Which hormone is released in response to low blood sodium levels?

The hormone released in response to low blood sodium levels is aldosterone. This steroid hormone, produced by the adrenal cortex, plays a critical role in regulating the body's electrolyte balance, particularly sodium and potassium. When blood sodium levels are low, aldosterone secretion increases in order to enhance reabsorption of sodium from the urine back into the bloodstream, thereby helping to elevate sodium levels. This mechanism also aids in retaining water and maintaining blood pressure.

Conversely, insulin is primarily involved in glucose metabolism, cortisol is connected to stress responses and metabolism, and parathyroid hormone mainly regulates calcium levels in the body. These hormones do not directly respond to low sodium levels, which emphasizes the specific role aldosterone plays in electrolyte homeostasis.