Final answer:
Angiotensin II increases renal vascular resistance by constricting the glomerular arterioles, aids in blood pressure regulation by reducing GFR and renal blood flow, and promotes fluid retention by stimulating aldosterone and ADH release.
Step-by-step explanation:
Angiotensin II is a potent vasoconstrictor involved in the regulation of blood pressure and renal function. It acts by constricting the blood vessels, including the afferent and efferent arterioles of the glomerulus, which leads to an increase in renal vascular resistance. This action reduces both glomerular filtration rate (GFR) and renal blood flow, especially during conditions such as blood loss or dehydration, to preserve blood volume. Moreover, angiotensin II also stimulates the adrenal cortex to release aldosterone, promoting sodium and water reabsorption, and triggers ADH release, resulting in water retention, which collectively help to maintain or raise blood pressure.