Final answer:
The hormone that decreases urine output by making the collecting tubules permeable to water is antidiuretic hormone (ADH), which helps conserve water and maintain blood pressure.
Step-by-step explanation:
The hormone that decreases the amount of urine by making the collecting tubules permeable to water is antidiuretic hormone (ADH), also known as vasopressin. This hormone is produced by the hypothalamus and released from the posterior pituitary gland.
ADH regulates water balance in the body by making collecting ducts in the kidneys permeable to water, which facilitates water reabsorption and decreases urine volume. This is an essential process for maintaining blood pressure and plasma osmolarity, particularly in situations of dehydration or physiological stress where water retention is necessary.