Final answer:
Urine volume is indeed regulated by hormones from the posterior pituitary gland, specifically ADH, and the adrenal cortex, including aldosterone. These hormones control the water and salt balance, thus affecting urine volume.
Step-by-step explanation:
The statement that urine volume is regulated mainly by hormones secreted by the posterior lobe of the pituitary gland and by the adrenal cortex is true.
The key hormone involved in this regulation is antidiuretic hormone (ADH), also known as vasopressin, which is produced in the hypothalamus and stored and released by the posterior pituitary gland. ADH plays a crucial role in controlling the amount of water reabsorbed in the collecting ducts and tubules of the kidney.
The adrenal cortex contributes by secreting aldosterone, part of the renin-angiotensin-aldosterone system, which regulates sodium and water balance, thereby affecting urine volume.
When the osmoreceptors in the hypothalamus detect an increase in the concentration of blood plasma, they signal the release of ADH. This hormone then acts on the kidneys to make them more permeable to water, leading to an increase in water reabsorption and a decrease in urine volume to normalise blood osmolarity.
Conversely, when blood osmolarity decreases, less ADH is released, leading to less water reabsorption and an increase in urine volume. This homeostatic regulation ensures the maintenance of an optimal internal environment.