03_-_O2_and_CO2_transport_in_blood

03_-_O2_and_CO2_transport_in_blood - Quantitative...

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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 system. We will assume the following conditions describe normal, resting tissues: gas solubility, s (M/ mmHg) atmosphere (mmHg) alveolar (mmHg) tissues (mmHg) O 2 1.4E-6 150 100 40 CO 2 3.3E-5 <1 40 46 Solubility, denoted k, s, and sometimes σ , reflects the ability of a solution at equilibrium with a gas or mixes of gases to hold a particular dissolved gas. [X]=s X *P X . 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 2 . 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 2 . A similar situation exists for dissolved carbon dioxide. Additional capacity comes from tying up O 2 and CO 2 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.
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Myoglobin and Hemoglobin serve as carriers and storage of oxygen. Hemoglobin is a major oxygen carrier in blood. Tetramer protein; each unit somewhat similar to myoglobin, present in muscle tissue. Binds four molecules of oxygen per molecule of Hb. Typical blood value of Hb is 2.3 mM. K D ~25 mmHg Myoglobin has one heme group and binds one oxygen. Michaelis-Menten-type binding They exhibit very different shaped curves Cooperativity Build upon the enzyme kinetics framework with the following adaptations: Leave out the product generation step. This is identical to Keener & Sneyd, with the assumption that k2=0. Simplification in that we will derive the Hill equation for two binding site, and just state
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This note was uploaded on 12/21/2010 for the course BMEN 4001 taught by Professor Kam during the Fall '10 term at Columbia.

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03_-_O2_and_CO2_transport_in_blood - Quantitative...

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