Correct Answer: B
Explanation:
The enzyme renin is secreted by the afferent arterioles of the kidney from specialized cells called granular cells of the juxtaglomerular apparatus in response to three stimuli:
A decrease in arterial blood pressure (that could be related to a decrease in blood volume) as detected by baroreceptors (pressure-sensitive cells). This is the most direct causal link between blood pressure and renin secretion (the other two methods operate via longer pathways).
A decrease in sodium levels in the ultrafiltrate of the nephron. This flow is measured by the macula densa of the juxtaglomerular apparatus.
Sympathetic nervous system activity, which also controls blood pressure, acting through the beta1 adrenergic receptors.
Human renin is secreted by at least 2 cellular pathways: a constitutive pathway for the secretion of prorenin and a regulated pathway for the secretion of mature renin.