Respiratory System Physiology

Introduction
Function

1. THE RESPIRATORY SYSTEM

2. RESPIRATION
The exchange of gases between the
atmosphere, lungs, blood, and tissues

3. OVERVIEW OF GASEOUS
EXCHANGE

4. Respiration
•Pulmonary ventilation=“breathing”
•External respiration=occurs within the lungs
•Internal respiration=occurs within the tissues

5. PHYSIOLOGICAL ANATOMY
•Nose and nasal
cavity
•Pharynx
•Larynx
•Trachea
•Bronchial tree
•Lungs
•Diaphragm

6. Trachea and Bronchial Tree

7. Conducting Zones

8. Lower Bronchial Tree

9. Alveoli and Respiratory Membrane

10. Functions of Respiratory system
• Respiratory
•Non respiratory –
1. LUNG DEFENCE-
 Humidify air
 Bronchial secretions- Immunoglobins- IgA,
Nictric oxide
 Prevent foreign body from reaching alveoli
PAMS ( pulmonary alveolar macrophages) –
attract polymorphic leucocytes that release
protease

11. 2. PULMONARY CIRCULATION
 Reservoir of Left ventricle
Filter – filters small blood clot, fat cells,
detached cancer cells, gas bubbles
Fluid exchange and drug absorption

12. Points to remember
 Both the lungs contain about 300
million alveoli
 Sympathetic stimulation of bronchus
causes bronchodilatation
 Alveolar lining epithelium contains
type II granular pneumocytes

13.  Pulmonary functional unit is alveolus
 Gaseous exchange takes place through
the respiratory bronchiole
 Particle size of diameter 2 micrometer
reaches alveoli
 capacity of conducting zone 150 ml
 PAM cells are also called dust cells
and originate from bone marrow

14. Substance filtered in pulmonary circulation
are small blood clot, fat cells, detached cancer cells,
gas bubbles

15. RESPIRATORY PHYSIOLOGY

16. Pressures
•Atmospheric pressure
•Alveolar pressure
(intrapulmonary pressure)
•Intrapleural pressure
•Boyle’s Law
–More volume=less pressure
–Less volume=more pressure

17. Thorax
•The thorax (or chest) is the closed cavity which
contains the lungs, heart and great vessels. The
thorax is lined by two thin layers of membrane –
the PLEURA – the inner (visceral) layer of which
covers the LUNGS. The outer (parietal) layer
covers the inner wall of the thorax.
•Elastic recoil of lungs tends to pull visceral layer
away from parietal layer. This creates
subatmospheric or negative intrapleural pressure
(about -2 mmHg).

18. MECHANISM OF BREATHING
The rhythmical changes in the capacity of the thorax are brought about by the action
of skeletal muscles. The changes in lung volume, with intake or expulsion of air,
follow.
In NORMAL QUIET BREATHING
INSPIRATION
External intercostal muscles actively contract: ribs and sternum move upwards and
outwards because first rib is fixed, width of chest increases from side to side and
depth from front to back increases.
Diaphragm contracts, length of chest increases. Capacity of thorax is increased
Pressure between pleural surfaces (already negative) becomes more negative:
from -2 to -6 mmHg

19. MECHANISM OF BREATHING
The rhythmical changes in the capacity of the thorax are brought about by the action
of skeletal muscles. The changes in lung volume, with intake or expulsion of air,
follow.
In NORMAL QUIET BREATHING
INSPIRATION
External intercostal muscles actively contract: ribs and sternum move upwards and
outwards because first rib is fixed, width of chest increases from side to side and
depth from front to back increases.
Diaphragm contracts, length of chest increases. Capacity of thorax is increased
Pressure between pleural surfaces (already negative) becomes more negative:
from -2 to -6 mmHg

20. Thoracic Volume and Inspiration

21. EXSPIRATION
External intercostal muscles relax: ribs and sternum more downwards and
inwards, width and depth of chest diminishes. Diaphragm relaxes – ascends –
length of chest diminishes. Capacity of thorax is decreased.
Pressure between pleural surfaces becomes less negative:
from -6 to -2 mmHg
Elastic tissue of lungs recoils
Air pressure in alveoli is now +1,5 mmHg (greater than atm. pressure)
Air is forced out of alveoli to atmosphere

22. Thoracic Volume and Expiration

23. In FORCED BREATHING
Muscles of nostrils and round glottis may contract to aid
entrance of air to lungs.
Extensors of vertebral column may aid inspiration.
Muscles of neck contract – move 1
st
rib upwards (and sternum
upwards and forwards).
Internal intercostal may contract – move ribs downwards
more actively.
Abdominal muscles contract – actively aid ascent of
diaphragm.

24. Changes in Thoracic Volumes

25. Factors Influencing Pulmonary
Ventilation
•Airway Resistance
•Surface Tension
•Lung Compliance

26.  Eupnoea is normal breathing
 With 1 cm descent of diaphragm 200-300 ml
of air is sucked in the lungs
 At the end expiratory position the lungs recoil
from the chest wall
 Surfactant causes compliance of lungs
Thyroxine increase the increases the size and
number of inclusions in type II cells
Glucocorticoids accelerates the maturation of
surfactants

27.  Trachea and bigger bronchi offers maximum
resistance
 Most comfortable position for diaphragm is the
sitting positon
 Ventilation perfusion ratio definition- Ratio of
alveolar air ventilation to pulmonary blood flow

28. Respiratory Volumes and Capacities

29. Copyright 2009, John Wiley & Sons, Inc.
Spirogram of Lung Volumes and
Capacities

30. Volumes and Capacities

31. Dead Space
•Anatomical dead space
•Alveolar dead space

32.  FEV1 is the most sensitive index to assess
obstructive lung disorder
 CO2 has higher solubility hence higher diffusion
capacity
 All the definitions of lung volume and capacities
 lungs with high compliance expands more
 obstructive and restrictive disorders

33. Gas Transport

34. Non-Respiratory Air Movements

35. Basic Properties of Gases
Dalton’s Law of Partial Pressures

36. Copyright 2009, John Wiley & Sons, Inc.
Exchange of Oxygen and Carbon
Dioxide
•Dalton’s Law
–Each gas in a mixture of gases exerts its own pressure as if
no other gases were present
–Pressure of a specific gas is partial pressure P
x
–Total pressure is the sum of all the partial pressures
–Atmospheric pressure (760 mmHg) = P
N2
+ P
O2
+ P
H2O
+ P
CO2
+
P
other gases
–Each gas diffuses across a permeable membrane from the
are where its partial pressure is greater to the area where its
partial pressure is less
–The greater the difference, the faster the rate of diffusion

37. Copyright 2009, John Wiley & Sons, Inc.
Henry’s law
–Quantity of a gas that will dissolve in a liquid is
proportional to the partial pressures of the gas
and its solubility
–Higher partial pressure of a gas over a liquid
and higher solubility, more of the gas will stay
in solution
–Much more CO
2
is dissolved in blood than O
2

because CO
2
is 24 times more soluble
–Even though the air we breathe is mostly N
2
,
very little dissolves in blood due to low
solubility
•Decompression sickness (bends)

38. Factors Influencing Gas Transport
and Hemoglobin Saturation

39. Copyright 2009, John Wiley & Sons,
Inc.
Transport of Oxygen and Carbon
Dioxide
•Oxygen transport
–Only about 1.5% dissolved in plasma
–98.5% bound to hemoglobin in red blood cells
•Heme portion of hemoglobin contains 4 iron atoms
– each can bind one O
2
molecule
•Oxyhemoglobin
•Only dissolved portion can diffuse out of blood into
cells
•Oxygen must be able to bind and dissociate from
heme

40. Copyright 2009, John Wiley & Sons, Inc.
Hemoglobin and Oxygen
•Other factors affecting affinity of
Hemoglobin for oxygen
•Each makes sense if you keep in mind that
metabolically active tissues need O
2, and
produce acids, CO
2, and heat as wastes
–Acidity
–P
CO2
–Temperature
–2,3 diphosphoglyceric acid (2, 3 DPG)

41. Factors Influencing Gas Transport
and Hemoglobin Saturation

42. Copyright 2009, John Wiley & Sons,
Inc.
Bohr Effect
–As acidity increases (pH
decreases), affinity of Hb
for O
2 decreases
–Increasing acidity enhances
unloading
–Shifts curve to right
•P
CO2
–Also shifts curve to right
–As P
CO2 rises, Hb unloads
oxygen more easily
–Low blood pH can result
from high P
CO2

43. Copyright 2009, John Wiley & Sons,
Inc.
Temperature Changes
–Within limits, as
temperature increases,
more oxygen is
released from Hb
–During hypothermia,
more oxygen remains
bound
•2,3-bisphosphoglycerate
–BPG formed by red
blood cells during
glycolysis
–Helps unload oxygen
by binding with Hb

44. Copyright 2009, John Wiley & Sons,
Inc.
Fetal and Maternal Hemoglobin
•Fetal hemoglobin has a
higher affinity for
oxygen than adult
hemoglobin
•Hb-F can carry up to
30% more oxygen
•Maternal blood’s
oxygen readily
transferred to fetal blood

45. At the Tissues

46. At the Lungs

47.  PO2 is less in arterial blood than the alveolar air
because of some venous blood moves through
myocardium into cavities of left heart
 O2 in dissolved form carried is 0.3ml/100 ml of
blood
 O2-Hb dissociation curve- characteristics,
significance of flat and steep part, factors shifting
curve to right and left
 Bohr’s effect and Haldane effect
 Myoglobin doesnot show Bohr effect
 Hematocrit value of venous blood is more than
arterial blood by 3 %

48.  Myoglobin binds with 1 mol of oxygen per mol
 Shifting affinity of oxygen to Hb makes the
curve sigmoid in nature
 Carbonic anhydrase is most important factor in
transport of CO2 inRBC
 transport of O2 and CO2 in blood
Ambient temperature doesnot determine the
amount of oxygen in blood

49. •Automatic control of respiration :
•Groups of neurons in medulla and pons
•Voluntary control is in cerebral cortex

50. Neural control of Respiration
Until recently, it was
thought the Dorsal
respiratory group of
neurons generate the basic
rhythm of breathing

It is now generally believed
that the breathing rhythm is
generated by a network of
neurons called the Pre-
Botzinger complex. These
neurons display pacemaker
activity. They are located
near the upper end of the
medullary respiratory
centre

51. Regulation of Respiration
•Medullary respiratory
center
–Dorsal respiratory center
(DRC)
–Ventral respiratory center
(VRC)
•Pontine center
formerly called the
Pneumotaxic center

53. •MEDULLARY RESPIRATORY
CENTRE

54. Dorsal Respiratory Group of Neurons (DRG)
The DRG of neurons in medulla responsible for
the basic rhythm of respiration.
vagal and the glossopharyngeal nerves, transmit
sensory signals into the respiratory center from:

(1) peripheral chemoreceptors,
(2) baroreceptors, and
(3) irritant receptors

55. What gives rise to inspiration?
PONS
MEDULLA
SPINAL CORD
Dorsal respiratory
group neurones
(inspiratory)
Fire in bursts
Firing leads to
contraction of
inspiratory muscles
- inspiration
When firing stops,
passive expiration

56. Ventral Respiratory Group (VRG)
Located in each side of the medulla
1.The neurons of the ventral respiratory group
remain almost totally inactive during normal
quiet respiration..
2.Providing the powerful expiratory signals to
the abdominal muscles during heavy
expiration.

60. PONTINE RESPIRATORY
CENTRE

61. The “apneustic centre”
Apneustic centre
Impulses from
these neurones
excite
inspiratory
area of
medulla
Prolong inspiration
Conclusion?
Rhythm generated in
medulla
Rhythm can be modified
by inputs from pons

62. The rhythm generated in the
medulla can be modified by
neurones in the pons:
“pneumotaxic
centre” (PC)
Stimulation
terminates inspiration
PC stimulated when
dorsal respiratory
neurones fire
Inspiration inhibited
Without PC, breathing
is prolonged
inspiratory gasps with
brief expiration
-
+

63. •VOLUNTARY CONTROL OF
RESPIRATION
•Genesis of inspiration
•Genesis of expiration

65. FACTORS AFFECTING
RESPIRATORY CENTRE
•Non chemical factors
1.Afferent from the higher centres stimulate
respiration
2.Vagal afferents from lung receptor – Hering-
Breuer reflex

66. The Hering-Breuer Inflation Reflex

Stretch receptors located in the muscular
portions of the walls of the bronchi and
bronchioles throughout the lungs transmit
signals through the vagi into the DRG of
neurons when the lungs become overstretched
and stops further inspiration.
This is called the Hering-Breuer inflation reflex.

67. In human the Hering-Breuer reflex is a
protective mechanism & not activated until
the tidal volume (greater than about 1.5 L/
breath).

68. “J receptors.”
A few sensory nerve endings in the alveolar
walls in juxtaposition to the pulmonary
capillaries ,stimulated by engorged
pulmonary capillaries or in pulmonary
edema as in congestive heart failure.
(Their excitation may give the person a feeling
of dyspnoea).

69. Joint receptors or
Proprioceptors
Impulses from moving limbs reflexly
increase breathing
Probably contribute to the increased
ventilation during exercise
Anesthesia. greatly depresses the respiratory
center

70. •Irritant receptors Irritant receptors
–Stimulated by inhaled irritants or mechanical
factors
Cause couging and sneezing in conducting zone
tachypnoea and bronchoconstriction in respiratory
zone
–In hospital triggered by
•Suctioning, bronchoscopy, endotracheal
intubation

71. •Baroreceptors
•Chemoreceptors

72. CHEMICAL REGULATION OF
RESPIRATION
•Depends on the P CO2, pH, and PO2
The changes are mediated via respiratory
chemoreceptors – Peripheral, Medullary,
pulmonary and myocardial receptors

73. CHEMICAL FACTORS
AFFECTING RESPIRATION
•Hypoxia
•CO2
•pH

74. Effect of pH on Respiration

75. The effect of low arterial PO2 on alveolar ventilation is
far greater under some conditions including the
following:
*pulmonary disease: no adequate gas exchange, too
little O2 is absorbed into the arterial bl. &at same time
the arterial PCO2& H+ conc. remain near normal or
are ↑↑because of poor transport of CO2 through the
membrane.
*acclimatization to low O2

76. Peripheral chemoreceptors

77. Influence of Chemical Factors on Respiration

78. Periodic Breathing
The person breathes deeply for a short interval
and then breathes slightly for an additional
interval, with the cycle repeating itself over and
over.

79. Cheyne-Stokes breathing, is characterized
by slowly waxing and waning respiration
occurring about every 40 to 60 seconds.
The basic cause of Cheyne-Stokes breathing
may occurs in everyone it can be found in
congestive heart failure, uremia and in
damage of respiratory center.

80. Cheyne-Stokes breathing, showing
changing PCO2

81. Sleep Apnea
Apnea: means absence of spontaneous breathing.
sleep apnea: apneas occur during normal sleep,
can be caused by obstruction of the upper
airways, especially the pharynx, or by
impaired central nervous system respiratory
drive.

82. Periods of apnea result in significant
decreases in P O2 and increases in PCO2
which greatly stimulate respiration. causes
sudden attempts to breathe, which result in
loud snorts and gasps followed by snoring
and repeated episodes of apnea.

83. Summary of ventilation control
Respiration is regulated by:
PO2 via chemoreceptor (carotid bodies in the
arteries)
PCO2 via chemoreceptor for H+ in both the
brain and body.
pH via the same chemoreceptor in brain and
body Direct voluntary control.

84.  The rhythmicity of respiration comes fron the
pons
 Pulmonary stretch receeptors inhibits
apneustic centre via vagus
 Hering breuer reflex, J receptors
 Sneezing, coughing by irritants n conducting
zone and tachypnoea and bronchoconstriction
in respiratory zone
 Alveolar PO2 below 60 mm Hg stimulates
ventilation
 Alveolar PCO2 above 60mm Hg depresses
respiration

85.  Dstruction of pneumotaxic centrre causes apneutic
respiration
 Sleep, deglutition and after hyperventilation are
physiological apnoea but Bezold –jarisch reflex is
not
 All affects of the chemical factors- Hyoxia, CO2,
Hydrogen ion
 Apnoea, Dyspnoea, Breath holding, Asphyxia,
Periodic breathing( Cheyne stokes respiration and
Biot’s breathing)
 Hypoxia- types, causes and characteristics
 Cyanosis