1 - O2 and CO2 Transport by Blood ( II )

Question 1

Objective: Explain the concept of P₅₀

Answer 1

• P₅₀ is Partial Pressure of Oxygen when Hb is 50% Saturated
  
  • ​Normal ~ 26 mmHg
• Increase P₅₀ = Right Shift
  
  • ​Unloading of Oxygen
• Decrease P₅₀ = Left Shift
  
  • ​Loading of Oxygen

Question 2

Objective: How can the affinity of Hb for O₂ be shifted?

Answer 2

• Left Shift: High Affinity - O₂ Taken Up
  
  • ​Carbon Monoxide (CO) poisoning - O₂ affinity increased
  • Low (or no) 2,3 DPG - elevated O₂
• Right Shift: Low Affinity - O₂ Unloaded
  
  • ​Anemia - Increase in DPG levels
  • Exercise - Increase Temperature, [H+], PCO₂
    
    • Think about during exercise, you want to unload O₂ at your tissues
  • High 2,3 DPG - Persistent hypoxia (high altitude), emphysema, Cong. HD

Question 3

Objective: Explain the role of 2,3 DPG in Hb affinity

Answer 3

• DPG levels have inverse relationship with P_aO₂
  
  • ​Relative to other DPG levels, highest DPG levels will have lowest P_aO₂ levels–it wants to unload O₂

Question 4

Objective: Explain the role of Fetal Hemoglobin (HbF)

Answer 4

• HbF P50 ~ 19, Adult Hb P50 ~ 27
  
  • HbF has LOWER P₅₀
• Fetal Hb has higher affinity for O₂ than Adult Hb
  
  • ​It has to “steal” O₂ from maternal blood
  • Due to 2,3-DPG, not Hb
• HbF can’t interact with 2,3-DPG (in adult RBCs, this decreases affinity of Hb for O₂)
• Pregnant women have 30% increase in DPG

Question 5

What can be caused by chronic hypoxemia?

Answer 5

• Generation of new RBCs
  
  • 2-3 weeks
• :) Increase in hematocrit and additional O₂ carrying capacity
• :( Increase in viscoity of blood creates additional workload on heart (polycythemia)

Question 6

Objective: Explain the transport of CO₂

Answer 6

• Transported in three forms:
  
  • Dissolved in plasma
  • Bicarbonate (HCO₃^_)
  • Bound to Hb (HbCO₂ = carbamino)
• Dissolved: 0.06 ml CO₂ / 100 ml/ mmHg
  
  • 20x greater diffusion than O₂
  • ΔP ~ 6 mmHg (vs. Arterial ~ 60 mmHg)
• Bicarbonate: “Hambruger/Chloride Shift”
  
  • Main transport (85%)
  • CO₂ + H₂O ↔ H₂CO₃ ↔ H⁺ + HCO₃^-
  • At Tissue: Diffuses into RBCs; catalyzed by carbonic anhydrase; to maintain neutrality, Cl^- moves back into the cell
  • At Lungs: Opposite; diffuses out of RBCs; CO₂ diffuses out into alveoli
• Carbamino Compounds: Bound to Hb
  
  • 5%, binds to deoxygenated Hb > oxygenated Hb; unloading at lungs occurs due to oxygenation of Hb

Question 7

What is the role of Hb in regards to H⁺ generation in cells?

Answer 7

Buffered by Hb

Minimizes the resulting change in H+ concentration

Question 8

How does CO₂ content in blood vary with PCO₂?

Answer 8

• Linear curve
• No saturation kinetics
  
  • Includes all forms of transport (dissolved, bicarb, Hb-CO2)

Question 9

What occurs to PCO₂ when two blood samples with different PCO₂’s are mixed?

Answer 9

• Linear saturation
• Average the two samples
  *

Question 10

How do you calculate the PO₂ of two mixed samples with different values?

Answer 10

• 1. Add Volumes blood
• 2. Use given PO₂ to determine O₂ Content
     * Add O₂ Contents
• 3. Calculate new Volume %
     * O₂ Content / Total Volume
     
     • # 2/#1
• 4. Determined new PO₂ from table (maybe within range)

Question 11

Objectives: What are four non-respiratory functions of the lung?

Answer 11

• Defense Mechanism - Macrophages engulf bacteria, immune system protects body from inhaled foreign microorganisms
• Air-Conditioning - Nasal mucosa and nasal turbinates heat and humidify the air
• Olfaction - Detect hazards by sniffing
• Filtration and Removal of Particles - Nasal hairs filter and remove particles
  
  • Mucus covered ciliated epithelium; always moves up the airway
  • Cigarette smoke impairs ciliary function

Question 12

Objectives: What are three more non-respiratory functions of the lung?

Answer 12

• Blood Filter - Filter/trap foreign particles; can “catch” clots
• Blood Reservoir - Blood vessels of lung accommodate about 500 ml of blood; reservoir for left ventricle
• Metabolism of Circulating Substances - Endothelial cells in lung are involved in betabolism of vasoactive substances in the circulation (may take multiple passes)