Bohr EffectBohr Effect

Normal dissociation curveNormal dissociation curve An increase or decrease in acidity, temperature, An increase or decrease in acidity, temperature,

or COor CO22 concentration causes a shift in the curve concentration causes a shift in the curve

This is due to an alteration in the molecular This is due to an alteration in the molecular structure of Hbstructure of Hb

Specifically, the Bohr effect is the presence of Specifically, the Bohr effect is the presence of HH++ ions in contracting muscle unloads O ions in contracting muscle unloads O22 from from

HbHb

Bohr effect is the reduced effectiveness of Bohr effect is the reduced effectiveness of hemoglobin to hold Ohemoglobin to hold O22, especially in PO, especially in PO22

ranges of 20-50 mm Hgranges of 20-50 mm Hg @PO@PO22 in alveoli, Bohr effect in pulmonary in alveoli, Bohr effect in pulmonary

capillary blood is negligiblecapillary blood is negligible– Allows Hb to load completely with OAllows Hb to load completely with O22 as the as the

blood passes through the lungs, even during blood passes through the lungs, even during maximal exercisemaximal exercise

Red-Blood-Cell 2,3-DPGRed-Blood-Cell 2,3-DPG

2,3-diphophoglycerate is produced within the RBC 2,3-diphophoglycerate is produced within the RBC during glycolysis (anaerobic)during glycolysis (anaerobic)

Binds loosely with subunits of Hb moleculeBinds loosely with subunits of Hb molecule Reduces the affinity for OReduces the affinity for O22, shifting the curve, shifting the curve

Enhances the unloading of OEnhances the unloading of O22 in the tissue in the tissue

Unlike the response of HUnlike the response of H++ ions to unload O ions to unload O22

quickly, 2,3-DPG operates at a slower rate, quickly, 2,3-DPG operates at a slower rate, allowing adaptations to gradual changes in Oallowing adaptations to gradual changes in O22

availabilityavailability

If POIf PO22 decreases, more O decreases, more O22 is released to the is released to the tissuestissues

High levels of 2,3-DPG in RBCs for those who High levels of 2,3-DPG in RBCs for those who live at high altitudes and those with live at high altitudes and those with cardiopulmonary disorderscardiopulmonary disorders

Half-life is small, ~6 hours if return to low Half-life is small, ~6 hours if return to low altitudesaltitudes

Endurance training may increase 2,3-DPG after Endurance training may increase 2,3-DPG after maximal exercise of short duration, while training maximal exercise of short duration, while training has no benefit during prolonged, steady-rate has no benefit during prolonged, steady-rate exerciseexercise

Females appear to have higher levels, may Females appear to have higher levels, may compensate for lower Hb levelscompensate for lower Hb levels

MyoglobinMyoglobin

Iron-protein found in skeletal and cardiac Iron-protein found in skeletal and cardiac tissuetissue

High concentration in red or oxidative fibersHigh concentration in red or oxidative fibers Similar to Hb in its ability to combine Similar to Hb in its ability to combine

reversibly with Oreversibly with O22

Each myoglobin molecule contains only one Each myoglobin molecule contains only one iron atom, carries one Oiron atom, carries one O22 molecule molecule

Mb + OMb + O22 MbO MbO22

Oxygen release at low pressuresOxygen release at low pressures

Myoglobin is an extra source of oxygen in muscle, Myoglobin is an extra source of oxygen in muscle, may facilitate the transfer of Omay facilitate the transfer of O22 to the mitochondria to the mitochondria

Especially in the beginning of exercise and during Especially in the beginning of exercise and during intense exercise, when there is a sharp drop in intense exercise, when there is a sharp drop in cellular POcellular PO22

Dissociation curve is rectangular hyperbolaDissociation curve is rectangular hyperbola Myoglobin binds and retains oxygen at low Myoglobin binds and retains oxygen at low

pressures much more readily than Hbpressures much more readily than Hb

Greatest release of oxygen occurs from Greatest release of oxygen occurs from MbOMbO22 when the tissue PO when the tissue PO22 drops to 5 mm drops to 5 mm

HG or lessHG or less Myoglobin has no Bohr effectMyoglobin has no Bohr effect

TrainingTraining

Slow twitch or slow oxidative fibers have Slow twitch or slow oxidative fibers have more myoglobinmore myoglobin

Myoglobin is some mammals is related to Myoglobin is some mammals is related to activity levelactivity level

Results in humans are unclearResults in humans are unclear

COCO22 transport in blood transport in blood

Dissolved (~10%)Dissolved (~10%) 20% CO20% CO22 bound to hemoglobin (carbamino- bound to hemoglobin (carbamino-

hemoglobin)hemoglobin) 70% as bicarbonate70% as bicarbonate

Regulation of blood pHRegulation of blood pH

Buffer system – secondsBuffer system – seconds– Phosphate buffer systemPhosphate buffer system– Carbonic/carbonate systemCarbonic/carbonate system– Blood proteins, esp. HbBlood proteins, esp. Hb

Respiratory system – minutesRespiratory system – minutes– Ventilation rate is controlled to keep sufficient CO2 in Ventilation rate is controlled to keep sufficient CO2 in

blood to maintain pHblood to maintain pH

Kidneys – daysKidneys – days– Excrete bicarbonate (HCOExcrete bicarbonate (HCO33

--) at a rate that optimizes pH) at a rate that optimizes pH

Functions of the respiratory systemFunctions of the respiratory system

Delivery of ODelivery of O22 to tissues to tissues

Disposal of CODisposal of CO22 produced by the tissues produced by the tissues

Maintenance of a stable blood pH @7.4Maintenance of a stable blood pH @7.4

Control of ventilation during exerciseControl of ventilation during exercise

Humoral stimuli: changes in physical and Humoral stimuli: changes in physical and chemical properties in blood from normal chemical properties in blood from normal values at restvalues at rest

Neural stimuli: originates in the brain center Neural stimuli: originates in the brain center – Respiratory Center– Respiratory Center– Mental conditions, e.g., emotionsMental conditions, e.g., emotions– Inflation and deflation (stretch) of the lungsInflation and deflation (stretch) of the lungs– Muscle contraction and limb movement or Muscle contraction and limb movement or

tension developmenttension development