Energy Production and O2 Consumption Flashcards
How does humidification reduce the pO2?
Dry air becoming humid –> water vapour added and dilutes O2
How does alveolar gas reduce pO2?
CO2 is added (displaces O2) and reduces the partial pressure of O2
What happens to nitrogen levels?
Stays same (80%)
Why is there very little change in pO2 during alveolar-capillary diffusion?
No diffusion barrier in healthy people as gap very thin
When can a diffusion barrier at the alveolar-capillary develop?
- Altitude when levels of O2 are low 2. Elite athletes as O2 cannot cross quickly enough for O2 that they’re using 3. Pulmonary diseases (pulmonary oedema, pulmonary fibrosis)
Why is pO2 of arterial blood less than pO2 of pulmonary capillary?
Due to ventilation-perfusion mismatch
How does ventilation-perfusion mismatch cause pO2 to drop?
In some areas of lung, not enough gas gets into alveolus for the amount of blood flowing past it. Blood doesn’t get fully oxygenated –> VQ ratio is less than 1. This blood then mixes with blood from other bits of lung where VQ is 1 or higher pO2 is 13 not 15
Why is the diffusion between capillary and mitochondria a big barrier?
O2 flows along systemic capillaries and O2 leaves blood Diffuses across capillary wall, interstitial space, across cell wall, through cytoplasm, into mitochondria where it is used
What pO2 is needed by mitochondria for aerobic respiration?
0.15 kPa
Why is mean tissue pO2 5kPa but mitochondria only need 0.15 kPa?
Oxygen reserve –> takes a lot to become hypoxic
What affects amount of O2 tissue cells receive?
Position Some live at arterial end of capillary where pO2 is high Some live at venous end where pO2 is low
What are the steps of the oxygen cascade
- Dry air
- Humid air
- Alveolar gas
- Pulmonary capillary
- Arterial blood
- Venous blood
- Cytoplasm
- Mitochondria
What does the oxygen cascade describe?
The transfer of O2 from air to mitochondria
What is the mean tissue pO2?
5 kPa
What is the definition of oxygen delivery?
The volume of oxygen leaving the heart in one minute (DO2)
What must be known to calculate oxygen delivery?
- The amount of oxygen in the blood (oxygen content)
- The amount of blood leaving the heart (cardiac output)
How can the oxygen content of the blood be calculated?
Oxygen carried by Hb + dissolved O2
Normally 19 ml.dl-1
What is the normal DO2?
1000 ml.min-1
Define oxygen consumption
The amount of oxygen used by the body in one minute (VO2)
What is the basal metabolic rate?
VO2 at rest (minimum amount used, normally only occurs when asleep)