metanephric mesenchyme
Summary
Metanephric mesenchyme is the embryonic tissue that gives rise to the nephrons and collecting system of the permanent kidney (metanephros). It forms around week 5 of gestation and is induced by the ureteric bud to differentiate into renal structures. Defects in this tissue lead to renal agenesis or dysplasia.
Detail
The metanephric mesenchyme is a specialized population of mesenchymal cells located in the posterior intermediate mesoderm that forms the basis of the permanent kidney. During the 5th week of embryonic development, the ureteric bud (an outgrowth from the mesonephric duct) invades this mesenchymal tissue and induces its differentiation through reciprocal signaling. The metanephric mesenchyme condenses around the tips of the branching ureteric bud and undergoes mesenchymal-to-epithelial transition to form the nephron components including Bowman's capsule, proximal tubule, loop of Henle, and distal tubule. Meanwhile, the ureteric bud itself forms the collecting ducts, calyces, renal pelvis, and ureter. Key signaling molecules include GDNF (glial cell line-derived neurotrophic factor) from the mesenchyme and its receptor RET on the ureteric bud, along with BMP4, FGF2, and Wnt signaling pathways. Disruption of these interactions results in congenital anomalies such as renal agenesis, multicystic dysplastic kidney, or polycystic kidney disease. The metanephric kidney begins functioning around week 10-12 of gestation.
Sources
- Langman's Medical Embryology
- Moore's The Developing Human
- First Aid for the USMLE Step 1
- BRS Embryology
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