Final answer:
Increased blood volume triggers a decrease in sympathetic activity in the heart and vasodilation of the renal arteries, which is detected by baroreceptors, leading to enhanced kidney filtration and maintenance of blood pressure.
Step-by-step explanation:
If blood volume increases, stretch receptors cause decreased sympathetic activity in the heart, and vasodilation of the renal arteries.
When blood pressure rises too high, the baroreceptors fire at a higher rate and trigger parasympathetic stimulation of the heart. As a result, cardiac output falls. Sympathetic stimulation of the peripheral arterioles will also decrease, resulting in vasodilation. These activities combined cause blood pressure to fall, which in the context of the kidneys, means increased blood flow due to the vasodilation of the afferent arterioles supplying the glomerulus, leading to an increased glomerular filtration rate (GFR) and water loss by the kidneys.
The kidneys are closely monitored by sympathetic nerves which, during increased blood pressure, reduce their activity. This reduction in sympathetic activity leads to relaxation and expansion of the renal arteries (vasodilation), which enhances filtration by allowing more blood to pass through the kidneys.