Liver lobule

The liver contains on the order of 50,000–100,000 lobules. In each one, plates of hepatocytes, one to two cells thick, radiate from the central vein (terminal hepatic venule) like spokes. Between the plates run the sinusoids, which receive mixed blood from terminal branches of the portal venule and hepatic arteriole in the portal triads at the lobule's corners. Blood flows centripetally along the sinusoids to the central vein, which drains to sublobular and then hepatic veins. Bile is secreted into canaliculi between hepatocytes and flows centrifugally, opposite to the blood, to the canals of Hering and the bile ductules of the portal triads.

Sinusoids are lined by fenestrated endothelium with no basement membrane; the fenestrae are grouped in "sieve plates" about 100–150 nm across. Kupffer cells sit in the lumen. Between the endothelium and the hepatocytes is the perisinusoidal space (of Disse). Hepatocyte microvilli project into it and exchange materials with plasma, and it contains the vitamin-A-storing stellate (Ito) cells. Lymph forms in this space.

The classic lobule is one of three ways to describe the same tissue. The portal lobule is a triangle centred on a portal triad and emphasises bile drainage. The hepatic acinus (of Rappaport) is a diamond whose axis is the terminal portal vessels and whose tips are two central veins. It divides the parenchyma into zones by oxygen and nutrient supply. Zone 1 (periportal) receives the most oxygen; it carries out gluconeogenesis, β-oxidation and urea synthesis and is first to regenerate. Zone 2 is intermediate. Zone 3 (centrilobular) is the most hypoxic and has the most cytochrome P450 (CYP2E1).