The Bohr Effect?

[NYMedic828]

I am having a little trouble comprehending the Bohr effect and can't really find any good articles/texts on it outside of wikipedia.

Is it basically just saying that when the acid content of cells in working tissues becomes higher, it allows for easier exchange of CO2 with oxyhemoglobin? Or am i completely on the wrong path?

My interest basically stemmed from reading up on hyperventilation and effects of respiratory alkalosis.

 

[VFlutter]

I am having a little trouble comprehending the Bohr effect and can't really find any good articles/texts on it outside of wikipedia.

Is it basically just saying that when the acid content of cells in working tissues becomes higher, it allows for easier exchange of CO2 with oxyhemoglobin? Or am i completely on the wrong path?

My interest basically stemmed from reading up on hyperventilation and effects of respiratory alkalosis.

My basic understanding of the topic is pretty much the same as yours. Oxygen dissociates from hemoglobin in an acidic environment ("Oxygen dumping") therefore allowing for an increased exchange in working tissue. So it sounds like in an alkaline environment oxygen would stay bound to the hemoglobin resulting in less oxygen to tissue?

It also plays a role in how CO2 is exhaled in the lungs but I am sure someone with a better Biochem background can explain that.

 

[VFlutter]

From my Patho book....


When hemoglobin molecules bind with oxygen, oxyhemoglobin (HbO2) is formed. Binding occurs in the lungs and is called oxyhemoglobin association or hemoglobin saturation with oxygen (SaO2). The reverse process, in which oxygen is released from hemoglobin, occurs in the body tissues at the cellular level and is called hemoglobin desaturation. When hemoglobin saturation and desaturation are plotted on a graph, the result is a distinctive S-shaped curve known as the oxyhemoglobin dissociation curve (Figure 32-18).

Several factors can change the relationship between PaO2 and SaO2, causing the oxyhemoglobin dissociation curve to shift to the right or left (see Figure 32-18). A shift to the right depicts hemoglobin's decreased affinity for oxygen or an increase in the ease with which oxyhemoglobin dissociates and oxygen moves into the cells. A shift to the left depicts hemoglobin's increased affinity for oxygen, which promotes association in the lungs and inhibits dissociation in the tissues.

The oxyhemoglobin dissociation curve is shifted to the right by acidosis (low pH) and hypercapnia (increased PaCO2). In the tissues the increased levels of CO2 and hydrogen ions produced by metabolic activity decrease the affinity of hemoglobin for oxygen. The curve is shifted to the left by alkalosis (high pH) and hypocapnia (decreased PaCO2). In the lungs, as CO2 diffuses from the blood into the alveoli, the blood CO2 level is reduced and the affinity of hemoglobin for oxygen is increased. The shift in the oxyhemoglobin dissociation curve caused by changes in CO2 and hydrogen ion concentration in the blood is called the Bohr effect.

The oxyhemoglobin curve is shifted also by changes in body temperature and increased or decreased levels of 2,3-diphosphoglycerate (2,3-DPG), a substance normally present in erythrocytes. Hyperthermia and increased 2,3-DPG levels shift the curve to the right. Hypothermia and decreased 2,3-DPG levels shift the curve to the left.

McCance, Kathryn L.. Pathophysiology: The Biologic Basis for Disease in Adults and Children, 6th Edition. Mosby, 112009. <vbk:9780323065849#outline(32.2.2.2.3)>.

 

[NYMedic828]

Thats another concept I never fully understood though I am sure it is very simple I am just misinterpreting it.

A shift in the O2 curve to the right, wouldn't that imply you move to the right on the X axis, and therefore Po2 is HIGHER and affinity for hemoglobin of oxygen is higher?

It was my understanding that in the presence of hypoxemia, oxygen does not have enough affinity for hemoglobin. This seems to contradict that concept?

 

[NYMedic828]

Thats another concept I never fully understood though I am sure it is very simple I am just misinterpreting it.

A shift in the O2 curve to the right, wouldn't that imply you move to the right on the X axis, and therefore Po2 is HIGHER and affinity for hemoglobin of oxygen is higher?

It was my understanding that in the presence of hypoxemia, oxygen does not have enough affinity for hemoglobin. This seems to contradict that concept?

 

[OzAmbo]

Bohrr was a chemist, perhaps a chem book may be the answer.

 

[Anonymous]

http://www.youtube.com/watch?v=-rCpkvE7uzo

 

[NYMedic828]

Wow! That video channel looks amazing.

Guess i found whatnot to do in the bus tomorrow between jobs!

Thanks!

 

[NYMedic828]

Its all so simple now...


pH up = hemoglobin has a harder time releasing oxygen.

pH down = hemoglobin has a harder time holding on to oxygen.

This whole time when I read "shifts to left, right" I literally took it as moving to the right on the baseline curve of the dissociation graph instead of literally forming a new curve entirely.

 

[jwk]

Right shift with an
Increase in
23DPG
pH
Temperature

They don't line up well in this format, but that's an easy mnemonic.

 

[JPINFV]

Thats another concept I never fully understood though I am sure it is very simple I am just misinterpreting it.

A shift in the O2 curve to the right, wouldn't that imply you move to the right on the X axis, and therefore Po2 is HIGHER and affinity for hemoglobin of oxygen is higher?

It was my understanding that in the presence of hypoxemia, oxygen does not have enough affinity for hemoglobin. This seems to contradict that concept?

As you already found out, when talking about "shifts" it's the entire curve that shifts, not a point along the curve.

However, where PO2 is higher, there is greater affinity. Hemoglobin has 4 binding areas for oxygen and once the first oxygen binds a change in the structure ("conformational change") occurs making it easier for the other 3 to bind ("taunt" structure changes to "relaxed"). This makes sense for the same reason why the shift makes sense. Where is oxygen present in high concentrations? Where is it present in low concentrations? If the purpose of hemoglobin is to move oxygen from places of high concentration to low concentration, then don't you want hemoglobin to bind weakly (i.e. release) oxygen in locations of low oxygen concentration?

 

[NYMedic828]

As you already found out, when talking about "shifts" it's the entire curve that shifts, not a point along the curve.

However, where PO2 is higher, there is greater affinity. Hemoglobin has 4 binding areas for oxygen and once the first oxygen binds a change in the structure ("conformational change") occurs making it easier for the other 3 to bind ("taunt" structure changes to "relaxed"). This makes sense for the same reason why the shift makes sense. Where is oxygen present in high concentrations? Where is it present in low concentrations? If the purpose of hemoglobin is to move oxygen from places of high concentration to low concentration, then don't you want hemoglobin to bind weakly (i.e. release) oxygen in locations of low oxygen concentration?

so when oxyhemoglobin passes by muscle that has been working harder than surrounding tissues and produced acids as a result it has a lower pH, thereby causing the oxygen to leave hemoglobin easier into the muscle when it passes by.

Right?

 

[Dwindlin]

so when oxyhemoglobin passes by muscle that has been working harder than surrounding tissues and produced acids as a result it has a lower pH, thereby causing the oxygen to leave hemoglobin easier into the muscle when it passes by.

Right?

Correct.