dxtxpx
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When arterial BP of an individual changes from 100 mmHg to 150 mmHg, GFR
a) remains unchanged
b) increases by 10%
c) increases by 50%
d) decreases by 25%
e) decreases by 50%
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| peekay
Forum Guru
Topics: 102
Posts: 588
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remains unchanged
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increases by 50 [percent cause the hydostatic pressure in the glomerular capilllary increases which is the main factor .. not 10 but 50 percent cause because slight changes in pressure cause huge changes in gfr
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| mjl1717
Forum Hero
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I like that reasoning and i think that logic would enhance or precipatate glomerulosclerosis
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| asmi
Forum Hero
Topics: 1043
Posts: 4,609
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yes i too agree with C
since increase in angiotensin II(constricts efferent arterioles)---> decrease in RPF---> increase in GFR.
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| dxtxpx
Forum Guru
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Posts: 1,233
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Peekay is correct  choice a) remains unchanged
Filtration of blood across glomerular basement membrane depends on difference between glomerullar capillary hydrostatic pressure (45 mmHg) and the sum of Bowman's capsule hydrostatic pressure (10 mmHg) and the plasma protein osmotic pressure (28 mmHg). Thus, the net pressure supporting glomerular filtration is 7 mmHg. Due to extreme porosity of fenestrated glomerular capillaries and the gaps between foot processes of podocytes, approx 180 L/day of glomerular filtrate is produced. GFR can easily be calculated as 125 mL/min. This rate is relatively invariant, even with large changes in BP. A substantial increae in BP will result in concomitant decrease in blood flow thru afferent arteriole due to smooth muscle contraction. Also, macula densa in distal convulated tubule detects changes in rate of production of glomerular filtrate and feeds back on afferent arteriole to autoregulate GFR
Stimulation of sympathetic nerve fibers to kidney causes vasoconstriction in afferent arteriole, leading to decreae in GFR. Factors that vasoconstrict efferent arterioles will increase GFR. Conversely, a decrease in vascular tone will result in an increase in GFR. Catecholamines are also potent vasoconstrictirs of afferent arterioles and will therefore cause a significant decrease in GFR
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