physiology of respiration

2. The respiration involves many chemical
reactions and functions. They are
1. Pulmonary Ventilation: The process of
moving air from the external
atmosphere/environment into and out of
the lungs is known as ventilation.
2. Pulmonary Diffusion: This is the process of
diffusion of gases (O2 and CO2) across
alveolar membrane. (External Respiration)
3. Transport of Gases: The blood circulation
transports the gases between the lungs and
the tissues.
4. Tissue Respiration: The O2 is utilized by the
tissues and it produces CO2. (Internal
Respiration)

3. Respiratory Functions:
 Pulmonary Ventilation
 Diffusion of O2 and CO2 between the alveoli
& the blood.
 Transportation of O2 & CO2 in the blood &
body fluids to & fro from the body’s tissue
cells.
 Regulation of Ventilation.
Non- Respiratory Functions
 Filtration: The pulmonary capillaries trap
and prevent emboli such as clots, gas
bubbles, fat globules from reaching the
systemic circulation.

4. Non- Respiratory Functions:
 Metabolic Functions: The pulmonary vessels have
large surface area of endothelial cells. Many
substances,enzyme and hormones secreted by the
damaged cells/during clotting process or externally
absorbed are destroyed by endothelial cells of lungs.
 Reservoir: Around 450ml of blood is stored in
pulmonary capillaries.
 Defense Mechanism: The Pulmonary tract contain
cilia, IgA and macrophages which makes the
defense line.
 Water Balance: Lungs play a role in water balance of
the body. 400 ml of vapor is lost through respiration
and it is increased in activity.
 Olfaction and Vocalization is also the functions of
the Respiratory System.

5. Mechanics of Respiration
 The whole process of respiration mainly
involves three basic steps;
1. Pulmonary Ventilation: It the process of
breathing which includes inhalation(inflow)
and exhalation (outflow) of air between the
lungs and external atmosphere.
2. External Respiration: is the exchange of
gases between alveoli of the lungs and the
blood in pulmonary capillaries across the
respiratory membrane.
3. Internal Respiration: is the exchange of
gases between the blood in systemic
capillaries and tissue cells. Also called as
cellular respiration.

6. Pulmonary Ventilation
1. Air flows between atmosphere and lungs
due to pressure difference.
2. The pressure difference is created by
contraction and relaxation of respiratory
muscles.
3. The pulmonary Ventilation can be
classified into Inhalation/Inspiration and
Exhalation/expiration.

7. Pulmonary Ventilation
1. Air flows between atmosphere and lungs
due to pressure difference. The pressure
difference is created by contraction and
relaxation of respiratory muscles.
2. The pulmonary Ventilation can be
classified into Inhalation/Inspiration and
Exhalation/expiration.

8.  Inhalation
 Before each inhalation the air pressure is
equal in lungs and atmosphere at sea level.
(760mmHg/1atm)
 Inhalation starts when the pressure in the
lungs is decreased than atmosphere.
 This occurs according to Boyle’s Law (The
inverse relationship between volume and
pressure.)
 If the size of a closed container is
increased then the pressure is decreased.
 The pressure difference is created by
increasing the size of the thoracic cavity
by diaphragm and intercostal muscles.

9. Inhalation
 The diaphragm contracts and become flattened
compressing the abdominal cavity and lowering
the dome. This increases the vertical diameter of
the thoracic cavity.
 The intercostal muscles contract and elevate the
ribs which increases the antero-posterior and
lateral diameter.
 In times of normal breathing the diaphragm is
pressed down about 1cm which creates 1-3
mmHg pressure difference (756mmHG) and this
will help in inhalation of 500ml of air.
 In times of strenuous breathing the diaphragm
may be pressed down to 10cm which creates 100
mmHg pressure difference and this will help in
inhalation of 2000-3000ml of air.

10. Inhalation
 This is supported by pleural
layers by decreasing the
pressure within.
(intrapleural pressure)
 The pressure inside the
lungs is called alveolar/
intrapulmonary pressure.
 Contraction of diaphragm is
responsible for 75% air
entering the lungs.
 Advanced pregnancy,
excessive obesity, tight
abdominal clothing can
prevent complete descent of
the diaphragm.

11. Exhalation
 This process also occurs
according to pressure
gradient.
 The pressure in the lungs
is greater than
atmosphere.
 Normal exhalation during
quiet breathing is a
passive process which
does not require and
special effort.
 It results from the
recoiling of diaphragm
and intercostal muscles.

12. Exhalation
 As the diaphragm relax its dome move
superiorly and relaxation of ribs/intercostal
muscles causes further depression of chest
cavity.
 The exhalation becomes an active process in
times of forceful breathing as in playing of a
wind instrument or exercise.
 This is supported by contraction of
abdominal muscles and other accessory
muscles.

13. Other Factors Affecting Pulmonary Ventilation
 Surface tension: It is present in all air water
interfaces. It is inward directed force which
is more in water and less in air. As seen in
soap bubble. (Soap decreases the surface
tension of water)
 The pulmonary surfactant is present in the
alveoli fluid. This is responsible for
pulmonary surface tension (a factor of
respiration).
 During exhalation it supports expelling the
air by decreasing the surface area/tension.
 It also prevents atelectasis by holding back
minimal air as trapped bubbles to maintain
the pressure.

14. Other Factors Affecting Pulmonary Ventilation
 Compliance of the Lungs: It is ability of the
lungs to expand easily. It is based on two factors
such as elasticity of the lungs and surface
tension. Normally the lung tissues have good
elasticity and surface tension is maintained by
pulmonary surfactant. It is reduced in times of
TB, Paralysis of intercostal muscles etc.
 Airway Resistance: It is created by the airways.
Larger trachea has less resistance an smaller
bronchioles have higher resistance. Resistance
is increased during exhalation an decreased
during inhalation. This is normal physiological
process. COPD is the increased airway
Resistance during inhalation.

15. Movements of Thoracic Cage

16. Factors holding lungs AGAINST the thorax
wall:
 Surface tension holding the "visceral" and
"parietal" pleura together. No connective
tissues.
 Intrapulmonary pressure is ALWAYS slightly
greater than intrapleural pressure by 4 mm
Hg.
Factors facilitating lung movement AWAY
from thorax wall
 Elasticity of lungs allows them to assume
smallest shape for given pressure conditions.
 Fluid film on alveoli allows them to assume
smallest shape for given pressure conditions.

17.  Eupnea: Normal Quiet Breathing.
 Hyperpnea: increased breathing as in increased
oxygen need.
 Dyspnea: difficult breathing.
 Apnea: temporary cessation of breathing.
 Hyperventilation: increased pulmonary ventilation
associated with Hyperpnea.
 Hypoventilation: decreased pulmonary ventilation
associated with Hypoventilation.
 Atelectasis (collapsed lung) - hole in pleural
"balloon" causes equalization of pressure and
collapse of the lung.
 Pneumothorax - abnormal air in the intrapleural
space, can lead to collapsed lung.
 Spirogram: Graphic record of respiratory rhythm.

18. Pulmonary Volumes
 Tidal volume (VT) – It is the volume of air that
enters or leaves the lungs at each natural
respiratory effort at rest. The normal volume
moving in/out is 500ml. Tidal volume plays a
significant role during mechanical ventilation to
ensure adequate ventilation without causing
trauma to the lungs. It is estimated based on a
patient's ideal body mass. (10-12 ml per kg body
weight or as prescribed by the Pulmonologist)
 Inspiratory reserve volume (IRV): It is the volume of
air that can be inhaled by a maximum inspiratory
effort over and above the inspired tidal volume. The
volume inhaled AFTER normal tidal volume when
asked to take deepest possible breath (3000ml).

19. Pulmonary Volumes
 Expiratory reserve volume (ERV): it is the
volume of air that can be exhaled by the
maximum expiratory effort after the end of
natural/passive expiartion. The volume exhaled
AFTER normal tidal volume when asked to
force out all air possible (1000ml).
 Residual volume (RV): It is the volume of air
that remains in the lungs after the maximum
expiratory effort. Air that remains in lungs even
after totally forced exhalation (1.2 L).

20. Spirometer
 A spirometer is an apparatus for measuring the
volume of air inspired and expired by the lungs. A
spirometer measures ventilation, the movement of air
into and out of the lungs. The spirogram will identify
two different types of abnormal ventilation patterns,
obstructive and restrictive.

21. Pulmonary Capacities
 Vital capacity (VC)/(FVC): It is the volume of
air that can be expelled by the most vigorous
expiratory effort after the deepest possible
inspiration.VC = VT + IRV + ERV (TOTAL
volume of air that can be moved). It is about
4.6L
 Total lung capacity (TLC): It is the sum of
vital capacity and residual volume. TLC = TV +
IRV + ERV + RV (the SUM of all volumes;
about 5.7 L).
 Functional residual capacity (FRC): It is the
volume of air left in the lungs at the end of
natural passive expiration.FRC=ERV + RV (all
non-tidal volume expiration).

22. Pulmonary Capacities
 Inspiratory capacity (IC): It is the volume of air that
can be inspired from natural end-expiratory level. IC=
VT + IRV (MAXIMUM volume of air that can be
inhaled).
 The Residual volume cannot be estimated by
Spirometry. Therefore FRC, TLC also cannot be
estimated by this method. RV, FRC, TLC can be
measured by using a method called nitrogen washout
method.
 A nitrogen washout can be performed with a single
nitrogen breath, or multiple ones. It can estimate
functional residual capacity. The multiple-breath test
more accurately measures absolute lung volumes.
The person exhales through a one-way valve
measuring nitrogen content and volume.

23. External & Internal Respiration
 Pulmonary ventilation brings fresh air into
lungs.
 The external respiration is the diffusion of
O2 from alveoli to capillary blood and CO2
from capillary blood to alveoli.
 The same process occurs at tissue level
which is called as Internal
Respiration/Tissue Respiration.
 The exchange of gases is governed by two
gas laws such as Dalton’s law and Henry’s
Law.

24. Dalton’s Law
 A mixture of gases present in a container,
each gas exerts a pressure according to its
concentration independently.
 The pressure of each gas in a mixture of
gases is known as partial pressure/tension.
(p)
 Environmental air is a mixture of 20.9%
oxygen and 78.6% nitrogen. (760 is the
atmospheric pressure.) There are other gases
also present in the atmospheric air such as
argon (0.93%), CO2 (0.04%), Other gases
(0.06%) but they are negligible in this
calculation.

25. Dalton’s Law
 The partial pressure (p) of oxygen at sea level is
21/100x760 = 160mmHg
 The partial pressure (p) of Nitrogen at sea level
is 79/100x760 = 600mmHg
 Total Pressure= pO2 + pN2 = 160+600 =
760mmHg.
 These partial pressure determine the movement
of gases in external as well as internal
respiration through a permeable membrane.
 The inhaled air has 20.9% O2 and 0.04% CO2
 The alveolar air/air from capillaries have 13.6%
O2 and 5.2% CO2.
 This will enable the diffusion of gases.

26. Henry’s Law
 The quantity of a gas that will dissolve in a
liquid is proportional to the partial pressure of
the gas and its solubility.
 The CO2 has the highest solubility and lowest
partial pressure.(0.3mmHg)
 The O2 has the moderate solubility and
moderate partial pressure.(158.8mmHg)
 The N2 has the Lowest solubility and Highest
partial pressure.(597.4mmHg)
 Example: The carbonated drinks release the
dissolved CO2 as soon as the cap is opened
because pressure is decreased. Dissolution is
possible in case of high pressure.

27. External Respiration
 External respiration is the pulmonary
exchange of gases from alveoli to pulmonary
capillaries.
 It converts deoxygenated blood coming from
the right ventricle to oxygenated blood that
goes to left atrium.
 This exchange of O2 and CO2 takes place in
pulmonary capillaries.
 O2 diffuse from alveolar air(PO2=105mmHg)
to blood in pulmonary
capillary(PO2=40mmHg). The diffusion
continues till the PO2 in pulmonary
capillary become equal to 100-105mmHg.

28. External Respiration
 CO2 diffuse from Pulmonary
capillaries(PCO2=45mmHg) to alveoli
(PCO2=40mmHg).
 The number of capillaries near alveoli in the
lungs is very large and blood flows slowly for
the proper gas exchange.
 During vigorous exercise the cardiac output
is increased and hence blood flow pulmonary
capillaries also increased.
 This is compensated by increasing the
rapidity and rate of respiration.

29. Internal Respiration
 Internal respiration is also called as
systemic gas exchange.
 The internal respiration takes place in all
tissues of the body.
 The PO2 in systemic circulation is
100mmHg and the same in cells is 40mmHg
because cells constantly use oxygen to
produce ATP. Hence as per the pressure
difference the O2 diffuse to cells across
plasma membrane.
 In return PCO2 in cells is 45mmHg and in
capillary its 40mmHg hence the diffusion
goes on.

30. Factors Affecting Internal and
External Respiration
 Partial Pressure difference of the gases. It
can be changed in case of geographical
differences such as high altitude.
 Surface area available for gas exchange: the
surface area may be decreased in case of
alveolar disorders and lobectomy.
 Diffusion distance: the respiratory
membrane and plasma membrane are very
thin permitting the easy transport of RBC.
 Molecular weight and solubility. O2 has less
molecular weight (sum of the atomic mass)
and CO2 has high solubility.

31. Internal and External Respiration

32. Dead Space
In physiology, dead space is the volume of air
which is inhaled that does not take part in the
gas exchange.
Anatomical dead space is that portion of the
airways (mouth, trachea and bronchioles) which
conducts gas to the alveoli but no gas exchange.
Alveolar dead space are ventilated but not
perfused. It is increased in case of pulmonary
diseases.
The total dead space (physiological dead space) is
the sum of the anatomical dead space and
alveolar dead space.

33. Transport of O2
 Oxygen does not dissolve in water so only
1.5% of inhaled O2 is dissolved in plasma.
 98.5 % of O2 is bound to Haemoglobin in
RBC.
 Each 100ml of blood contains 20ml of O2. in
this 0.3ml is dissolved state and 19.7ml is
bound to haemoglobin.
 The Heme portion of haemoglobin contains
4 atoms of iron which can bind 4 molecules
of oxygen to form oxyhaemoglobin.
 The binding of O2 to Haemoglobin is
determined by Partial pressure of O2

34. Transport of O2
 Saturation is the term used for this binding
process and is used in percentile form.
 If the blood has less amount of Hb or less
PO2 it can result in partial saturation of Hb
(50%).
 The binding is stronger and greater in
pulmonary capillaries since the PO2 is
higher(100mmHg)
 The unbinding of Hb and O2 takes place at
tissues due to decreased PO2(40mmHg).
 Only 25% of O2 is used by cells in rest and
it can increase at the time of exercise.

35. Transport of O2
 SPO2/SAO2 is the term used in medical
science to note the saturation rate of O2 in
humans.
 In normal cases it is nearly 100% (96-99%)
 If the level is below 90 percent, it is
considered low resulting in hypoxemia.
 below 80 percent may compromise organ
function, such as the brain and heart
(Oxygen administration is necessary)
 Pulse oximetry is a method used to estimate
the percentage of oxygen bound
to hemoglobin in the blood (using infra red
rays to assess saturated Hb)

36. Factors affecting Affinity of Hb for O2
In addition to partial pressure there are some other
factors that increase the affinity of Hb & O2.
1. pH (Acidity): as acidity increases (decreased pH)
the affinity also decreases and vice versa. It starts
the unbinding of O2 from Hb. pH can be disturbed
from diet. Most high protein foods/
carbohydrates/fats (such as meat, fish, poultry,
eggs and grains) are acid-forming. Because these
food require more acid and recycling and longer
duration for digestion. Most fruits and vegetables are
alkaline-forming. The citric fruits are acidic in
nature but it is easily digested hence does not create
more acids.

37. Factors affecting Affinity of Hb for O2
2.PCO2: CO2 can also bind to hemoglobin. This
depend on the partial pressure of CO2 in blood. As
more CO2 bind to Hb the unbinding of O2 can
occur. Decreased P of CO2 in blood can increase the
affinity of O2 to Hb. As CO2 enters blood in is
temporarily converted into Carbonic acid by a
catalyzing enzyme called carbonic anhydrase (CA).
This further gets separated into H+ ions and
bicarbonate ions. This increases pH and supports
unbinding of O2 from Hb.
3.Temperature: Hyperthermia can increase the
unbinding of O2 from Hb. Heat is produced by
increased metabolic activities such as exercise which
require more O2. Hypothermia has opposite reaction
on Hb and O2.

38. Factors affecting Affinity of Hb for O2
4. BPG (bisphosphoglycerate/diphosphoglycerate).
It is found in RBC which decrease the affinity
of Hb and O2 and helps in unbinding.BPG is
produced during glycolysis to produce ATP.
Certain hormones such as thyroxine, GH
increase the formation of BPG. The level of
BPG is also higher in people living in higher
altitudes.

39. Transport of CO2
Under normal resting conditions each 100ml of
deoxygenated blood contains 53ml of CO2. There
are three forms of CO2 transport.
 Dissolved CO2: 7% of CO2 get dissolved in
plasma.
 Carbamino compounds: 23% of CO2 combines
to proteins such as Hb to form
carboxyhemoglobin/carbaminihemoglobin and
transported in blood. This is influenced by
pCO2.
 Bicarbonate ions: 70% of CO2 id diffused into
plasma due to increased solubility and forms
carbonic acid. This further divides into H+ ions
and HCO3- ions(bicarbonate ions)

40. Transport of CO2
 The HCO3- ions accumulate in RBC. Some
move out to blood plasma down
concentration gradient but chloride ions
moves in return to the RBC to maintain the
electric balance which is called as Chloride
Shift.
 The amount of CO2 transport depends on
the level of saturation of O2 with Hb. If the
oxyhemoglobin level decreases then
carboxyhemoglobin will level increase. This
inverse relationship is called Haldane
effect.

41. Regulation of Respiration
Respiratory Centre: This is
located in Medulla and
Pons. It comprise of three
areas.
 Medullary Rhythmicity
Area: This controls the
rhythm of respiration. It
has both Inspiratory and
Expiratory area. This also
manages b rhythm during
quiet and forceful
breathing. It also controls
the muscles of respiration.

42. Regulation of Respiration
 PneumotaxicArea:
Located in the upper
Pons. It send
inhibitory
Inspiratory impulses
when the lungs are
full of air.
 Apneustic Area:
Located in the lower
Pons. It stimulates
Inspiration to have
deep breathing as
and when necessary.

43. Regulation of Respiration
 Cortical Influences: The cerebral cortex is
connected to respiratory centre hence the
breathing can be suspended for some time
voluntarily. This helps in prevention of
irritating and foul gases from entering the
lungs. But it resumes after strong
stimulation to respiratory centre due to
increased PCO2 in body. It also helps in
altering respiration during emotional
stimuli such as crying and laughing.

44. Regulation of Respiration
 Chemoreceptor: It controls respiration by
sensing levels of O2 and CO2 in body. The
primary chemoreceptor are located in
medulla which sense the CSF and
secondary chemoreceptor are locate din
aortic bodies/arch of the aorta to sense the
blood.
 Baroreceptor: Located in bronchi and
bronchioles which sense over stretching
due to hyperventilation. This will activate
the Pneumotaxic area to initiate inhibitory
inspiartory mechanism.

45. Regulation of Respiration
 Limbic System: Anticipation of anxiety
increase respiration.
 Temperature increase respiration:
increased body activity.
 Pain: Stops respiration temporarily.
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