Respiration 2 - Gas Partial Pressures Drive Lung and Tissue Exchange
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What is atmospheric pressure normally at sea level?
Describe the composition of air
79% nitrogen and 21% oxygen
What are the partial pressures of nitrogen and oxygen?
- 560mmHg - nitrogen
- 160mmHg - oxygen
What are tension and partial pressure denoted as?
PO2 increases/decreases by the time it gets down to the lungs and venous blood?
What direction do oxygen and carbon dioxide move in at the level of the lungs?
Oxygen is driven from the alveolar air into the venous blood. Carbon dioxide is driven from the venous blood into the alveolar air.
What does internal respiration refer to?
Internal respiration refers to the properties of the respiratory and circulatory systems to deliver oxygen from the air to a cell's mitochondria for cellular respiration and then transport carbon dioxide back to the lungs for removal from the body
What factors can lower the pressure head for oxygen and reduce maximum possible O2 uptake by tissue?
Lowering barometric pressure (increasing altitude) or breathing a lower proportion of oxygen
What is the alveolar O2 tension and CO2 tension?
- Oxygen = 100mmHg
- Carbon dioxide = 40mmHg
What is blood flow rate described as?
What will happen if the rate of CO2 production at the tissues and removal from the lungs does not match?
It will create an acid base problem
Which area of the brain controls breathing?
The respiratory centre in the medulla
What chemoreceptors detect PO2 and PCO2?
- PO2 - carotid bodies
- PCO2 - medullary CSF receptors
The carotid bodies are connected by sympathetic/parasympathetic fibres to the respiratory centre?
What happens if there is a low PO2 in the arterial blood?
Carotid bodies detect this and cause more firing in the parasympathetic nerves leading up to the respiratory centre to stimulate alveolar ventilation
True or false: the carotid bodies are very sensitive?
False: oxygen tension must fall considerably before they are activated
How is breathing altered during panting?
During panting dogs take tiny little breaths to ensure air is only moved in the dead space and not the respiratory zone. This is to try and not upset alveolar ventilation, and consequently, respiration.
What protein present in the blood increases the oxygen affinity of RBCs?
Describe the curve for Hb saturation
A Hb saturation curve has a sigmoid shape. Hb has a plato over a wide range of oxygen tensions - it is pretty much saturated from 80-140mmHg.
Under what conditions does oxygen saturation of Hb decrease?
When temperature increases or pH decreases
Why would an increase in temperature/decrease in oxygen affinity at low pH be beneficial in working muscles?
Working muscles are warmer and generate a low pH so it is beneficial to the body that under these circumstances oxygen unloads from Hb more efficiently
What are the different ways carbon dioxide can be carried in the bloodstream?
- Some CO2 can be dissolved in the plasma
- Some can react with amino groups on proteins in plasma to form a carbamino group
- Most diffuses into a RBC where an enzyme causes CO2 to form carbonic acid, which dissociates into bicarbonate and H+. Bicarbonate diffuses out of the RBC in exchange for a Cl- ion.
What is the enzyme present in RBCs that causes CO2 to form carbonic acid?
What happens to the H+ ion produced in the CO2 reaction in RBCs?
It is accepted by Hb but this reduces oxygen affinity so oxygen is liberated from the Hb
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