Why during prerenal renal failure blood pressure drops while during inrarenal renal failure it goes up?

Question

I read this in the book. Thank you for your help.

Answer 1

Pre-renal renal failure is primarily due to a drop in the circulating blood volume. This may occur due to dehydration as a consequence of diarrhoea or vomiting, due to loss of blood due to bleeding, leaking of fluid from the capillaries as part of an inflammatory response due to infection etc. Once the capacity of the body to compensate for this is overcome, there is a drop in blood pressure. The blood vessels in the kidneys constrict and the kidneys try to conserce as much fluid as possible. When the capacity of the kidneys to restrict fluid is maximal and the blood volume is still low, the kidney tubules start getting damaged due to a lack of blood suppy and acute tubular necrosis results followed by complete anuria.
When renal failure is primarily due a disease of the kidney itself the kidney is not able to regulate the fluid balance of the body normally. Salt and water retention results in an increase in blood pressure.