Problem 14 - Biology Today and Tomorrow with Physiology

Question

14\. Kidneys adjust the blood acidity by increasing or decreasing the of ___________ \(\mathrm{H}^{+}\) a. filtration b. reabsorption c. secretion d. both a and b

Step-by-Step Solution

Answer

The correct option is c. secretion.

Step 1: Understanding the Role of the Kidneys

The kidneys help maintain the balance of electrolytes, fluids, and blood acidity by filtering the blood, reabsorbing necessary substances, and secreting waste products. In this context, we are considering how the kidneys regulate blood acidity.

Step 2: Analyzing Blood Acidity Regulation

To regulate blood pH, the kidneys modulate the concentration of hydrogen ions (H extsuperscript{+}) in the blood. They lower blood acidity by secreting H extsuperscript{+} into the urine and increase acidity by reabsorbing H extsuperscript{+} back into the bloodstream.

Step 3: Choosing the Correct Option

The act of secreting H extsuperscript{+} into the urine is the kidney's primary method for decreasing blood acidity, justifying the role of secretion in adjusting blood H extsuperscript{+} concentration.

Step 4: Conclusion: Correct Answer

The correct answer is c. secretion, as it describes the process that directly involves modifying the blood's acidity through H extsuperscript{+} ion regulation.

Key Concepts

Blood Acidity Regulation

The human body needs to maintain a delicate pH balance to function correctly. The kidneys play a crucial role in keeping our blood pH within a narrow range, typically around 7.4.
The kidneys regulate blood acidity primarily through the modulation of hydrogen ions, denoted as \( \mathrm{H}^{+} \).
By managing the concentration of these ions, the kidneys can either increase or decrease the blood’s acidity. This regulation is necessary to prevent conditions that result from abnormal pH levels, such as acidosis or alkalosis.

• In acidosis, blood becomes too acidic, with a pH lower than 7.35.
• In alkalosis, blood is too alkaline, with a pH higher than 7.45.

Thus, through hormonal signals and direct action, the kidneys ensure the balance of these ions, affecting the blood's overall acidity.

Hydrogen Ion Secretion

Secretion of hydrogen ions is a key mechanism by which the kidneys regulate blood acidity. This process involves the active transport of \( \mathrm{H}^{+} \) ions from the blood into the renal tubules to be excreted out of the body through urine.
This mechanism lowers the blood's acidity levels since the expulsion of \( \mathrm{H}^{+} \) ions reduces the concentration of acid in the bloodstream.
Notably, the secretion process often promotes the reabsorption of bicarbonate, \( \mathrm{HCO}_3^- \), which acts as a buffering agent in blood.
This balance is achieved by:

• Actively transporting \( \mathrm{H}^{+} \) ions into the urine.
• Facilitating the conservation and reabsorption of bicarbonate ions back into the blood.

Such actions exemplify the kidney's remarkable ability to maintain homeostasis, underlining its crucial role in acid-base balance.

pH Balance in Blood

The pH balance in the blood is a measure of how acidic or alkaline it is. Normal blood pH levels need to remain tightly regulated because even a slight deviation can have significant effects on the body's metabolism and enzyme functions.
To achieve this pH balance, the kidneys work alongside the respiratory system to tightly control the levels of \( \mathrm{H}^{+} \) and bicarbonate ions in the bloodstream.
When the kidneys secrete excess \( \mathrm{H}^{+} \) ions, they help to prevent acidosis by removing excess acid. Conversely, when retaining bicarbonate ions, they aid in preventing alkalosis.
This intricate balance serves to:

• Maintain optimal enzymatic and cellular functions.
• Keep the blood pH around the optimal range of 7.35 to 7.45.
Through these functions, the kidneys ensure that the body's internal environment remains stable despite potential challenges posed by diet, metabolism, or disease.