pH and Buffers

H+ and OH-

I lied. Water or H2O actually exists as H+ cations and OH- anions. It’s as if Mickey Mouse here did a Van Gogh move and chopped its ear off. The ear, or the hydrogen leaves with its proton, but not with its electron. Remember that hydrogen’s electron is attracted to anything else but its corresponding proton. The OH part leaves with all the electronsNegatively charged subatomic particles found in atoms., making it an anionA negatively charged ion. because it has one extra electron.

H+ cations will be incredibly significant to use in this class because these are what the pH scale measures. pH is not a measurement of acidity, but a measurement of the ration of H+ cations to OH- anions. When they are in the proportion of twice as many hydrogen cations(H⁺): Protons that influence pH levels in body fluids. as OH- anions then we have waterThe universal solvent essential for life.. The problem is that your body make H+ cations all day long. No, it does not make the corresponding OH- anions, just the H+ cations. This tips that balance or proportion of H+ to OH- making the cations outweigh the anions. Since pH is a measurement of that proportion, the pH changes also.

pH

This is the pH scale. I want to point out that this is a man-made scale. We needed some way to quantify pH and this scale is it. The pH scale ranges from 0 to 14. The numbers indicate something about the proportion of H+ cations to OH- anions. In the pictures on the right, you can see that proportion of H+ cations and OH- anions. Let’s start at the mid-point of the pH scale, which is a pH of 7, or neutralA solution with a pH of 7. pH. This means that the numbers of H+ cations is equal to the number of OH- anions. No, 7 does not mean that there are 7 cations and 7 anions. In factA statement based on direct observation that is repeatedly confirmed. the 7 is the result of a logarithmic equation that we will not concern ourselves with here. Water is neutral. Blood is slightly higher than neutral and comes in at about 7.35 to 7.45.

Let’s move on to acidicA solution with a pH below 7, having a higher concentration of H⁺ ions. substances. These are substances that have a value lower than 7 on the pH scale. These substances have an excess of H+ cations compared to the OH- anions. These include orange juice and coffee. There are also non-consumables like battery acidA substance that releases hydrogen ions (H⁺) in solution., which has a pH close to that of your stomach. Oh, and heartburn is over-acidity of your stomach contents. As well as the burping up of those contents, but that’s for another lecture. I once had a student ask me what was the pH of the most acidic things on Earth. “0!” I proclaimed. But, then he asked what would happen if we discovered something more acidic than that. We’d rearrange the logarithmic equation so that the new substance was 0. He replied that was cheating. Yes, but that’s science – we have to adjust for new discoveries. If acidity means excess H+ cations, and you are making H+ cations all day long. Without making the corresponding OH- anions, then your blood is becoming acidic throughout the day. Your negative feedbackA control mechanism that reverses a change in the body to maintain homeostasis. mechanisms are reversing that change to keep your blood in the correct pH range. Complicating this is also the fact that carbon dioxide is acidic and you are making that all day long too. Your life is basically a big battle to keep from being acidic. Don’t worry, it’s not just humans that do this, it’s all living things.

We have a feel for acidity. It encompasses values on the pH scale and the proportion of H+ cations to OH- anions. You are drawn to that part of the pH scale. The values of 7 to 14 on the pH scale reflect alkalinity or basicA solution with a pH above 7, having a lower concentration of H⁺ ions. substances. Tums. Rolaids. What other heartburn meds can you think of? Oh, blue cheese to pair with those hot, spicy, and acidic wings. Powerful cleaners such as bleach and ammonia also fall at this range of the scale. We don’t deal with alkalinity in the human body nearly as much as we deal with acidity.

Sources of H+

Hydrogen ionsCharged atoms or molecules. (H⁺), or protons, are constantly produced during normal metabolic processes. You are always making hydrogen cations, which means that you are always going acidic throughout your day. Your life is a battle to be less acidic.

You create hydrogen cations in several ways. They form through the breakdown of proteinsLarge molecules made of amino acids with various functions in the body.. They also come from anaerobicprocess that does not use oxygen respirationThe process of gas exchange, including ventilation, external and internal respiration., from lipid metabolismThe sum of all chemical reactions in the body., and from the loading and transport of gases in internal respirationThe exchange of gases between the blood and body tissues.. It’s all about these hydrogen cations. Managing these will manage pH. During anaerobic respiration (e.g., during intense exercise), glucoseA simple sugar that is the main source of energy for cells. is broken down into lactic acid which releases H⁺ when it dissociates in blood. In starvation, untreated diabetes, or low-carb diets, the body breaks down fats for energyThe capacity to do work or cause change.. The liverA large organ that produces bile, detoxifies blood, and stores nutrients. converts fatty acids into ketone bodies which release H⁺ when they dissociate. When the body breaks down amino acids, nucleic acids, or phospholipids, it produces phosphoric acid (H₃PO₄). This acid quickly dissociates into hydrogen cations and phosphate groups.

So, there are many sources of hydrogen cations making your ECF pH go more acidic during the day. There are three mechanisms that counteract this tendency toward acidity: buffersSubstances that resist changes in pH. in your blood, respiratory mechanisms, and renal mechanisms. They are also used in that order. If the kidney has gotten involved, you are on thin ice. It doesn’t get involved in pH management unless the other two systems have been completely exhausted.

Blood Buffers

Thankfully, there are substances in your blood that are called buffers. Buffers resist a change in pH by absorbing the excess H+ cations or the excess OH- anions. If your blood is acidic, there are substances that can bond with the excess H+ cations, raising your blood’s pH. These are buffers. They help resist change. They also help bring it back into the correct range.

The bicarbonate(HCO₃⁻) – A crucial buffer in blood that helps maintain pH balance; formed when carbon dioxide anion is one that is important to know in this class. This is HCO3- and it is made using the carbon dioxide that your cellsThe basic structural and functional units of life. make in cellular respiration. You might also know of sodium(Na⁺): Major ECF cation; important for fluid balance, nerve function. bicarbonate which is baking soda. Bicarbonate is a blood buffer and has an almost limitless supply since you make it all day long. This is beneficial. You are making those acidic H+ cations all day long. The alkaline bicarb anion bonds with them. It removes their effect on your pH.
The body has three main mechanisms for buffering The process of stabilizing pH by binding or releasing H⁺ ions. pH changes in the blood: chemical buffers, respiratory adjustments, and urinary mechanisms. Chemical buffers act fast and are used first.

The protein buffer systemUses amino acid side chains to bind/release H⁺; important in ICF and plasma. is concerned with the loading and unloading of oxygen from hemoglobinThe oxygen-carrying protein in red blood cells that gives blood its red color.. In internal respiration, hemoglobin dropped of oxygen but also released a hydrogen cation in the process.

What happens if all the buffers in your blood are occupied, but you are still acidic? Your lungs and your kidneys also play a part in managing your pH. But, they don’t like to do anything unless the blood buffers are all exhausted. Remember I said that carbon dioxide is acidic? Well, if your blood is too acidic, your breathing rate will increase. It will try to blow off the carbon dioxide you are making. This process raises your pH. If your blood is too basic, your respiratory rate will decrease. Your body tries to hold in that acidic carbon dioxide. This action helps lower your pH. If the lungs aren’t able to effect the desired change, the kidney will take action. It will reluctantly manage those H+ for you.

Collecting Duct pH Management

Variable reabsorptionThe process of fluid moving back into capillaries from surrounding tissues due to colloid osmotic p and secretionThe process of moving substances from the blood into the nephron tubule to be excreted in urine. of hydrogen and bicarbonate ions contribute to pH homeostasisThe maintenance of a stable internal environment in the body. of the extracellular fluids, including blood. Thus far, you have seen two examples of acid-base regulation throughout the renal tubule and collecting system. The cells of the proximalCloser to the point of attachment or origin. tubule secrete hydrogen ions to reabsorb bicarbonate ions. The intercalated cells of the late distal tubule and collecting system actively secrete hydrogen ions under the influence of aldosteroneA hormone that increases sodium and water reabsorption in the kidneys, helping regulate blood pressu. Another mechanism in renal tubule cells is stimulated when the pH of the blood becomes abnormal.

If the pH of the blood decreases and becomes too acidic, enzymesProteins that speed up chemical reactions in the body. in the tubule cells will act. They remove the amino group (-NH2) from the amino acidThe building blocks of proteins, consisting of an amino group, carboxyl group, and side chain. glutamine in the cytosol. In doing this, the cells generate two ammonia moleculesGroups of atoms bonded together. (NH3) and two bicarbonate ions. The ammonia is then secreted, and the bicarbonate ions are reabsorbed. In the filtrateThe fluid that is filtered from the blood into the nephron and will eventually become urine., the ammonia molecules bind and buffer hydrogen ions to form the ammonium ion (NH4 +). Both ammonia buffering and bicarbonate ion reabsorption help to raise the pH of the blood back to normal. If the pH of the blood increases, making it too alkaline, the tubule cells will reabsorb fewer bicarbonate ions from the filtrate, excreting them in the urineThe liquid waste excreted by the kidneys. and lowering the pH of the blood