Principles of Gas exchange

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What 2 Gas laws are important in gas exchange?: Dalton's: pressure of one gas in a mix is independent of others.
Henry's: Concentration of a gas is limited by its diffusion constant and proportional to its partial pressure.
So what is Barometric pressure?: The total of the individual partial pressures of N2, O2, etc.
What is Po2 in atmosphere?: Pbarometric x O2 fraction

760 x .21 = 160 mmHg
What is Po2 in lungs?: (760 - water vapor)x.21= 150
What does Henry's law mean?: The conc of gas in a liquid (blood) depends on the partial pressure of it in the air above the liquid.
What 4 things affect diffusion?: 1. Increasing membrane SA
2. Increasing diff. coefficient.
3. Increasing Conc. gradient
4. Decreasing thickness of memb.
What is "Diffusing Capacity"?: The max amount of gas the lungs can transfer to the blood.
What 2 things limit Diffusion?: -Perfusion
-Diffusion
How does Perfusion affect gas diffusion from lungs to blood? Does this occur in normal or diseased states?: Perfusion is blood flow; when decreased, less blood transfers.
This can occur normally.
How does Diffusion affect gas flow from lungs to blood? In what states is it decreased?: Well it's obvious. Decrease occurs in diseased states.
Which limiting factor has more impact on transfer of o2 from lungs into blood?: PERFUSION (blood flow).
Why is perfusion more important?: B/c when blood flows past alveoli, O2 levels btwn the 2 structures EQUILIBRATE. Therefore perfusion is approx equal to diffusion; decreasing perfusion has profound effects on diffusion.
Why doesn't Diffusion changes alter the amt of O2 transferred to blood?: Because Diffusion is movement of O2 in both directions - lungs to blood, and blood to lungs. Doubling only doubles both directions of movement.
What is ONE instance in which o2 transfer to blood IS diffusion limited?: in Extremely Strenuous exercise: the rate of blood flow is too fast to allow equilibration and O2 doesn't diffuse.
How does pulmonary hydrostatic pressure compare to systemic? What is typical value?: It is mch lower to prevent filtration (would cause edema).
Typical val: 10 mm Hg
When does pulmonary filtration and edema occur?: In left heart failure - backed up blood flow increases Pressure in lung capillaries.
What is systemic artery MAP? What is it at the beginning of systemic capillaries? In the right ventricle and pulmonary artery?: Systemic MAP = 93
At beginning = 20
Right ventric= 15
Pulm capills = 10
What 3 things can regulate pulmonary vascular resistance?: 1. CO cardiac output
2. Autonomic nervous sys.
3. Hypoxia
What does exercising do to pulmonary circulation (not truly though): 1. Incr. Cardiac Output CO
2. Incr. MAP
3. Incr. pulm pressure
4. Causes filtration/edema
5. you die
What allows you to exercise without dying? How?: Decreasing Total Periph Resist.

B/c CO = MAP x TPR; since MAP doesn't change TPR must.
What is the major regulator of MAP in the lungs?: resistance - by changing the number of open capillaries and increasing their radii.
What are the formal terms for increasing the radii and number of open capillaries?: Distention and Recruitment.
What is the effect of Recruitment and Distention?: Decreased TPR, so that when CO increases MAP doesn't change and you don't get pulmonary edema.
What are 3 benefits of Recruitm and Distention?: 1. No filtration (edema)
2. Decreased velocity, allows time for equilibration.
3. Increased SA for gas exch.
What is the effect of autonomic regulation of lung vasculature resistance?: not important.
What can alter lung vasc resistance other than the ANS and TPR?: Hypoxia.
If you're matching bl flow to airflow, what will hypoxia do?: Decrease blood flow.
What does decreased blood flow do to capillaries?: decreases - constricts them.
Seems counter to reason, but you DON'T WANT blood to go where there is no O2; it's a waste.
What is the effect of high altitude on pulmonary circulation?: It causes a general vasoconstriction of pulm capillaries. Therefore the heart must work harder.
don't forget to look at gasexchng in lungs and tissues: ok
What are the 2 forms that oxygen is found/transported in blood? How much of each?: -Dissolved - 0.3mL in 100mL
-Bound to Hemoglobin - 20.1 mL
Why is so little O2 dissolved in blood?: O2 just dissolves poorly in plasma.
At a Po2 of 100 mm Hg, how much oxygen is bound to Hb?: Hemoglobin is saturated, so 20.1 mL of O2 in 100 mL blood.
What is the Po2?: Only dissolved oxygen in blood - none of the HbO2 counts.
For functioning, which form of O2 is more important? What are 3 reasons for why?: Dissolved.
1. Its amount determines Po2
2. The tissues only use dissolv.
3. Chemoreceptors only detect dissolved O2.
What values of Po2 are important? Where are they seen?: 100: lungs
60: lungs still
40: Tissue
25: Active tissue
What perc. of Hb is bound at Po2 of 100?: 100% or close to it.
Po2 100 occurs in lungs where oxygen pressure is 100%.
What perc. of Hb is bound at Po2 of 60?: almost 100% in spite of low O2
Po2 60 occurs in lungs still, but within the plateau - Safety factor/device.
What perc. of Hb is bound at Po2 of 40?: -75% Hb satn.
Po2 40 occurs in TISSUES.
As blood flows past tissues, O2 is transferred to tissues in need.
What perc. of Hb is bound at Po2 of 25?: 50% Hb satn. Because O2 dissolved diffuses to tissues, more dissoc. from Hb to replace the diffused. STEEP curve.
Review: At what pressure is Hb 100% saturated almost 100%? 75%? 50%?: 100 and almost 100 = lungs
75 = tissues
50 = active tissues.
What major effect (name) influences the Hb diss. curve?: the BOHR effect.
What is the bohr effect?: Co2/H+ can bind Hb and decrease its affinity for oxygen.
How is the Hb diss curve affected by a -Shift to the left? -Shift to the right?: To the left: increases Hb affinity for O2, so more is Hb-bound at any given Po2.
To the right: easier to deliver.
75% satn Hb occurs at what Po2? What if curve shifts to left? To right?: 75% is normally at Po2 of 40.
-If you shift to left, 75% is saturated until 25 Po2.
-If shift to right, 75% is shifted only until 60 (in normal conditions 100% would be satd at this Po2!)
What causes the oxygen diss curve to shift to the left?: -decreased DPG
-Decreased CO2, H+, and Temp.
What causes the O2 diss curve to shift to the right?: -Increased DPG
-Increaesd Co2, H+, and Temp.
(more acidic - active tissue)
What are 4 causes of hypoxia?: 1. Diffusion impairment (due to pulmonary edema)
2. Decreased atm Po2 (due to high altitudes)
3. Anemia
4. Carbon monox poisoning
What 2 hypoxia causes are detected by chemoreceptors?: Impaired diffusion
Decreased atmosph. Po2
So what in general do chemoreceptors detect?: Decreased O2 PRESSURE in the blood.
How do anemia and CO poisoning alter blood oxygen levels?: NOT by changing Po2, but by decreasing O2 CONTENT b/c Hb is unable to deliver it.
what is carboxyhemoglobin?: Hb bound to Hb - it has a very high affinity for CO.
what does Hb get in exchange for O2 delivery?: CO2.
In what 3 forms is CO2 transported? How much of each form is found?: -Dissolved in plasma, 10%
-Bound to protein (Hb), 30%
-As Bicarbonate, 60%
What enzyme catalyzes formation of Carbonic acid H2CO3, and where is it found?: Carbonic anhydrase, in RBCs.
As blood flows past tissues, what is the CO2 transfer process?: 1. Co2 dissolv in tissues diffuses to blood plasma, then into RBCs.
2. In RBCs, some CO2 binds H2O and converts to H2CO3 then dissociates into Hco3- and H+.
3a.HCO3-is exchanged for Cl- into/from plasma. (Cl shift)
3b. H+ binds HbO2- and makes Methemoglobin (HHb) in exch for O2 transfer to tissue.
4. HHb reacts w/ any other CO2 to form CarbaminoHb.
Because of transfering HCO3- to the plasma , what do RBCs get loaded w/ as they pass tissues?: Chloride ions - due to the Cl- shift.
What and Where is the Haldane effect?: In the lungs - when O2 binds Hb, less CO2 binds Hb.
what and where is the Bohr effect?: In the tissues - increased CO2 and H+ decrease O2 affinity of Hb.

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