Under which of the following circumstances do the kidneys help the body retain fluid?

• A. When blood pressure is elevated
• B. When aldosterone levels are low
• C. When the body is in a state of overhydration
• D. When antidiuretic hormone (ADH) levels are high

Answer: (D)

Verified step by step guidance

1. Understand the role of the kidneys in fluid balance: The kidneys are responsible for filtering blood and maintaining fluid and electrolyte balance in the body. They adjust the amount of water excreted in urine based on the body's needs.
2. Learn about antidiuretic hormone (ADH): ADH, also known as vasopressin, is a hormone that helps the body retain water by signaling the kidneys to reabsorb more water back into the bloodstream, reducing urine output.
3. Identify the conditions under which ADH levels are high: ADH levels increase in response to dehydration or low blood volume, signaling the kidneys to conserve water to maintain homeostasis.
4. Analyze the given options: Evaluate each condition to determine if it would lead to increased ADH levels. Elevated blood pressure typically does not increase ADH, low aldosterone affects sodium balance rather than water directly, and overhydration would decrease ADH levels.
5. Conclude with the correct circumstance: High levels of ADH occur when the body needs to retain fluid, such as during dehydration or low blood volume, making 'When antidiuretic hormone (ADH) levels are high' the correct answer.