What is the primary buffer system in the ECF?

Correct Answer: C

Rationale: The primary buffer system in the extracellular fluid (ECF) is the bicarbonate/carbonic acid system. This system helps maintain the pH of the blood within a narrow range by accepting or releasing hydrogen ions. Carbonic acid can donate hydrogen ions to lower pH, while bicarbonate can accept hydrogen ions to raise pH. Haemoglobin primarily functions as an oxygen transporter in the blood and does not play a significant role as a buffer in the ECF. Chloride/hydrochloric acid is more involved in the stomach's acidic environment and is not a primary buffer system in the ECF. Phosphate is a buffer system mainly found in the intracellular fluid and urine, not in the ECF. Therefore, option C is the correct answer as it is the primary buffer system in the ECF, while the other options are not as directly involved in maintaining the ECF pH balance.

Correct Answer: A

Rationale: The correct answer is A because sympathetic activity does not directly regulate renal secretion of H+. Sympathetic activity mainly affects blood flow and blood pressure regulation in the kidneys. In contrast, choices B, C, and D all describe factors that do influence the regulation of renal H+ secretion. B explains how respiratory dysfunction can trigger increased H+ secretion, C emphasizes the role of CO levels in determining H+ secretion, and D points out that elevated plasma [H+] leads to increased renal H+ secretion. Therefore, A is the only option that does not accurately describe how renal secretion of H+ is regulated.

Correct Answer: A

Rationale: Metabolic acidosis occurs when the body produces too much acid or fails to remove enough acid. Aspirin poisoning can lead to metabolic acidosis by increasing the production of lactic acid and impairing the kidney's ability to excrete acid. Severe vomiting and severe diarrhea can cause metabolic alkalosis due to loss of stomach acid or bicarbonate, respectively. Emphysema is associated with respiratory acidosis due to impaired gas exchange, not metabolic acidosis. Therefore, the correct answer is A (aspirin poisoning).

Correct Answer: D

Rationale: The correct answer is D (15/10). This ratio represents a decrease in bicarbonate (HCO3-) and an increase in carbonic acid (H2CO3), which indicates a respiratory acidosis condition. In respiratory acidosis, there is an accumulation of carbon dioxide (CO2) leading to increased carbonic acid formation. The other choices are incorrect because they do not reflect the appropriate changes in HCO3- and CO2 levels corresponding to respiratory acidosis. Choice A (40/1) and B (20/2) indicate alkalosis conditions with higher HCO3- levels, while choice C (20/5) suggests a normal ratio not reflective of an acid-base disorder.

Correct Answer: A

Rationale: Step 1: When the body synthesizes a more complex molecule, it often involves a series of chemical reactions that lead to the formation of the new molecule. Step 2: These reactions are typically energy-consuming and involve changes in molecular structures that cannot be easily reversed. Step 3: Once a substance is used in these irreversible reactions to form a more complex molecule, it cannot be restored to its original form. Step 4: Therefore, the statement that the process is irreversible and the original substance cannot be restored is true. Summary: Choice A is correct because the process of synthesizing a more complex molecule in the body involves irreversible reactions that permanently change the original substance. Choices B, C, and D are incorrect as they do not accurately describe the irreversible nature of this process.