Question

Which of the following is involved in the body’s primary blood-buffering mechanism? A. Fluid intake B. Absorption of nutrients in the gastrointestinal system C. Carbon dioxide produced from metabolism D. Reabsorption in the kidney

Short answer

C. Carbon dioxide produced from metabolism

Step-by-step solution

Understanding Blood-Buffering Mechanism

The blood-buffering mechanism is crucial for maintaining pH balance in the body. It primarily involves maintaining a stable pH despite changes in metabolism and intake of various substances.

Evaluating Each Option

Let's evaluate each provided option to see how it relates to the primary blood-buffering mechanism:A. Fluid intake affects blood volume but not directly pH balance.B. Absorption of nutrients impacts metabolism but doesn't directly buffer blood pH.C. Carbon dioxide (CO2) produced from metabolism forms an essential part of the bicarbonate buffer system to regulate pH.D. Reabsorption in the kidney helps in maintaining electrolyte balance and pH but is not the immediate buffer mechanism.

Identifying the Correct Answer

Given the options, the primary buffer mechanism involves the bicarbonate buffer system where CO2 combines with water to form carbonic acid, which then dissociates to bicarbonate and hydrogen ions:\[\text{CO}_2 + \text{H}_2\text{O} \rightleftharpoons \text{H}_2\text{CO}_3 \rightleftharpoons \text{H}^+ + \text{HCO}_3^- \]This system regulates pH swiftly and effectively.

Key concepts

Bicarbonate Buffer System

The bicarbonate buffer system is vital in regulating the pH of blood and other bodily fluids. It helps maintain a stable pH level by balancing the concentrations of carbonic acid (H₂CO₃) and bicarbonate ions (HCO₃⁻).

When CO₂ produced from metabolism enters the bloodstream, it reacts with water to form carbonic acid:
\[\text{CO}_2 + \text{H}_2\text{O} \rightleftharpoons \text{H}_2\text{CO}_3\]

Carbonic acid then dissociates into hydrogen ions (H⁺) and bicarbonate ions:
\[\text{H}_2\text{CO}_3 \rightleftharpoons \text{H}^+ + \text{HCO}_3^- \]

This reaction can move in both directions (reversible), allowing the body to add or remove H⁺ ions to keep the blood's pH within a narrow range.

If the pH drops (becomes acidic), the reaction shifts to remove excess H⁺ by forming carbonic acid. Conversely, if the pH rises (becoming more alkaline), carbonic acid dissociates to release H⁺ and lower the pH.

This buffering system works quickly, making it the primary regulator of pH in the blood.

Carbon Dioxide Metabolism

Carbon dioxide (CO₂) is a byproduct of cellular respiration, a process where cells generate energy from nutrients. When cells metabolize nutrients, CO₂ is produced and released into the bloodstream.

In the blood, CO₂ plays a crucial role in the bicarbonate buffer system. It reacts with water to form carbonic acid, contributing to pH regulation:
\[\text{CO}_2 + \text{H}_2\text{O} \rightleftharpoons \text{H}_2\text{CO}_3\]

The enzyme carbonic anhydrase, found in red blood cells, speeds up this reaction. As a result, CO₂ can be rapidly converted to and from carbonic acid and bicarbonate ions, facilitating pH balance.

This interaction helps transport CO₂ from tissues to the lungs, where it is exhaled. Properly functioning CO₂ metabolism is essential for maintaining the acid-base balance in the body.

pH Regulation

Maintaining the pH of blood and other bodily fluids is critical for proper cellular function. The normal pH range of blood is approximately 7.35-7.45. Deviations from this range can disrupt cellular processes and lead to serious health issues.

The body has several mechanisms to regulate pH:

• Bicarbonate Buffer System: This primary system quickly neutralizes excess acids or bases in the blood.
• Respiratory System: By adjusting the rate and depth of breathing, the body can control CO₂ levels. Hyperventilation decreases CO₂ (raising pH), while hypoventilation increases CO₂ (lowering pH).
• Renal System: The kidneys help maintain long-term pH balance by excreting or reabsorbing H⁺ and HCO₃⁻. This process is slower compared to the bicarbonate buffer system but is vital for sustained pH regulation.

A balance between these mechanisms ensures the body can effectively manage pH changes due to diet, metabolism, and environmental factors.

In summary, the bicarbonate buffer system, CO₂ metabolism, and the lungs and kidneys all interact to regulate pH and keep it within a healthy range.