A renal corpuscle is the initial filtration structure of a nephron, consisting of a glomerulus enclosed by a glomerular capsule, also called Bowman's capsule. Blood flows through the glomerular capillaries, while filtered fluid enters the surrounding capsular space and then the proximal tubule. The blood pathway and the tubular-fluid pathway are adjacent but distinct.[ref]
Kidneys by the National Cancer Institute. nephron organization: glomerulus and surrounding epithelial capsule
The glomerular filtration barrier includes capillary endothelium, a basement membrane and the specialized surface formed by podocytes. These biological cells extend processes around the capillaries. In a 1999 study, antibody-based localization placed the membrane protein nephrin at the slit diaphragm between podocyte processes, connecting a named molecular component to the physical filtration interface.[ref]
Nephrin is specifically located at the slit diaphragm of glomerular podocytes by V. Ruotsalainen and others. Abstract and immunolocalization results
A section supplies a useful scale comparison: the rounded structure containing a capillary tuft and its surrounding capsule is the renal corpuscle, whereas the glomerulus is the tuft inside it. Counting those as separate complete filtration units would double-count parts of the same unit. Filtered water and small solutes still undergo later processing, so the fluid first leaving a corpuscle is not identical to final urine.
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