Osmoreceptors in the hypothalamus monitor the osmotic concentration of the ECF and secrete _______ in response to higher osmotic concentrations. 
(a) BNP
(b) ANP
(c) aldosterone
(d) ADH

Verified step by step guidance

1. Understand the role of osmoreceptors: Osmoreceptors are specialized neurons located in the hypothalamus that detect changes in the osmotic concentration (osmolality) of the extracellular fluid (ECF). When the osmotic concentration increases, it indicates that the ECF is more concentrated, often due to dehydration or increased solute levels.
2. Recall the hormone secreted in response to increased osmotic concentration: The hypothalamus responds to high osmotic concentration by signaling the posterior pituitary gland to release a hormone that helps conserve water and restore balance.
3. Identify the hormone options given: BNP (B-type natriuretic peptide), ANP (atrial natriuretic peptide), aldosterone, and ADH (antidiuretic hormone).
4. Match the hormone function to the stimulus: BNP and ANP are involved in reducing blood volume and pressure by promoting sodium and water excretion. Aldosterone promotes sodium retention but is secreted by the adrenal cortex in response to different stimuli. ADH, also known as vasopressin, is secreted by the posterior pituitary in response to increased osmotic concentration to promote water reabsorption in the kidneys.
5. Conclude that the correct hormone secreted by osmoreceptors in response to higher osmotic concentration is ADH.

Key Concepts

Osmoreceptors and Osmoregulation

Osmoreceptors are specialized neurons in the hypothalamus that detect changes in the osmotic concentration of the extracellular fluid (ECF). When the ECF becomes more concentrated (hyperosmotic), these receptors trigger physiological responses to restore balance, such as hormone secretion to regulate water retention.

Antidiuretic Hormone (ADH) Function

ADH, also known as vasopressin, is a hormone secreted by the posterior pituitary in response to signals from osmoreceptors. It acts on the kidneys to increase water reabsorption, reducing urine output and diluting the blood plasma to lower osmotic concentration.

Distinction Between BNP, ANP, Aldosterone, and ADH

BNP and ANP are hormones involved in reducing blood volume and pressure by promoting sodium and water excretion. Aldosterone increases sodium retention to raise blood volume. ADH specifically responds to osmotic changes by controlling water retention, making it the correct hormone secreted in response to high osmotic concentration.