Exam 3, L4 Flashcards
(37 cards)
What three forms does CO₂ exist in the blood?
Dissolved (5%), carbamino compounds (5%), and bicarbonate (90%)
What enzyme catalyzes the conversion of CO₂ to H₂CO₃?
Carbonic anhydrase (in RBCs)
What happens when CO₂ binds to amine groups on proteins?
Forms carbamino compounds and releases protons, contributing to acidosis.
Why is it counterintuitive that CO₂ is mainly transported as bicarbonate?
Because CO₂ is acidic, but is carried in the form of a base (HCO₃⁻), though protons are also generated and buffered.
What is the CO₂ content of arterial blood?
~48 mL/dL
What is the CO₂ content of venous blood?
~52.5 mL/dL
How much CO₂ is offloaded at the lungs per deciliter of blood?
~4.5 mL
Why are separate CO₂ curves used for arterial vs. venous blood?
Because deoxyhemoglobin carries more CO₂ — known as the Haldane effect.
What happens to CO₂ in peripheral tissues?
It diffuses into plasma, enters RBCs, forms bicarbonate, and some binds to proteins.
What buffers protons in RBCs during CO₂ transport?
Deoxyhemoglobin (a good H⁺ acceptor)
What happens in the lungs to offload CO₂?
CO₂ diffuses into alveoli, carbamino bonds break, H⁺ recombines with HCO₃⁻ → CO₂ is exhaled.
What role does chloride shift play in gas exchange?
Maintains electrochemical balance as HCO₃⁻ is exchanged for Cl⁻ in and out of RBCs.
What is the Haldane effect?
Deoxygenated hemoglobin binds more CO₂, enhancing venous CO₂ transport.
What is the Bohr effect?
Increased CO₂ and H⁺ lower Hb’s O₂ affinity → promotes O₂ unloading at tissues.
How long does blood spend in pulmonary capillaries at rest?
0.75 seconds
How long does gas exchange normally take?
~0.25 seconds
What happens during exertion?
Transit time can drop to 0.25s — adequate only if lungs are healthy.
What condition makes O₂ exchange diffusion-limited?
Conditions like pulmonary edema or fibrosis, where PO₂ doesn’t equilibrate.
What is perfusion-limited gas exchange?
Gas equilibrates rapidly; uptake depends on blood flow (e.g., O₂, N₂O).
What is diffusion-limited gas exchange?
Gas doesn’t equilibrate; limited by membrane barrier (e.g., CO in DLCO tests).
Why is CO used to measure DLCO?
Because it doesn’t equilibrate — uptake depends purely on diffusion ability.
What is the normal V/Q ratio?
~0.8 (4.2 L/min ventilation / 5 L/min perfusion)
What happens with no ventilation but normal perfusion?
Shunt — V/Q = 0
What happens with ventilation but no perfusion?
Dead space — V/Q → ∞
