The glomerular capsule, or Bowman's capsule, is the cup-like epithelial structure surrounding the glomerulus in a renal corpuscle. Its outer wall and its visceral layer, formed by podocytes, enclose a capsular space. Fluid crossing the glomerular filtration barrier enters that space and then passes into the proximal tubule.[ref]
Kidneys by the National Cancer Institute. nephron organization: glomerulus and surrounding epithelial capsule
The space, its contents and its wall are distinct. In a section, identify the capillary tuft first, then the narrow receiving region around it, then the outer capsule. A renal corpuscle includes the tuft and capsule together; the capsule alone is not a second glomerulus. This observation prevents an anatomical label from being mistaken for an independent filtration unit.
The receiving compartment also matters mechanically. In a simplified filtration model, increasing hydrostatic pressure in the capsular space opposes fluid movement from the glomerular capillaries. Measuring only arterial pressure would therefore miss one side of the trans-barrier driving difference. Direct glomerular and tubular pressure measurements were an important part of the 1971 rat experiments establishing the physical basis of glomerular filtration.[ref]
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