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)
How can metabolic rate be measured?
- Direct calorimetry
- Indirect calorimetry (measuring O2 consumption)
- Arterio-venous CO2 difference
- Inspired-expired O2 volume difference
What is the normal rate of VO2?
200ml/min-1
What are the factors affecting VO2?
- Exercise / level of activity
- Temperature –> metabolic rate doubles with every 10 degrees Celcius
- Age –> peak at 0-2 years, then falls for rest of life
- Gender –> males tend to have higher O2 consumption
What is problem of using arterio-venous CO2 difference to measure O2 consumption?
Difficult as blood returns to heart from different parts of body. E.g. brain consumes more O2. Samples from pulmonary artery must be taken when all blood has been mixed together in right ventricle
What is problem with inspired-expired O2 volume difference?
Dead space –> where gas exchange hasn’t occured
What are METs?
Metabolic Equivalent Task
Number of multiples of your normal resting O2 consumption. Depends on activity you’re doing.
What can METs be used for?
Assessing fitness
What are the physiological responses of anaemia?
- Increased 2,3-DPG shifts O2-Hb curve to right
- Reduced blood flow to non-essential organs (skin pale)
- Increased O2 extraction from blood (O2 returning to heart is less)
- Increase in cardiac output (tired the whole time)
Define respiratory exchange ratio
The ratio of CO2 production (VCO2) to O2 consumption (VO2).
Respiratory quotient = RER at rest
What is RER affected by?
Acid base balance
Hyperventilation
Metabolic fuel
How does a carb-based diet affect O2 consumption?
C6H12O6 + 6O2 = 6CO2 +6H2O (purely carb diet you need to consume less oxygen). RER is 1.0
How does a fat-based diet affect RER?
C17H35COOH + 26O 2= 18CO2 + 18H2O (purely fat diet you need to consume more oxygen as produce more CO2 and use more O2). RER is 0.7
What is cardio-pulmonary exercise testing?
Patient gets on bike and slowly make resistance harder
VCO2 is plotted against VO2
Used to work out risk of certian surgeries and chance of survival
Describe the cardio-pulmonary exercise testing graph
- Gradient of line –> RER (CO2 production to O2 consumption)
- Anaerobic threshold –> amount of O2 they are consuming at the time they become anaerobic
What is the anaerobic threshold used for?
Correlates with complication rate after surgery
What are the 3 stages of the generation of energy?
- Glycolysis
- Tricarboxylic acid cycle (TCA cycle or Krebs cycle)
- Oxidative phosphorylation
Where does glycolysis occur?
In the cytoplasm
What occurs during glycolysis?
Glucose converted to pyruvate or lactate (no O2 required)
How many ATP molecules are generated during glycolysis?
2 ATP molecules per glucose –> inefficient at generating energy
Where does the TCA cycle occur?
Mostly in the mitochondria
What occurs during the TCA cycle?
Acetyl CoA (from glycolysis)/pyruvate converted to CO2
How many molecules of ATP are created during TCA cycle?
38 molecules per glucose –> efficient
Where does oxidative phosphorylation occur?
In mitochondria
How does oxidative phosphorylation occur?
H+ (provided by NADH) combines with O2 to produce water (difficult reaction so there are enzymes involved)
ATP produced
Why is oxidative phosphorylation inefficient?
Reactive oygen species (such as superoxide and hydrogen peroxide) are produced which leads to propagation of free radicals which damage cells and contribute to disease and possible ageing
What is cellular hypoxia?
When insufficient O2 is delivered to mitochondria
What are the 3 causes of hypoxia?
- Anoxic (lack of oxygen in blood)
- Stagnant (lack of blood supply)
- Anaemic (lack of Hb)
What is angina?
Not enough oxygen-rich blood flowing to heart muscle
Form of stagnant hypoxia
What is shock?
Delivery of oxygen to the organs is low, causing organ damage and sometimes death
