The sinusoidal lining cells in "normal" human liver. A scanning electron microscopic investigation

Area of Science:

• Hepatology
• Microscopic Anatomy
• Cell Biology

Background:

• Human liver sinusoids are lined by fenestrated endothelial cells, forming a barrier crucial for substance exchange.
• The fenestrations' structure and distribution may vary across different liver zones, influencing sinusoidal permeability.
• Previous studies have suggested zonal heterogeneity in liver sinusoidal structure, but fenestration characteristics require detailed investigation.

Purpose of the Study:

• To quantitatively analyze the fenestrations in human liver sinusoids using scanning electron microscopy.
• To compare the number, size, and porosity of fenestrations between acinar zone 3 and zone 1.
• To investigate potential zonal gradients in sinusoidal permeability.

Main Methods:

• Scanning electron microscopy (SEM) was employed on 13 human liver biopsy samples with normal sinusoidal architecture.
• Fenestrations were counted in acinar zone 3 and zone 1.
• Porosity was estimated using a Texture Analysing System (TAS) on SEM micrographs.

Main Results:

• A significant zonal gradient was observed, with zone 3 exhibiting a higher median number of fenestrations (23.5/µm²) compared to zone 1 (19.2/µm²).
• Sinusoidal porosity increased towards the terminal hepatic vein (9.1% in zone 3 vs. 7.6% in zone 1).
• This increased porosity in zone 3 is attributed to a higher prevalence of fenestrations measuring 100 nm or less in diameter.

Conclusions:

• Human liver sinusoids display zonal heterogeneity in fenestration number and size distribution.
• The observed zonal gradient in fenestrations suggests varying permeability along the sinusoid, potentially influencing blood-hepatocyte transport.
• These findings may have implications for understanding hepatocellular function and metabolic zonation within the liver.