Correct Answer: D

Rationale: This is correct because prolonged bed rest can cause hypocalcemia, or low serum calcium level. Calcium is stored in the bones and is released into the blood when the bones are stressed by weight-bearing activities. When a person is on bed rest, the bones are not stimulated and the calcium remains in the bones, leading to a decrease in serum calcium level. This is incorrect because too much butter consumption does not affect the serum calcium level directly. Butter is a source of fat and calories, which can affect the cholesterol and triglyceride levels, but not the calcium level. However, too much butter consumption can cause obesity, which can increase the risk of osteoporosis and fractures. This is incorrect because hyperparathyroidism can cause hypercalcemia, or high serum calcium level. Hyperparathyroidism is a condition where the parathyroid glands produce too much parathyroid hormone (PTH), which regulates the calcium and phosphorus balance in the body. PTH stimulates the release of calcium from the bones into the blood, leading to an increase in serum calcium level. This is incorrect because excessive ingestion of vitamin D can also cause hypercalcemia, or high serum calcium level. Vitamin D is a fat-soluble vitamin that helps the body absorb calcium from the food and supplements. When a person takes too much vitamin D, the calcium absorption is increased and the serum calcium level rises.

Correct Answer: A

Rationale: Renal failure can cause hyperkalemia because the kidneys are unable to excrete excess potassium from the body. This can lead to high levels of potassium in the blood, which can affect the heart and muscles. Diarrhea can cause hypokalemia, not hyperkalemia, because it can lead to loss of potassium from the gastrointestinal tract. This can result in low levels of potassium in the blood, which can also affect the heart and muscles. Blood transfusion can cause hyperkalemia if the blood is old or hemolyzed, meaning that the red blood cells have broken down and released potassium into the plasma. This can increase the potassium levels in the recipient's blood. Diaphoresis, or sweating, can cause hypokalemia, not hyperkalemia, because it can lead to loss of potassium from the skin. This can also lower the potassium levels in the blood.

Correct Answer: C

Rationale: This is incorrect because this represents respiratory alkalosis, not acidosis. Respiratory alkalosis is characterized by a high pH and a low PCO2. This is incorrect because this represents a mixed disorder, not a pure respiratory acidosis. A mixed disorder occurs when both the pH and the PCO2 are abnormal, but in opposite directions. This is correct because this represents respiratory acidosis. Respiratory acidosis is characterized by a low pH and a high PCO2. This is incorrect because this represents normal values, not respiratory acidosis. Normal values for pH and PCO2 are 7.35 to 7.45 and 35 to 45 mmHg, respectively.

Correct Answer: A

Rationale: This is correct because an isotonic solution has equal solute concentration on both sides of a semipermeable membrane, resulting in no net movement of water.

Correct Answer: D

Rationale: Kidney function is not indicated by the PaCO2 level, but rather by the creatinine and blood urea nitrogen (BUN) levels. The kidneys are responsible for regulating the HCO3- level, which is the other component of the carbonic acid-bicarbonate buffer system. Bicarbonate buffers are not indicated by the PaCO2 level, but rather by the HCO3- level. Bicarbonate buffers are substances that can accept or donate hydrogen ions to maintain the pH of the blood. They are part of the carbonic acid-bicarbonate buffer system, which is the main buffer system in the body. Phosphate buffers are not indicated by the PaCO2 level, but rather by the PO4^3^- level. Phosphate buffers are substances that can accept or donate hydrogen ions to maintain the pH of the intracellular fluid and the urine. They are part of the phosphoric acid-phosphate buffer system, which is the second most important buffer system in the body. Lung ventilation is indicated by the PaCO2 level, which is the partial pressure of carbon dioxide in the blood. Lung ventilation is the process of moving air in and out of the lungs, which affects the amount of carbon dioxide exhaled. The lungs are responsible for regulating the PaCO2 level, which is the other component of the carbonic acid-bicarbonate buffer system.