Balancing Act

Well it’s about time! pH balance is fascinating stuff. I guarantee this is one of the spiciest topics yet..3 peppers, Scout’s honor (was never a boy scout). We just can’t rap about physiology without giving a shot out to our body’s mad acid/base buffering skillz. Party people throw your hands up…if you want to, and stay tuned.

makes my back sore just looking at her

makes my back sore just looking at her

That’s right my friends we’re talking about acids and bases today! DJ, turn the music up because we’re about to get all the way down. The body loves to stay in balance…oh wait, that is a painfully broad statement isn’t it? Put a different way, if there is one thing the body HATES it’s being out of balance. In this case we’re talking about pH. If you don’t remember basic chemistry 101 or never had it (consider yourself lucky), pH deals with acids and bases, and that whole pH scale, which measures hydrogen ions (H+ ions vs OH ions) in a solution. The presence and concentration of those ions give substances distinct chemical characteristics…the neutral, harmless purr of a glass of milk or the flesh eating burn of battery acid. The scale has a range of 0 to 14 with 7 being neutral. So pure water kept close to room temperature would measure at about 7 and something like orange juice with a pH of 3 would be lower on the scale and thus more acidic. Basic, or alkaline substances would be higher in pH, as in higher than 7.

man, this diagram is about as exciting as an unsalted, stale pretzel but you get the point

man, this diagram is about as exciting as an unsalted, stale pretzel but you get the point

And here’s the Respiratory part of it…

So… I’m sorry to be the one to tell you this but…your cells produce volatile acid. Yeah, they’ve been doing it while you weren’t looking this entire time. Feel a little betrayed? Hey, I’m here for you. Of course, by that I mean that they produce waste in the form of CO2 (the byproduct of aerobic metabolism). That dirty ole CO2, in the presence of water, which is basically everywhere, produces H2CO3 (AKA carbonic acid which gives soft drinks that snappy fizz that burns oh so good) and your cells do this 24hrs a day 365 days a year no smoke breaks, no sick days, no time off for good behavior. Now these sneaky substances will begin to build up, alter your pH balance, and cause all manner of unhipness unless they are buffered or purged from our bodies(good word right? I may not do drugs but I am hooked on phonics). Typically since it is a volatile substance it can be released by the lungs to be set free into the atmosphere (about 15,000 mmol/day). CO2 produced by tissue cells diffuses into red blood cells. RBC’s are armed with carbonic anhydrase [every time you see the ending -ase think enzyme of course] which facilitates this fun little reaction where the wandering CO2 combines with H2O to form H+ & HCO3 and that equation, if you’re nerdy (awesome) like me and just have to know, looks like this…

[CO2 + H2O –>H2CO3 –>H+ + HCO3]

That nasty ole CO2 can now leave the red cell to be transported to the lungs in the plasma as HCO3, what the cool kids (scientists) call carbonate. The lonely H+ also gets buffered by the red cells. Now that the HCO3 has reached the lungs it will re-enter the reds and be reversibly converted back into CO2 & water by that same carbonic anhydrase. That nasty ole CO2 can now diffuse into the lung alveoli to be exhaled, released into the atmosphere like pigeons at a magic show (come on, the kid in you wants to smile).

Why does the CO2 need to be converted into carbonate in the first place if it’s just going to be converted right back into CO2? CO2 is crazy reactive and we don’t want it binding with any ole molecule willy nilly while it’s exposed in our plasma. Also, the hemaglobin protein in our red cells binds both oygen and CO2. Increased intake of CO2 results in that whole carbonic acid business whenever the CO2 makes contact with the water in our plasma which means more H+ ions will be released into the blood which, as we mentioned before, are the heart and soul of acidity in the first place.

Hey, slow down Speed Racer, where are you going? There’s more to this story…

You see that was just how our body rids itself of the CO2/volatile compounds. Cellular metabolism also produces NON-volatile acids that require a little more metabolic gynastics from our bodies(salicyclic acid, lactic acid, ketoacids). Now it is our kidneys that come into play here adding that vital buffering, “make it all better” compound, HCO3 back into the plasma so that the volatile acids can dissociate with it. So if I can take you back to chemistry 101 for a minute, pretty much all of your acidic substances H2SO4, H2PO4, etc. are going to have their hydrogen ions dissociate in water. Now that H+ can be coerced away by that molecular smooth talker HCO3 yet again, leaving the other nasty bits (technical term) to be excreted in the urine. Meanwhile the H+ joins with our HCO3 in the very same reaction we chatted about before by the very same carbonic anhydrase which frees up the CO2 again, to be released into the lungs…again.

Acidosis – reminds me of a Pink Floyd Album

considered making a drug reference here...but let's not ruin the magic

considered making a drug reference here…but let’s not ruin the magic

Many physiology texts will differentiate respiratory acid/base balance from metabolic even though they both ultimately involve the lungs at some point as a final purging step for CO2. That’s mostly due to the fact that when things go out of wack with your pH balance it is linked to either a respiratory or metabolic(kidney) impairment. The two main routes our body takes to compensate for pH is by respiring CO2 through the lungs and by excreting acidic wastes in the urine via the kidneys.

There is a considerably narrow pH range that healthy human blood tends to stay within, 7.35-7.45. When the blood pH drops below this range cellular damage can occur. So here’s the thing, we have all these fancy pants enzymes and protein complexes that make all the necessary biochemical reactions in our cells possible. Every single one of these enzymes and biochemical pathways have temperatures and pH ranges where they function best or not at all. Think of the bloodstream as an environment or habitat for our living cells.That habitat has to be maintained or those cells will cease to thrive.

Respiratory Acidosis – when CO2 attacks..

just think candy bar wrappers in the backseat and this image totally works

just think candy bar wrappers in the backseat and this image totally works

With respiratory acidosis if you are hypoventilating for some reason (not getting enough oxygen and not expelling enough CO2) the CO2 will build up in the blood (hypercapnea) like so many candybar wrappers in the backseat of a subaru packed with roadtripping Spring Breakers. The kidneys will typically look out for us, compensating with increased secretion of all that stray H+ (which is awful nice). The H+ will eventually be excreted in the urine as H2PO4 after it combines with some HPO4 that I suppose was just hanging out in the nephrons (tiny functional units) of the kidneys. The kidneys will also add HCO3 back into the plasma to buffer CO2 another day. You just gotta love those kidneys…maybe you should send a thank you note.

A number of things can lead to respiratory acidosis, but primarily anything that impairs ventilation like drugs (opiates, anesthetics, powerful sedatives), or cardiopulmonary disease can have adverse effects on your body’s respiratory buffering system.

Metabolic Acidosis – Respect the Kidneys

Hey, remember when I was rambling earlier about how the kidneys feed bicarbonate (HOC3) back into the bloodstream to help manage pH? (it was a good story and you really enjoyed it) Well when you have metabolic acidosis you are basically experiencing a significant decrease in plasma HCO3. So in this situation your blood is becoming more acidic because Its ability to buffer acids has been compromised in some way. This can occur in renal failure, lactic acidosis (the build up of lactate through anaerobic cell metabolism), uremia, and from toxins among other things. This can often result in hyperventilation as you gasp to bring in more oxygen into the lungs. The kidneys begin to compensate for this by secreting more Hin order to be evacuated in the urine in the form of H2PO4.

Now you’re probably saying “Whoa now, if the blood can become too acidic can’t it also become too alkaline? That’s when I give you this stunned look like “Wow, what a great question” to which I would reply…

“But that does happen..and there’s definately more to it…”

Sorry, just not in this article. Are you kidding, look how long this thing is already, but stay tuned for part II where we’ll get into Alkalosis. I promise it’ll be loaded with physiology goodness. Stay curious, stay classy, and never stop learning my friends 🙂

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