L10 Energy Production and Oxygen Consumption Flashcards
What is the effect of humidification on oxygen partial pressure?
The partial pressure of oxygen in the air is 21kPa. The effect of humidification reduces the partial pressure of oxygen to 19.9kPa.
(101-6.3)* 0.21 = 19.9 kPa
What is the effect of alveolar gas on partial pressure of oxygen?
As air is exhaled, it mixes with carbon dioxide. The effect of this is to reduce further the partial pressure of oxygen by the pressure of carbon dioxide.
= 19.9 - 5 = 14.9 kPa
When there is a high CO2 concentration ins the alveolus, the individual will become hypoxic as well as more oxygen is displaced from the alveolus. The opposite is true in hyperventilation where the CO2 level decreases and so O2 increases.
What is the effect of alveolar-capillary diffusion on partial pressure of oxygen?
In healthy individuals this has no effect on the partial pressure of oxygen as the gap between the alveolar wall and the capillary wall is very small. The diffusion is highly efficient.
A barrier may occur at altitude where oxygen concentrations are low and in elite athletes as these athletes use a lot of oxygen and so not all of the oxygen can move across. This can also occur due to pathological reasons. In pulmonary fibrosis, or in pulmonary odema, a barrier to the removal of oxygen may develop. In normal circumstances however, this can be ignored.
What is the effect of ventilation-perfusion mismatch on partial pressure of oxygen?
The pO2 in the venous end by the time it has left the lung is now 13.6kPa. In this simplistic view of the lungs, the venous blood will move towards the alveolus and be fully oxygenated. If all the lung was perfect, the arterial PO2 would be 14.9 kPa as well. However in some areas of the lungs, not enough blood gets to the lungs for the amount of air that is flowing through it. The VQ ratio is lower than 1 in these areas. The blood passing through this area is not fully saturated. When this blood mixes with blood from other areas of the lung where there is a VQ ratio of 1 or higher, the partial pressure of oxygen decreases from 14.9 kPa to 13.6kPa. This is the main cause of the decrease in oxygen partial pressure from the pulmonary capillary.
What is the effect of tissue diffusion and diffusion within the cell on partial pressure of oxygen?
By the time the blood gets to the bodies tissue, the partial pressure of oxygen is 5kPa. This reduces to 0.15kPa by the time it gets to the mitochondria This is as some mitochondria are very far from the capillary whereas some are quite close.
What is oxygen delivery?
The amount of oxygen leaving the heart in one minute (D O2).
What are normal values for basal metabolic rate?
It is Relative to body size:
BMR = 45 W.m-2
VO2= 4.8 ml.min-1.kg-1
What factors affect Oxygen consumption (VO2)?
- Sex - The proportion of adipose tissue is greater in females than males. Adipose tissue has a low metabolic rate and so males have a higher oxygen consumption, per kilogram than males.
- Age - It peaks at 18-24 years old. It then falls for the rest of life. As a result, older adults are more prone to coldness and so hypothermia. This is as they cannot generate the heat they need to stay warm when the environment is cold.
- Temperature - If the temperature of the body changes, the oxygen consumption can change drastically. The Q10 shows that the metabolic rate increase by 50% by a 10 degree increase in temperature. Making the patient hypothermia, the damage is low due to a lower metabolic demand.
What are the physiological responses to anaemia?
ncrease 2,3-DPG shifts O2-Hb curve so that more oxygen dissociates from haemoglobin at the tissues
- Reduced blood flow to non-essential organs such as the skin and bowel. This is why someone who is anaemic is pale in attempt to conserve blood.
- The blood returning to the heart will have less oxygen due to an increased oxygen extraction. At rest we normally extract 25% blood. In anaemia this may be increased to 30-50%.
- Increased cardiac output which in effect keeps the deliver of oxygen the same. The cardiac output is always high. If they develop angina, the first thing you test for is anaemia. This is as the heart is fine, but not enough oxygen is being delivered to the heart causing angina. The most common symptom of anaemia is fatigue due to compensation.
At high altitudes, mountaineers compensate by increasing their haemoglobin count
What is the respiratory exchange rate?
The ratio between carbon dioxide production and oxygen consumption. The respiratory exchange rate at rest is equal to they respiratory quotient. The quotient depends on the fuel source:
- For carbohydrates, RQ = 1
- For Lipids, RQ = 0.7
- For Protein, RQ = 0.8
It also depends on the acid-base balance and hyperventilation.
What are normal values of oxygen delivery and oxygen consumption?
Oxygen consumption: amount of oxygen used per minute (approximately 250 ml.min-1)
Oxygen delivery: total O2 leaving the left heart per minute (approximately 1000 ml.min-1)
What are the 3 causes of cellular hypoxia?
- Anoxia - lack of oxygen in the blood and so no oxygen delivered to the cell. This is due to respiratory failure. The lungs are not getting oxygen into the blood.
- Stagnant - lack of blood supply to the cell and so no oxygen.
Examples: In the heart, in angina, there is a narrowing of the coronary artery and the blood flow through the tissue is not adequate enough for supply of the tissue beyond it. Whole body hypoxia can occur in shock, there is inadequate delivery of blood form the heart to the tissues.
Anaemia - lack of haemoglobin (cytotoxic hypoxia), the oxygen delivered cannot be used or there is not enough oxygen in the blood due to anaemia.
- Stagnant - lack of blood supply to the cell and so no oxygen.
What is glycolysis?
An anaerobic process used to release energy. It occurs in the cytoplasm and so does not require mitochondria. It reduces glucose to pyruvate or lactate and so does not require oxygen. It leads to a net gain of 2 ATP molecules. It is greatly inefficient. Erythrocytes must use glycolysis as they do not contain any mitochondria.
What is the Kreb’s cycle?
The tricarboxylic acid cycle, the kreb’s cycle, is an aerobic process used to release energy. It occurs mostly in the matrix of the mitochondria. It uses acetyl CoA from glycolysis or from lipids or protein metabolism to form carbon dioxide. It generates 2 ATP molecules per glucose molecule. It makes high energy molecules such as NAD or FAD.
How can you measure VO2?
• Arterio-venous CO2 difference - how much oxygen leaves the heart and oxygen that returns to the heart. This can be used to work out how much oxygen is removed from the blood as it goes back to the body. The blood returning to the heart will have had different amounts of oxygen removed, as there are different oxygen demands. To find the oxygen concentration of the blood returning to the heart you would need to sample this using blood from the pulmonary artery where all the blood has been mixed together in the right ventricle.
- Inspired-expired O2 volume difference - This is more common. This is difficult to do with dead space as some of the gas was not involved in gaseous exchange. This can be used to work out the amount of oxygen consumed.
