Liver Structure

A fibrous capsule encloses the liver, and connective tissue divides the organ into a large right lobe and a smaller left lobe. The falciform ligament is a fold of visceral peritoneum that separates the lobes and fastens the liver to the abdominal wall anteriorly. The liver also has two minor lobes, the quadrate lobe, near the gallbladder, and the caudate lobe, close to the vena cava (fig. 17.28). The area where the three lobes meet and blood vessels and ducts enter or exit the liver is the porta hepatis.

A fold of visceral peritoneum called the coronary ligament attaches the liver to the diaphragm on its superior surface. Each lobe is separated into many tiny hepatic lobules, which are the liver's functional units (fig. 17.29). A lobule consists of many hepatic cells radiating outward from a central vein. Vascular channels called hepatic sinusoids separate platelike groups of these cells from each other. Blood from the digestive tract, which is carried in the hepatic portal vein (see chapter 15, p. 633), brings newly absorbed nutrients into the sinusoids (fig. 17.30). At the same time, oxygenated blood from the hepatic artery mixes freely with the blood containing nutrients, then flows through the liver sinusoids and nourishes the hepatic cells.

Often blood in the portal veins contains some bacteria that have entered through the intestinal wall. However, large Kupffer cells, which are fixed to the inner lining (endothelium) of the hepatic sinusoids, remove most of the bacteria from the blood by phagocytosis. Then the blood passes into the central veins of the hepatic lobules and moves out of the liver via the hepatic vein.

Within the liver lobules are many fine bile canals, which receive secretions from the hepatic cells. The canals of neighboring lobules unite to form larger ducts, and then converge to become the hepatic ducts. These ducts merge, in turn, to form the common hepatic duct.

Essentials of Human Physiology

Essentials of Human Physiology

This ebook provides an introductory explanation of the workings of the human body, with an effort to draw connections between the body systems and explain their interdependencies. A framework for the book is homeostasis and how the body maintains balance within each system. This is intended as a first introduction to physiology for a college-level course.

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