Why r bicarbonate ions removed from red blood cells

Looking at the chloride shift i don't get why HCO3- needs to be removed from the red blood cell in the first place. Can somebody help?

Reply 1

macpatgh-Sheldon

20

Hi,
HCO3- ions are formed by reaction of H2O and CO2 - so high level of bicarbonate ions indicate higher levels of CO2 this is the case in the metabolizing tissues where the process of respiration uses up oxygen and produces CO2.

In the lungs the blood must "get rid of" CO2 and "pick up" oxygen so by releasing HCO3- ions, we are effectively exhaling CO2 as a result, yeah?

There is a highly complex explanation as to how the intricately involved properties of haemoglobin achieve all this - if you are studying for a medical degree or a BSc in biology, let me know and I shall go through it for you, but for A level the above is sufficient.

M

Reply 2

Hii84y4

OP

11

Original post by macpatgh-Sheldon

Hi,
HCO3- ions are formed by reaction of H2O and CO2 - so high level of bicarbonate ions indicate higher levels of CO2 this is the case in the metabolizing tissues where the process of respiration uses up oxygen and produces CO2.

In the lungs the blood must "get rid of" CO2 and "pick up" oxygen so by releasing HCO3- ions, we are effectively exhaling CO2 as a result, yeah?

There is a highly complex explanation as to how the intricately involved properties of haemoglobin achieve all this - if you are studying for a medical degree or a BSc in biology, let me know and I shall go through it for you, but for A level the above is sufficient.

M

I read online that HCO3- would affect pH or cause the cell to rupture as water would be drawn in by osmosis due to high HCO3- ion concentration. Are either of these true?

(Btw I study physiotherapy thank you for your help :smile:

(edited 5 months ago)

Reply 3

macpatgh-Sheldon

20

Original post by Hii84y4

Looking at the chloride shift i don't get why HCO3- needs to be removed from the red blood cell in the first place. Can somebody help?

Hi,
With relevance to physiotherapy and the importance of muscle anatomy & physiology therein, all I would be inclined to clarify in your mind is to know that in the lungs, deoxyhaemoglobin releases the H+ ions [formed by the reaction below] as these are displaced from the Hb by the binding of O2 to Hb.

H2O + CO2 ------> H+ + HCO3-

Oc H+ ions tend to reduce pH [cos H+ ions are what make an acid acidic], but remember that carbonic acid [H2CO3] is a weak acid, so the conc-n of H+ is not unduly high. Nevertheless, it is true that release of H+ ions [which will be followed by HCO3- ions due to electrostatic forces] from the erythrocyte will help control pH within the red cell.

The Bohr effect [shifting of the oxygen dissociation curve to the right in the presence of high levels of CO2 [hence of low pH] or of chloride] reduces the affinity of Hb for O2 so that in this situation [importantly in the metabolizing tissues including muscle], more oxygen is released to allow cells to respire [I mean the chemical process of respiration, not breathing, which is strictly speaking, called "ventilation"]. The Bohr shift also facilitates binding of H+ and CO2 to Hb, thus aiding its removal from tissues.

As to rupture of erythrocytes due to influx of water by osmosis, I have not come across any clinical situation where that occurs [there are several other causes of haemolysis], so I would say it is only theoretically possible, and would advise you to ignore this point to avoid confusion.

One final point to mention: please learn about myoglobin [present in muscle] and its differences from haemoglobin in terms of affinity for oxygen, since that is directly relevant to your profession.

Best wishes,
M.

(edited 4 months ago)

Reply 4

Hii84y4

OP

11

Thank you for clearing things up for me!

Why r bicarbonate ions removed from red blood cells

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