Structure of the Kidney

Hilum renale expands into a central cavity known as sinus renalis.
The sinus renalis contains pelvis renalis and calyces renales, surrounded by adipose tissue housing branches of blood vessels and nerves.
Lined by a continuation of capsula fibrosa, providing protection and structure.
Kidney parenchyma is composed of cortex (outer layer) and medulla (inner layer).

Cortex renalis, or the outer layer, is dark brown, soft, and granular.
The cortex is approximately 4-5 mm wide.
Cortical parts extend into the medulla as columnae renales, supporting both structure and function.
Medullary rays, or radii medulares, are stripes radiating from the medulla to the cortex.

Medulla appears light brown and consists of striated conical structures known as pyramides renales, numbering between 12 and 15.
Each pyramidal base is directed towards the cortex, while their pointed apices are directed towards the pelvis renis.
Several apices fuse to create a structure called papilla renalis.

On the papilla renalis, foramina papillaria are present, serving as points through which urine is secreted.
Each papilla renalis is surrounded by a calyx renalis minor, collecting urine from the papillae.
These minor calyces unite to form calyx renalis major, usually 2-3 in number.
The fusion of major calyces creates a funnel-shaped sac called pelvis renalis (or pyelon).
As pelvis renalis exits sinus renalis, it reduces in size before continuing as ureter, transporting urine to the bladder.