(C8-16) SLIDE 61: Liver, human (H&E) See refs. above for human liver.

Over the years, some of these slides have deteriorated, so that they are almost useless, while others are still fine. If the slide you are examining has cracks in it and is hard to focus, don’t waste one more second on it, but find another one from a different slide box of someone else in your group. Once you find a good one, look for the many lobules cut in cross section. Because there is so little connective tissue in the human liver, the boundaries of the classic lobules are difficult to define. However, it is best to start by identifying central veins (C in C8), which are distinguished by their round or oval appearance, their position at the center of radiating cords of parenchymal cells, and the near lack of connective tissue surrounding them, compared to the pig (C8, and defined by lines in C9). Sinusoids enter the central veins (C9). The sinusoids are filled with erythrocytes and the endothelium is seen as a thin dark line with dark flat nuclei. At the periphery of the lobule, portal canals can be recognized by their connective tissue (T in C8, and the central portion of slides C10-C11). The portal canals contain bile ducts lined with simple cuboidal epithelium (B), an arteriolar branch of the hepatic artery (A), and a portal vein of larger diameter than the arteriole (P). These three structures constitute the "portal triad" (thus the "T" in C8), but the portal canals also contain small lymphatic vessels (L in C10) as well as autonomic nerves (invisible in this slide). A continuous "mura" (M) of hepatocytes can be seen surrounding the portal canal (C11). The space of Disse (D) is found between the endothelium and the hepatocytes (C12). This space is conspicuous on some slides but not on others. Sublobular veins (S) can be recognized by their large diameter, a thin but definite adventitia and the lack of sinusoids draining into them (C13). Bile canaliculi can often be seen at higher magnifications. If you carefully examine several continuous cell borders, you may see small circular profiles of canaliculi (upper three arrows in C14 and arrows in C15). Also, if you're lucky, you may find bile canaliculi cut in longitudinal section (lower arrow in C14). Don’t be dismayed if you can’t find bile canaliculi in this slide. They are impossible to miss in the next slide (slide 65). While you’re observing at high power, look for larger hepatocyte nuclei (C16). These are polyploid nuclei.