Can someone please help with Haemoglobin graphs?

Original post by ZackenIsUglyAF

Thank you for bumping my thread :ahee:

now hopefully someone will answer my biological question, i can call in @iEthan , you can get banned and we can get back to our lives :h:

Reply 2

CC I'm in the middle of answering your question :love:

(edited 8 years ago)

Reply 3

Original post by CoolCavy

Hey

Sorry but i've been looking at haemoglobin graphs for days and it still won't click really. From what i understand the shape is caused by the following:

sorry i just need to clear this up cos losing the will to live with these graphs :redface:

What you have said is spot on :yep:

But it's probably important to explore why the graph is this shape as opposed to logarithmic or just a straight line graph.

The reason it is a Sigmoidal graph aka the S shaped curve...is because of the structure of haemoglobin.

As you know haemoglobin is what binds the Oxygen to the Red blood cells. One haemoglobin molecule can bind up to four oxygen molecules in 4 places. Well the shape of the curve results from the way in which each oxygen molecule binds to those specific sites within the haemoglobin molecule.

The reason the graph is of a lower gradient i.e not as steep at the beginning is because binding of the first molecule is quite difficult. However, once the first molecule binds, the structure of haemoglobin changes slightly and the other sites almost open out and this allows the oxygen to bind to those sites easier and quicker. Therefore after the first part where the first sites are full, the graph steepens as it is easier and quicker for the oxygen to bind to the subsequent sites in the haemoglobin.

Then eventually the graph levels off. This is because there is just less Oxygen around to fill the last sites up in the haemoglobin so it slows down.

The shape is therefore a result of normal almost 'diffusion' principles, but coupled with the specific and dynamic structure of haemoglobin.

The shape of the curve results from the interaction of bound oxygen molecules with incoming molecules. The binding of the first molecule is difficult. However, this facilitates the binding of the second, third and fourth, this is due to the induced conformational change in the structure of the haemoglobin molecule induced by the binding of an oxygen molecule.

at a higher altitude there is less oxygen in the atmosphere so this would cause a lower partial pressure right? so more oxygen would disassociate? Yes less oxygen in the atmosphere.
would this move the graph to the left? Yes :yep:

that animals in higher altitude have red blood cells with a lower affinity for oxygen because their cells need to get oxygen more quickly? the animals' red blood cells would need a higher affinity for oxygen to get it more quickly, not lower.

(edited 8 years ago)

Reply 4

Original post by Ethereal World

thank you so much emma :colondollar:

xxx
i still don't get why it would move right tho? surely it would go left because then at lower partial pressures where there is les oxygen the oxygen would unload faster so it would have a lower saturation? :redface:

sorry lovely this direction thing just confuses me :colondollar:

Reply 5

Star Light

Original post by CoolCavy

Hey

Sorry but i've been looking at haemoglobin graphs for days and it still won't click really. From what i understand the shape is caused by the following:

sorry i just need to clear this up cos losing the will to live with these graphs :redface:

Here's my take on things :smile:

It's important to consider both the lungs and the respiring tissues when using this curve - also that oxygen partial pressure is a direct function of it's concentration (concentration = partial pressure x solubility constant), nothing more complex than that. Oxygen concentration/partial pressure is high in the pulmonary capillaries in the lungs, as they are adjacent to regularly ventilated air in the alveoli which diffuses across; partial pressure is low in the tissues as oxygen is actively consumed by aerobic respiration.

The main reason oxygen is unloaded from haemoglobin at tissues is because of the low oxygen partial pressure in the plasma. There's also the Bohr effect, where the high concentration of CO2 and low pH cause the curve to shift to the right, so at a given partial pressure of oxygen, less is stored in haemoglobin, so more is available to tissues; but the main reason Hb gets less saturated is due to the lowered partial pressure. This oxygen then continues diffusing through the red blood cell, plasma, capillary wall and tissue fluid to enter cells down a gradient.

At altitude, the pO2 (partial pressure of oxygen) in the alveoli is decreased, because atmospheric pressure decreases, so the pO2 in the pulmonary capillaries is lower too. If you look at the shape of the curve, this doesn't cause much of a problem until you start to get to fairly low pressures - the end-stage of the graph is flat, so lowering pO2 has little effect on Hb saturation to begin with. However, at serious altitude, the Hb can be significantly less saturated, so the blood oxygen capacity is reduced. So it's not as if more oxygen would dissociate - just less would bind to begin with when red blood cells enter the lung. This in itself does not shift the graph in either direction! Hb still has the same properties, and CO2/pH has not changed!

The most common adaptation of mammals at altitude is to have a higher concentration of haemoglobin in the blood, known as polycythaemia - this is done by the kidneys detecting the lower pO2 in the arteries and releasing erythropoeitin, a hormone which causes blood marrow to synthesise more red blood cells. If you have only 80% haemoglobin saturation, but 25% extra haemoglobin, your blood oxygen capacity stays the same.

Another response less understood is the release of a chemical called DPG, diphosphoglycerate, at altitude, found in some animals. This causes the graph to shift to the right, so at the tissues more oxygen releases from Hb, but at the lungs, less oxygen is able to bind to it - therefore this is not a particularly helpful response, and many physiologists think it's ineffective.

Any questions about this stuff, please ask! It's important to understand this.

Reply 6

Lord Samosa

tfw you realise you can't remember your A-level biology :indiff:

Reply 7

Original post by CoolCavy

thank you so much emma :colondollar:

sorry lovely this direction thing just confuses me :colondollar:

Sorry yes, in terms of A LEvel Biology it does shift to the left, you're right!!!

At a high altitude an animal's haemoglobin can bind oxygen at a lower partial pressure than that of low altitude animal. This would cause a shift in the graph to the left.

There is an added layer of complexity which Star light added, which is why I said about it shifting to the right initially:

Another response less understood is the release of a chemical called DPG, diphosphoglycerate, at altitude, found in some animals. This causes the graph to shift to the right, so at the tissues more oxygen releases from Hb, but at the lungs, less oxygen is able to bind to it - therefore this is not a particularly helpful response, and many physiologists think it's ineffective.

^^ BUt i wouldn't worry about this for A Level.

Just focus on it shifting to the left at higher altitudes.

Reply 8

Original post by Star Light

Thank you very much for writing all that :hugs:

the thing that is confusing me is that in my book is that it says:

'Organisms that live in an environment with a low concentration of oxygen have a haemoglobin with a higher affinity for oxygen and the disassociation curve is to the left'

that doesn't make sense to me because surely they would want to have a lower affinity so more oxygen disassociates more easily and they can get more oxygen in their lower O2 environment? :redface:

Original post by Ethereal World

Thanks emma :hugs:

i still don't get this tho lol :frown:

so if a llama was up a mountain or something it would have a lower affinity for oxygen? im so confused lol

Original post by Lord Samosa

tfw you realise you can't remember your A-level biology :indiff:

it's alright samosa :lol:

it's the thought that counts x

Reply 9

Original post by CoolCavy

Thank you very much for writing all that :hugs:

Thanks emma :hugs:

i still don't get this tho lol :frown:

so if a llama was up a mountain or something it would have a lower affinity for oxygen? im so confused lol

it's alright samosa :lol:

it's the thought that counts x

I will chat to you about it on Skype :mmm:

Reply 10

Original post by Ethereal World

I will chat to you about it on Skype :mmm:

Thanks emma :redface:

that might be easier lol and then i can stop posting :colondollar:

Reply 11

Original post by CoolCavy

Thanks emma :redface:

that might be easier lol and then i can stop posting :colondollar:

Yeah stop posting you silly birch. :rofl:

Reply 12