Major Calyx
Major calyces are larger chambers formed by joining minor calyces before the renal pelvis.
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.
Last updated on May 9, 2025
