Diurnal variation in urine excretion is primarily influenced by which hormone?

Diurnal variation in urine excretion is primarily influenced by vasopressin, also known as antidiuretic hormone (ADH). This hormone plays a crucial role in regulating the body's water balance. It is secreted by the posterior pituitary gland in response to changes in plasma osmolality and blood volume.

During the night, vasopressin secretion increases, leading to concentrated urine production and reduced urine volume. In contrast, during the day, vasopressin levels drop, resulting in more diluted urine and increased urine output. This hormone ensures that the body conserves water during sleep and allows for greater excretion during waking hours, which reflects the body's natural circadian rhythm.

The other hormones mentioned do not have a direct and significant impact on the diurnal variation of urine excretion. Insulin primarily regulates glucose metabolism, glucagon helps raise blood glucose levels, and thyroid hormone influences metabolism and growth but does not play a pivotal role in the regulation of urine volume based on the time of day.