Quantitative Physiology I / Molecular and Cellular Systems, BMEN E4001x
Notes 03 - Oxygen and Carbon Dioxide transport in blood and Hemoglobin
Chapter 28,29 of B & B;
A major role of blood is oxygen and carbon dioxide transport between
lungs and tissues.
While this isn’t completely in the framework
of understanding cellular physiology, it is a key example of how
chemical kinetics and equilibria provide a functional, elegant
We will assume the following conditions describe normal, resting tissues:
solubility, s (M/
Solubility, denoted k, s, and sometimes
, reflects the ability of a solution at equilibrium with a
gas or mixes of gases to hold a particular
This is Henry’s Law. Solubility is dependent on a wide range of factors, including temperature,
solvent, and gas.
Dissolved gas is simply not enough to handle this transport.
A typical number for oxygen demand for a 70 kg person at rest is ~ 11 mmol/min of O
This was originally cast as 250 ml/min, but let’s just focus on the mole version.
If you want this
conversion, assume standard conditions; 1 atm, 273 K. Using the ideal gas law, 1 mole of gas
takes up 22.4 L.
Now, taking the numbers above and assuming a 5 L/min cardiac output:
dissolved gas capacity = cardiac output * change in partial pressure * solubility
= 5 L/min * 60 mmHg * 1.4E-6 M/mmHg
= 0.4 mmol/min O
A similar situation exists for dissolved carbon dioxide.
Additional capacity comes from tying up O
in complexes in blood.
This section, based on parts of B&B Ch. 28, deals with how our treatment of multimolecular
binding makes up this capacity, and is presented as examples of how physiology results from
the elaboration of simple concepts into complex systems. We will deal with the equilibrium
conditions of gas transport, assuming these gases reach equilibrium with various forms in the
lungs and tissues.
Further elaboration of these concepts, will be taken up in Ch. 29 in QPII,
and in the final module of AQPI.