Correct Answer: D

Rationale: This is incorrect because the adrenal gland is not involved in the thirst mechanism. The adrenal gland is responsible for producing hormones such as cortisol, aldosterone, and adrenaline, which regulate stress response, blood pressure, and metabolism. This is incorrect because the cerebral cortex is not involved in the thirst mechanism. The cerebral cortex is the outer layer of the brain that is responsible for higher cognitive functions such as memory, language, and reasoning. This is incorrect because the pituitary gland is not directly involved in the thirst mechanism. The pituitary gland is a small gland at the base of the brain that produces hormones that control growth, reproduction, and metabolism. However, the pituitary gland does secrete antidiuretic hormone (ADH), which is regulated by the hypothalamus and affects water balance in the body. This is correct because the hypothalamus is the location of the thirst mechanism. The hypothalamus is a part of the brain that regulates many bodily functions such as temperature, appetite, sleep, and emotions. The hypothalamus also monitors the blood osmolarity and triggers the sensation of thirst when the blood is too concentrated.

Correct Answer: B

Rationale: This is incorrect because filtration is a passive transport mechanism that does not require cellular energy. Filtration is the movement of fluid and solutes across a membrane due to hydrostatic pressure. This is correct because active transport is a transport mechanism that requires cellular energy in the form of ATP. Active transport is the movement of molecules across a membrane against their concentration gradient, using carrier proteins. This is incorrect because diffusion is a passive transport mechanism that does not require cellular energy. Diffusion is the movement of molecules from an area of higher concentration to an area of lower concentration, until equilibrium is reached. This is incorrect because osmosis is a passive transport mechanism that does not require cellular energy. Osmosis is the movement of water across a semipermeable membrane from an area of lower solute concentration to an area of higher solute concentration.

Correct Answer: A

Rationale: Diffusion is the process by which small ions such as glucose, oxygen, and carbon dioxide redistribute themselves through semipermeable membranes from areas of higher concentration to areas of lower concentration. This is how these molecules move across the cell membrane and the capillary wall. Osmosis is the process by which water moves through semipermeable membranes from areas of lower solute concentration to areas of higher solute concentration. This is how water balance is maintained across the cell membrane and the capillary wall. Blood pressure is the force exerted by the blood on the walls of the blood vessels. It is not a process by which small ions redistribute themselves through semipermeable membranes, but rather a factor that influences the movement of fluids and solutes across the capillary wall. Rehydration is the process of restoring the fluid balance in the body by drinking fluids or receiving intravenous fluids. It is not a process by which small ions redistribute themselves through semipermeable membranes, but rather a treatment for dehydration.

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.

Correct Answer: D

Rationale: This is incorrect because sodium level of 145 mEq/L is within the normal range of 135 to 145 mEq/L. Sodium is not directly affected by respiratory alkalosis, but it may be altered by fluid balance or other conditions. This is incorrect because magnesium level of 1.3 mEq/L is within the normal range of 1.3 to 2.1 mEq/L. Magnesium is not directly affected by respiratory alkalosis, but it may be altered by renal function or other conditions. This is incorrect because phosphorus level of 3.0 mg/dL is within the normal range of 2.5 to 4.5 mg/dL. Phosphorus is not directly affected by respiratory alkalosis, but it may be altered by calcium balance or other conditions. This is correct because potassium level of 3.0 mEq/L is below the normal range of 3.5 to 5.0 mEq/L. Potassium is inversely related to hydrogen ions, which are decreased in respiratory alkalosis. As hydrogen ions move out of the cells to buffer the blood, potassium ions move into the cells to maintain electrical neutrality. This causes hypokalemia, or low potassium level.