Test 2 (Gas Transport) Flashcards
Alveolar Oxygen
Alveolar Oxygen = Oxygen Concentration in the Lungs - Oxygen used by Tissue
Solubility of O2 in Plasma (or Water)
***0.3 mL O2/ dL Blood/ 100 mm Hg
- So if the PaO2 is 100 mm Hg, each dL of blood will carry 0.3 mL O2!!!!!!
- In order to meet our metabolic demands (250 mL O2/min), out hearts would have to pump at 83 LITERS OF BLOOD/ MIN!!!!! (Impossible)
IMPORTANT NOTE:
- When we refer to the PaO2 (the partial pressure of Oxygen in the Arterial Blood), we are referring to the DISSOLVED OXYGEN!!!!!!!!
Hemoglobin
- Helps carry the Oxygen instead of all of is having to be dissolved, which is impossible!
- An EQUILIBRIUM is achieved between the Plasma and the Hb
The Hb-O2 Dissociation Curve
- Any PO2 above 60 mm Hg, we are at least at 85% Saturated with Oxygen. This is crucial where is we get sick, we can still meet the Oxygen Demand. This also means that our Oxygen content (using normal values we used before) is at least:
- ** 20.1 mL O2/ dL Blood x 85% = 17 mL O2/ dL Blood!!!!!!!
- There is a huge range of PO2 where we have a NORMAL AMOUNT of Oxygen being the same with Hb Saturation
- Once we DROP BELOW 50 or 40, the amount of Oxygen Hb is holding DROPS DRAMATICALLY!!!
Changing the Hb-O2 curve of HbA
LEFT SHIFT:
- Represents an INCREASE in the AFFINITY of Hb for O2
WHAT CAUSES THE CURVE TO SHIFT TO THE LEFT:
- LACTIC ACID
- This left shift is associated with whats happening IN THE LUNGS!!!!!!!
- A left shift means that there is a HIGHER AFFINITY for Oxygen on Hb
RIGHT SHIFT:
- Represents a DECREASE in the AFFINITY of Hb for O2
WHAT CAUSES THE CURVE TO SHIFT TO THE RIGHT:
- Associates with whats happening IN THE TISSUE!!!
- What the O2 to leave the Hb and go to the Tissue
Factors Which Produce Shifts in the Hb-O2 Curve
1) CO2 and/ or pH
- The Bohr Effect
- High CO2 or Low pH: RIGHT SHIFT
- Low CO2/ high pH: LEFT SHIFT
2) TEMPERATURE
- Increased: Right Shift
3) Certain Metabolites (2,3 DPG)
- Increased: Right Shift
Benefits of altering the Hb-O2 Curve
When do we see INCREASES in:
- CO2 and/ or H+
- Temperature
- 2,3 DPG
IN THE TISSUE!!!!!!!!!!*
At the Tissue
- Not all the Oxygen is taken up by the Tissue, ask indicated by the Venous PO2 of 40 mm Hg
(PaO2: 95 ——> PvO2: 40) - The O2 Saturation of Venous Blood is about 75%
Giving us an O2 content of:
20.1 mL O2/ dL Blood x 75% = 15.2 mL O2/ dL Blood!!!!!!!
a-v O2 Difference
- The difference between the arterial O2 content and the venous O2 content
*****IMPORTANT: This represents HOW MUCH OXYGEN is USED by the Tissue being PERFUSED!!!
- 8 mL O2/ dL Blood - 15.2 mL O2/ dL Blood = 4.6 mL O2/ dL Blood!!!!!!!!!
- This is whats used by the whole bodies Tissues!
- The a-v O2 Difference varies substantially from Tissue to Tissue
a) Adipose tissues removes VERY LITTLE O2 from the Blood
b) Skeletal Muscle removes much more O2
- The Reason: OXYGEN UTILIZATION by the two Tissues is very different!!!
There is a consistent relationship between the amount of O2 consumed and the CO2 produced
- This relationship (ratio) is determined by the fuel being utilized by the cells:
1) If the fuel is CARBOHYDRATES:
- There is a 1: 1 ratio
- 1 CO2 produced for every 1 O2 consumed
2) If the fuel is FATS:
- The ratio is 7:10 or 0.7!!!!!!
- 7 CO2 produced for every 10 O2 consumed
3) Usually a MIX OF FUELS is being used:
- 200 mL CO2 produced for every 250 mL O2 consumed
- Ratio 8: 10 or 0.8!!!!!!!
The Respiratory Quotient (RQ)
- The ratio between CO2 PRODUCED and the O2 CONSUMED is called the RESPIRATORY QUOTIENT or RQ!!!!!!!!
- It is calculated according to the equation:
RQ = (Volume of CO2 Produced)/ (Volume of O2 Consumed)
RQ = V(dot) CO2 / V(dot) O2
= (200 mL CO2 produced) / (250 mL O2 consumed)
= 0.8!!!!!!
How much CO2 can dissolve in the Plasma?
- CO2 has a much greater SOLUBILITY in Water (And therefore Plasma) than O2
The Solubility of CO2 is:
6 mL O2/ dL Blood/ 100 mm Hg
- Since the PCO2 of the Venous Blood is 45 mm Hg, there is about 2.7 mL CO2 DISSOLVED in each dL of Blood!!!
- Once again, we’ need a Cardiac Output considerably higher than 5 Liters/ min to deal with the volume of CO2 produced every minute (about 200 mL CO2)
Carrying CO2 in the Blood: Carbamino Compounds
- CO2 can combine with Plasma proteins or Hb to form CARBAMINO COMPOUNDS
- It does not bind to the HEME GROUP of the Hb, but the AMINE GROUP of the Chains!!!!
- The presence of O2 of the Heme reduced the AFFINITY of the Hb chain for the CO2!!!!
- This is called the HALDANE SHIFT!!!!!!!
***The VOLUME of CO2 carried this way is also about 3 m:/ dL of Blood (About 7% of the Total)
Carrying CO2 in the Blood: as HCO3
- Most of the CO2 in the blood is carried as BICARBONATE (HCO3)
**86% of the Total
** 44 mL of CO2
Carbonic Anhydrase
- It is found in RBC and acts on CO2 and Water to form Carbonic Acid. Which dissociated quickly into H+ and Bicarbonate
- Bicarbonate is shunted out of the Plasma and can be measured
- Bicarbonate has a NEGATIVE CHARGE
- CHLORINE gets pumped into the cells for EVERY BICARBONATE PUMPED OUT, to keep the NEGATIVE PRESSURE
**This process is occurring in the VENOUS BLOOD
