Final answer:
Aldosterone is the steroid hormone released in response to low blood sodium or high blood potassium, leading to increased sodium reabsorption and potassium secretion in the kidneys, which is vital for osmotic and electrolyte balance.
Step-by-step explanation:
The Steroid Hormone for Electrolyte Balance
The steroid hormone secreted in response to decreased blood sodium (Na⁺) or increased blood potassium (K⁺) is aldosterone. Aldosterone is a type of mineralocorticoid produced in the adrenal cortex that plays a crucial role in regulating the balance of these electrolytes. When blood sodium levels decrease or blood potassium levels increase, aldosterone is released, prompting the renal tubules to reabsorb more sodium and secrete more potassium. This aids in maintaining an osmotic balance, as water follows the reabsorbed sodium, thus managing both fluid and electrolyte levels in the body. In cases such as Addison's disease, where aldosterone production is deficient, there is a risk of fatal sodium loss and elevated potassium levels in the blood.
The mechanism of action of aldosterone involves the regulation of gene expression that leads to the synthesis of proteins responsible for the active transport of sodium and the passive excretion of potassium in kidney tubules, thereby directly affecting the body's fluid and electrolyte balance.