Organ
Renal medulla and pyramids
The tubular and vascular core of the concentrating system
High-yield
Loops, collecting ducts and vasa recta cooperate in the medulla to establish, use and preserve the osmotic gradient required for water conservation.
Overview
The medulla is organized into pyramids with bases facing cortex and papillae facing minor calyces. Parallel tubules and vessels give it a striated appearance. A pyramid and its associated cortex form a renal lobe.
Reference facts
- Location
- Deep to the cortex, with pyramid bases at the corticomedullary boundary and tips projecting toward the sinus.
- Parts
- Outer and inner medulla contain segment-specific loops and collecting ducts, together with descending and ascending microvessels.
- Blood supply
- Predominantly supplied through vasa recta associated with juxtamedullary efferent circulation.
- Innervation
- Renal sympathetic activity influences tubular transport and medullary vascular resistance.
- Function
- Supports countercurrent multiplication and exchange and hormone-regulated water and urea transport for urine concentration.
Clinical correlation
Limited oxygen availability combined with active salt transport makes outer-medullary tubules vulnerable to ischemic injury. Papillary necrosis is associated with disorders including sickling, diabetes, obstruction, infection and some analgesic exposures; these are distinct injury patterns, not a fixed sequence of infarction.
Frequently asked questions
Where are the renal medulla and pyramids located?
Deep to the cortex, with pyramid bases at the corticomedullary boundary and tips projecting toward the sinus.
What do the renal medulla and pyramids do?
Supports countercurrent multiplication and exchange and hormone-regulated water and urea transport for urine concentration.
What are the parts of the renal medulla and pyramids?
Outer and inner medulla contain segment-specific loops and collecting ducts, together with descending and ascending microvessels.
What is the blood supply of the renal medulla and pyramids?
Predominantly supplied through vasa recta associated with juxtamedullary efferent circulation.