RCIS Practice Test 2026 – All-in-One Exam Prep

The correct choice, indicating that all the listed organ systems do not cause changes in pH, reflects an understanding of how these systems interact with the body's acid-base balance.

The gastrointestinal and endocrine systems play a crucial role in digestion and metabolism, which can influence pH levels indirectly through the absorption and secretion of various substances. For example, digestive enzymes and gastric secretions can affect acidity but aren't primarily responsible for long-term pH regulation.

The heart and vascular systems primarily focus on the circulation of blood and do not directly regulate pH. Their main function is to transport oxygen and nutrients, with acid-base balance being a secondary effect of metabolic processes.

The kidneys and lungs are vital in maintaining acid-base homeostasis through the excretion of hydrogen ions and the regulation of bicarbonate reabsorption (by kidneys) and carbon dioxide elimination (by lungs). They play a direct and significant role in regulating blood pH. Therefore, they are not included as systems that do not cause changes in pH.

While each system has its unique functions, their primary roles are not about directly causing changes in pH. This understanding validates the answer, as none of the mentioned organ systems are primarily responsible for acid-base regulation in the immediate sense.