[Campbell Biology P.1043] A person experiences an increase in blood osmolarity above the norm... | Practice Question

A person experiences an increase in blood osmolarity above the normal range e.g., after eating salty food or profuse sweating . Which of the following accurately describes the body's homeostatic response, according to the provided text and Figure 44.19?

  • A: Osmoreceptors in the hypothalamus trigger ADH release from the anterior pituitary, leading to decreased water reabsorption.
  • B: Osmoreceptors in the hypothalamus monitor blood osmolarity and, when it rises, trigger ADH release from the posterior pituitary; thirst is generated, and water reabsorption in the collecting duct increases, all working to restore normal blood osmolarity.
  • C: The kidneys respond by producing large volumes of hypoosmotic urine to quickly excrete excess solutes and water.
  • D: ADH secretion is inhibited, leading to increased urine volume and further reduction of blood osmolarity.

Explanation

When blood osmolarity rises, osmoreceptors in the hypothalamus detect this change. They then trigger two main responses: increased release of ADH from the posterior pituitary and the generation of thirst. ADH promotes water reabsorption in the kidney's collecting ducts, and drinking water due to thirst directly reduces blood osmolarity. Both actions work synergistically to restore blood osmolarity to its normal range 275-295 mOsm/L , thereby completing the negative feedback loop and inhibiting further ADH secretion.