= Renal pelvis
The <renal pelvis> is the expanded collecting region of the <kidney> that receives <urine> from the <major calyx> passages and continues into the <ureter>. It lies downstream of the <collecting duct system> and the <renal calyx> network. Its function is to collect and route their combined output, rather than to carry out <glomerular filtration>.<Kidneys by the National Cancer Institute>[internal anatomy: calyces, pelvis and continuity with ureter]{ref}
Trace the drainage sequence from a single <renal pyramid>: its <collecting ducts> open at a <renal papilla>, the receiving <minor calyx> joins a larger <major calyx>, and the latter drains toward the <renal pelvis>. A longitudinal anatomical specimen exposes these nested connections directly. The surrounding <kidney> tissue and the space receiving its output are different structures.<Longitudinal section through Kidney by the Manipal Museum of Anatomy and Pathology>[specimenEXC002: minor/major calyces, renal pelvis and ureter]{ref}
For a steady illustrative <mass balance>, suppose two incoming passages supply $0.4$ and $0.6\,\mathrm{mL/min}$. If pelvic storage is unchanged and there is no other inflow or loss, the <ureter> must carry $1.0\,\mathrm{mL/min}$. Sampling there measures pooled output: it cannot, by itself, reveal which upstream <nephron> produced a particular change in <urine> composition.
Back to article page
