A. What happens to blood pressure in the glomerular capillaries when the normal

Question

A. What happens to blood pressure in the glomerular capillaries when the normal vasoconstrictor signals (such as Sym activation and angiotensin release) are increased?

B. What happens to blood pressure in the glomerular capillaries when overall blood volume is greatly increased?

C. Do the mechanisms that adjust how much filtrate is formed in the glomeruli also adjust the composition of the filtrate relative to the blood plasma? In other words, will you start filtering different things because you’ve started making more or less filtrate?

Explanation / Answer

Ans.1 : A powerful renal vasoconstrictor, angiotensin II, can be considered a circulating hormone as well as a locally produced autacoid because it is formed in the kidneys as well as in the systemic circulation. Because angiotensin II preferentially constricts efferent arterioles,increased angiotensin II levels raise glomerular hydrostatic pressure while reducing renal blood flow. It should be kept in mind that increased angiotensin II formation usually occurs in circumstances associated with decreased arterial pressure or volume depletion, which tend to decrease GFR. In these circumstances, the increased level of angiotensin II, by constricting efferent arterioles, helps prevent decreases in glomerular hydrostatic pressure and GFR; at the same time, though, the reduction in renal blood flow
caused by efferent arteriolar constriction contributesto decreased flow through the peritubular capillaries, which in turn increases reabsorption of sodium and
water.

Ans.2 : When overall blood volume is greatly increased the blood pressure in the glomerular capillaries will also increase which will in turn increase the glomerular filteration rate (GFR).

Ans.3 : The composition of the filterate relative to the blood plasma always remains nearly constant. So, we can say that the mechanisms that adjust how much filtrate is formed in the glomeruli does not adjust the composition of the filtrate relative to the blood plasma.

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