= Capsular space
The <capsular space> is the fluid-receiving space within the <glomerular capsule>, between its outer wall and the visceral surface formed by <podocytes>. <Glomerular filtration> delivers <water> and filterable <solutes> into this space, which is continuous with the lumen of the <proximal tubule>. It belongs to the tubular-fluid pathway, rather than the lumen carrying <blood> through glomerular <capillaries>.<Anatomy and Physiology 2e by J. Gordon Betts and others>[Section25.4: renal corpuscle and capsular space]{ref}
A useful tracing exercise follows two routes through a <renal corpuscle>. <Blood> enters and leaves through vessels; filtered fluid crosses the <glomerular filtration barrier>, enters the <capsular space> and exits into the tubule. A section showing both routes does not show direct mixing of whole <blood> with the capsular contents.
The receiving <hydrostatic pressure> also opposes further <filtration>. If every other term in a simplified trans-barrier pressure model is fixed, raising receiving pressure by $5\,\mathrm{mmHg}$ lowers net driving pressure by the same amount. This hypothetical subtraction explains why arterial pressure alone is insufficient. In 1971, direct glomerular and proximal-tubular pressure measurements in rats were combined to estimate the driving force for ultrafiltration.<The Dynamics of Glomerular Ultrafiltration in the Rat by Barry M. Brenner and others>[Abstract: servo-null micropipette measurements and pressure difference; quantitative correction noted on publisher page]{ref}
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