Gas Exchange and Transport Flashcards
What governs the movement of gas between the liquid and gaseous environment?
Diffusion
Diffusion is responsible for movement of gas…
…near zero velocity environment of the alveolar sac
What is partial pressure?
The pressure of each individual gas in a mixture of gases.
What does Henry’s Law express?
Relationship between partial pressure and the amount of gas in a physical solution.
Henry’s law equation?
Concentration = (Solubility)(Partial Pressure)
What is the total gas pressure comprised of?
It is the sum of the partial pressures of each individual gas
Partial pressure is a good measure of tendency to ________
Diffuse
In a mixture gasses act as though they occupy ____% of the volume.
100%
Equation for partial pressure of a specific gas.
P = (Moles of X) (Total Pressure)
P-H2O in the lungs?
47 mmHg
Effects of additional water pressure in the lung?
Proportionally lowers the partial pressures of the other gasses.
Diffusion is inversely proportional to
Explain this in the context of a lighter gas
sqrt (MW)
Smaller gasses will achieve equilibrium faster
Determine the equation set up required for the diffusion ration of O2 (MW=32) and CO2 (MW=44)
Dif-Co2/Diff-O2 = sqrt[32/44]
Equ. for diffusion through liquid.
Diff-X/Diff-y = sqrt[(MW-Y)/MW-X)] X (solx/soly)
What is Fick’s Law of Diffusion all about?
Rate of Diffusion of Gas Across a Membrane
Equation for Fick’s Law of Diffusion.
Vol = [(Diffusion Coefficient)(Mem. Surface Area)(PP1-PP2)] / Membrane Thickness
Should you have Fick’s Law Memorize?
Sounds like yes.
In the respiratory system, conductance =
1/Resistance
Name three sources of Membrane resistance to diffusion to Oxygen.
Alveolar Capillary Interface
Plasma
Erythrocyte Membrane
Equation for Chemical Reaction Resistance.
1 / (O2 volume combining with hemoglobin/minute)(Pulmonary Capillary Volume)
What is Chemical Reaction Resistance?
The resistance to diffusion of O2 imposed by the chemical reaction of O2 with hemoglobin.
What is (o2 volume reacting with hemoglobin)(Pulmonary Cap. Volume) referring to?
Reaction rate of O2 and Hemoglobin for the Entire Lung
What is Diffusive Resistance?
Total Diffusive Resistance of the Lung
Equation for diffusive resistance?
Diffusive Resistance = Membrane Resistance + Chemical Reaction Resistance
Typically Membrane Resistance and Chemical Rxn Resistance are >, <, or =.
Approximately =
What might make Chemical Rxn Resistance much larger?
Why is this almost never a problem?
Hb saturation
O2 entering the lungs is far from saturated
Other than Oxygen, what compound may be influenced heavily by chemical resistance in the lungs.
CO2
How does exercise tend to influence the end capillary Po2?
It doesn’t typically, due to the built in safety factor
What happens with capillary Po2 at high altitudes?
With lower PO2, time for end capillary equilibration is prolonged (due to steep dissociation curve of hemoglobin.
How might thickening of the blood/gas barrier influence end capillary PO2?
End capillary PO2 may not reach alveolar
Express diffusion capacity in terms of Fick’s Law
Lung Diffusion Capacity = Rate of Diffusion/(Palv-Pcap)
What is the diffusion capacity….really?
The volume of gas moving per unit time for a given difference in PP of gas
Unit type used for diffusion capacity?
Conductance
1/Resistance
Relationship of diffusion capacity and Body Surface Area
Bigger Body = Bigger Diffusion capacity
Relationship of Diffusion capacity and training?
More training = recruitment of unused capillaries = Bigger Diffusion capacity
Relationship of Diffusion capacity and thickening of alv/cap membrane
Decreases
Relationship of Diffusion capacity and alv. surface area?
Decreases
Seen in Emphysema
Normal ph level?
7.35-7.45
Normal PA-O2?
80-10- mmHg
Normal Sa-O2?
95-100%
Normal Pa-CO2
35-45 mmHg
HCO3- conc?
22-26 meq/L
Pressure gradients move O2 through what pathway?
Inspired Air>Alveoli>Systemic arterial blood>tissues
Pressure gradiaents of CO2 through what pathway?
Tissues>Systemic Venous Blood>Alveoli>Expired Gas
What causes difference in gas composition of inspired and alveolar air? (3)
Anatomic Dead Space (Incomplete Exchange)
Constant Absorption of O2, Secretion of CO2
Humidification decreasing PP of all gasses
How much blood bypasses the pulmonary capillaries?
2-3%
What gets around the pulmonary capillaries?
Blood in non-exchanging portions of the lungs
Coronary Venous Blood that goes straight to left ventricle
What is the Ventilation/Perfusion Ratio (concept)?
Ratio of alveolar ventilation to alveolar blood flow
Average V/Q ratio?
0.8
4L/min / 5L/min
If an alveoli can’t open, what is the V/Q?
Physiological Shunt
Approx. 0
If a lesion prevents any bloodflow to alveoli, what happens to V/q? (Physiological Dead Space)
Approaches infinity
Two types of maladies that can cause ventilation perfusion mismatch.
Uneven Ventilation
Uneven Perfusion
Ventilation is greatest at _____ and poorest at ____.
Base. Apex
Why are ventilation changes seen across the lung?
The gradient of intrapleural pressure from apex to base.
Alveoli in what part of lungs have greatest compliance? Why?
Base. Surfactant Effects
Why do alveoli in the lungs have lower potential energy?
Relaxed elastic elements.
How does gravity influence perfusion of the lung
Gravity increases hydrostatic pressure below the heart and decreases it below.
Amount of O2 typically dissolved in blood.
So What?
0.29 ml/dl
Not enough to support life
Where is the other 98.5% of oxygen in the blood?
Hemoglobin
Why is there 25X more CO2 than O2 in the blood?
Higher solubility in water
Weight of hemoglobin?
64.5k MW
Basic molecular structure of hemoglobin?
4 subunits (2 alpha, 2 beta) with a polypeptide chain complexed with a heme
What is a heme group?
A porphyrin ring with one ferrous iron atom
What do heme groups do?
Reversibly binds O2 in an oxygenation reaction
Can Fe3+ bind oxygen?
No
How is the heme sandwich avoided?
Proximal Histidine binds Fe2+ and distal histidine (E7 prevents apposition of the second heme group.
Who occupies the binding site in deoxyhemoglobin?
H+
What does the property of cooperativity mean for hemoglobin?
Binding of one molecule of O2 facilitates the binding of other O2s
Hill Plot logs values of ______ vs. _______
O2 combining with hemoglobin/1- (02 comb. with Hb)
Log PO2
What is the slope of a Hill Plot Called? What does it represent?
Hill Coefficient
Cooperativity
Approximate Hill Coefficient of Hb?
3 (So 3 cooperative binding sites)
Give an example of an oxygen carrier with a Hill Coefficient of 1.
Myoglobin
Increased CO2 shifts the dissociation curve…
Right
Decreasing affinity of O2 (Bohr Effect)
What does the Haldane Effect say?
High PO2 results in dissociation of H+ and CO2 from Hb
Mneumonic for Oxy dissociation curves?
CADET, Face Right
CO2, Acid, 2,3-DPG, Exercise and (Increased) Temperature
What is BPG?
A highly anionic organic phosphate in fetal RBCs
Why is it BPG in fetuses important?
It makes infant oxygen affinity greater than mom’s, so they can snag oxygen from her blood.
Describe Salt Links in Deoxy Hb.
- Made from carboxy terminal amino acids.
Holds in “Tense Form”
What happens to salt links in oxygenation?
Shifts alpha1 and beta2 subunits, breaking strong salt links for weaker ones.
Greater molecular movement. “Relaxed Form”
Role of the porphyrin ring in cooperativity?
It is energetically difficult for the first O2 to get Fe2+ into a planar position.
Future broken salt bridges make later positioning easy
The oxygen saturation curve is in a _______ shape.
Sigmoidal
How does anemia influence O2 delivery?
It may be fine at high PO2 and fall dramatically as O2 saturation drops.
Flattened Oxygen saturation relationship at high PO2 ensures…
..complete saturation despite wide PO2 variations.
PO2 required in cells to sustain life?
30 mmHg
Give an example of a time where the steep part of the SAturation/PP curve is a big deal
Exercise at high altitudes
You slide down the curve to way low O levels
DPG is upregulated in ________
Poorly oxygenated erythrocytes
Right Shift –> Greater Delivery
Two scenarios in which DPG upregulation is likely important?
High Altitude Living
Lung Disease
How are carbamino compounds made?
Combination with Plasma Proteins
The all-powerful CO2 in serum rxn
CO2+H2O H2CO3 H+ + HCO3-
Why are bicarbonate generating reactions so slow in the blood?
No enzymes to catalyze them
Review Dissolved CO2 equation on Page 8-17.
I don’t really know what to do with this.
Form most CO2 takes in RBCs
Bicarbonate
Enzyme that catalyzes the rxn of CO2+H2O?
Carbonic Anhydrase
How does HCO3- get out of the RBC?
How is electroneutrality maintained?
Anion Exchanger
Cl- in for each HCO3- out
Why is the hematocrit of venous blood higher than arterial?
Each CO2 adds an HCO3-/Cl-, triggering net movement of water into the cell
Name two places carbonic anhydrase is found.
RBCs
Capillary Endothelium
What does cap endo carbonic anhydrase do?
Facilitates Bicarbonate –> CO2 transition
What do Hb molecules do with their extra H+ bound?
Upon oxygenation, liberate it to Convert HCO3- to CO2
Two influences on the CO2-dissociation curve
Amount of Oxygenation
Haldane Effect
With deoxygenation of tissues, Hb affinity for ____ increses.
CO2
Pulmonary system has comparatively ____ pressure, _____ resistance, and ____ compliance
Low
Low
High
Why are pressure, resistance, etc. diff in pulmonary?
Different Ventricle Thickness
Very little smooth muscle in arterioles
Which circulation has lower mean capillary pressure?
Pulmonary
What are extra-alveolar vessels?
Large extraparenchymal arteries/veins on the lung surface
Smaller arteries and veins in parenchyma
Large extra-alveolar vessels are exposed to?
subatmospheric intrathoracic pressure
Where are smaller extra-alveolar art/veins?
Tethered by connective tissue to alveoli (and thus expand with inflation)
How is pulmonary vascular resistance lowered in exercise?
Distention of Microvessels
Recruitment of poorly perfused capillaries
Why would a patient purse their lips in exhalation?
To increase airway resistance, thus improving airflow to lungs
What to look for –
Post-partum woman, leg pain, high respirations, difficulty walking, cyanotic
Pulmonary Embolism
