3 - Pulmonary Gas Exchange Flashcards
At rest, blood becomes saturated with O2 by the time it’s passed through _______ of the capillary.
This means:
the first 1/3
At baseline blood stays in the capillary three times longer than it needs to
This is why during exercise, even though flow may not increase the partial pressure and amount of time in the capillary are sufficient to supply enough O2
What is the PO2 at the arterial end of the capillary?
Interstitial fluid?
Venous end of the capillary?
Intracellular?
95
40
40
23 (average)
When blood flow increases, what happens to interstitial PO2?
When blood flow decreases?
It increases
Decreases
What partial pressure gradient of O2 (PO2) is required to drive cellular respiration?
Cellular PO2 only needs to be 1-2 mmHg lower than interstitial, but the average in cell is 23 and interstital is 40, so there’s plenty of safety net
What is the PCO2 at the arterial end of the capillary?
intracellular PCO2?
Interstitial PCO2?
Venous end of the capillary?
40mmHg
46mmHg
45mmHg
45mmHg
Because CO2 can diffuse so much easier, it doesn’t need as much of a partial pressure gradient
When blood flow increases, what happens to interstitial PCO2?
When blood flow decreases?
decreases
increases
Under normal conditions, how much O2 is transported from the lungs to the tissues for each 100 ml of blood flow?
5ml O2/100ml Blood
(total 19.4 ml delivered, 14.4 ml leave capillaries still attached)
If during exercise the muscle interstital PO2 falls to 15mmHg from 40mmHg, how much O2 will be transported to the tissues?
About 3-4 times as many ml O2/100ml blood
Normal is 5, may be increased to 15
(19.4ml delivered, 4.4ml leave the capillary)
What is the utilization coefficient?
percentage of blood that gives up its O2 as it passes through the capillaries
What is the utilization coefficient normally at rest?
25%
What does a shift to the right on the oxyhemoglobin dissociation curve cause?
Decreased Hgb affinity for O2:
Enhanced release of O2 from blood to tissues
Enhanced oxygenation of blood in the lungs
What is the Bohr Effect?
An increase in CO2 or H ions causes O2 to be displaced from hemoglobin, causing a shift to the right
A decrease in 2,3-BPG causes a shift to the _______
right
important in adapting to low tissue perfusion
A shift to the right in the blood results in a shift to the _______ in the lungs
left
As long as cellular PO2 is greater than 1mmHg, O2 avialability is not a limiting factor in cellular respiration.
What is?
The concentration of ADP in the cell
The more ADP there is in the cell, the more oxygen will be consumed in order to convert it to ATP
The rate of O2 consumption in the cells is determined by:
the rate of ADP conversion to ATP
During CO poisoning, the PO2 is ______
normal
In addition to 100% oxygen, what else can be given to speed up displacement of CO?
CO2
stimulates respiratory drive and increases alveolar ventilation
Under normal resting conditions, how much CO2 is transported from the tissues to the lungs?
4ml CO2/100ml blood
When CO2 diffuses into the blood from the tissues, it reacts with water to form _______ with the help of ________
carbonic acid
carbonic anhydrase
Immediately after CO2 reacts with water to from carbonic acid, it dissociates into ________
HCO3 and H+
What is the chloride shift?
When carbonic acid dissolves into HCO3 and H, the H bind to the hemoglobin and the bicarb is shuttled back and forth across the red blood cell membrane in exchange for chloride (to maintain isoelectric status)
Because of this, venous RBCs have a much higher intracellular [Cl] the arterial RBCs
Carbonic anhydrase CO2 conversion is responsible for what percentage of CO2 transport?
70%
What percentage of CO2 is transported to the lungs via carbamino bonding with Hgb and plasma proteins?
30%
What is the haldane effect?
Binding of O2 with Hgb displaces CO2 from the blood
Why does the haldane effect occur?
Combining O2 with hemoglobin in the lungs converts the blood from a weak acid system to a strong acid system
The H ions that were bound to hemoglobin are released and combine with bicarb, dissociating into water and CO2
The CO2 is then released into the alveoli and is expired
What is the respiratory exchange ratio?
(Rate of CO2 output) / (rate of oxygen uptake)
THIS IS THE SAME R USED IN THE ALVEOLAR GAS EQUATION
What is a normal R?
What effects R?
Usually around 0.825
Different diets (just carbs would be 1, just fats would be 0.7)
The epithelium consists of:
Bronchi
Bronchioles
Alveoli
Goblet cells and ciliated cells
columnar cuboidal
squamous
Clusters of alveoli are sometimes called _______
acinus
What are pores of Kohn?
tiny septa from alveolus to alveolus that allow collateral ventilation
How many alveoli does a normal adult have?
480 million!
What are Type I and Type II alveolar cells?
Type I provide structure and stability
Type II secrete surfactant
Besides decreasing surface tension, what does surfactant do?
decrease release of proinflammatory mediators
Prevents oxidative injury
regulates the role of fibroblasts in airway remodeling
Describe perfusion pressure in:
Zone I
Zone II
Zone III
I: PA > Pa > PV
II: Pa > PA > PV
III: Pa > PV > PA
