Lecture 26 - Control of Ventilation Flashcards
Partial pressures of O2 and CO2 in the blood are determined by what two factors?
alveolar ventilation and blood flow to the alveoli
What is the ventilation/Perfusion (V?Q) ratio?
it is the relationship between blood flow and alveolar ventilation. The nature of the ratio will determine how much gas exchange is taking place
What does a V/Q = 1 suggest?
this implies that the ventilation and perfusion are equal, and that there is a balance such that optimal gas exchange is occurring
What is a “V/Q mismatch” or “V/Q inequality”?
any deviation from V/Q = 1
What does V/Q = zero mean?
there is no ventilation, even though perfusion continues. therefore, there can be no gas exchange, and blood perfusing that part of the lung will return to the heart without releasing CO2 or picking up O2 (aka shunting)
what are three possible reasons for a V/Q = zero?
small airway collapse
hypoventilation
absorption of O2 (atelectasis)
alveolar hypoxia (PaO2 <70 mmHg) induces ______ constriction to the arterioles that supply the hypoxic alveoli
constriction. The net effect of this is to divert the blood away from poorly ventilated areas of the lung, minimizing the shunt effect and maximizing PaO2
what does a V/Q = infinity mean?
there is no perfusion, while ventilation continues. Therefore there is no gas exchange, and air that is being moved in and out of the lung will not pick up CO2, and the blood will not have its O2 absorbed.
What is another term for when V/Q= infinity?
This is referred to as “dead space ventilation” since gas moves in and out of the body without any gas exchange occurring
what are two things that can cause V/Q= infinity?
blood clot, profound hypotension
What are the different mechanisms by which CO2 is transported in the body?
- Dissolved in plasma
- bound to Hb
- bicarbonate ions in the plasma
what are the two methods of O2 transport in the body?
1.Dissolved in plasma
2. bound to Hb
what are the three forms of Co2 in the plasma?
- dissolved in the plasma
- combined with plasma proteins
- combined with water to form H2Co3
overall, Co2 transport in the plasma only accounts for __% of the total CO2 transport in the body
10%
Out of all the methods of CO2 transport, what are the most important?
the reactions that occur in the red blood cells.
Explain the three mechanisms of C02 transport in red blood cells
Co2 readily diffuses into RBCs
Terminal proteins on RBCs can buffer Co2 levels by forming carbamino compounds
Inside RBCs, carbonic anhydrase can convert CO2 + H2o ->H2Co3 -> HCO3- + H+
what is the name of the enzyme that facilitates the conversion of CO2 into carbonic acid in the RBCs?
carbonic anhydrase
write out the chemical equation for the hydration reaction of water with CO2 that occurs in RBCs.
CO2 + H2O <-> H2CO3 <-> HCO3- + H+
what happens as more and more HCO3- is formed from the hydration of CO2 within RBCs?
the HCO3- will diffuse out of the RBC along its gradient into the plasma. This will cause a charge imbalance where the inside of the RBC will lose negative charge. To compensate this, Cl- diffuses into the RBCs, in a mechanism known as a “chloride shift”
explain a chloride shift and why it happens
a chloride shift describes how Cl- will diffuse into an RBC after the RBC has lost it’s HCO3- to the plasma. This happens to maintain the charge balance within the RBC and the plasma
why are RBC’s in venous blood slightly larger than those found in arteriole blood?
water diffuses into the RBC’s during venous circulation
