Respiration Flashcards
What are the 2 major components of the respiratory system?
- Lungs: Gas exchange organ designed to maximise the rate if O2 intake.
- Cardiovascular system: Transports O2 to all tissues in the body.
What is the structure of the airway?
The airway is divided into 24 generations divided into 2 groups:
- 0-16 is the conducting zone. No gas exchange occurs here so it is termed the anatomical dead space.
- 17-23 is the respiratory zone. Alveoli are located on the branches of airway in these generations and gas exchange occurs.
What are the functions of the conducting zone?
- Warms and humidifies air before it enters lungs. This prevents excess water/heat loss from the alveoli exchange surface.
- Distributes air across the alveoli.
- Removes dust and pollutants from the air before it reaches alveoli.
What are the consequences of the very large total cross-sectional surface area in the respiratory zone?
- Substantial decrease in velocity of air.
- Movement of air becomes dependent on diffusion.
- Pollutants drop out of the air and are trapped by mucous lining the bronchioles.
How are the lungs adapted to maximise gas exchange?
- Ventilation ensures that the alveoli are constantly supplied with air saturated in O2. This ensures there is high [C1].
- High blood flow (entire CO) in pulmonary circulation ensures that the alveoli are constantly supplied with blood low in O2, minimising [C2].
- Large number of alveoli maximises surface area.
- Intimate relationship between alveoli and capillaries minimises diffusion distance.
What is the purpose of the respiratory system?
Acts as an evolutionary adaptation to the limitations of gas exchange by simple diffusion across the external surface of larger organisms.
What is the purpose of ventilation?
To generate pressure gradient between the atmosphere and alveoli required for air flow.
What are the sequence of events during inspiration?
- Respiratory muscles cause an expansion in the volume of the pleural cavity.
- This causes a decrease in intrapleural pressure from -5 cmH2O to -8 cmH2O..
- Transpulmonary pressure becomes more +ve, causing the lungs to expand until the elastic properties of the lungs matches new intrapleural pressure.
- Expansion of the lungs causes intra-alveolar pressure to fall below atmospheric pressure (-1 cm H2O).
- Pressure gradient is generated between the atmosphere and alveoli.
- Air flows into the alveoli, from the atmosphere, down the airway.
- Air continues to flow into the alveoli until intra-alveolar pressure equilibrates with atmospheric pressure.
Why is such a small pressure gradient needed in order to generate airflow during inspiration?
Because the airway offers very little resistance to airflow.
What is the importance of the pleural cavity at end-expiration?
At end-expiration, the chest wall has a natural tendency for outwards elastic recoil. Lungs have tendency for inwards elastic recoil. This causes expansion of the pleural cavity, which generates -ve intrapleural pressure that opposes elastic recoil of chest wall and lungs. This keeps lungs expanded.
What is the clinical significance of the pleural cavity?
When the pleural cavity becomes punctured, the intrapleural pressure is lost and the lungs deflate. This is called a pneumothorax.
What are the different transmural pressures?
Transpulmonary pressure = P(A) - P(pl)
Trans chest wall pressure = P(pl) - P(B)
Trans system pressure = P(A) - P(B)
What is a capacity?
A volume which is a function of 2 or more basic volumes.
What is the process of expiration?
- Inspiratory muscles relax and/or expiratory muscles contract.
- Volume of pleural cavity decreases.
- Intrapleural pressure becomes less negative.
- Intrapleural pressure no longer large enough to oppose the elastic recoil tendencies of the lungs and/or intrapleural pressure becomes positive and forces lungs to shrink.
- Lungs decrease in volume.
- Intra-alveolar pressure increases above atmospheric pressure.
- Pressure gradient set up between alveoli and atmosphere.
- Air flows out of alveoli into the atmosphere.
What is STPD?
Temperature = 273 K Pressure = 1 atm = 760 mmHg Humidity = 0
Why is lack of humidity important for perfect gas calculations?
Water is not a perfect gas in the normal physiological range as n (no. moles) changes with temperature.
What happens to air as it enters the lungs?
- Air is saturated with water.
2. O2 diffuses from alveolar air to blood while CO2 diffuses from blood to air.
What are the normal values for inspiratory PO2 and PCO2?
PIO2 ≃ 149 mmHg (BTPS)
PICO2 = 0.28 mmHg (BTPS) ≈ 0 mmHg
What are the normal values of expiratory PO2 and PCO2?
PAO2 ≃ 100 mmHg (BTPS)
PACO2 ≃ 40 mmHg (BTPS)
What are the different types of dead spaces?
- Anatomical dead space = Conducting zone
- Alveolar dead space = Wasted air in alveoli with no/reduced blood supply
- Physiological dead space = Anatomical dead space + Alveolar dead space
What is the alveolar ventilation rate (V(A))?
Volume of fresh air entering the alveoli per unit time that actually take part in gas exchange.
How can V(A) be changed?
- Increasing breathing frequency (given tidal volume > dead space volume)
- Increase tidal volume
According to the alveolar ventilation equation, how can PACO2 be controlled?
- By controlling V(A).
- PACO2 is inversely proportional to V(A).
- Increasing V(A) decreases PACO2 and vice versa.
What is the significance of PAO2 and PACO2?
PAO2 and PACO2 are equal to PaO2 and PaCO2 as they reach equilibrium in the lungs.