Question

What effect does Angiotensin II have on the kidneys? Briefly describe the downstream effect or how it ultimately impacts fluid volume: A patient with chronic kidney disease presents with anemia. Why does anemia occur with with chronic kidney disease?

Answer 1

Q-1 : Angiotensin II (AII) is an octapeptide, which is formed from angiotensin I with in the RAS in a reaction catalysed by angiotensin-converting enzyme, and it is very powerful vasoconstrictor

angiotensin II serves atleast three min functions in the kidney : autoregulation of GFR , reduction of salt excretion Through direct and indirect action on renal tubular cells, and growth modulation of renal cells expressing AT1 receptors

a. Regulation of GFR angiotensin II plays an important role in the regulation of GFR and renal blood flow by constricting The efferent and afferent arterioles are constricted by angiotensin II, the efferent arteriole has a greater Increase in resistance due to smaller basal diameter , which may be partly due to different mechanisms of constriction because calcium channel blockers abolish the afferent response while having little or no effect on the increase in efferent tone. The net effect is elevation of hydraulic pressure in the glomerular capillary (Pgc),which tends of maintain the GFR even under condition of renal hypoperfusion. In contrast, at higher concentrations, angiotensin II can lower GRF by lowering the surface area available for filtration and by sensitising the afferent arteriole to the constricting signal of the tubuloglomerular feedback

b. Sodium and water regulation angiotensin II promotes expansion of plasma volume by promoting renal sodium and water reabsorption. Angiotensin II mediates this by directly stimulating sodium reabsorption in the early proximal tubule and by increasing the secretion of aldosterone from the adrenal cortex, which in turn promotes sodium reabsorption in the cortical collecting tubule.

c. Growth modulation of renal cells angiotensin II induces hypertrophy of proximal tubule epithelial cells in vitro. It also exerts similar growth-promoting effects on mesangial cells these observation suggest a potential role for angiotensin II in mediating renal hypertrophic response to nephron loss after injury.

Q- 2: when kidney are diseased or damaged, they do not make enough EPO. As a result, the bone marrow make fewer red blood cells, causing anemia when blood has fewer red blood cells, it deprives the body of the oxygen it needs. Other common causes of anemia in people with kidney disease include blood loss from Hemodialysis and low levels of the following nutrients found in food:

- iron

- vitamin b12

- folic acid

these nutrients are necessary for red blood cells to make hemoglobin, the main oxygen-carrying protein in the red blood cells.