Hydrostatic pressures (renal and otherwise)

[ihatescience]

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From Costanzo's book:

"In systemic capillaries, hydrostatic pressure falls along the length of the capillary; in glomerular capillaries, it remains constant along the entire length"

Can someone explain why it remains constant in the glomerular capillaries-- isn't fluid being "filtered" into bowman's space through the glomerular capillary barrier (the ultrafiltrate, ie: initial form of urine). Wouldn't this cause the pressure within the glomerular capillaries to decrease along the length as well?

Thanks a lt!