== Introduction ==

The liver functions as a vast biosynthetic chemical factory, synthesizing large complex molecules from substances brought to it in the blood, particularly substances recently absorbed by the intestine and transported by the portal blood system. All of the biochemical functions of the liver are carried out by the epithelial parenchymal cells of the liver, the hepatocytes. Hepatocytes are responsible for bile synthesis and secretion, excretion of bilirubin, protein carbohydrate and lipid metabolism, storage (vitamins A, D and B12 and iron as ferritin), and conjugation and elimination of metabolites and toxins.

=== Blood Supply to a Lobule ===

At the periphery of the lobules, in the angles between 2 or 3 adjacent lobules, lie the interlobular septa or portal canals consisting of connective tissue, and containing a branch of the hepatic artery, a branch of the portal vein, a small bile duct, a lymphatic vessel and small nerves. The blood that enters a lobule is supplied from the vessels in the portal system. Both venous and arterial blood enters a lobule. The venous blood enters the sinusoids directly from the smallest branches of the portal vein. Only a small volume of arterial blood enters the sinusoids directly from the smallest branches of the hepatic artery. Most of the arterial blood goes through a capillary bed to enter the small branches of the portal vein before going on to the sinusoids. Blood in the sinusoids “bathes” the hepatocytes before passing into the central vein from which it flows into a sublobular (intercalated) vein. Sublobular veins progressively unite to form the collecting veins that progressively join to form the hepatic veins. Two or more hepatic veins empty directly into the inferior vena cava.

Remember that lymph and bile flow from a lobule in a direction opposite to the flow of blood in the sinusoids.

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== Gallbladder ==

The pear-shaped gallbladder shows marked variation in size and shape among different individuals. Anatomically, it consists of a neck, a body, and a blindly ending fundus. Histologically, its wall consists of a mucosa, a muscularis, a perimuscular layer of connective tissue, and a serosa or fibrosa.

Mucosa - The mucosa consists of an epithelium, its basement membrane, and an underlying lamina propria of loose connective tissue. The tall, simple columnar epithelial cells of the mucosa are absorptive in nature. They have basal ovoid nuclei and on their luminal surface is a thin striated border (demonstrated by EM). No goblet cells are present in this epithelium. The mucosa of the non-distended gallbladder is irregularly folded, somewhat resembling villi when it is sectioned. These folds largely disappear when the gallbladder is filled.

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=== Slide 152 Liver and Gallbladder, (H&E) ===