid
cartilage if larynx is obstructed
• Intubation is passing a tube from mouth or nose through
larynx and into trachea
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Bronchi and Bronchioles
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•
•
•
Primary bronchi supply each lung
Secondary bronchi supply each lobe of the lungs (3 right + 2 left)
Tertiary bronchi supply each bronchopulmonary segment
Repeated branchings called bronchioles form a bronchial tree
Lung Volumes and Capacities
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•
•
•
•
Tidal volume = amount air moved during quiet breathing
MVR= minute ventilation is amount of air moved in a minute
Reserve volumes ---- amount you can breathe either in or out above that
amount of tidal volume
Residual volume = 1200 mL permanently trapped air in system
Vital capacity & total lung capacity are sums of the other volumes
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Structures within a Lobule of Lung
• Branchings of single arteriole,
venule & bronchiole are wrapped
by elastic CT
• Respiratory bronchiole
– simple squamous
• Alveolar ducts surrounded by
alveolar sacs & alveoli
– sac is 2 or more alveoli sharing
a common opening
Histology of Lung Tissue
Photomicrograph of
lung tissue showing
bronchioles, alveoli
and alveolar ducts.
Cells Types of the Alveoli
• Type I alveolar cells
– simple squamous cells where gas exchange
occurs
• Type II alveolar cells (septal cells)
– free surface has microvilli
– secrete alveolar fluid containing surfactant
• Alveolar dust cells
– wandering macrophages remove debris
Details of Respiratory Membrane
• Find the 4 layers that comprise the respiratory membrane
Alveolar-Capillary Membrane
• Respiratory membrane = 1/2 micron thick
• Exchange of gas from alveoli to blood
• 4 Layers of membrane to cross
– alveolar epithelial wall of type I cells
– alveolar epithelial basement membrane
– capillary basement membrane
– endothelial cells of capillary
• Vast surface area = handball court
Double Blood Supply to the Lungs
• Deoxygenated blood arrives through pulmonary
trunk from the right ventricle
• Bronchial arteries branch off of the aorta to
supply oxygenated blood to lung tissue
• Venous drainage returns all blood to heart
Breathing or Pulmonary Ventilation
• Air moves into lungs when pressure inside lungs is
less than atmospheric pressure
– How is this accomplished?
• Air moves out of the lungs when pressure inside
lungs is greater than atmospheric pressure
– How is this accomplished?
• Atmospheric pressure = 1 atm or 760mm Hg
Boyle’s Law
• As the size of closed container decreases, pressure inside is
increased
• The molecules have less wall area to strike so the pressure on
each inch of area increases.
Dimensions of the Chest Cavity
• Breathing in requires muscular activity & chest size changes
• Contraction of the diaphragm flattens the dome and increases the
vertical dimension of the chest
Muscles of Inhalation and Exhalation
Copyright © 2014 John Wiley & Sons, Inc. All rights reserved.
Labored Breathing
• Forced expiration
– abdominal mm force
diaphragm up
– internal intercostals
depress ribs
• Forced inspiration
– sternocleidomastoid,
scalenes & pectoralis
minor lift chest upwards
as you gasp for air
Intrapleural
pressures
or Intrathoracic
pressures
&
Alevolar
or Intrapulmponic
pressures
• Always subatmospheric (756 mm Hg)
• As diaphragm contracts intrapleural pressure decreases
even more (754 mm Hg)
Alveolar Surface Tension
• Thin layer of fluid in alveoli causes inwardly
directed force = surface tension
– water molecules strongly attracted to each
other
• Causes alveoli to remain as small as possible
• Detergent-like substance called surfactant
produced by Type II alveolar cells
– lowers alveolar surface tension
– insufficient in premature babies so that alveoli
collapse at end of each exhalation
Compliance of the Lungs
• Ease with which lungs & chest wall expand
depends upon elasticity of lungs & surface
tension
• Some diseases reduce compliance
– tuberculosis forms scar tissue
– pulmonary edema - fluid in lungs & reduced
surfactant
– Paralysis
• So high compliance is good, low is bad - makes breathing
more difficult
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Pneumothorax
• Pleural cavities are sealed cavities not open to
the outside
• Injuries to the chest wall that let air enter the
intrapleural space
– causes a pneumothorax
– collapsed lung on same side as injury
– surface tension and recoil of elastic fibers
causes the lung to collapse
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Airway Resistance/Anatomic Dead Space
• Resistance to airflow depends upon airway size
– increase size of chest
• airways increase in diameter
– contract smooth muscles in airways
• decreases in diameter, e.g. asthma, COPD,
and also cigarette smoking
• Anatomic Dead Space = 150 ml ( normal value)
500 ml TV – 150 ADS = actual gas exchange
leaves 500 – 150 = 350 of “fresh” (20.93% O2,
0.03% CO2) air entering the lungs with each
inhalation.
Breathing Patterns
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•
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Eupnea = normal quiet breathing (yu-p-ne a)
Apnea = temporary cessation of breathing (ap ne a)
Dyspnea = difficult or labored breathing (disp-ne a)
Tachypnea = rapid breathing (tak-ip-ne a)
Diaphragmatic breathing = descent of diaphragm
causes stomach to bulge during inspiration
• Costal breathing = just rib activity involved
Modified Respiratory Movements
• Coughing
– deep inspiration, closure of glottis & strong
expiration blasts air out to clear respiratory
passages
• Hiccuping
– spasmodic contraction of diaphragm & quick
closure of glottis produce sharp inspiratory sound
• Valsalva maneuver
- forced exhalation against a closed glottis as may
occur when lifting a heavy weight
• Chart of others on page 868
The Gas Laws
Boyle’s Law – the pressure of a gas
varies inversely with its volume (if
temperature remains constant).
Gay-Lussac’s Law – the pressure of a gas
increases directly in proportion to its
(absolute) temperature.
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The Gas Laws
Dalton’s Law – in a mixture of gasses,
each gas exerts a partial pressure,
proportional to its concentration.
Henry’s Law – the quantity of a gas that
will dissolve in a liquid (e.g. blood
plasma) is directly proportional to its
partial pressure, if temperature remains
constant.
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What is the Composition of Air?
• Air = 20.93% O2, 79.04% N2 and 0.03% CO2
• Alveolar air = 14% O2, 79.04% N2 and 5.2% CO2
• Expired air = 16% O2, 79.04% N2 and 4.5% CO2
– Anatomic dead space = 150 ml of 500 ml of tidal
volume
– Functional residual volume (1.2 L) + residual
volume (1.2 L)
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Dalton’s Law
• In a mixture of gasses, each gas exerts a partial
pressure, proportional to its concentration.
• Each gas in a mixture of gases exerts its own pressure
•
•
•
•
as if all other gases were not present
partial pressures denoted as p
Total pressure is sum of all partial pressures
atmospheric pressure (760 mm Hg) = pO2 + pCO2 + pN2 +
pH2O
Thus in atmospheric air with a total pressure of
760 mm Hg, O2 which makes up 20.93% - has a
partial pressure of 20.93/100 x 760 = 159.1 mmHg
Henry’s Law
• The quantity of a gas that will dissolve in a
liquid is directly proportional to its partial
pressure, if temperature remains constant.
OR
• The quantity of a gas that will dissolve in a
liquid depends upon the amount of gas
present and its solubility coefficient
Lung Perfusion
Partial Pressures of Respiratory
Gases at Sea Level
Partial pressure (mmHg)
Gas
% in
dry air
Dry
air
Alveolar
air
Arterial
blood
Venous
blood
Diffusion
gradient
Total
100.00
760.0
760
760
706
0
H2O
0.00
0.0
47
47
47
0
20.93
159.1
105
100
40
60
0.03
0.2
40
40
46
6
79.04
600.7
568
573
573
0
O2
CO2
N2
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The Processes of Respiration
• Pulmonary ventilation – or breathing, is the mechanical flow of
air into (inhalation) and or out of (exhalation) the lungs
• External respiration – is the exchange of gases between the
alveoli of the lungs and the blood in the pulmonary capillaries. In
this process, pulmonary capillary blood gains O2 and loses CO2
• Internal respiration – is the exchange of gases between blood
in systemic capillaries and tissue cells. The blood loses O2 and
gains CO2. Within cells, the metabolic reactions that consume
O2 and give off CO2 during the production of ATP termed cellular
respiration
___________________________________________________
• Gas transport – is the transport of O2 from the lungs to the
systemic tissues and the transport of CO2 from the systemic
tissues to the lungs.
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External Respiration
• Gases diffuse from areas of
high partial pressure to areas
of low partial pressure
• Exchange of gas between
alveolar air & blood
• Deoxygenated blood becomes
100% saturated with O2
• Compare gas movements in
pulmonary capillaries to tissue
capillaries
Rate of Diffusion of Gases
• Depends upon partial pressure of gases in air
– pO2 at sea level is 159.1 mm Hg
– 10,000 feet (~3000 m) is 110 mm Hg / 50,000 feet is
18 mm Hg
• Large surface area of our alveoli
• Diffusion distance is very small (0.5 µm)
• Solubility & molecular weight of gases
– O2 smaller molecule diffuses somewhat faster
– CO2 dissolves 24x more easily in water so net outward
diffusion of CO2 is much faster
Internal Respiration
• Exchange of gases between
blood & tissues
• Conversion of oxygenated
blood into deoxygenated
• Observe diffusion of O2 inward
– at rest 25% of available O2
enters cells
– during exercise more O2 is
absorbed
• Observe diffusion of CO2
outward
Oxygen Transport in the Blood
• Oxyhemoglobin contains 98.5% chemically
combined oxygen and hemoglobin
– inside red blood cells
• Does not dissolve easily in water
– only 1.5% transported dissolved in blood
(plasma)
Carbon Monoxide Poisoning
• CO from car exhaust & tobacco smoke
• Binds to the Hb heme group more
successfully than O2
• CO poisoning
• Treat by administering pure O2
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Carbon Dioxide Transport
• Is carried by the blood in 3 ways
– dissolved in plasma
– combined with the globin part of Hb molecule
forming carbaminohemoglobin
– as part of bicarbonate ion
• CO2 + H2O combine to form carbonic acid (H2CO3) that
dissociates into hydrogen ions (H+) and bicarbonate ions
(HCO3-)
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Oxyhemoglobin Dissociation Curve
(Hemoglobin saturation and oxygen partial pressure)
• Blood is almost fully
saturated at pO2 of
60mm
– people OK at high
altitudes & with some
diseases
• Between 40 & 20 mm
Hg, large amounts of O2
are released as in areas
of need like contracting
muscle
Acidity & Oxygen Affinity for Hb
• As acidity
increases, O2
affinity for Hb
decreases
• Bohr effect
• H+ binds to
hemoglobin &
alters it
• O2 left behind
in needy
tissues
pCO2 & Oxygen Release
• As pCO2 rises
with exercise, O2
is released more
easily
• CO2 converts to
carbonic acid &
becomes H+ and
bicarbonate ions
& lowers pH.
Temperature & Oxygen Release
• Metabolic activity
& heat
• As temperature
increases, more
O2 is released
Summary: Hb-O2 Dissociation Curve
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Role of the Respiratory Center
• Respiration
controlled by neurons
in pons & medulla
• 3 groups of neurons
– medullary rhythmicity
– pneumotaxic
– apneustic centers
Negative Feedback Control of Breathing
Copyright © 2015 John
Wiley & Sons, Inc. All
rights reserved.
CONDITIONS AT VARIOUS ALTITUDES
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Partial Pressures of Respiratory
Gases at Sea Level
Partial pressure (mmHg)
Gas
% in
dry air
Dry
air
Alveolar
air
Arterial
blood
Venous
blood
Diffusion
gradient
Total
100
706
0
H2O
0.00
47
0
573
0
O2
CO2
N2
600.7
Tortora & Grabowski 9/e 2000 JWS
568
573
23-59