Physiology of respiration

1. PHYSIOLOGY OF RESPIRATION
Lung volumes and capacities
SELINA SRAVANTHI
SAROJINI NAIDU VANITA PHARMACY MAHA VIDYALAYA,
TARNAKA, HYDERABAD, TELANAGANA

2. RESPIRATION
Pulmonary Ventilation : Breathing exchange of gases
between atmosphere of lungs and alveoli.
External (pulmonary) Respiration: between alveoli and
blood in pulmonary capillaries.
Blood gains O2 and loses CO2
Internal (Tissue) Respiration/ celullar respiration: exchange
of gases between blood and tissue cells.
Blood loses O2 and gains CO2

3. MUSCLES OF BREATHING
•Intercostal muscles
•External Intercostal muscles – extend downwards
and forward from lower border of rib to the upper
border of the next rib below. (inspiration)
•Internal Intercostal muscles - extend downwards
and backwards from lower border of rib to the upper
border of the next rib below. (expiration active)
•Diaphragm (inspiration)
•Dome shaped muscular structure
•Separates thoracic and abdominal cavities.
•Diaphragm supplied by phrenic nerves.
• Accessory muscles
•Stenocleidomastoid muscles, scalene muscles,
pectoralis minor- forced inspiration

8. PUMONARY VENTILATION - Inhalation and exhalation are
due to pressure differences.
INHALATION:
•Just before air enters lungs, air pressure in lungs =
atmospheric pressure.
•For air to flow into lungs, air pressure in the alveoli must be
lower than atmospheric pressure-increase in size of lungs
•For normal Inhalation – diaphragm and external
intercostal muscles contract.
•Diaphragm flattens lowering dome- increases the
thoracic cavity (responsible for 75 % of air entering)
•1 cm – 500 mL, 1-3 mm Hg difference of pressure
• 10 cm – 2-3 L of air 100 mm Hg pressure difference.
•External Intercostal muscles contract – elevate the ribs –
increase antero-posterior and lateral diameters of the chest
cavity. (responsible for 25 % of air entering)

9. •Pressure between the pleural cavities – intrapleural
pressure – subatmospheric. (756 mm Hg) results in 2
mg lesser (754 mm Hg)
•parietal and visceral pleura adhere together due to
surface tension and subatmospheric pressure.
•During expansion of thoracic cavity – parietal pleura is
pulled outwards in all directions – visceral pleura and
lungs are pulled along – increasing the volume of the
lungs.
•Pressure – alveolar pressure drops from 760 mm Hg to
758 mm Hg
•Air flows as long as pressure difference exists.
•During deep forceful inhalations accessory muscles
involved.
•Normal inhalation, during exercise, forced ventilation-
muscular contraction involved – hence ACTIVE

10. EXHALATION:
•Pressure in lungs is greater than atmosphere- exhalation
takes place
•Normal exhalation- PASSIVE PROCESS – no muscular
contractions.
•Result of elastic recoil of chest wall and lungs.
•Recoil of elastic fibres
•Inward pull of surface tension due to film of alveolar fluid
•Diaphragm relaxes- dome shaped.
•External intercostals relax- ribs depressed.
•Lung volume is decreased.
•Alveolar pressure -762 mm Hg

11. EXHALATION:
•Exhalation ACTIVE – during forceful breathing – playing
wind instrument/ exercise
•Exhalation Muscles- Abdominal Muscles & internal
intercostal muscles contract- increase pressure.
•Abdominal muscle contract – inferior ribs move downward
and force the diaphragm superiorly.
•Internal intercostal muscles contract – pulls ribs inferiorly.
•Intrapleural pressure is always less than alveolar pressure.
•Sometimes it may exceed atmospheric pressure during
forceful exhalation- cough.

14. OTHER FACTORS AFFECTING PULMONARY VENTILATION
•Surface tension of Alveolar fluid
•Compliance of Lungs: high compliance- easily expand, low
compliance – resist expansion.
Related to surface tension and elasticity
•Airway resistance:
Airflow = pressure of alveoli- pressure of atmosphere
Resistance

15. LUNG VOLUMES AND LUNG CAPACITIES
•Healthy Adult - 12 Breaths/ Min
• Each inhalation/ Exhalation – 500 mL of air in and out of lungs.
•Volume of one breath – TIDAL VOLUME (VT)
•MINUTE VENTILATION (MV) – Total Volume Of Air Inhaled /
Exhaled Each Minute
•MV = 12 breaths/ min x 500 mL/ min = 6 L/ min
•Apparatus to measure volume of air exchanged during breathing –
Spirometer/ Respirometer.
•Record – Spirogram- Inhalation-upward deflection, Exhalation-
downward deflection
•In adult 70% of tidal volume reaches the respiratory region. Other
30% remains in the conducting zones.
•Conducting Airways- not undergo respiratory exchange-
ANATOMIC (RESPIRATORY) DEAD SPACE.
•ALVEOLAR VENTILATION RATE – volume of air that actually
reaches the respiratory zone.
• 350mL/ breath x 12 breaths / min = 4200 mL/min
•FEV 1.0 -is the forced expiratory volume in 1 sec

17. EXCHANGE OF OXYGEN AND CARBON DIOXIDE
•Exchange of oxygen and carbon dioxide between alveolar air
and pulmonary blood vessels – PASSIVE DIFFUSION
•Depends on DALTON’S LAW & HENRY’S LAW
•DALTON’S LAW – each gas in a mixture exerts pressure as if
no other gases are present.
•Pressure of a specific gas – partial pressure.
•Atmospheric pressure = PN2 + PO2 + PH2O + PCO2 +Pgases
•Alveolar air has less O2 (13.6 % vs 21%) and more CO2 (5.3%
vs 0.04%)
•Gas exchange decreases O2 content and increases CO2 content
of alveolar air.
•Air humidified as it passes through the moist mucosal linings.
•As water vapor increases the O2 content of air decreases.
•Exhaled air contains more O2 than alveolar air (16% vs 13.6%)
and less CO2 (4.5% vs 5.3%)
•Exhaled air = alveolar air + inhaled air in anatomical dead space

18. •HENRY’S LAW – quantity of a gas dissolved in liquid is
proportional to partial pressure of gas and solubility.
•Solubility of CO2 is 24 times more than O2.
•Nitrogen narcosis/ rapture of the deep – giddiness, similar to
alcohol intoxication.
•Decompression sickness- bubbles in tissues- joint pain,
diziness, shortness of breath, fatigue, paralysis, unconciousness.

19. CHANGES IN PARTIAL
PRESSURES DURING
INTERNAL AND EXTERNAL
RESPIRATION
Rate of gas exchange depends on:
•Partial pressure difference of gases
•Surface area
•Diffusion distance
•Molecular weight and solubility of
gases

20. TRANSPORT OF O2
AND CO2 IN BLOOD