Page 245 - Veterinary Histology of Domestic Mammals and Birds, 5th Edition

Digestive system (apparatus digestorius) 227

Interlobular vein Portal canal
VetBooks.ir Interlobular bile duct artery and vein, and
including interlobular
Hepatic artery
interlobular bile duct

Central vein

1 2 3
Liver cell plates
Hepatic sinusoid Liver lobule
Vasa capillaria
interlobaria Loose connective
Interlobular bile tissue
duct
Interlobular vein
Interlobular artery Sublobular veins

Sublobular veins
1 = Zona peripheralis, 2 = Zona intermedia, 3 = Zona centralis
10.68 Three-dimensional reconstruction of liver lobules illustrating the three metabolically active zones (zona
peripheralis, zona intermedia and zona centralis) and vascular supply.

The hepatic artery passes into the liver together with the liver. Together with the deep lymph vessels, they drain into
portal vein. Its branches, the interlobular arteries, accom- the hepatic lymph nodes (lnn. hepatici).
pany the interlobular veins. Both vascular systems lie at
the external boundary of the liver lobules and, together LIVER LOBULE (LOBULUS HEPATICUS)
with an interlobular bile duct (ductus interlobularis bil- The liver is composed of lobules. Lobule formation is
ifer) occupy the portal canal (Figure 10.68). Within the influenced by the distribution of hepatic vessels during
interlobular connective tissue, the interlobular arteries embryonic development. Hepatic lobules are structural
and veins undergo terminal division into arterioles and and functional units comprising hepatocytes of ectoder-
venules, then capillaries (vasa capillaria interlobularia) mal origin and mesodermally derived sinusoids. They are

that enter the liver lobules at right angles to the portal defined in different ways (Figure 10.69), according to the
canal. vascular structure, or structures, that form(s) the central
Immediately after entering the lobule, the arterial and axis (portal canal, branches of the interlobular arteries
venous systems unite with the sinus capillaries (hepatic and veins or the central vein). The resulting units are the:
sinusoids, vasa sinusoidea) (Figure 10.68), which contain
mixed arterio-venous blood. · portal lobule (= functional unit, emphasises the
The sinusoids are thin-walled vessels with a relatively glandular, exocrine nature of the liver),
large lumen. They are radially arranged, passing inwards · hepatic acinus (vascular focus, reflects the meta-
from the outer edge of each liver lobule. At the middle bolic function of the liver) and
of the lobule the sinusoids converge to form the central · classic polyhedral liver lobule with central vein
vein (v. centralis) (Figures 10.68, 10.70, 10.71 and 10.73). (morphological unit of the liver).
Within the lobules, the sinusoids pass between hepatic cell
plates, or laminae (laminae hepatis), permitting exten- In the portal lobule (represented by lines connecting the
sive exchange between the blood and hepatocytes. The central veins of three adjacent liver lobules), the portal
central veins merge to form the contractile sublobular canal is at the centre and the drainage area of its com-

veins (Figure 10.68) and then hepatic veins that drain ponent bile canaliculi is circumscribed. In this view of the
collectively into the caudal vena cava. liver lobule, emphasis is placed on the glandular (secre-
The liver contains an extensive network of lymph tory) function of the liver (Figure 10.69, A).
vessels. Lymph drains into deep lymph vessels in the inter- The definition of the lobule as a hepatic acinus views
stitial connective tissue, which pass to the superficial zones the lobule as a vascular unit supplied by the interlobular
of the liver. Lymph vessels leave the liver at the hepatic arteries and veins (Figure 10.69, B). An acinus comprises
porta. Superficial lymph capillary networks associated an interlobular artery and vein, their terminal branches
with the tunica subserosa also converge at the hilus of the (as its central axis) and portions of the two immediately

Vet Histology.indb 227 16/07/2019 15:01