Final answer:
Aldosterone and ADH are the hormones that cause kidneys to conserve fluid in response to conditions like gastroenteritis. Aldosterone increases sodium reabsorption while ADH increases water reabsorption in the kidney tubules.
Step-by-step explanation:
When a patient develops gastroenteritis and experiences frequent loose stools and reduces urine output, their body must conserve fluid to prevent dehydration. Two key hormones are involved in this conservation of fluid by the kidneys: aldosterone and antidiuretic hormone (ADH).
Aldosterone, released by the adrenal cortex, principally acts on the kidney tubules to promote reabsorption of sodium ions (Na+), which in turn leads to the reabsorption of water, thereby decreasing urine output and conserving fluid. It is regulated by the renin-angiotensin system and is released in response to lower blood pressure and lower blood sodium levels. ADH, also known as vasopressin, is secreted by the posterior pituitary gland and stimulates the insertion of water channels, known as aquaporins, into the cell membranes of kidney tubules, which increases water reabsorption. This action helps maintain blood volume and pressure.
The correct answer to the student's question is 1) Aldosterone and ADH, they cause the kidneys to conserve fluid by increasing sodium and water reabsorption.