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1. Respiratory Physiology
DR. GIRISH JAIN
DEPARTMENT OF RESPIRATORY MEDICINE
MHATMA GANDHI MEDICAL COLLEGE, JAIPUR

2. Respiration
• It is the process by which the body takes oxygen in and utilizes and
removes CO2 from the tissues into the expired air.
• The term respiration includes 3 separate functions:
• Ventilation:
• Breathing.
• Gas exchange:
• Between air and capillaries in the lungs.
• Between systemic capillaries and tissues of the body.
• 02 utilization:
• Cellular respiration.

3. • Mechanical process that moves air in
and out of the lungs.
• [O2] of air is higher in the lungs than in
the blood, O2 diffuses from air to the
blood.
• C02 moves from the blood to the air by
diffusing down its concentration
gradient.
• Gas exchange occurs entirely by
diffusion: Diffusion is rapid because of
the large surface area of alveoli and the
small diffusion distance.
Ventilation:-

5. Two type of Respiration
1. External Respiration
2. Internal Respiration
External respiration
• Also known as BREATHING
• It is the transfer of gas between respiratory organs such as lungs and
the outer environment.
• oxygen is taken up by capillaries of lung alveoli and carbon dioxide is
released from blood simultaneously.

6. Internal respiration
• Also known as Tissue Respiration/Cellular Respiration
• Involves the movement of O2 and CO2 between the blood capillaries
and cells and tissue.
• Oxygen is released to tissues or living cells and carbon dioxide is
absorbed by the blood
• These processes can only happen if a diffusion gradient is present.

7. Functions of the Respiratory System
• Gas Exchange
• O2, CO2
• Acid-base balance
• CO2 +H2O←→ H2CO3 ←→ H+ + HCO3-
• Phonation (voice production )
• Pulmonary defense:-Free alveolar macrophages (dust cells)
• Pulmonary metabolism and handling of
bioactive materials
• Route for water loss and heat elimination
• protective reflexes (apnoea, laryngospasm)
• defensive reflexes (cough, sneeze)
• Enhances venous return during inspiration
-

8. Anatomy of Respiratory Tree

10. Airways of the lungs
1. Upper airways
2. Conducting airways
3. Respiratory airways

11. Upper airway
• Comprises of nose and mouth that lead to pharynx then larynx
• It helps in filtering out large particles-
 30- 50 micron particles do not enter the nose.
 5- 10 micron particles are generaly impacted in the nasopharynx and do not
entre the conducting airway.
 1 and 5 micrometers settle in the smaller bronchioles as a result of
gravitational precipitation.
• It also warms and humidify the air as it enters the body

12. Conducting airways
The lower respiratory tract starts after the
larynx and divides to the smallest regions
which form the exchange membranes
• Trachea
• Primary bronchi
• Secondary bronchi
• Tertiary bronchi
• Bronchioles
• Terminal bronchiole
In conduction zone no gas exchange
occurs

13. Section of Bronchus

14. Bronchial Section - microscopic Terminal Bronchioles - bifurcation

15. Respiratory airways
• It consists of the respiratory bronchioles, alveolar ducts, and alveolar sacs, which
collectively comprise the Terminal Respiratory Unit (TRU).
• The TRU is distal to and a direct continuation of the terminal bronchioles. It is the site of
gas exchange with the pulmonary capillary blood.
• The gas exchange airway typically begins with the appearance of the respiratory
bronchioles.
• The distinguishing feature of TRU is the presence of alveoli.
Alveoli
 Air sacs
 Honeycomb-like clusters
 ~ 300 million.
 Large surface area (60–80 m2).
 Each alveolus: only 1 thin cell layer.
 Total air barrier is 2 cells across (2 mm) (alveolar cell and capillary endothelial cell

16. 2 types of alveolar
cells:
• Alveolar type I:
Structural cells.
• Alveolar typeII:
Secrete
surfactant.

17. Alveoli under microscope EM of the alveoli

18. • The epithelial layer gradually becomes reduced from pseudostratified columnar to
cuboidal.
• The smooth muscle layer disappears in the alveoli.
• The fibrous layer contains cartilage only in bronchi and gradually becomes thinner.
Airway wall structure

20. Weibel model
Dichotomous branching airway- total 23 generation
• The first 16 generations make up the conducting airways ending in
the terminal bronchioles.
• The next 3 generations constitute the respiratory bronchioles, in
which the degree of alveolation steadily increases. This is the
transitional zone.
• Finally, there are 3 generations of alveolar ducts and 1 generation of
alveolar sacs. These last four generations constitute the true
respiratory zone.

23. MUSCLES OF REPIRATION
INSPIRATION
•DIAPHRAGM
•EXTERNAL INTERCOSTAL MUSCLE
•INTERCHONDRAL PART OF INTERNAL
INTERCOSTAL OF C/L SIDE
DEEP INSPIRATION
•ERRECTOR SPINAE
•SCALENE MUSCLE
•PECTORAL MUSCLE
•STERNOCLEIDOMASTIOD
EXPIRATION
•PASSIVE PROCESS
FORCED EXPIRATION
•MUSCLES OF ANT.
ABDOMINAL WALL
•INTERNAL INTERCOSTAL
MUSCLE

25. Muscle Nerve supply
Diaphragm Phrenic nerve C3-C5
Intercostal muscles Intercostal nerves
Sternocleidomastoid Spinal accessory– motor
Scalenes Anterier – ventral rami of C3- C6
Posterier – ventral rami of C5 – C7
Pectoralis Major Medial & lateral pectoral nerve

26. Thoracic Cavity
• Diaphragm:
• Sheets of striated muscle divides anterior body cavity into 2 parts.
• Above diaphragm: thoracic cavity:
• Contains heart, large blood vessels, trachea, esophagus, thymus,
and lungs.
• Below diaphragm: abdominopelvic cavity:
• Contains liver, pancreas, GI tract, spleen, and genitourinary tract.

27. Diaphragm
• The diaphragm has three parts
1. Costal portion, made up of muscle fibers that are attached to the
ribs around the bottom of the thoracic cage;
2. Crural portion, made up of fibers that are attached to the
ligaments along the vertebrae;
3. Central tendon, into which the costal and the crural fibers insert.
• The central tendon is also the inferior part of the pericardium.
• The crural fibers pass on either side of the esophagus and can
compress it when they contract.

28. Nerve Supply:-
Motor Phrenic nerve C3-C5
Sensory Central tendon phrenic nerve
Periphery lower six intercostal nerves.
• The costal and crural portions are innervated by different parts of the phrenic
nerve and can contract separately.
• For example, during vomiting, intra-abdominal pressure is increased by
contraction of the costal fibers but the crural fibers remain relaxed, allowing
material to pass from the stomach into the esophagus.

29. Injury to the upper cervical spinal cord:
• Interrupt transmission of the stimulus to breathe from the respiratory
centers in the brain stem to the diaphragm and other ventilatory
muscles.
• The phrenic nerve roots that supply the diaphragm arise from spinal
segments C3 to C5.
• Patients with acute injury at this level or above usually require
mechanical ventilation.
• C1-2 spinal injury - permanently ventilator-dependent
• C3-4 injuries - least partial ventilator independence.
• Lesions below C4 are usually compatible with unassisted ventilation
unless there are complicating processes such as intrinsic lung disease
or impaired mental status

30. RESPIRATORY MOVEMENTS:-
Action:
Contraction: The dome
moving downward,
increases the volume of
thoracic cavity which
results in inspiration.
Relaxation: the dome
returns to the former
position, reduces the
volume to the thoracic
cavity, resulting in
expiration.

31. • Inspiration – Active process
• Diaphragm:- constitutes 65- 75 % in inspiratio
• Diaphragm contracts - increased thoracic volume vertically.
• External Intercostals contract, expanding rib cage - increased thoracic volume
laterally.
• More volume -> lowered pressure -> air in.
• Negative pressure breathing
• External intercoastal muscles:-
• Extends from inferior border of the rib above to the superior border of the rib
below in the downward , forward and medial direction
• Innervated by intercoastal nerves

32. Brings about two types of
action –
1. Bucket handle movement
• Occurs in lower ribs
• On muscle contraction
oblique ribs get elevated ,
become horizontal
• Transverse diameter
increases
2. Pump handle movement
• On muscle contraction
the sternum moves
anteriorly , increasing AP
diameter
• Occurs in upper ribs

33. • Expiration – Passive
• Due to recoil of elastic lungs.
• Less volume -> pressure within alveoli is just above atmospheric
pressure -> air leaves lungs.
• Note: Residual volume of air is always left behind, so alveoli do
not collapse.
• In forceful expiration:-
• 1.Internal intercoastal muscles contract and making the ribs
oblique
• 2.Abdominal muscles contract and increase the intra-abdominal
pressure which pushes the diaphragm upwards and decrease the
intrathorasic volume

34. • Pressures:-
• lung is elastic structure that collapses like a balloon ,
• It expels all its air through trachea.
• No attachments between lung and walls of chest cage, except where
it is suspended at its hilum from mediastinum.
• Lung “floats” in thoracic cavity, surrounded by thin layer of pleural
fluid that lubricates it.
• Continuous suction of excess fluid through lymphatic channels
between the visceral pleura and the parietal pleura.

36. • Pleural pressure:-
• Pleural pressure is the pressure of the fluid in the thin space between
the lung pleura and the chest wall pleura. This is normally a slight
Suction so, slightly negative pressure.
• The normal pleural pressure at the beginning of inspiration is about –
5 centimeters of water, which is the amount of suction required to
hold the lungs open to their resting level.
• Then, during normal inspiration, expansion of the chest cage pulls
outward on the lungs with greater force and creates more negative
pressure, to an average of about –7.5 centimeters of water.

38. • Alveolar pressure:-
• Alveolar pressure is the pressure of the air inside the lung alveoli.
• When the glottis is open and no air is flowing into or out of the lungs,
the pressures in all parts of the respiratory tree upto the alveoli, are
equal to atmospheric pressure, which is considered to be zero
reference pressure in the airways—that is, 0 centimeters water
pressure
• To cause inward flow of air into the alveoli during inspiration, the
pressure in the alveoli must fall to a value slightly below atmospheric
pressure (below 0).

39. • During normal inspiration, alveolar pressure decreases to about –1
centimeter of water. This slight negative pressure is enough to pull 0.5
liter of air into the lungs in the 2 seconds required for normal quiet
inspiration.
• During expiration, opposite pressures occur: The alveolar pressure
rises to about +1 centimeter of water and this forces the 0.5 liter of
inspired air out of the lungs during the 2 to 3 seconds of expiration.

43. Transpulmonary pressure
• Expansion of alveoli depends on the achievement of an appropriate
distending pressure across alveolar walls.
• This distending pressure or transpulmonary pressure is the difference
between alveolar (PA) and pleural (Ppl) pressures.
• It is the pressure difference between that in the alveoli and that on the
outer surfaces of the lungs, and it is a measure of the elastic forces in the
lungs that tend to collapse the lungs at each instant of respiration called the
recoil pressure.
• Larger the lung expansion , larger will be the transpulmonary

44. • Restrictive ventilatory defect.
• Decreased Vital Capacity.
• Decreased FRC.
• Decreased TLC.
• Decreased RV.
• Decreased end expiratory lung volume.
• Increased end expiratory thoracic volume?.
• Slightly decreased DLCO.
Expansion of the pleural space is accommodated
partly by deflation of the lung and partly by relative
expansion of the ipsilateral chest wall.
Effects of Pneumothorax in Lung

46. summarize
• Transpulmonary pressure is always positive
• Intrapleural pressure is always negative.
• Alveolar pressure moves from slightly positive to slightly negative as a
person breathes.
• For a given lung volume the transpulmonary pressure is equal and opposite
to the elastic recoil pressure of the lung.
• Transpulmonary pressure at end expiration is 5 cm of water
• Transpulmonary pressure at end inspiration is higher and lungs contain
more air

47. Pulmonary Volumes:-
1. The tidal volume is the volume of air inspired or expired with each
normal breath; it amounts to about 500 milliliters in the adult male.
2. The inspiratory reserve volume is the extra volume of air that can be
inspired over and above the normal tidal volume when the person inspires
with full force; it is usually equal to about 3000 milliliters.
3. The expiratory reserve volume is the maximum extra volume of air that
can be expired by forceful expiration after the end of a normal tidal
expiration; this normally amounts to about 1100 milliliters.
.

48. 4. The residual volume is the volume of air remaining in the lungs after the
most forceful expiration; this volume averages about 1200 milliliters

50. Pulmonary Capacities
1. The inspiratory capacity equals the tidal volume plus the inspiratory reserve
volume. This is the amount of air (about 3500 milliliters) a person can breathe
in, beginning at the normal expiratory level and distending the lungs to the
maximum amount.
2. The functional residual capacity equals the expiratory reserve volume plus
the residual volume. This is the amount of air that remains in the lungs at the
end of normal expiration (about 2300 milliliters).

51. 3. The vital capacity equals the inspiratory reserve volume plus the tidal volume plus the
expiratory reserve volume. This is the maximum amount of air a person can expel from the
lungs after first filling the lungs to their maximum extent and then expiring to the maximum
extent (about 4600 milliliters).
4. The total lung capacity is the maximum volume to which the lungs can be expanded with
the greatest possible effort (about 5800 milliliters); it is equal to the vital capacity plus the
residual volume.

52. VC = IRV + VT + ERV
VC = IC + ERV
TLC = VC + RV
TLC = IC + FRC
FRC = ERV + RV

54. Minute respiratory volume
• The minute respiratory volume is the total amount of new air moved
into the respiratory passages each minute; this is equal to the tidal
volume times the respiratory rate per minute.
• The normal tidal volume is about 500 milliliters, and the normal
respiratory rate is about 12 breaths per minute. Therefore, the minute
respiratory volume averages about 6 L/min

55. Thank You