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Vascularization and glomerular ultrastructure in the pig mesonephros
Abstract:
Vascularization of the pig mesonephros was investigated in embryos 5-8 cm in length. Vascular injections with microfil were cleared and dissected; corrosion casts were studied under the scanning electron microscope (SEM). Perfusion-fixed tissue was used for SEM and transmission electron microscope (TEM) studies, including freeze-fracture specimens. The branches of one mesonephric artery carry up to 15 glomeruli. Several glomeruli occupy the same arterial branch, with very short afferent arterioles proper. The efferent vessels, frequently 2-5, leave the extensive vascular pole opposite the entering arteriole and split into peritubular capillaries radiating towards the superficial veins. These capillaries form vascular regions in the shape of flattened pyramids. Along its course, one nephron is supplied by vessels derived from 4-7 glomeruli. The nephrons have less vascular contact than in the definitive kidney. The ultrastructure of the single mesonephric vessels matches the metanephric counterparts. Epithelioid cells with renin granules are common in afferent arterioles, larger arteries, and efferent vessels. The lobulated glomeruli are up to 750 micron long and flattened, showing the usual features of podocytes, mesangial cells, and an attenuated endothelium with fenestrations between 50 and 250 nm. It partially retains its own basement membrane. There is no proximal mesangium.
Insights
The pig mesonephros vascular system features multiple glomeruli per arterial branch, with nephrons receiving blood supply from several glomeruli. This study details its unique vascular architecture and ultrastructure.
Area of Science:
- Embryology
- Renal Physiology
- Comparative Anatomy
Background:
- The mesonephros is a transient kidney in embryonic development.
- Understanding its vascularization is crucial for comprehending kidney development and function.
Purpose of the Study:
- To investigate the vascular architecture and ultrastructure of the pig mesonephros in embryos.
- To compare mesonephric vascularization with that of the definitive kidney.
Main Methods:
- Vascular injections with Microfil followed by corrosion casting.
- Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM) on perfusion-fixed tissue.
- Freeze-fracture techniques for ultrastructural analysis.
Main Results:
- Mesonephric arteries supply multiple glomeruli (up to 15) with short afferent arterioles.
- Efferent vessels branch into peritubular capillaries supplying individual nephrons from 4-7 glomeruli.
- Mesonephric glomerular ultrastructure and vascular cells (e.g., epithelioid cells with renin granules) resemble those in the metanephros.
Conclusions:
- The pig mesonephros exhibits a distinct vascular organization with extensive glomerular supply to nephrons.
- Its vascular ultrastructure is similar to the developing definitive kidney, suggesting conserved developmental mechanisms.
- The mesonephros possesses specialized vascular cells, indicating potential endocrine or regulatory functions during development.