Download Lecture Note - Lung

Anatomy of Respiratory System
Anatomy of Respiratory System
Respiratory system function is to supply body with
oxygen and dispose of carbon dioxide.
 Organs which involves in respiratory function are nose,
pharynx, larynx, trachea, bronchi and lungs.
 Our interest are in organs involve in breathing
mechanism and gas exchange.
The Lungs
 Lungs are large organ exist in pair.
 The apex of lung located just deep to clavicel.
 The base of lung is the broad area resting on the
diaphragm.
 Surface of lung covered with pulmonary.
 There is pleural fluid which allows lungs glide easily over
thorax wall during breathing movements.

Anatomy of Respiratory System
Anatomy of Respiratory System
Anatomy of Respiratory System
Bronchiole and Alveoli
 Main bronchi will divide into smaller branches after
entering the lungs.
 Bronchioles is the smallest passageway.
 Terminal bronchioles lead into respiratory zone
structures.
 Respiratory zone includes respiratory bronchioles,
alveolar ducts, alveolar sacs and alveoli.
 All other respiratory passages are called conducting
zone structures.
 Alveoli is where the gas exchange happens.
 It is also called air sacs.
 Alveoli walls composed of single, thin layer of squamous
epithelial cells.
Anatomy of Respiratory System
Anatomy of Respiratory System






External surfaces of alveoli are covered with a
cobweb of pulmonary capillaries.
Respiratory membrane composed of alveolar
and capillary walls, fused basement membrane
and occasional elastic fiber.
This is where gas exchange occurs where gas
flow on one side and blood on the other.
Gas exchange occur by simple diffusion through
respiratory membrane.
O2 pass from alveolar air into capillary blood.
CO2 leaves blood to enter gas-filled alveoli.
Anatomy of Respiratory System
Physiology of Respiratory System
Respiration Events
 Pulmonary ventilation : air move into and out of
the lungs so that gases in air sacs continuously
changed. This process is callled breathing.
 External respiration : gas exchange between
pulmonary blood and alveoli.
 Respiratory gas transport : oxygen and carbon
dioxide transported to and from the lungs and
tissue cells of the body via the bloodstream.
 Internal respiration : at systemic capillaries, gas
exchange is made between blood and tissue
cells.
Physiology of Respiratory System
Respiration Volumes and Capacities
Physiology of Respiratory System






TLC : volume of air that the lungs contains at the
end of maximal inspiration. It is equal to total
volume of lungs.
VC : amount of air that can be forced out of the
lungs after maximal inspiration.
TV : amount of air breathed in and out during
normal respiration.
RV : amount of air remaining in the lung after
maximal exhalation.
ERV : amount of air that can be expelled after
the end of expiratory level of normal breathing.
FRC : amount of air that stays in the lung during
normal breathing.
Physiology of Respiratory System
Respiratory Cycle/Mechanism
 Respiration works by changing the volume of chest cavity.
 Before inspiration :




Onset of inspiration :





Respiratory muscles relax.
Intrapulmonary pressure equals atmospheric pressure
No air flowing
Inspiratory muscles (especially diaphragm) contract.
Thoracic cavity enlarge.
Lungs forced to expand.
Intrapulmonary pressure less than atmospheric pressure,
thus air flows into lungs due to pressure gradient.
Intrapulmonary volume increases and air within the lungs
spread out to fill larger space.
Physiology of Respiratory System






Air continues to move into lungs.
Air stops flow into lungs when there is no further
gradient i.e. intrapulmonary pressure equals to
atmospheric pressure.
Intrapulmonary volume decreases and air inside
the lungs are forced more closely together.
Intrapulmonary pressure rises until higher than
atmospheric pressure.
Air flows out to equalize the pressure inside and
outside the lungs.
Then expiration ends, inspiratory muscles relax,
chest cavity and lungs return to original size.
Physiology of Respiratory System
Physiology of Respiratory System
Gas Transport in Blood
 O2 attaches to hemoglobin molecules inside red
blood cells to form oxyhemoglobin (HbO2).
 Small amount of O2 dissolved in plasma.
 Most CO2 transported in plasma as bicarbonate
ion (HC O3 -).
 CO2 is released from bicarbonate ion form
before diffused to alveoli.
 Bicarbonate ions combine with hydrogen ions in
red blood cells to form carbonic acid (H2CO3).
 Carbonic acid splits to form water and CO2. CO2
will then diffuses from blood to enter alveoli.
Physiology of Respiratory System
Physiology of Respiratory System
Factors underlying gas exchange and
transport :
 Ventilation of the lungs i.e. volume flow rate of
gas.
 Composition of gas mixture.
 Permeability of materials which separates gas
from blood in pulmonary alveoli.
 Pattern of pressure and flow through the
airways.
 Distribution of inspired air and circulating blood.
 Gas carrying capacity of blood.
Physiology of Respiratory System
Partial Pressure
 Definition : Pressure of any one type of gas in a mixture
of gases.
 In a mixture of gases, each gas has a partial pressure
which is the pressure the gas would have if it occupied
the volume alone.
 E.g : partial pressure of gases in inspired air are O2 (158
mmHg), CO2 (0.3 mmHg), N2 (596 mmHg).
 Sum of individual gas partial pressure in a gas mixture
will give the total gas mixture pressure.
 Equation for pressure of ideal gas :

pV = nRT
 p:pressure,V:volume,n:no of moles,R:gas constant,
T:absolute temp.
Physiology of Respiratory System

Dalton’s Law equation :

Pressure exerted by mixture of gases equal to the sum
of the partial pressures exerted by each gas.
Partial pressure of any gas in a gas mixture is the
fractional concentration of that gas in total.
E.g : dry atmospheric air contain 20.93% O2, 0.04% CO2
and 79.03% N2. So :
PO2 = (20.93/100) x 760 = 159 mmHg
PCO2 = (0.04/100) x 760 = 0.3 mmHg
PN2 = (79.03/100) x 760 = 601 mmHg


Physiology of Respiratory System
Gas Diffusion
 Gas diffuses from areas of high pressure to areas of low
pressure.
 Rate of diffusion depends on concentration gradient and
nature of barrier between two areas.
 Mixture of gases in contact with liquid will dissolve in the
liquid.
 The dissolve of gas depends on partial pressure and its
solubility in liquid.
 Diffusion constant of gas :

d ∞ [S/√(MW)]
 d:diffusion const, S:solubility of gas in liquid,
MW:molecular weight
Physiology of Respiratory System
Uptake of O2 into Blood
 Mixed venous blood from pulmonary artery has PO2
about 40 mmHg.
 Alveolar has PO2 about 100 mmHg.
 Mixed venous has relatively stable PO2.
 PO2 in alveolar varies with the phase of breathing cycle;
higher at end-inspiration and lower at end-expiration.
 Average gradient between mixed venous and alveolar
PO2 is 60 mmHg or more.
 O2 taken up into pulmonary capillary blood until it is in
equilibrium with alveolar air.
 Initial rate of uptake is rapid because large PO2 gradient
from alveolus to capillary before gradient reduce.
 Rate transfer then decrease until PO2 reach equilibrium.
Physiology of Respiratory System
Physiology of Respiratory System
Physiology of Respiratory System
Gas Transfer Rate
 Greater surface for diffusion results greater net rate of gas transfer.
 Net rate of gas transfer or conductance :




: rate(volume/time), d: diffusion const, A: area of alveolar surface,
T: diffusion distance, P1-P2: pressure gradient across capillary bed.
Thus rate is proportional to area of alveolar surface in contact with
functioning pulmonary capillaries.
Inversely proportional to diffusion distance.
Diffusion pathway for O2 are : alveolar diffusion, diffusion through
alveolar surface lining layer, diffusion through alveolar-capillary
membrane, diffusion through plasma, diffusion through red cell
membrane, diffusion through intracellular fluid of red cell and finally
chemical combination with hemoglobin.
Physiology of Respiratory System
Diffusion Capacity
 Definition : Volume of gas taken up into pulmonary
capillary blood from alveoli per unit time divided by the
pressure gradient for that gas across the alveolarcapillary interface.




It is a measurement of the lung’s ability to transfer gases.
For O2 :
: mean pulmonary capillary PO2.
Diffusion capacity for O2 decreased in disease such as
sarcoidosis and beryllium poisoning that cause fibrosis of
alveolar walls and produce alveolar-capillary block.