(Figure X.). The bile duct (b.d.) branches again and again, and ends at
last in the final pits, the lobuli (lb.), which are lined with secretory
epithelium, and tightly packed, and squeeze each other into polygonal
forms. The blood supply from which the bile would appear to be
mainly extracted, is brought by the portal vein, but this blood is
altogether unfit for the nutrition of the liver tissue; for this latter
purpose a branch of the coeliac artery, the hepatic serves. Hence in
the tissue of the liver we have, branching and interweaving among
the lobuli, the small branches of the bile duct (b.d.), which carries
away the bile formed, the portal vein (p.v.), the hepatic artery (h.a.),
and the hepatic vein (h.v.). (Compare Section 45.) Figure X.b shows
a lobule; the portal vein and the artery ramify round the lobules-- are
inter-lobular, that is (inter, between); the hepatic vein begins in
the middle of the lobules (intra-lobular), and receives their blood.
(Compare X.a.) Besides its function in the manufacture of the
excretory, digestive, and auxiliary bile, the liver performs other
duties. It appears to act as an inspector of the assimilation material
brought in by the portal vein. The villi, for instance, will absorb
arsenic, but this is arrested and thrown down in the liver. A third
function is the formation of what would seem to be a store of
carbo-hydrate, glycogen, mainly it would appear, from the sugar in the
portal vein, though also, very probably, from nitrogenous material, though
this may occur only under exceptional conditions. Finally, the nitrogenous
katastates, formed in the working of muscle and nerve, and returned
by them to the blood for excretion, are not at that stage in the form of
urea. Whatever form they assume, they undergo a further metabolism
into urea before leaving the body, and the presence of considerable
quantities of this latter substance in the liver suggests this as a fourth
function of this organ-- the elaboration of urea.