Ch. 1 Structure and Fx.
Lung:
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Prime fx is to allow oxygen to move from the air into the venous blood and carbon dioxide to
move out
Metabolizes some compounds, and filters unwanted materials from the circulation
o Agents removed by the lungs:
 PGE1, PGE2 and PGE2a -- Almost completely removed
 Leukotrienes-- Almost completely removed
 Seratonin-- 85-95% removed
 Norepinephrine-- Approximately 30% removed
 Bradykinin-- Approximately 80% removed
 Angiotensin I-- Approximately 70%converted to Angiotensin II
 ATP, AMP-- 90% removed
o Non-respiratory Fx of lungs
 As a reservoir for the left ventricle
 As a filter for the circulatory system
 As a metabolic organ (chemical filter) uptake –removal
- gets the entire cardiac output
- has a very large surface area
o Misc Fx:
 Acts as a chemical filter to protect the systemic circulation from vasoactive
compounds –5Ht, bradykinin, amines
 Activates compounds – ang I to ang II
 Synthesis and release – nitrous oxide, endothelins
 Removal of xenobiotics
Acts as reservoir for blood
Blood-Gas Interface
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Oxygen and co2 move b/t air and blood by simple diffusion – from area of high to low partial
pressure
Fick’s law – amt. of gas that moves across a sheet of tissue is proportional to the area of the
sheet but inversely proportional to its thickness
Blood-gas barrier :
o exceedingly thin
o Has an area of b/t 50-100 sq. meters (b/c of high # of bv’s wrapped around alveoli)
Alveoli:
o 300 million in the human lung
Gas is brought to one side of the blood-gas interface by airways, and blood to the other side by
bv’s
Airways and Airflow
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Conduction Zone:
o Trachea:
 divides into right and left main bronchi, which then divide into lobar,
and segmental bronchi
 turbulent flow w/ fast velocity
o Process continues (by division of 2) into lobar  segmental branches 
terminal bronchioles (smallest airways w/out alveoli) @ x16 divisions
o All of these divisions make the conducting airways
 Fx is to lead inspired air to the gas exchanging regions of lung
 Anatomic dead space (of conduction zone):
 Conducting airways contain no alveoli and therefore take no
part in gas exchange
 Vol = 150ml
o Cilia:
 Upper respiratory zone cilia:
 Move large paticle debris/mucus backward and down (i.e. into
the naso/oral pharynx)
 Lower respiratory zone cilia:
 Moves large particle debris/mucus up (hacking up a lugee)
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Mucociliary layer is resp. for upper respiratory system -- regulates air,
adj. humidity so that when it reaches the trachea it's at appropriate
conditions
Particulate matter depends on the following:
 Inertia  sticks to mucus
 Sedimentation  for laminar flow
 Diffusion  (browning – motion?) random movements
Air that reaches the lung is usually sterile
Respiratory Zone:
 17th – 23rd divisions after primary bronchi
 17th division is first site of gas exchange
 Makes up most of the lung
 Vol. = 2.5-3 L at rest
o Respiratory bronchioles:
 Division of terminal bronchioles
 Have occasional alveoli
o Alveolar Ducts:
 Completely lined with alveoli
 Alveolated region of lung where gas exchange occurs
 Holes in the alveolar walls are called the Pores of Kohn
o 70 square meters are total surface are for gas exchange
 As cross sectional area increases:
 Velocity goes down
 Flow becomes less turbulent
Acinus
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o Portion of lung distal to a terminal bronchiole
Partial pressure of gas:
o Found by multiplying its concentration by the total pressure
o i.e. dry air has 20.93% O2. Its partial pressure (PO2) at sea level is 20.93/100 x
760 = 159 mmHg
o When air is inhaled into the upper airways, it is warmed and moistened, and
water pressure is then 47mmHg, so that the total dry gas pressure is only 76047 = 713 mmHg. The PO2 of inspired air is therefore 20.93/100 x 713 = 149 mm
Hg. A liquid exposed to a gas until equilibration takes place has the same partial
pressure as the gas.
 Problem: what is the PO2 of moist inspired gas of a climber on the
summit of Mt. Everest (i.e. barometric pressure is 247 mmHg)
 So,… x/100 x 760 = 247 mmHg
 X = 32 mmHg
Inspiration
o During inspiration, the vol. of the thoracic cavity increases and draws air into the
lungs
 Increase in vol. is d/t
 contraction of the diaphragm
o Contraction of diaphragm causes it to descend
 action of the intercostals muscles, which raise the ribs
o This increases the cross-sectional area of the thorax
 Inspired air flows down to about the terminal bronchioles by bulk flow
o Beyond that, combined cross-sectional area is so large that forward velocity of
the gas becomes small
o Diffusion of gas is dominant mech. Of ventilation in the respiratory zone
 b/c velocity of gas falls rapidly in the region of terminal bronchioles,
inhaled dust frequently settles there
o Airways
 Divided into a conducting zone and respiratory zone
 Volume of the anatomic dead space is about 150 ml
 Volume of the alveolar region is about 2.5-3.0 liters
 Gas movement in the alveolar region is chiefly by diffusion
o Normal breath of about 500ml requires a distending pressure of less than 3cm
water (child=30cm)
Blood Vessels and Flow
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Pulmonary bv’s form a series of branching tubes from the pulmonary artery to the capillaries
and back to the pulmonary veins (i.e. similar to branching of airways)
Initially, the arteries, veins, and bronchi run close together
o Toward periphery of lung, the veins move away to pass b/t lobules, whereas the arteries
and bronchi travel together down the centers of the lobules
Capillaries
o are easily damaged
o Forms (almost) continuous sheet of blood on the alveolar wall
o Increasing the pressure in capillaries, or inflating the lungs to high volumes  can raise
the wall stresses of capillaries to point at which ultrastructural changes can occur
 Capillaries then leak plasma and even RBC’s into alveolar spaces
Diameter of capillary segment is about 10 micrometers (just large enough for RBC to
pass)
o Each RBC spends about ¾ sec in the capillary network and traverses 2-3 alveoli
Mean Pulmonary arterial pressure of about 20cm water (15 mmHg) is required for flow of
6L/min (compared to soda straw=120cm water)
Bronchial circulation
o Lungs additional blood system
o Supplies conducting airways down to about the terminal bronchioles
o Flow through the bronchial circulation is a mere fraction of that through the pulmonary
circulation
o Lung can fx fairly well w/out it (i.e. post lung transplant)
Summary:
o Whole output of rt. Heart goes through the lung
o Diameter of the capillaries is about 10micrometers
o Thickness of much of the blood-gas barrier is less than 0.3 micrometers
o Blood spends about ¾ sec in the capillaries
o Flow of oxygen through blood-gas barrier from alveolar gas to Hb:
 Surfactant  epithelial cell  interstitium  endothelial cell  plasma 
RBC membrane
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2 special Problem s that the lung must overcome
I.
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Stability of the Alveoli
b/c of surface tension of the liquid lining the alveoli, relatively large forces develop that tend to
collapse the alveoli
some of the cells lining the alveoli secrete a material called surfactant
o surfactant:
 dramatically lowers the surface tension of the alveolar lining layer
 increases stability
 first thing inhaled oxygen comes into contact with on way to bloodstream
II.
Removal of Inhaled Particles
 surface area of 50-100 square meters
 large particles are filtered out in the nose
 smaller particles deposit in the conducting airways are removed by a moving staircase of mucus
that continually sweeps debris up to the epiglottis where it is swallowed
 Alveoli:
o Have no cilia, and particles deposited there are engulfed by macro’s
o Foreign material is then removed from lung via the lymphatics/blood flow
o Leukocytes also participate in the defense rxn to foreign material
Ch. 2 Ventilation (How gas gets to the alveoli)
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Various bronchi that make up the conducting airways can be represented by a single
tube labeled – anatomic dead space
Typical Volumes and flow w/in the lungs
o Tidal Volume = 500 ml
 With each inspiration about 500 ml of air enter the lung
o Total ventilation = 7500ml/min
o Anatomic dead space = 150 ml
o Frequency = 15/min
o Alveolar ventilation = 5250 ml/min
o Pulmonary blood flow = 5000 ml/min
 Alveolar vent. / pulmonary blood flow ~= 1
o Alveolar gas = 3000 ml
o Pulmonary capillary blood = 70ml
Lung volumes based on a spirometer
o Note: total lung capacity, fx’al residual capacity, and residual volume cannot
be measure with a spirometer
o Total Lung capacity ~ 7L
o Vital capacity ~5L
o Tidal volume ~ ½ L
o Functional residual capacity ~3L
Lung Volumes
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Vital Capacity: the exhaled volume
Residual Volume: the amt. of gas that remains in the lung after a maximal expiration
Functional residual capacity: the volume of gas in the lung after a normal expiration
o Neither the functional residual capacity nor the residual volume can be measured with
a simple spirometer
o Helium dilution method
 Measures only communicating gas, or ventilated lung volume
 How to calculate the previous listed: patient inhales a small amt. of helium, and
helium concentrations in the spirometer and lung become the same
 b/c no helium is lost; the amt. of helium present before equilibration
(concentration times volume) is:
o C1 x V1
 After equilibration:
o V2 = V1 (C1 – C2) / C2 or:
 C1 x V1 = C2 x (V1 + V2)
o Body plethysmograph
 Another way of measuring the fx’al residual capacity (FRC)
 Measures the total volume of gas in the lung, including any that is trapped
behind closed airways
 A large airtight box (like telephone booth)
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At the end of a normal expiration, a shutter closes over a mouthpiece and
subject is asked to make respiratory efforts. As the subjet tries to inhale, he
expands the gas in his lungs, and lung volume increases, and the box pressure
rises b/c its gas volume decreases
Boyle’s Law: pressure x volume is constant (at constant temp.)
P1 = pressure in box before inspiratory effort
P2 = pressure in box after inspiratory effort
V1 = preinspiratory box volume
Delta V = change in volume of the box/lung
 P1 V1 = P2 ( V1 – delta V)
W/ Boyle’s Law applied to gas in the lung:
 P3 V2 = P 4 ( V2 + delta V)
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Where P3 and P4 are the mouth pressures before and after the
inspiratory effort, and V2 is the FRC
 Thus FRC can be obtained
o In young normal subjects – ventilated lung volume ~= communicating gas
o In lung disease – ventilated volume may be considerably less than the total volume b/c
of gas trapped behind obstructed airways.
Lung Volume summary:
o Tidal volume and vital capacity can be measured with a simple spirometer
o Total lung capacity, fx’al residual capacity and residual volume need an additional
measurement by helium dilution or the body plethysmograph
o Helium is used b/c of its very low solubility in blood
o Body plethysmograph depends on boyle’s Law PV =K at constant temp.
Ventilation
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Suppose:
o Volume exhaled w/ each breath is 500 ml
o RR = 15 breaths/min
 Total volume leaving the lung each minute  500 x 15 = 7500 ml/min (total
ventilation)
o Total Ventilation: the volume of air entering the lung is very slightly greater b/c more
oxygen is taken in than carbon dioxide is given out
o Anatomic Dead space: about 150 ml from each 500 ml of air inhaled enters the
anatomic dead space (30%)
Alveolar Ventilation: the volume of fresh air entering the respiratory zone each minute is (500 –
150) x 15 = 5250 ml/min
o Represents the amount of fresh inspired air available for gas exchange (specifically, the
alveolar ventilation is also measured on expiration, but the volume is almost the same)
o How to determine alveolar ventilation:
o 1) measure the volume of the anatomic dead space and calculate the dead space
ventilation (volume x respiratory frequency); this is then subtracted from the total
ventilation
 V=volume, T=tidal, D=dead, A=alveolar
 VT = VD + VA (VT x n = VD x n + VA x n) where n = respiratory frequency
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VE = VD + VA where:
 VE= expired total ventilation
 VD=dead space
 VA= alveolar ventilation (vol. of alveolar gas in the tidal volume NOT the
total volume of alveolar gas in the lung)
 Or VA = VE - VD
 Note: the alveolar ventilation can be increased by raising either tidal volume or
respiratory frequency
 Increasing the tidal volume is often more effective b/c this reduces the
proportion of each breath occupied by the anatomic dead space
2)measure the concentration of CO2 in expired gas
 Because all expired CO2 comes from the alveolar gas
 VCO2 = VA x ( % CO2 / 100)
 Or VA = (VCO2 x 100 / % CO2)
 Fractional concentration: %CO2/100  denoted as FCO2
 Thus, alveolar ventilation can be obtained by dividing the CO2 output by the
alveolar fractional concentration of this gas
 Note: partial pressure of CO2 (denoted PCO2) is proportional to the fractional
concentration of the gas in the alveoli
 i.e.: PCO2 = FCO2 x K
 or: VA = (VCO2 / PCO2) x K
 Tidal Volume (VT) is a mixture of gas from the anatomic dead space (VD) and a
contribution from the alveolar gas (VA).
 b/c PCO2 of alveolar gas and arterial blood are identical: the arterial PCO2 can be
used to determine alveolar ventilation
 If the alveolar ventilation is halved (and CO2 production remains unchanged),
the alveolar and arterial PCO2 will double
Anatomic Dead Space
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Normal value = 150ml
Increases w/ large inspirations (b/c of the traction