PHYSIOLOGY respiaratory

1. Physiology
Of
Respiratory System
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2. Outline
- General functions of the respiratory system
- Functional anatomy of the respiratory system
- The mechanics of breathing
- Gas exchange and transport
- Acid base regulation
- Control of ventilation
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3. Introduction:
• Breathing is essential for life!
• A breath in, a breath out, 12 to 15 per minute
• An average, 6 L of air per minute enters into the
lungs.
• Small changes in blood chemistry, mood, level of
alertness, and body activity affects the rate of
consumption.
• Resting O2 consumption averages about 250
ml/min, and CO2 production averages about 200
ml/min.
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4.  Respiration:
• The process of taking up oxygen and
removing carbon dioxide from cells in the
body.
• Respiration takes place in two stages:
1. Gas exchange, and
2. Cellular respiration.
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5. 1. Gas exchange: occurs at two levels.
– The first level involves the transfer of oxygen and
carbon dioxide between the atmosphere and the lungs.
– The second level involves the exchange of oxygen and
carbon dioxide and occurs between the systemic blood
and the metabolically active tissue.
– The movement of oxygen and carbon dioxide in and out
of cells occurs by simple diffusion.
 External respiration
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6. 2. Cellular respiration፡
• A series of complex metabolic reactions that break down
molecules of food, releasing carbon dioxide, water and
energy at mitochondria.
 Internal respiration
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External
Respiration
Internal Respiration

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9. Functions of Respiratory System:
1. Primary function:
 Exchange of gases between the atmosphere and blood
2.Secondary function:
 Warming and humidification of inspired air
Olfaction (Perfume######)
 Regulation of acid-base balance
 Protection from inhaled pathogens and irritants
 Vocalization
 Metabolization and activation of certain biologically
active substances (bradykinin Vs angiotensin II by ACE)
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10. Functional Structures of Respiratory System:
General structural setup:
• Air passages
• Lungs
• Pleural sac
• Thoracic cage
• Muscles of breathing
• Nerve centers in the brain
stem
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11. • Respiratory system Can be classified according to either
structure or function:
i. Structurally:
1. The upper respiratory system:
• The nose, nasal cavity, pharynx, larynx and
associated structures.
2. The lower respiratory system:
•Trachea, bronchi, and lungs.
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12. ii. Functionally:
1. The Conducting Zone:
• Consists of a series of inter-connecting cavities
and tubes both outside and within the lungs.
• The nose, nasal cavity, pharynx, larynx,
trachea, bronchi, bronchioles, and terminal
bronchioles;
• Their function is to filter, warm, and moisten air
and conduct it into the lungs.
• No gas exchange takes place.
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13. 2. The Respiratory Zone:
• Consists of tubes and tissues within the lungs
where gas exchange occurs.
• These include the respiratory bronchioles,
alveolar ducts, alveolar sacs, and alveoli.
• Are the main sites of gas exchange between air
and blood in alveolar capillary
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14. Air way Branching:
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16. The Alveoli:
• Are thin-walled, inflatable air sacs, with diameter of 200-250 μm.
• The fundamental unit of gas exchange.
• Adult lungs contain 300 to 500 million alveoli with a combined
internal surface area of approximately 75 m2 .
• A network of billions of capillaries surrounds each alveolus and
brings blood into close proximity with air inside the alveolus.
• Oxygen and carbon dioxide move across the thin-walled alveolus
by diffusion.
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17. Alveoli have walls made up of 3 cell types
1. Pneumocytes-type I:
• Major lining cells, where gas exchange takes place;
2. Type II Pneumocytes:
• That are less in number and constitute thicker
granulocytes responsible for the production of
pulmonary surfactant.
3. Type III Pneumocytes-
• Large phagocytic macrophage cells found in alveolar
cavities.
• These cells keep alveolar surfaces sterile by removing
debris and microbes.
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21. Alveolus and surrounding pulmonary capillaries:
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22. The lining of the airways:
• The trachea, bronchi, and larger bronchioles are lined
with fine, hair-like ciliary cells.
• These are covered with a thin layer of mucous that
catches foreign material.
• The cilia rhythmically beat and move the mucous-
trapped material up to the throat where it can be
swallowed or spit out,
and thus eliminated from the body.
 This process is called the mucociliary escalator.
• This defends the air passages against bacterial infection
and toxins.
• Ciliary activity can be reduced by smoking leading to
lung infection.
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23. Motor Innervation of Respiratory Muscles:
• Diaphragm: Phrenic nerves arising from C3-5.
• Intercostal muscles: Intercostal nerves from thoracic
segments.
• Tracheobronchial tree:
– Parasympathetic → bronchial smooth muscle
constriction and glandular secretions increases.
– Sympathetic → bronchial smooth muscle dilatation and
decreased bronchial secretions decrease.
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24. Blood Circulation:
• Pulmonary circulation: Starts in right ventricle
→ pulmonary trunk→ pulmonary arteries →
pulmonary capillaries→ pulmonary veins →
left atrium.
• The Pulmonary arteries:
– Conduct deoxygenated blood from right heart to lungs to
be oxygenated.
– Branch profusely, along with bronchi and ultimately feed
into the pulmonary capillary network surrounding the
alveoli.
• The Pulmonary veins – carry oxygenated
blood from lungs to the left atrium.
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27. Pulmonary Capillaries:
• Resting capillary volume = 70ml
• Maximum capillary volume = 200ml
• Unique feature of these capillaries:
Distension: increase in caliber (diameter)
Recruitment: opening up of previously closed
capillaries during high O2 demand.
• Blood stay in these capillaries for about 0.8 secs.
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28. Characteristics of pulmonary circulation:
• Blood Pressure = 25/8 mmHg
• Low resistance
• Low pressure
Bronchial circulation:
• 1% of the cardiac output (50 ml/min)
• nutritive blood supply to the lung
• vascular resistance is high
• Controlled by bronchomotor nerve
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29. The Mechanics of Breathing
The physics of the lungs, airways, and chest
wall—deals with how the body moves air in
and out of the lungs, producing a change in
lung volume (VL).
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30. NB:
• The interaction between the lungs and the thoracic cage
determines lung volume.
• The lungs have a tendency to collapse because of their
elastic recoil.
• The chest wall also has an elastic recoil. However, this
elastic recoil tends to pull the thoracic cage outward.
• Thoracic cage forms a solid casing around the lung to
protect and prevent its collapse by the elastic outward
recoil of its tissues.
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31. Opposing Elastic Recoils of the Lungs and Chest wall
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32. Muscle of Respiration:
• The respiratory muscles that accomplish
breathing do not act directly on the lungs to
change their volume.
• Instead, these muscles change the volume of
the thoracic cavity, causing a corresponding
change in lung volume.
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34. Muscle of inspiration:
i. Diaphragm:
– Is the main muscle of inspiration.
– Contraction of the diaphragm enlarges the cavity in
which the lung is enclosed, increasing volume.
– At rest, during inspiration, the diaphragm contracts and
pushes the abdominal contents downward.
– The downward movement also pushes the rib cage
outward.
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35. • Obesity, pregnancy, and tight clothing around the
abdominal wall can hamper the effectiveness of the
diaphragm in enlarging the thoracic cavity.
• Damage to the phrenic nerves can lead to paralysis of the
diaphragm.
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36. II. External intercostal muscles.
• Lie between the ribs
• Elevate the ribs and the sternum upward and outward.
• Enlarges the thoracic cavity in both the lateral (side-to-
side) and antero-posterior (front-to-back) dimensions.
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37. Accessory Muscles of Inspiration:
• assist the diaphragm in creating sub atmospheric pressure in the
lungs.
• With deep and heavy breathing, the accessory muscles contract and
pull the rib cage upward and outward.
• The major accessory muscles of inspiration are:
• Scalene muscles
• Sternocleidomastoid muscles
• Pectorals muscles
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38. 28 July 2022 38
Active
↓
Nerve impulse
↓
Contraction of:
• Diaphragm
• External intercostal
• Accessory muscles
Contraction of:
Diaphragm
Increase vertical
dimension of
thorax by its
descent (1.5 cm
up to 7cm)
↓
Contributes 70%
of TV
Contraction of
External intercostals
↓
Increase anteroposterior
dimension of thorax
↓
Contributes 30% of TV
Accessory muscles are involved when TV > 800ml/breath during inspiration
Inspiration

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40. Expiration:
• Is passive during resting conditions.
• The diaphragm relaxes and returns to its dome shape, and the
rib cage is lowered.
• Thoracic cavity decreases in volume(size)
• During forced expiration, the internal intercostal muscles
contract and pull the rib cage downward and inward.
• The abdominal muscles also contract and help pull the rib
cage downward, compressing thoracic volume.
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EXPIRATION reduction of chest cavity↓volume of thorax
↓lung vol.
Passive at rest Active during exercise
Elastic recoil
of:
Surface tension
effect of:
Nerve
impulses
Contraction of :
Stretched
tissues in
thorax, lungs,
↓
30% of TV
Fluid lining
alveoli and
respiratory
bronchioles
↓
70%TV
Contraction
of
expiratory
muscles
(internal
intercostal
muscle)
abdominal
muscles
including pelvic
floor muscles
↓
Upward
movement of
diaphragm.

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43. Pressure and Volume changes during
Pulmonary Ventilation
• Gases, like liquids, follow to the shape of their container.
• Unlike liquids, gases always fill their container.
• In a large volume, the gas molecules will be far apart and the
pressure will be low.
• If the volume is reduced, the gas molecules will be compressed
and the pressure will rise up.
• Boyle’s Law:
• States that the pressure exerted by a gas is inversely
proportional to its volume at constant temperature.
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44. 1. Atmospheric (barometric) pressure
• the pressure exerted by the weight of the air in the
atmosphere on objects on Earth’s surface (760 mm Hg at
sea level).
2. Intra-alveolar pressure(intrapulmonary Pressure):
• pressure within the alveoli.
 Air flows into and out of the lungs by reversing pressure
gradients established between the alveoli and atmosphere
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45. • Movement of air into and out of the lungs results from
changes in thoracic volume, which cause changes in
alveolar volume.
• The changes in alveolar volume produce changes in
alveolar pressure.
• The pressure difference between barometric air pressure
and alveolar pressure (PB- Palv) results in air
movement.
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46. 3. Pleural Pressure:
• The pressure in the pleural cavity between the lung and
chest wall; the pressure within the pleural sac.
• Is critical for lung inflation and deflation;
• It also rises and falls during respiration, but is usually
about -4cmHg less than intrapulmonary pressure.
• Always negative !!
• Ppl = -3mmHg to –10 mmHg
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48. Transpulmonary pressure (Mural Pressure)
• The difference between the alveolar pressure and pleural
pressure.
• Transpulmonary pressure (Palv – Ppl) keeps the alveoli open.
• Keeps the lungs inflated and prevents the lungs from
collapsing.
• The more positive it becomes, the more the lungs are distended
or inflated.
• If intrapleural pressure is equalized with intrapulmonary or
atmospheric pressure, lung collapse will occur immediately.
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49. During inspiration
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50. During expiration:
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52. Physical factors affecting Pulmonary Ventilation
A. Airway Resistance:
B. Elastic Properties of the Lung and Chest wall
 Elastic recoil (Elasticity)
 Stretchability (Compliance )
C. Alveolar Surface Tension
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53. A. Airway Resistance:
• Friction in the respiratory passageways is the major
non-elastic source of resistance to gas flow.
• F = ΔP/R
• Gas flow inversely changes with resistance, which is
mainly determined by conducting tube diameter.
• Greatest resistance is in the bronchi.
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54. Factors Increasing Airway Resistance
• Inhaled irritants
• Accumulation of mucus or infectious material
• Parasympathetic stimulation(Vagal tone),
• Histamine,
• Edema of the walls
• Allergy-induced spasm of the airways
• Airway collapse
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55. B. Elastic Properties of the Lung and Chest wall
I. Elastic Recoil
• Refers to how readily the lungs re-bound after having been
stretched
• Is the tendency of an elastic structure to oppose stretching.
• The lungs naturally have a tendency to collapse because of the
presence of elastin protein that favors elastic recoil.
They are held open by the negative pleural pressure.
• The chest wall naturally expands, but is also held by the
negative pleural pressure.
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56. II. Lung Compliance
• The ease which can be expanded is called lung
compliance
• index of the effort required to expand the lungs (to
overcome recoil). It does not relate to airway
resistance
• The higher the lung compliance, easier to expand the
lungs at any transpulmonary pressure.
• The less compliant the lungs are, more work required
to produce a given degree of inflation.
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58. C. Alveolar Surface Tension:
• Lungs secrete and absorb fluid, normally leave a very thin film of
fluid on alveolar surface.
• The force of attraction between water molecules in the alveolar
wall is called alveolar surface tension.
• This cohesive force resists any force that tends to increase the area
of the surface.
• This liquid film that coats the alveolar walls is always acting to
reduce the alveoli to their smallest size.
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59. • Surface water molecules create substantial surface tension.
• Alveolar surface tension creates inward recoil which leads to
alveolar collapse.
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60. Pulmonary Surfactant
• complex mixture of lipids and proteins secreted by the
Type II alveolar cells.
• have both hydrophilic region and a hydrophobic region,
they localize to the surface of an air-water interface.
• It intermingles between the water molecules in the fluid
lining the alveoli and lowers alveolar surface tension.
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61. Role of surfactant:
• Reduces surface tension on alveolar surface membrane
thus reducing tendency for alveoli to collapse
• Increases lung compliance (distensibility)
• Reduces lung’s tendency to recoil
• Makes work of breathing easier(easier to inflate the
lungs).
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62. Respiratory distress syndrome of the newborn
• Developing fetal lungs normally cannot synthesize
pulmonary surfactant until late in pregnancy.
• Especially , infants born prematurely may lack sufficient
levels of surfactant.
• May develop respiratory distress syndrome (RDS).
• The infant must make very strenuous inspiratory efforts to
overcome the high surface tension in an attempt to inflate
the poorly compliant lungs.
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63. The work of breathing:
• In quit breathing , energy is utilized during inspiration to
expand the lungs against their elastic forces and to
overcome air way resistance.
• Normally requires only about 3% of total energy
expenditure.
• The work of breathing may be increased :
1. When pulmonary compliance is decreased
2. When airway resistance is increased
3. When elastic recoil is decreased( expiratory effort)
4. When there is a need for increased ventilation( exercise)
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64. 1. Breathing Frequency
2. Minute ventilation (MV),
3. Alveolar Ventilation
4. Spirometry
5. Blood gas analysis
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Measurements of Lung Functions

65. Minute Ventilation:
• It is the total volume of air moved in or out of the
lungs per minute.
• Tidal volume times breathing frequency
• Frequency = 12 breaths /min in adults
• MV = VT X f
= 500ml/12breaths/min= 6000ml/min
Alveolar ventilation:
• The volume of air reaching to alveoli per minute.
VA = (VT -Vd)f
=(500ml-150ml)12 breaths/min
= 4200ml/minute
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66. Dead Space
it is a volume of air wasted in airways where gas exchange
does not take place.
1. Anatomic dead space: Part of respiratory system where
gas exchange does not take place
• Conduction air ways are fixed dead space
• Its volume is about 150 ml
2. Alveolar dead space
• alveoli containing air but without blood flow in the
surrounding capillaries.
• Unperfused but ventilated alveoli
3. Physiologic dead space
• Sum of anatomic and alveolar dead space
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67. Lung volumes and Capacities
• Different degrees of effort in breathing move different volumes of air
in and out of the lungs.
• The capacity of the lungs varies with the size and age of the person.
• Taller people have larger lungs than do shorter people.
• As age increase our lung capacity diminishes as lungs lose their
elasticity and the respiratory muscles become less efficient.
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68. Spirometer:
• A device that measures the volume of air inspired and
expired and therefore the change in lung volume.
• The record is called a spirogram.
• Inhalation is recorded as an upward deflection, and
exhalation is recorded as a downward deflection.
• Four Primary volumes — do not overlap
• The lung capacities are various combinations of these four
primary volumes.
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69. Simple Spirometer
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70. Lung Volumes
1. Tidal Volume (VT):
• The volume of air entering or leaving the lungs during
a single breath..
• ~ 500 ml
2. Inspiratory Reserve Volume (IRV):
•The extra volume of air that can be maximally inspired
over and above the typical resting tidal volume.
• ~ 3000ml
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71. 3. Expiratory Reserve Volume (ERV):
• additional volume that can be expired forcefully
after a passive expiration
• ~ 1000 ml
4. Residual Volume (RV): The minimum volume of
air remaining in the lungs after a maximal exhalation.
• ~ 1200 ml
•Can not be measured directly with a Spirometer
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72. Lung Capacities
1. Vital Capacity (VC): The maximum volume of air that
can be exhaled after a maximal inspiration (IRV + VT+
ERV).
~ 4500ml
2. Inspiratory Capacity (IC)
The maximum volume of air that can be inspired at the end of a
normal quiet expiration.
(IC= IRV + TV)
~ 3500 ml
3. Functional Residual Capacity (FRC):
The volume of air remaining in the lungs after a normal
exhalation (ERV + RV). ~ 2200 ml
4. Total Lung Capacity (TLC): The maximum amount of
air that the lungs can accommodate (IC + FRC).
~5700 ml
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74. Forced expiratory volume in1second(FEV1)
• The volume of air that can be expired during the first
second of expiration in a VC determination.
• Usually, FEV1 is about 80% of VC;
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75. Clinical Aspects of Spirometry
• Measurement of the lungs’ various volumes and capacities is useful
to the diagnostician.
• Two general categories of respiratory dysfunction yield abnormal
results during spirometry.
1. Obstructive lung disease:
• More difficulty emptying the lungs than filling
• Asthma, Chronic bronchitis, Emphysema
 Functional residual capacity & Residual volume (RV) are
elevated.
 The FEV1/VC% is decreased
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76. 2. Restrictive lung diseases
• The lungs are less compliant than normal
• Pulmonary fibrosis
• Acute respiratory distress syndrome
 Characterized by reduced TLC
 Inspiratory capacity, VC are reduced
 FEV1/ FVC ratio may be normal or high in restrictive
disease.
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77. Gas Exchange in the Lungs
• The ultimate purpose of breathing is to provide a
continual supply of fresh O2 to the blood and remove
CO2 from the blood.
• Blood acts as a transport system for O2 and CO2
between the lungs and tissues.
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78. Respiratory Membrane
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80. Simple passive diffusion
For both pulmonary capillary and tissue capillary levels
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81. Factors affecting diffusion of Gases
I. Physical properties of gases
– Solubility coefficient of gas
– Absolute temperature of fluid
– Molecular weight of gas
II. Lung properties
– Thickness of path length of membrane (L=0.5µm)
– Size of alveolar surface area
– Permeability of membrane
– Pulmonary capillary blood volume
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82. Fick’s Law of diffusion
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83. III. Other factors
– Partial pressure difference b/n alveoli and capillaries (p)
– Alveolar ventilation (VA)
– Contact or transit time of gas (Normal = 0.8 secs.)
– Disease conditions-
• alveolar fibrosis,
• asbestosis,
• airway or capillary obstruction,
• edema, etc.
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84. Dalton’s law of partial pressure
• the total pressure exerted by a mixture of gases is the sum
of the pressures exerted independently by each gas in the
mixture.
• Also, the pressure exerted by each gas (its partial
pressure) is directly proportional to its percentage in the
total gas mixture.
Basic Composition of Air in the atmosphere
– 79% Nitrogen
– 21% Oxygen
– ~ 0.03% Carbon Dioxide
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85. Concept of partial pressures
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86. Partial Pressure Gradients
• A difference in partial pressure between the alveolar air
and pulmonary capillary blood.
• Similarly, partial pressure gradients exist between
systemic capillary blood and surrounding tissues.
• A gas always diffuses down its partial pressure gradient
from the area of higher partial pressure to the area of lower
partial pressure.
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87. • Gas partial pressures in systemic capillaries depends on
the metabolic activity of the tissue.
• Oxygen:
– Systemic arteries PO2 = 100 mmHg
– Systemic veins PO2 = 40 mmHg
• Carbon dioxide
– Systemic arteries PCO2 = 40 mmHg
– Systemic veins PCO2 = 46 mmHg
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90. Ventilation-Perfusion relationships (VA/Q)
• The relative difference between alveolar ventilation (VA) and blood
flow (Q) is known as the VA/Q ratio.
• The V/Q ratio is the crucial factor in determining alveolar and,
therefore, pulmonary capillary PO2 and PCO2.
• Both ventilation and blood flow to the lung is non-uniform because
of the resistive and elastic properties of the lung and chest well.
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91. In the upright posture
• Relative lung volume is greater at the apex
• Lung is less compliant at the apex
• Regional lung ventilation is greatest at the base
• Perfusion is greatest at the base.
• In the normal lung VA/Q ≈ is 0.8 approximately
• When there is a V/Q mismatch, it causes hypoxemia.
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93. Gas Transport in the Blood
1. Transport of O2:
• O2 delivery to a particular tissue depends on the:
 Amount of O2 entering the lungs,
 Adequacy of pulmonary gas exchange,
 Blood flow to the tissues,
 Capacity of the blood to carry O2.
NB; O2 transport can be achieved through two major ways
I. Dissolved form (1.5%)
II. hemoglobin bound form (oxyhemoglobin) (98.%)
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94. i. Physically dissolved in plasma
• Oxygen dissolves in blood and this dissolved oxygen exerts a pressure.
• Thus, PO2 of the blood represents the pressure exerted by the dissolved
gas,
• The amount dissolved (PO2) is the primary determinant for the amount of
oxygen bound to hemoglobin (Hb).
• There is a direct linear relationship between PO2 and dissolved oxygen
• When PO2 is 100 mm Hg, 0.3 mL O2 is dissolved in each 100 mL of
blood (0.3 vol %).
• Maximal hyperventilation can increase the PO2 in blood to 130 mm Hg
(0.4 vol%).
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95. There is a direct linear relationship between PO2 and dissolved oxygen
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96. Transport of O2 cont…
ii. Chemically bound with hemoglobin (oxyhemoglobin)
• Hemoglobin, an iron-bearing protein molecule contained
within the RBCs, can form a loose, easily reversible
combination with O2.
• 98.5 % of oxygen combines with hemoglobin
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98. • Each Hb consists of:
– A globin portion composed of 4 polypeptide chains &
– Four iron containing pigments called heme groups
• Each iron atom can bind one oxygen molecule
• Up to 4 molecules of O2 can bind one Hb molecule
• Each gram of Hb combines with 1.34 mL O2.
• With normal Hb levels, each dL of blood contains about 20 mL O2.
• When 4 oxygen molecules are bound to Hb, it is 100% saturated, with
fewer, it is partially saturated.
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101. • Hb + O2 ↔ HbO2(Reversible).
• Cooperative binding → Hb’s affinity for O2 increases as
its saturation increases (similarly its affinity decreases
when saturation decreases).
• In the lungs where the partial pressure of oxygen is high,
the rxn proceeds to the right forming (OxyHemoglobin).
• In the tissues where the partial pressure of oxygen is low,
the rxn reverses and forming (deoxyhemoglobin).
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102. The Oxygen-Hemoglobin Dissociation Curve
• Describes the relationship between the arterial PO2 and Hb saturation.
• The O2 –Hb dissociation Curve plots the percent saturation of Hb as
a function of the PO2.
• Shows how much haemoglobin is saturated with oxygen.
• The higher the partial pressure of oxygen, the higher percentage of
oxygen saturation to haemoglobin.
• Oxygen associates with haemoglobin at the lungs and dissociates at
the tissues.
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•In the lungs the partial
pressure is approximately
100mm Hg. at this Partial
Pressure haemoglobin has a
high affinity to 02 and is 98%
saturated.
•In the tissues of other organs a
typical PO2 is 40 mmHg here
haemoglobin has a lower
affinity for O2 and releases
some but not all of its O2 to the
tissues.
•When haemoglobin leaves the
tissues it is still 75% saturated.

105. Factors affecting the saturation of oxygen to
hemoglobin (affinity)
• Temperature
• Partial pressure of gases
• PH change/ [H+]
• Level of 2,3DPG
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106. 2,3-Diphosphoglycerate
• 2,3-DPG is a byproduct of glycolysis (specially, end product of
metabolism in erythrocytes)
• RBCs contain no mitochondria.
– Rely on glycolysis
• 2,3-DPG increases with intense exercise and may increase due to
training and in high altitude.
• Helps deliver O2 to tissues.
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108. Right shift of the curve
• Occur when the affinity of haemoglobin for oxygen is decreased.
• Unloading of oxygen from the arterial blood to the tissues is
facilitated.
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109. Left shift of the curve
• Occur when the affinity of hemoglobin for O2 is increased.
• Unloading of O2 from arterial blood into tissues is more difficult.
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110. Fetal hemoglobin
• Fetal hemoglobin (Hb-F) differs from adult hemoglobin (Hb-A)
in structure and in its affinity for O2.
• Hb-F has a higher affinity for O2.
• Thus, when PO2 is low, Hb-F can carry up to 30% more O2 than
maternal Hb-A.
• As the maternal blood enters the placenta, O2 readily transferred
to fetal blood.
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112. Carbon Monoxide:
• CO and O2 bind to same site on Hb.
• Has more than 250 times the affinity for Hb than oxygen.
• It will quickly and almost irreversibly bind to Hb → CO
poisoning
• CO+ Hg → Carboxyhemoglobin
• Even though the Hb concentration and PO2 are normal, the O2
content of the blood is seriously reduced.
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114. Carbon Dioxide Transport
• CO2 is an important end product of aerobic cellular
metabolism and is, therefore, continuously produced by
body tissues.
• After formation, CO2 diffuses into the venous plasma,
where it is 24 times more soluble than O2 and then passes
immediately into red blood cells
• CO2 is carried in the plasma with 3 forms
– 5% dissolved CO2, which is free in solution.
– 5% carbaminohemoglobin, bound to hemoglobin.
– 90% in the form of bicarbonate
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116. • Bicarbonate leaves the red blood cells in exchange for
chloride (called a chloride shift) to maintain electrical
neutrality and is transported to the lungs
NB
– CO2 entering the red blood cells causes a decreased pH that
facilitates O2 release.
– In lungs, O2 binding to Hb lowers the CO2 capacity of blood
by lowering the amount of H+ bound to Hb.
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118. Regulation of Ventilation
Components of respiratory Regulation:
1. Neural Control centers
2. Chemoreceptors… (Peripheral and Central)
3. Effectors- Lungs, respiratory muscles
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119. Neural regulation of respiration:
1. Voluntary breathing center:
- Cerebral cortex
2. Automatic (involuntary) breathing center
- Medulla oblongata
- Pons
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120. The medullary respiratory center:
Dorsal respiratory group (DRG)
– responsible for the inspiratory rhythm;
– input comes from the vagus and glossopharyngeal nerves
– output is via the phrenic nerve to the diaphragm
ventral respiratory group (VRG)
– innervates both inspiratory and expiratory muscles
– But, primarily responsible for expiration.
– It becomes active only during exercise.
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121. Pontine respiratory center
Exert “fine-tuning” over the medullary center produce
normal, smooth inspirations and expirations.
Apneustic center (lower pons)
– prevents the inspiratory neurons from being switched off, thus
providing an extra boost to the inspiratory drive.
Pneumotaxic center (upper pons)
– sends impulses to the DRG that help “switch off ” the inspiratory
neurons, limiting the duration of inspiration.
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124. Hering–Breuer Reflex
• When the tidal volume is large (greater than 1 liter), as during
exercise, the Hering–Breuer reflex is triggered to prevent over
inflation of the lungs.
• Pulmonary stretch receptors within the smooth muscle layer of
the airways are activated by stretching of the lungs at large tidal
volumes.
• Action potentials from these stretch receptors travel through
afferent nerve fibers (vagus) to the medullary center and inhibit
the inspiratory neurons.
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125. Chemical control of Respiration
• Chemoreceptors:
i. Central chemoreceptors: medulla
• stimulated by ↑ [H+] or ↑Pco2 in the CSF ƒ
ii. Peripheral chemoreceptors:
 Carotid body
 Aortic body-
–Stimulated by arterial PO2↓ or [H+] ↑
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127. Sensitivity of the receptors
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