Which of the following is not true about the anatomy of the urinary system?

A. It increases both Na⁺ and K⁺ reabsorption. It increases both Na⁺ and K⁺ secretion: This contradicts the actual function. Aldosterone causes Na⁺ reabsorption and K⁺ secretion, not reabsorption of both.
B. It increases Na⁺ reabsorption and K⁺ secretion: Aldosterone acts on the distal tubules and collecting ducts of the nephron, causing sodium reabsorption (to increase blood volume/pressure) and potassium excretion.
C. It reduces Na⁺ reabsorption and K⁺ secretion: This is the opposite of aldosterone's action.
D. It causes the urine to be more diluted: Aldosterone causes sodium (and water) retention, leading to concentrated urine. Dilution of urine is more associated with ADH inhibition.

A. Posterior pituitary releases ADH: Dehydration increases blood osmolarity. This is sensed by hypothalamic osmoreceptors. In response, the hypothalamus signals the posterior pituitary to release antidiuretic hormone (ADH). ADH then acts on the distal convoluted tubules and collecting ducts of the kidney to promote water reabsorption, thereby concentrating the urine and reducing blood osmolarity.

B. Adrenal medulla releases aldosterone: Aldosterone is released from the adrenal cortex, not medulla, and is more responsive to low sodium or high potassium, not directly to osmolarity.

C. Kidneys release erythropoietin: Erythropoietin is released in response to hypoxia, not dehydration or osmolarity.

D. Anterior pituitary releases oxytocin: Oxytocin is released by the posterior pituitary, and it is not involved in osmolarity or water balance.

E. Adrenal cortex releases norepinephrine: Norepinephrine is released by the adrenal medulla, and is involved in fight-or-flight, not osmolarity regulation.