Pulmonary physiology questions

[Kiwiology]

So for fun, you know, as you do, I was reading my A&P book (what's that? what on earth is wrong with me? I know, I need help! ... but there was nothing good on TV or Netflix)

Now where somewhere along the way (perhaps on the way to Solla Sellew on Horton the Elephant) I got confoozle'd ...

Here is the diagram from Marieb 7e showing the effect of temperature, PCO2 and blood pH on the O2Hb dissociation curve.

I don't understand the trend here, this graph is bloody useless!

1. What I think it says is that increased temperature, PCO2 or pH decrease the O2Hb binding and shift the curve to the left whereas decreasing CO2, temperature or pH increases O2Hb binding; shfiting the curve to the right?

2. Marieb says if the O2Hb bond is decreased it allowes for more offloading of O2 at the cellular level (presumably to meet some whacky defecit) now in theory, this would impair the ability of the HHb to take up O2?

3. CO2 enters the plasma by diffusion and binds to H20 to form H2CO3- (carbonic acid) and then the carbonic acid dissacociates, releasing H+ which increases pH. When this phenomina occurs in the CSF it causes the central chemoreceptors to activate and trigger breathing (yay for breathing) but why does the H2C03 disassociate to release the H+ ?

Whacky stuff this pulmonology .... much easier to say "air goes in and out" dont ya think?

Thanks

[NRPinNEPA]

I can't see the posted image, but does it look something like this?

H+ + HCO3 <-> H2CO3 <-> H2O + CO2

If so you're getting into the bicarbonate buffer system and acid-base balance.

Edited January 9, 2010 by EMTinNEPA

[Kiwiology]

H+ + HCO3 <-> H2CO3 <-> H2O + CO2

If so you're getting into the bicarbonate buffer system and acid-base balance.

Why, Why must every time I don't understand something must it come back to the bloody acid base system!

That's what it's supposed to look like for q. 1 and 2

[chbare]

So for fun, you know, as you do, I was reading my A&P book (what's that? what on earth is wrong with me? I know, I need help! ... but there was nothing good on TV or Netflix)

Now where somewhere along the way (perhaps on the way to Solla Sellew on Horton the Elephant) I got confoozle'd ...

Here is the diagram from Marieb 7e showing the effect of temperature, PCO2 and blood pH on the O2Hb dissociation curve.

I don't understand the trend here, this graph is bloody useless!

1. What I think it says is that increased temperature, PCO2 or pH decrease the O2Hb binding and shift the curve to the left whereas decreasing CO2, temperature or pH increases O2Hb binding; shfiting the curve to the right?

Increased temp, Increased CO2, and DECREASED PH causes a right shift. This causes hemoglobin to have a decreased affinity for oxygen and favors release of oxygen. In right shift extremes, hemoglobin may be hesitant to on load oxygen. You are correct.

2. Marieb says if the O2Hb bond is decreased it allowes for more offloading of O2 at the cellular level (presumably to meet some whacky defecit) now in theory, this would impair the ability of the HHb to take up O2?

Per above, you are correct that a right shift may impar on loading of oxygen.

3. CO2 enters the plasma by diffusion and binds to H20 to form H2CO3- (carbonic acid) and then the carbonic acid dissacociates, releasing H+ which increases pH. Decreases PH. When this phenomina occurs in the CSF it causes the central chemoreceptors to activate and trigger breathing (yay for breathing) but why does the H2C03 disassociate to release the H+ ?

This is very difficult to explain and JPINFV or one of the docs may be able to break it down; however, multiple factors play a role in H2CO3 decomposition in an aqueus environment. Factors such as electronegativity, pKa, Keq, amount of CO2 present, and other variables effect the decomposition of carbonic acid. In addition, the human body uses an enzyme carbonic anhydrase to catalyze this process, so it's even more complicated. Also, it helps to realise that when hydrogen ions dissociate, you really do not have a free proton running around for that long. Typically, the proton will associate its self with a water molecule due to the electronegativity of the oxygen to create the hydronium ion (H30+). You want to piss people off, be a smart ass and never use the term hydrogen ion (within the human body at least) and simply say hydronium ion instead.

Whacky stuff this pulmonology .... much easier to say "air goes in and out" dont ya think?

It's actually more chemistry than anything else, and it is complicated IMHO.

Thanks

Also remember these equations people spit out: H30 + HC03 <-> H2CO3 <-> H20 + CO2 & H20 + CO2 <-> H2CO3 <-> H30 + HCO3,

have a tendancy to form an equilibrium. Not equal parts, but no net change in reactant and product amount over time. Unfortunately, the human body is so dynamic that there is a constant struggle to maintain equilibrium. With that, something known as le chatelier's principle comes into play. Essentially, when you change any number of variables such as concentration of products, reactants or change temperature or pressure and you change the system, thus causing the system to attempt to re-establish equilibrium.

A simple example: Reactants = A & B, Product = C. Formula in equilibrium = A + B <-> C. Now, let's play: I increase the amount of reactant A, le chatelier's principle dictates the formula will shift to the right and make more of the product C in order to re=establish equilibrium. Likewise, adding product C will cause a left shift and production of more A & B in order to re-establish equilibrium. This can help explain what giving somebody bicarb can increase the CO2 levels. Clearly, a bit more complicated but a good start to understanding more than the simple formulas you learn.

Hope that helps.

Take care,

chbare.

[chbare]

I wanted to apologize as I realize that my prior post contains several typos. I was on shift and utilizing my iPhone. It's no excuse, but I wanted to address the errors.

Take care,

chbare.

[JPINFV]

First thing to note is that a catalyst only decreases the energy of activation (think energy needed to start a car vs energy needed to keep a car running. The energy needed to start a car is the energy of activation of the car). It can't make reactions happen that wouldn't happen otherwise. Granted, some reactions are so unfavorable that you wouldn't see it occur without the use of a catalyst, however "unlikely" and "unfavorable" are different than "won't."

Acids, in it's most basic form, are something that can donate a hydrogen ion (H+, proton). There are other definitions of acids, however things like Lewis acids and bases give me a headache. What allows the hydrogen ion to come loose from an acid is movement of electrons away from the hydrogen. Essentially (there are some caveats with electron pairing and all) all atoms want their outer most electron orbits to be completely full and this can be accomplished by either taking or donating electrons from other molecules (ionic bonding) or sharing electrons (covalent bonding). Donating works because if you can empty out all of the electrons from the outermost orbit, then it essentially ceases to become an orbit. The second to last orbit (which is, by definition, full) becomes the outermost orbit. This brings us to the periodic table of the elements.

For the purpose of this, ignore the dark blue middle area. The far right column (He (hydrogen), Ne (neon), etc) contains the Noble Gasses. All of these gasses have their orbits completely full of electrons making them nonreactive. The molecules on the right all need electrons to fill their orbits, so they attempt to take electrons from other molecules. On the other side, the molecules on the left all want to get rid of their electrons so that they can empty out their outermost orbit. This comprises the concept of electronegativity. The larger the difference between the electronegativity of two atoms, the more likely one is going to give up their electron to the other. When this happens, the atom giving up the electron becomes positively charged while the one receiving an electron becomes negatively charged. Positive and negative charges attract and we have an ionic bond. Also, since the is a negative and positive ions are bounded to each other, the net charge is zero. Partial charges is what causes molecules to be polar as well as causes phenomenons like hydrogen bonding.

This is important for acids because a molecule can be like a big game of tug-of-war. Let's say we have molecules A, B, and C. A is the most electronegative and C is the least electronegative. Let's further say that A bonds to B and B bonds to C (A-B-C). A can be pulling so hard on the electrons of around B that it can end up pulling on the electrons around C. Now instead of having the electrons somewhat centrally located, there are more electrons around A and less electrons around C. This gives A a partial negative charge and C a partial[b/] positive charge. If C donated electrons making the atom itself a positive ion, this can allow C to leave (dissociate) from the molecule, such as when a hydrogen ion leaves an acid.

So we combine H2O and CO2 to form carbonic acid.

Oxygen is only 2 spaces away from the noble gas column, so it's pretty electronegative. Hydrogen is on the furthest left column, so it wants to give away it's electrons. However, if you look towards the middle, there's another hydrogen atom that's double bonded to a carbon atom. It really wants those electrons too. So that middle oxygen pulls on the electrons on carbon, which results on carbon pulling electrons away from oxygen because carbon hates losing it's electrons (it's somewhere in the middle, so while it doesn't want to take from other atoms, it isn't going to give up electrons either without a fight). So the outer oxygens pull electrons even further from the hydrogen. This gives the hydrogen a partial positive charge and the oxygen a partial negative charge. The hydrogen ion is already positive, and now that it's bond is also a partial positive it decides to take off. The hydrogen enters the solution causing the pH to go down as the concentration of hydrogen (and H3O since hydrogen can readily leave H30)

Also remember these equations people spit out: H30 + HC03 <-> H2CO3 <-> H20 + CO2 & H20 + CO2 <-> H2CO3 <-> H30 + HCO3,

have a tendancy to form an equilibrium. Not equal parts, but no net change in reactant and product amount over time. Unfortunately, the human body is so dynamic that there is a constant struggle to maintain equilibrium. With that, something known as le chatelier's principle comes into play. Essentially, when you change any number of variables such as concentration of products, reactants or change temperature or pressure and you change the system, thus causing the system to attempt to re-establish equilibrium.

A simple example: Reactants = A & B, Product = C. Formula in equilibrium = A + B <-> C. Now, let's play: I increase the amount of reactant A, le chatelier's principle dictates the formula will shift to the right and make more of the product C in order to re=establish equilibrium. Likewise, adding product C will cause a left shift and production of more A & B in order to re-establish equilibrium. This can help explain what giving somebody bicarb can increase the CO2 levels. Clearly, a bit more complicated but a good start to understanding more than the simple formulas you learn.

Hope that helps.

Take care,

chbare.

Le Chantelier's principal. The basics of it's relatively simple. Let's say you have a balloon sitting on a table. The balloon is at equilibrium. Now imagine that you have a camera with a resolution high enough and frame rate high enough that you can see molecules moving around inside. Now you pick up the balloon and squeeze just one side of it. In real time, the part of the balloon not inside your hand bulges because the pressure inside the balloon increases (the pressure in the balloon inside your hand also increases, but the force on excreted by the pressure on the inside of your hand is transmitted through the balloon wall and into your hand). For all intents and purposes, this is instantaneous in real time. It's kinda of like turning on a light. We all know that light has a speed, however the speed is so great that turning on a light in a room makes it look like the light travels instantaneously through out the room.

So you have this camera and you're filming the molecules inside the balloon as you squeeze on a part of it. The instant that you squeeze you increase the pressure in that part of the balloon putting the air inside the balloon out of equilibrium. The air molecules start bumping up against each other and over time (instantly in real time, but we are looking in super duper slow motion) even the molecules the furthest away from your hand are now moving at the same increased speed. Equilibrium is restored until you move your hand. So if you change the conditions in one part of the balloon, you end up with a change in the entire balloon.

To transfer this to chemistry, if A+B<->E+F, if you "squeeze" the E+F side (e.g. add more of E, F, or both), the equation bulges at the A+B side as the reaction reverses until you reach equilibrium again. Now you can "squeeze" an equation by adding more of a product or reactant OR if a specific environment is preferential to one side (say A+B likes a positively charged solution) changing it to or away from that environment.

[chbare]

Thanks JPINFV!

I want to go a little off topic and focus on the concept of electronegativity. This single concept explains a large portion of the conceptual aspect of how chemistry effects acid base relationship. Clearly, electronegativity effects multiple important concepts such as molecular geometry as well. As stated, the more electronegative something is, the more it wants to pull on the electron. So, if you have an element with low electronegativity combined with an element of high electronegativity, the high element will have substantial pull on the electron/s of the low element. We typically measure electronegativity by the Pauling scale. It ranges from the lowest at 0.7 (Cesium), to the highest at 4 (Fluorine).

The following table sums up the electronegativity of the various elements:

I had to memorize this table in chemistry, but understanding it was the "ah-ha" moment for me regarding understanding concepts like polar and non-polar.

So, let's try it with regard to acid base concepts since that is more relevant to the topic at hand.

Let me give you a common acid hydrochloric acid (HCl). It is known as a strong acid because it gives up all of it's available hydrogen ions. What exactly makes HCl behave like an acid? Let's use electronegativity to explain.

H has a value of 2.1 and Cl has a value of 3. It is pretty obvious who is most electronegative. Therefore, the Cl has a very strong pull on the electron of hydrogen. The hydrogen nucleus (single proton) (AKA hydrogen ion) can easily leave in an aqueous solution because Cl pulls so strongly on the electron leaving behind a proton. Of course, the positive charge of the proton will then be attracted to other molecules with a negative or partial negative charge.

Electronegative concepts also help explain the concept of polar versus non polar. Take a molecule of water for example: H2O. The oxygen has a higher electronegativity and pulls on the electrons causing a partial negative charge of the oxygen and a partial positive charge on the hydrogen atoms. This difference in partial charge not only creates a characteristic shape, but makes the water molecule polar.

However, lets take two oxygen atoms covalently bound (O2). Well, oxygen is 3.5 and oxygen is 3.5. The difference is 0. You basically have equal sharing of electrons, and you have a non polar molecule.

Take care,

chbare.

[Kiwiology]

*Kiwi gets that glazed over look in his eyes ....

Looks like I have some reading up to do

[rock_shoes]

*Kiwi gets that glazed over look in his eyes ....

Looks like I have some reading up to do

At the very least you understand why so many of us encourage people to take university level chemistry on a regular basis. I don't have much to add to the chemistry lesson as the others have covered the required background pretty well. It does get much easier once you have the basics under your belt. Know, the different types of bonds (ionic, covalent, hydrogen bonds, etc.), the concept of electro-negativity, the octet rule, and most importantly that chemistry is actually governed by fairly simple rules. No matter how complicated an aspect of chemistry seems, it's actually fairly understandable if you break things down into their most basic parts.

While I will always suggest pursuing formal education on the subject, this site should help you get started.

Introduction to General Chemistry

[melclin]

Is this not high school chemistry in the states?

I sure hated it at the time (electron shell filling patterns and I did not get along) but I'm glad as hell I did it.