Oxygen release from oxyhemoglobin

Figure 10.25. Effect of pH and CO2 concentration on the oxygen affinity of hemoglobin. Lowering the pH from 7.4 (red curve) to 7.2 (blue curve) results in the release of O2 from oxyhemoglobin. Raising the CO2 partial pressure from 0 to 40 torr (purple curve) also favors the release of O2 from oxyhemoglobin.

A mathematical model of the control system for erythropoiesis is presented. It is postulated that the rate of erythropoiesis is controlled by a hormone, erythropoietin, which is released from the kidney in response to reduced renal oxygen supply. Equations are developed relating erythropoietin release to arterial oxyhemoglobin concentration, and hemoglobin production to plasma erythropoietin concentration, with appropriate time delays. Effects of plasma volume changes during hypoxia are included. The model simulates the dynamic response of the erythropoietic system to a step decrease in the pOt of inspired air. Contributions of the parameters and relationships to the predicted response are analyzed. The model response compares favorably with experimental data obtained from mice subjected to different degrees of hypoxia. 

Major components of the model are shown in Figure 1. In the model the controlled variable is oxyhemoglobin concentration (the product of hemoglobin concentration and percent oxygen saturation). Erythropoietin is released from the kidney according to an exponential relationship (Equation 1) relating oxyhemoglobin concentration to the rate of erythropoietin release. 

Hemogiobin Soiubiiity and Sickle-Cell Anemia 486 Positron Emission Tomography (PET) 883 The Cooperative Release of Oxygen from Oxyhemoglobin 992 Tobacco Mosaic Virus and Atomic Force Microscopy 1058... 

Figure 7.9 Delivery of oxygen to peripheral tissue by oxyhemoglobin. Production of protons from COz and HzO, catalyzed by carbonic anhydrase (CA) and their uptake by hemoglobin are also shown. The pC02 in peripheral tissues is high and p02 is low, causing the conversion of hemoglobin R forms into the T forms with the concomitant release of 02. (Reproduced by permission from Bunn HF, Forget BG. Hemoglobin Molecular, Genetic, and Clinical Aspects. Philadelphia WB Saunders, 1986, p. 41.)...

The greater the dmation of the exposure to CO, the concentration of CO in the inhaled air, and the alveolar ventilation, the greater the total amount of COHb. While the uptake of CO by Hb is very rapid, the release of CO from COHb complex is extremely slow. As the concentration of COHb increases the formation of oxyhemoglobin at any concentration of oxygen in the inhaled air decreases. There is a strong case for using COHb concentration as a predictor of CO toxicity (Renwick and Walton, 2001). 

---