Major Calyx - Structure, Location, Function, Diagram

The major calyx is a larger funnel-shaped structure in the kidney that receives urine from two or more minor calyces. It is part of the renal collecting system and acts as an intermediate conduit between the minor calyces and the renal pelvis. Each kidney typically has 2 to 3 major calyces — upper, middle (optional), and lower — depending on anatomical variation.

Structure

Major calyces are formed by the confluence of several minor calyces. Like the rest of the collecting system, they are lined with transitional epithelium (urothelium), allowing them to expand and contract with varying urine volumes. Their walls contain smooth muscle to help propel urine into the renal pelvis via peristaltic waves.

Key Characteristics:

Shape: Wide, funnel-like chambers
Epithelium: Transitional (urothelium), resistant to stretch and urine contact
Number: Usually 2–3 per kidney (upper, lower, sometimes middle)

Location

Major calyces are situated in the renal sinus, between the minor calyces and the renal pelvis:

Structure	Relation to Major Calyx
Minor calyces	Drain into the major calyx
Renal pelvis	Receives urine from the major calyces
Renal pyramids	Indirect source of urine via minor calyces

Function

The major calyx functions as part of the passive drainage pathway for urine:

Urine collection: Receives urine from multiple minor calyces
Urine conduction: Transfers urine to the renal pelvis without altering its composition
Reservoir role: Acts as a temporary holding chamber for urine during peristalsis

Clinical Significance

Hydronephrosis: Obstruction downstream in the renal pelvis or ureter can cause back-pressure and dilation of major calyces
Kidney stones: May lodge at the junctions of minor and major calyces or in the major calyx itself
Calyceal deformities: May be congenital or acquired and are visible on radiological imaging (e.g., IVU, CT urography)
Surgical access: Endourological procedures (e.g., percutaneous nephrolithotomy) often navigate through calyces to access deeper kidney structures

The major calyx is a critical collecting structure within the kidney, serving as a passage for urine from minor calyces to the renal pelvis. Its architecture allows smooth, uninterrupted urine flow, and any disruption can have significant urological consequences.