[011] Body acid-base reaction and carbon dioxide gas (GB#112C01) | 基礎医学教育研究会(KIKKEN)Lab

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Oxygen bonding is called “oxidation”, but “oxidation” and “acidity” are apparently different things. There are not many people who are convinced soon after being told so in Japan. Regarding the acidity and alkalinity of the blood that is sometimes talked about in the streets of Japan, there seems to be some people who think that blood will become acidic when sucking a lot of oxygen by repeating deep breaths. Actually, repeating a deep breath, the blood tends to be alkaline. People who think acidity as “the nature of oxygen” will not understand anything at all.
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● Oxygen does not become acidic

Is not it such a thing as a Japanese student who suffers from such a thing? Because in English, oxygen is oxigen, oxidation is oxidation, while acidity is acidity, acidification which is becoming a topic in recent years is acidification at all because words are different. In fact, if I thought that, oxygen in the West was named “acidic element” in the meaning. That’s right. Originally it is true that acidity was thought to be due to oxygen. Actually, however, oxygen was not an element of acid. Still, now in English, there is less confusion since the acid is given a different word from oxygen. In Japanese, acidity may be good even if it is said to be “vinegar”, but it is already late.。

● Acidity and alkalinity are determined by the concentration of hydrogen ions

The explanation of what acidity or alkalinity is, has become a difficult thing because it pursued a unified explanation that can be used in various industries in the chemical industry. However, in considering the physiology of the human body, the following classical explanation will be sufficient. It is because the liquid in the human body is an aqueous solution and the temperature is almost constant at body temperature.
Acid is a substance which shows acidity when solved alone in water. Acidity is not “oxygen” but hydrogen ion ( H⁺ ) of another cation has occurred and the concentration of H⁺ in water is increasing.

On the other hand, when dissolving in water together with an acid, a substance that reacts to produce a salt is called a base, and when a base is dissolved alone in water, it shows alkalinity. Therefore, alkalinity is also called “basic”. Alkaline (basic) is a state in which the concentration of hydroxide ion ( OH^– ) of anion occurs and is higher than that of hydrogen ion.
Both hydrogen ion and hydroxide ion are parts where water molecules ( H₂O ) are separated. Since the concentration of hydrogen ions in water decreases according to the increased amount of hydroxide ions, the degree of basicity can be determined by measuring the hydrogen ion concentration. The reason is that there is regularity that the hydrogen ion concentration and the hydroxide ion concentration are multiplied by “molar concentration (mol/L)” to be 10^-14 in the aqueous solution.

● Just right 4 to 25

When the concentration of hydrogen ions is expressed by pH, the optimal value of blood flowing in the body is said to be pH 7.40 ± 0.05. That is to say it ranges from pH 7.35 to pH 7.45. Neutral pH equals the concentration of hydrogen ion and hydroxide ion concentration in water is pH 7.0, which is basic when the value is larger, and acidity when the number becomes smaller from 7.0 will be learned in junior high school. Therefore blood is slightly inclined to the basic side rather than neutral, it is said to be weakly alkaline.

Although it is said to be “slightly”, the hydrogen ion concentration is 3.98 × 10^-8 mol/L and the hydroxide ion concentration is 25.1 × 10^-8 mol/L, its concentration ratio is 4:25, so that the hydrogen ion has only about one sixth of the hydroxide ion. At pH 7.35, which is the lower limit of the normal range, the hydrogen ion concentration rises to 4.47 × 10^-8 mol/L, which is approximately one-fifth of the hydroxide ion concentration 22.3 × 10^-8 mol/L. At the upper pH of 7.45, the hydrogen ion concentration drops to 3.55 × 10^-8 mol/L. This is one eighth of the oxide ion concentration (28.2 × 10^-8 mol/L). Although it seems that the numerical value is expressed in terms of pH, it seems to be slight change, but in terms of actual concentration it is quite a big difference as a condition of the environment in one fifth and one eighth. In terms of salt and sugar, the difference in delicate taste seems to come about. Except for a very temporary one, if the state of blood falls out of this normal range, it indicates that the condition of the body is bad regardless of the cause or result, and it will not be unreasonable to die if it is badly deviated .

● Acid substance in the body

When hydrogen chloride (HCl) dissolves in water, it dissociates into H⁺ and Cl^– and generates H⁺. So this is acid. An aqueous solution of hydrogen chloride is called hydrochloric acid.
Sodium hydroxide (NaOH) is a base because it produces a salt of sodium chloride by reaction with HCl of acid in water, resulting in HCl + NaOH → NaCl + H₂O. When solved alone in water, it dissociates as NaOH → Na ⁺ + OH^– and increases the hydroxide ion, so it shows alkalinity.
When hydrochloric acid dissociates, chlorine ion Cl^– of anion occurs, and when sodium hydroxide dissociates, sodium ion Na⁺ of cation is formed. However, chlorine ions and sodium ions are not directly related to “acidity/alkalinity”. In at least the aqueous solution, the ratio of hydrogen ion and hydroxide ion determines “acidic/alkaline”.

Also, acidic and alkaline and so on are said to be the nature of the aqueous solution when dissolved in water, so it is not necessarily just what hydrogen ions or hydroxide ions come out of the substance before it is dissolved in water. It is also possible to take OH^– by depriving H⁺ from water molecules (H₂O). So whether various substances in the world become acidic or alkaline, whether acidity is strong or weak, etc. depends on the constituent elements and the nature of the structure. Therefore, it is almost impossible to judge only by the chemical formula of a substance unless it is an expert who studied to a certain extent. After all, amateurs have to study the nature of each substance to know steadily.
In the physiology of school there are only a few substances that need to study acidic and alkaline mechanisms. Hydrogen ion ( H⁺ ) and bicarbonate ion ( HCO₃^– ), bicarbonate ion ( H₂CO₃ ), and so on.
Besides, textbooks come with many names of acids, amino acid, lactic acid, fatty acid, hydrochloric acid, phosphoric acid. However, these substances, whether it is or not, are important, but they rarely matter the acidity and alkalinity of the substances. So do not worry.
　

● Carbon dioxide occurs in large quantities

Carbonic acid is considered to be the most metabolic product occurring in the body. Each of the cells making the body respirates and generates carbon dioxide (CO₂). Carbon dioxide is a gaseous substance generated from carbonic acid, so “carbonic acid” is not a gas as it is, so this name also sometimes confuses amateurs in Japan. By the way, “san” of tan-san-gus (carbon deoxide gus) is acid, but “san” of ni-sanka-tanso (CO₂) should be oxigen, so it gets more and more bumpy.
Carbon dioxide reacts with water molecules and becomes carbonic acid. Part of the carbonic acid (H₂CO₃) is separated in water to bicarbonate ion HCO₃^– and hydrogen ion. Because it produces hydrogen ions, it is acid.

CO₂ ＋ H₂O　→　H₂CO₃
　　　　　　　H₂CO₃　→　HCO₃^－ ＋ Ｈ^＋

It is necessary to carry carbon dioxide gas (CO₂) generated in large quantities in the body, but in the state of gas only one tenth of the amount generated can be dissolved in water. For this reason, most of them are carry on in the form of bicarbonate ions (HCO₃^–) that are sufficiently soluble in water, with the help of a special enzyme called “carbonic anhydrase”. At that time, hydrogen ions (H⁺) are generated, so that the blood becomes acidic when left alone. Advantageously, however, there is a mechanism to temporarily hide this hydrogen ion in another form. When reaching the lungs, this H⁺ is also converted back into bicarbonate ions to carbonate. Carbonic acid is divided into water and carbon dioxide gas, carbon dioxide gas is mixed with exhaling air and thrown away.

HCO₃^－ ＋ H^＋　→　H₂CO₃
　　　　　　　H₂CO₃ →　H₂O　＋ CO₂↑

Hydrogen ions generated by the carbon dioxide gas exhaled by the cells eventually become zero and do not make the body acid.
So, why does blood tend to alkaline when repeating a deep breath? When you breathe excessively, carbonic acid gas is spilled excessively. Then, the hydrogen ion is unnecessarily cleaned up accordingly. Hydroxide ions increase as hydrogen ions decrease. This is leaning to alkalinity. Oxygen did not matter.

※ Although it is slightly confusing about carbonate, “carbonated water” shows weak acidity while “sodium carbonate” has the word “acid” in Japan, but its aqueous solution is not acidic and weakly alkaline.

※ red ● indicates where carbonic anhydrase is working, but not very strict. It’s a rough guide.

○ Referenced sites

・Etymology of oxygen ⇒ Chie-no-izumi Wiki oxygen Last-modified: 2006-07-16 (Sun)
・Etymology of hydrochloric acid ⇒ On the Origin of the Name of “Hydrochloric Acid” and “Chlorine” from “舎密開宗”(pdf)
・Properties of hot spring chemical / aqueous solution ⇒
5 Chemistry of hot spring 5-2 Properties of aqueous solution (1) Dissolution and ion
・The sodium carbonate solution will become basic ⇒ A basic foundation

・When you want to know more about acid-base equilibrium, ⇒ Medicine of lipids and thrombosis
・What is pH? Hydrogen ion concentration

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○ Referenced books

・細胞の分子生物学， ニュートンプレス; 第5版 (2010/01)
・カラー図解 人体の正常構造と機能 全10巻縮刷版，坂井 建雄，日本医事新報社
・人体機能生理学，杉 晴夫，南江堂
・トートラ人体解剖生理学　原書8版，丸善
・イラスト解剖学，松村 讓兒，中外医学社
・柔道整復学校協会編「生理学」，南江堂
・東洋療法学校協会編「生理学」，医歯薬出版株式会社

rev.20160507，rev.20160717，rev.20161220，rev.20170126，rev.20170502, rev.20180503.