University:
Western Sydney University
Course:
MEDI 2003 | Clinical Sciences 2
Academic year:

2024
Views:

416

Pages:

2
Author:

Mariam A. A.

Oxygen Transport Around the Body Two Ways of Oxygen Transport • • Positive cooperativity Only a little proportion of oxygen is carried in plasma, as oxygen has a low solubility. The vast majority of oxygen is carried on Hb • • When an oxygen molecule binds to a Hb, this increases the oxygen affinity (tendency to bind). This means that it will be easier for the second O2 to binds, and even easier for the third etc. Hb saturation table Molecules of O2 bond Saturation • • 0 0% 1 25% 2 50% 3 75% 4 100% When there is 0 molecules of O2 bound we call this the T state From 1-4 we call this the R state Oxyhaemoglobin Dissociation curve • • • This curve tells us about the relationship between oxygen saturation of Hb and partial pressure of atrial oxygen O2 saturation to Hb is affected by PO2 The greater the PO2 the greater the oxygen saturation of Hb. However, after a certain extent at about 84 mmHg the curve reaches the plateau phase, where regardless of how much oxygen you add, it will not affect the curve, because all O2 binding sites are occupied. Effect of CO2 on curve • CO2 - During anerobic metabolism CO2 dissolves in blood plasma -> increases PCO2 -> CO2 gets into RBC - Carbonic anhydrase combines CO2 & H2O to form carbonic acid which the dissociates into HCO3- and H+ (note these are equilibrium reactions) - CO2 binds to terminal amino acid in globin sub-units -> carbaminohemoglobin - There will be H+ build up -> decrease in pH - CO2 does not compete with O2 for the same binding spot; however, it stabilises the T-state of Hb -> decreases O2 affinity -> increased O2 loading Effect of temp on curve • Temperature - An increase in temperature impacts upon the bond between iron and O2 causing the T state - This decreases O2 affinity and thus increasing the unloading of O2 to needy tissues Effect of 2,3 DPG on curve • 2,3 DPG - This is a metabolic product of glycolysis in RBC - This is produced in hypoxic conditions - It is negatively charged, and it binds in the middle of the Hb molecule, which is positively charged -> stabilises T state -> decrease Hb affinity for O2 -> increasing O2 unloading to needy tissues Shifts in curve • • To the right if: - Increased PCO2 - Increased temp - Increased 2,3 DPG - Decreased pH ➢ The curve shifts to the right because a higher PO2 needed to overcome the above factors in order and saturate Hb. To the left: - The opposite of the above Bohr’s effect vs Haldane’s affect Bohr’s effect • haemoglobin’s oxygen binding affinity is inversely related to both the concentration of carbon dioxide and to acidity Haldane’s effect • oxygenation of blood promotes the release of carbon dioxide.