Question

The kidneys help to maintain acid-base balance by a. the secretion of \(\mathrm{H}^{+}\)in the distal regions of the nephron. b. the action of carbonic anhydrase within the apical plasma membranes. c. the action of carbonic anhydrase within the cytoplasm of the tubule cells. d. the buffering action of phosphates and ammonia in the urine. e. all of these means.

Short answer

The kidneys maintain acid-base balance by utilizing all of the mentioned mechanisms: secretion of \(H^{+}\) in the distal regions of the nephron, action of carbonic anhydrase within the apical plasma membranes and the cytoplasm of tubule cells, and the buffering action of phosphates and ammonia in the urine. Therefore, the answer is "e. all of these means."

Step-by-step solution

Understanding kidney's role in regulating acid-base balance

Kidneys play a crucial role in maintaining the acid-base balance in our bodies. They have the ability to excrete acidic or basic urine, depending on the body's requirements. This is accomplished by either reabsorbing bicarbonates or secreting hydrogen ions (\(H^{+}\)) in the nephrons.

Understanding the secretion of \(H^{+}\)

The cells in our kidney's nephrons have the ability to secrete \(H^{+}\) in the distal parts of the nephron. This process is critical as it helps eliminate excess acids from our body.

Understanding the role of carbonic anhydrase

Carbonic anhydrase is an enzyme found within the apical plasma membranes and the cytoplasm of tubule cells in the kidneys. Its primary function is to catalyze the conversion of carbon dioxide and water into carbonic acid, which then dissociates to produce bicarbonate and \(H^{+}\).

Understanding the buffering action of phosphates and ammonia

Phosphates and ammonia in the urine act as buffers, meaning they can absorb \(H^{+}\) to prevent its concentration from increasing excessively. This is another way by which kidneys manage the body's acid-base balance.

Conclusion

Based on these biological facts about kidney function and acid-base balance, the answer to the given exercise is "e. all of these means". This signifies that all the mechanisms referred to in the options (secretion of \(H^{+}\) in nephrons, intra- and extra-cellular activity of carbonic anhydrase, and the buffering action of urine phosphates and ammonia) are indeed utilized by the kidneys to maintain the body's acid-base balance.

Key concepts

Acid-Base Balance

The kidneys are an essential part of maintaining the acid-base balance in our body. This balance is crucial because it ensures that our body's pH levels stay within a narrow range, crucial for the proper functioning of various physiological processes. When the body becomes too acidic or too basic, it can hinder cellular functions and metabolic processes.

The kidneys control this balance by adjusting the pH of the blood through the reabsorption or excretion of hydrogen ions ( H^{+} ) and bicarbonate ions ( HCO_3^- ). When the blood is too acidic, kidneys will excrete more hydrogen ions and reabsorb bicarbonate. Conversely, if the blood is too basic, they might reabsorb hydrogen ions and excrete bicarbonate.

This dynamic process ensures the body's internal environment remains stable, facilitating key biological functions.

Hydrogen Ion Secretion

Hydrogen ion secretion is a vital process that takes place primarily in the distal regions of the nephrons in the kidneys. This process is indispensable in regulating the excess acid in our body.

Here's how it works:

• A specialized group of cells in the distal nephron segment actively secrete hydrogen ions into the tubular fluid.
• This allows for the precise elimination of acids from the body, adjusting to the body's varying needs.
• It's a mechanism that directly contributes to the acid-base balance by lowering acidic concentrations in the blood.

This hydrogen ion secretion is crucial in ensuring that bodily fluids remain within a healthy pH range, safeguarding overall bodily functions.

Carbonic Anhydrase

Carbonic anhydrase is an enzyme that plays a central role in handling the body's acid and base levels, especially in the kidneys. This enzyme is located in several kidney locations, including the apical plasma membranes and the cytoplasm of tubule cells.

The remarkable role of carbonic anhydrase includes:

• It facilitates the rapid conversion of carbon dioxide (CO₂) and water (H₂O) to carbonic acid (H₂CO₃) within kidney cells.
• Carbonic acid then quickly dissociates into bicarbonate ( HCO_3^- ) and hydrogen ions ( H^{+} ).
• Through this reaction, carbonic anhydrase helps regulate the pH level by influencing the levels of bicarbonate and H^{+} in the bloodstream.

This enzymatic action is vital for both the excretion of acids and the recapturing of bicarbonate, supporting the larger goal of maintaining a stable internal pH.

Urinary Buffers

Urinary buffers like phosphates and ammonia have key roles in managing the body's acid load. They play special roles by absorbing excess hydrogen ions ( H^{+} ) in the urine, crucially modulating the pH level within the urinary tract.

Here's the breakdown:

• Phosphate ions ( HPO_4^{2-} ) present in urine can combine with free hydrogen ions to form dihydrogen phosphate ( H_2PO_4^{-} ), which is then excreted.
• Ammonia ( NH_3 ), derived from amino acids, can also bind with hydrogen ions to form ammonium ( NH_4^+ ), trapping hydrogen ions in urine.

By utilizing these buffers, the kidneys effectively handle large amounts of hydrogen ions without significantly altering the urine's pH. This strategy not only helps in eliminating excess acids safely but also in safeguarding the delicate balance of our body's acid-base status.