23. Control Of Breathing Flashcards
How is gas diffusion facilitated in the body?
Large pressure gradients
Large SA
Gases with advantageous diffusion properties
Specialised mechanisms for CO2 and O2 transport
What is the partial pressure of O2 in the anatomical dead space?
What is the partial pressure of CO2?
150 mmHg
0 mmHg
How is partial pressure calculated?
Pgas = Fraction of gas in mixture x barometric pressure (760)
How much dissolved oxygen is present in the blood?
3 mL/L of blood
0.003 mL O2/100 mL blood for each mmHg of PO2
What are the tissues oxygen requirements at rest?
What are the tissues oxygen requirements at exercise?
250 mL O2/min
Can get up to 3000 mL O2/min
Where is the site of O2 bonding in the haemoglobin?
The reduced ferrous iron (Fe+++) in each heme group
How does the saturation of haemoglobin change as PO2 increases?
Hb saturates quicker at higher pH and lower temperatures
How does changing PO2 affect saturation of Hb?
If PO2 drops from 100 to 60, there is little change in Hb saturation. If PO2 drops below 40, O2 rapidly dissociates from Hb to meet the tissue demands
What is the O2 carrying capacity of Hb?
1g Hb combines with 1.39 mL O2
~150g Hb/1 L of blood
O2 capacity = 208 mL O2/1 L of blood
What is the normal respiratory exchange ratio?
What does it represent?
0.8
The rate of expired CO2 to O2 uptake
What is the most common form of CO2 in blood?
Converted to bicarbonate (70%). Rest bound to Hb or dissolved
How is acid-base balance maintained in the body?
By the conversion of CO2 to HCO3 and H+ ions or vice versa
What do peripheral chemoreceptors respond to?
Decreases in PO2
How do peripheral chemoreceptors act?
Send neural signals to the NTS which increases ventilation to restore PO2
When does hyperventilation occur?
When PO2 drops below 60 mmHg
