Three hormone loops on one kidney.

Three feedback loops on one body: osmoreceptors → ADH, low GFR → renin → angiotensin II → aldosterone, atrial stretch → ANF which opposes them; see urine volume, blood pressure and GFR respond.

After a blood loss, restore GFR to 125 mL/min with ANF switched on and off, and identify which loop ANF is fighting.

ADH makes more dilute urine; ANF works with renin–angiotensin.

• Kidney function is monitored and regulated by hormonal feedback involving the hypothalamus, the JGA and, to some extent, the heart.
• Osmoreceptors respond when blood volume, body fluid volume or ionic concentration changes. Losing too much fluid activates them; they act on the hypothalamus, and antidiuretic hormone (ADH), also called vasopressin, is released from the neurohypophysis.
• ADH makes water reabsorption easier in the later parts of the tubule, so it prevents diuresis. When body fluid volume rises, the osmoreceptors switch off and ADH release is suppressed, completing the feedback.
• ADH also constricts blood vessels, raising blood pressure; higher blood pressure increases glomerular blood flow and so GFR.
• A fall in glomerular blood flow, glomerular blood pressure or GFR activates the JG cells to release renin. Renin converts angiotensinogen in blood to angiotensin I, which is further converted to angiotensin II.
• Angiotensin II is a powerful vasoconstrictor, so it raises glomerular blood pressure and GFR. It also activates the adrenal cortex to release aldosterone.
• Aldosterone makes the distal parts of the tubule reabsorb more Na⁺ and water, which again raises blood pressure and GFR. This whole chain is the renin–angiotensin mechanism.
• More blood flowing into the atria of the heart can release Atrial Natriuretic Factor (ANF). ANF dilates blood vessels (vasodilation) and lowers blood pressure, so it acts as a check on the renin–angiotensin mechanism.

Teaching this idea? Put the simulation on your own page or LMS with this code.