lecture 26 Flashcards
what are the mix of gases we breath?
78% nitrogen
21% oxygen
0.033% CO2
dalton’s law
the total pressure exerted by a mixture of gases equals the sum of pressures exerted by all individual gases
partial pressure of O2 in atmosphere
160 mm Hg
partial pressure of CO2 in atmosphere
0.25 mm Hg
Hypoventilation
- decreasing our ventilation rate below 12 breaths/min
- PO2 will decrease because we slow down breathing
PCO2 will increase because we’re blowing out less CO2 (CO2 will build up)
hyperventilation
- increasing our ventilation rate below 12 breaths/min
- PO2 will increase because your bringing in more
- PCO2 will decrease because your blowing out more CO2
Alveolar partial pressures and explain the reasoning behind it
PO2: 100 mm Hg
PCO2: 40 mm Hg
- because stale air and anatomical dead space and diffusion happens right away
O2 and CO2 diffuse across_________________
alveolar epithelial cells (type 1) and capillary endothelial cells
rate of diffusion is governed by ficks law
Rate of diffusion is directly proportional to:
1. Surface Area (A)
2. Membrane permeability (D= diffusion constant)
3. Partial pressure gradient (P)
Rate of diffusion is inversely proportional to
1. Diffusion distance (T): membrane thickness and interstitial fluid
- T is squared
Gases diffusing down there partial pressure gradient
Pulmonary circulation:
- alveolar PO2 > venous PO2 (100>40)
- alveolar PCO2 < venous PCO2 (40<46)
Systemic circulation:
- arterial PO2 > tissue PO2 (100>40)
- arterial PCO2 < tissue PCO2 (40<46)
Hypoxia
Oxygen depleted state
Factors that decrease the amount of O2 reaching alveoli
- low O2 content in atmosphere
- Low alveolar ventilation
- decreased lung compliance (loose elasticity or compliance can impair O2 uptake
- increased airway resistance (bronchoconstriction, paracrine factors, autonomic control
- CNS depression (drugs, alcohol overdose) - Rate and depth of breathing
- Adequate perfusion of alveoli
What can impair rate of gas exchange
- Emphysema
- Asthma
- Fibrotic lung disease
- Pulmonary edema
Emphysema
- is distruction of alveolar wall which decreases surface area for gas exchange
- loss of elastance
- happens when u smoke a lot
Result: Decrease surface area available for gas exchange which decreases diffusion rate and potentially lead to hypoxia
Asthma
- local or systemic release of broncoconstrictors which increase resistance in air ways
- not enough air getting into lungs in the first place
- partial pressure gradient decreases
Result: partial pressure of O2 will be much less than 100 mm Hg because O2 isn’t getting into the alveoli in the first place