What is osmoregulation and give an example in humans?

• A. Regulation of blood pH via breathing.
• B. Regulation of water and solute concentrations; kidneys maintain blood osmolarity.
• C. Regulation of body temperature.
• D. Movement of ions across neurons.

Answer: (B)

Osmoregulation is the control of water and solute balance in body fluids. In humans, the kidneys manage this by adjusting how much water and which solutes are reabsorbed or excreted in urine, keeping blood osmolarity fairly constant. A helpful example is how ADH (vasopressin) changes the kidneys’ water handling: when you’re dehydrated, ADH is released and makes the collecting ducts more permeable to water, so more water is reabsorbed and urine becomes concentrated, helping restore normal osmolarity; after drinking a lot of water, ADH levels drop, water reabsorption decreases, and urine becomes more dilute to bring osmolarity back down.

Other options don’t fit osmoregulation: regulating blood pH via breathing is about acid-base balance, not water and solute balance; regulating body temperature is thermoregulation; movement of ions across neurons is related to nerve signaling, not overall osmotic balance.