1. RESPIRATORY MECHANISM

2. Mechanics of respiration:
At rest:
Inspiration:
- Diaphragm conrtraction→chest volume↑ (lungs expansion) →intrapleural pressure ↓→alveolar pressure<atmospheric pressure→air is sucked into the lungs.
(At the end of an inspiration, alveolar pressure=atmospheric pressure and airflow stops )
Expiration:
- Diaphragm relaxation→chest volume↓ (lungs conrtraction) →intrapleural pressure ↑→alveolar pressure>atmospheric pressure→ air is pushed out of the lungs. Therefore, expiration is a passive process. (At the end of an exspiration, also alveolar pressure=atmospheric pressure and airflow stops )

3. Figure: The mechanics of pulmonary ventilation.

4. Figure: Inspiration and Expiration.

5. Stronger ventilation:
- Muscles of the chest wall help produce changes in chest volume beyond that produced by the contraction and relaxation of the diaphragm.
- Contraction of the external intercostal muscles helps increase the volume of the chest for stronger inspiration. while contraction of the internal intercostal muscles helps to decrease chest volume for stronger expiration.

6. Lung Pressures:
- Atmospheric pressure: It is the pressure excreted by the weight of air in atmosphere. It is about 760 mmHg. - Intrapulmonary pressure (alveolar pressure): It is the pressure of the air inside the alveoli. - Intrapleural pressure: It is the pressure of the fluid in the thin space between the lung pleura (visceral pleura) and the chest wall pleura (parietal pleura). It is always less than Intrapulmonary pressure. - Transpulmonary pressure: It is the difference beween the alveolar pressure and intrapleural pressure.

7. Figure: Lung pressure change during inspiration and expiration.

8. Lung Volumes:
- Tidal volume (TV): The volume of air inspired or expired during a normal inspiration or expiration; its amount is about 500 mL in the adult male. - Inspiratory reserve volume (IRV): The amount of air inspired forcefully after inspiration of normal tidal volume (3000 mL). - Expiratory reserve volume (ERV): The amount of air forcefully expired after expiration of normal tidal volume(1100 mL) - Residual volume (RV): The volume of air remaining in respiratory passages and lungs after the most forceful expiration (1200 mL).

9. Figure: Lung volume and capacity.

10. Lung Capacities:
- Inspiratory capacity (IC): The maximal amount of air which can be inspired after a normal expiration. IC = Tidal volume (TV) + Inspiratory reserve volume (IRV) - Vital Capacity (VC): The maximum amount of air which can be expired after a maximal inspiration. VC= Inspiratory reserve volume (IRV) + Tidal volume + Expiratory reserve volume (ERV) - Total lung capacity (TLC): The amount of air contained in the lungs at the end of maximal inspiration. TLC = Vital capacity + Residual volume (RV) - Functional residual capacity (FRC): The amount of air that remains in the lungs at the end of normal expiration. FRC = Expiratory reserve volume (ERV)+ Residual volume (RV)

11. Figure: Lung capacities.

12. Pulmonary Ventilation:
- Respiratory rate or frequency: The number of breaths taken per minute (12 breaths/min). - Pulmonary ventilation: The amount of air inspired per minute. Pulmonary ventilation = Respiratory rate X Tidal volume = 12 breaths/min X 500 ml = 6 L/min. - Alveolar ventilation: The total volume of fresh air entering the alveoli per minute. = respiratory rate X (Tidal volume – Dead space volume) = 12 X (500 – 150)= 4.2 L/min Minute ventilation: Total amount of air moved into and out to of Respiratory system per min.

13. - Anatomical dead space: The volume of conducting air ways at which there is no gaseous exchange (about 150ml) increase with age.
- Alveolar dead space: Volume of inspired air that is not used for gas exchange .
- Physiological dead space: The sum of Anatomic and Alveolar dead space.

14. Gas exchange in the lungs:
Air-Blood barrier (Pulmonary membrane, respiratory membrane, Alveolar-Capillary barrier):
The membrane which gas exchange occurs which is about 0.2 µm.
The alveolar-capillary barrier is composed of:
- A thin alveolar epithelium
- An epithelial basement membrane
- A thin interstitial space between the alveolar basement membrane and capillary basement membrane.
- A capillary basement membrane that in many places fuses with the alveolar epithelial basement membrane
- The capillary endothelial membrane
The total surface area of the respiratory membrane is about 70m2 in the normal adult human male.

15. Figure: Alveolar respiratory membrane.

16. Law of Partial Pressures
Dalton’s Law
Law of Partial Pressures
“each gas in a mixture of gases will exert a pressure independent of other gases present” Or
The total pressure of a mixture of gases is equal to the sum of the individual gas pressures.
Atmospheric components
Nitrogen = 78% of our atmosphere
Oxygen = 21% of our atmosphere
Carbon Dioxide = 0.033% of our atmosphere
Water vapor, krypton, argon, …. Make up the rest
PATM = PN2 + P02 + PC02 + PH20= 760 mm Hg.

17. Changes in Partial Pressure:
In inspired air:
PO2=160 mmHg
PCO2=0.3 mmHg
PH2O=5.7 mmHg
PN2=596 mmHg
In alveolar air (mixing with dead space air):
PO2=104 mmHg
PCO2=40 mmHg
In venous blood entering the lungs:
PO2=40 mmHg
PCO245 mmHg
O2 diffuses across the respiratory surfaces into blood, CO2 flows from blood to alveolar air.
Expired air is saturated with water vapor.

18. Arterial blood leaving the lungs:
In expired air:
PO2=120 mmHg
PCO2=27 mmHg
PH2O=47 mmHg
PN2=565 mmHg
Arterial blood leaving the lungs:
PO2=95 mmHg
PCO2=40 mmHg
In the tissues, concentrations of gases and pressures exerted by them vary depending on the amount of metabolic activity going on in the tissue at any one time.
PO2=20 mmHg
PCO2=46 mmHg
O2 flows from blood to tissues, and CO2 from tissues to blood.