Bohr Effect  Normal dissociation curve  An increase or decrease in acidity, temperature, or CO 2 concentration causes a shift in the curve  This is due to an alteration in the molecular structure of Hb  Specifically, the Bohr effect is the presence of H + ions in contracting muscle unloads O 2 from Hb

 Bohr effect is the reduced effectiveness of hemoglobin to hold O 2, especially in PO 2 ranges of mm Hg 2 in alveoli, Bohr effect in pulmonary capillary blood is negligible –Allows Hb to load completely with O 2 as the blood passes through the lungs, even during maximal exercise

Red-Blood-Cell 2,3-DPG  2,3-diphophoglycerate is produced within the RBC during glycolysis (anaerobic)  Binds loosely with subunits of Hb molecule  Reduces the affinity for O 2, shifting the curve  Enhances the unloading of O 2 in the tissue  Unlike the response of H + ions to unload O 2 quickly, 2,3-DPG operates at a slower rate, allowing adaptations to gradual changes in O 2 availability

 If PO 2 decreases, more O 2 is released to the tissues  High levels of 2,3-DPG in RBCs for those who live at high altitudes and those with cardiopulmonary disorders  Half-life is small, ~6 hours if return to low altitudes  Endurance training may increase 2,3-DPG after maximal exercise of short duration, while training has no benefit during prolonged, steady- rate exercise  Females appear to have higher levels, may compensate for lower Hb levels

Myoglobin  Iron-protein found in skeletal and cardiac tissue  High concentration in red or oxidative fibers  Similar to Hb in its ability to combine reversibly with O 2  Each myoglobin molecule contains only one iron atom, carries one O 2 molecule  Mb + O 2  MbO 2

Oxygen release at low pressures  Myoglobin is an extra source of oxygen in muscle, may facilitate the transfer of O 2 to the mitochondria  Especially in the beginning of exercise and during intense exercise, when there is a sharp drop in cellular PO 2  Dissociation curve is rectangular hyperbola  Myoglobin binds and retains oxygen at low pressures much more readily than Hb

 Greatest release of oxygen occurs from MbO 2 when the tissue PO 2 drops to 5 mm HG or less  Myoglobin has no Bohr effect

Training  Slow twitch or slow oxidative fibers have more myoglobin  Myoglobin is some mammals is related to activity level  Results in humans are unclear

CO 2 transport in blood  Dissolved (~10%)  20% CO 2 bound to hemoglobin (carbamino- hemoglobin)  70% as bicarbonate

Regulation of blood pH  Buffer system – seconds –Phosphate buffer system –Carbonic/carbonate system –Blood proteins, esp. Hb  Respiratory system – minutes –Ventilation rate is controlled to keep sufficient CO2 in blood to maintain pH  Kidneys – days –Excrete bicarbonate (HCO 3 - ) at a rate that optimizes pH

Functions of the respiratory system  Delivery of O 2 to tissues  Disposal of CO 2 produced by the tissues  Maintenance of a stable blood

Control of ventilation during exercise  Humoral stimuli: changes in physical and chemical properties in blood from normal values at rest  Neural stimuli: originates in the brain center – Respiratory Center –Mental conditions, e.g., emotions –Inflation and deflation (stretch) of the lungs –Muscle contraction and limb movement or tension development