Control of Respiration and Body Acid–Base Balance Help

Introduction to Respiration and Body Acid-Base Balance

The next logical question for the inquiring mind to consider is this: “Why do we breathe? What is the normal stimulus or goad that causes our diaphragm to contract, thereby resulting in inspiration?”

The answer is direct. The major stimulus for inspiration is a slight increase in the carbon dioxide (CO ₂ ) concentration and acidity (H ⁺ ion) level within our bloodstream. As Figure 18.5 (A) reveals, carbon dioxide produced from cell metabolism/respiration (Chapter 4) quickly reacts with H ₂ O within our erythrocytes. This reaction results in H ₂ CO ₃ as its product. H ₂ CO ₃ is the symbol for the chemical compound carbonic (car- BAH -nik) acid. The carbonic acid molecules quickly breakly down into hydrogen ions, symbolized as H ⁺, and bicarbonate (buy- CAR -buh-nut) ions, symbolized as .

Body Acids

Hydrogen (H ⁺ ) ions, and carbonic acid (H ₂ CO ₃ ) are both classified as body acids, substances that either donate hydrogen ions (such as H ₂ CO ₃ ) or that consist of hydrogen ions (such as a pool of H ⁺ ions, itself).

Normoventilation

During normoventilation ( NOR -moh-ven-tih- LAY -shun) – breathing at a “normal” rate and depth – the person exhales just enough CO ₂ to prevent acidosis ( AH -sih- DOH -sis). Acidosis is an “abnormal condition of” (-osis) too much body “acid.” Because the person exhales just enough CO ₂ , there isn’t time for too much CO ₂ to accumulate within the erythrocytes and build up too much carbonic acid, H ₂ CO ₃ , or H ⁺ ions. Acidosis, therefore, is presented, and a healthy state of acid-base balance is achieved.

Fig. 18.5 Respiration and body acid-base balance. (A) Body acid creation in RBCs. (B) Hyperventilation (“excessive” breathing). (C) Hypoventilation (“deficient” breathing).

Hyperventillation - Alkolosis and Acidosis

Hyperventilation And Alkalosis

“What happens to the body if you blow off too much CO ₂ ?” the curious reader may ponder. Blowing off or exhaling too much CO ₂ is what happens during hyperventilation ( HIGH -per-ven-tih- LAY -shun). Hyperventilation is the act of breathing at an “above normal or excessive” (hyper-) rate and depth for current metabolic conditions. A person under great and sudden stress, for example, may fall into a state of emotional hyperventilation. Since they are hysterically crying and sobbing, they are breathing too hard and fast for their current metabolic condition – a state of rest rather than exercise. When this person hyperventilates (Figure 18.5, B), too much CO ₂ is exhaled from the body. Thus, not enough CO ₂ is left to react with H ₂ O inside the erythrocytes. And there is not enough carbonic acid (H ₂ CO ₃ ) or hydrogen ion (H ⁺ ) produced.

The resulting state is alkalosis ( AL -kah- LOH -sis). Technically speaking, alkalosis is an “abnormal condition of” (-osis) not enough body acid, or too much base or alkali ( AK -kah- lye ). In general, a base or alkali is a H ⁺ ion acceptor. (Bases and alkali will be discussed in more detail, along with the digestive system, in Chapter 19.) If a person hyperventilates for too long, body acid levels fall way below their normal range, and a state of alkalosis follows. The person may well get dizzy and pass out.