Final answer:
Juxtaglomerular cells of the afferent arteriole are modified smooth muscle cells involved in blood pressure regulation through renin secretion and response to blood osmolarity changes.
Step-by-step explanation:
The type of cells that make up the juxtaglomerular cells of the afferent arteriole are smooth muscle cells. These modified smooth muscle cells play a crucial role in regulating blood flow to the glomerulus and the renal blood pressure by secreting renin in response to changes in blood pressure. When the blood osmolarity is too high or too low, these cells can contract or relax accordingly, to decrease or increase the glomerular filtration rate (GFR). Additionally, they respond to signaling from the macula densa to release renin, which is involved in the renin-angiotensin system that increases blood pressure and regulates electrolyte balance.