Homeostasis

The hypothalamus interprets the sensory input and determines the response. Choice A is wrong as this is negative feedback. The effector organs are the skeletal muscles (which are not a “pathway”).

Electrolytes such as sodium, potassium, chloride, bicarbonate, calcium, phosphate and magnesium ions have an upper and lower limit to their healthy concentrations in the body’s solutions. Electrolyte balance is the metabolic process that ensures that these ions are within their range. Electrolyte balance involves more than just the two ions in choice B, more than just preventing their loss in urine as in choice C, but does include urinary losses, which are missing from choice D.