KEY EAS, external anal sphincter IAS, internal anal sphincter IG, intestinal glands LN, lymphatic nodules Lym, lymphocytes MM, muscularis mucosae SC, simple columnar epithelium ST, stratified epithelium StC, stratified cuboidal epithelium StCol, stratified columnar epithelium StS, stratified squamous epithelium StS(k), stratified squamous epithelium (keratinized) arrow, termination of muscularis mucosae diamonds, junctions between epithelial types
Digestive System III: Liver, Gallbladder, and Pancreas
LIVER / 628 Overview / 628 Liver Physiology / 629 Blood Supply to the Liver / 631 Structural Organization of the Liver / 632 Liver Lobules / 633 Blood Vessels of the Parenchyma / 636 Perisinusoidal Space (Space of Disse) / 636 Lymphatic Pathway / 638 Hepatocytes / 639 Biliary Tree / 641 GALLBLADDER / 643 PANCREAS / 647 Overview / 647 Exocrine Pancreas / 647 Duct System of the Exocrine Pancreas / 649 Endocrine Pancreas / 649 Functions of Pancreatic Hormones / 651 Regulation of Islet Activity / 653 Folder 18.1 Clinical Correlation: Lipoproteins / 630 Folder 18.2 Clinical Correlation: Congestive Heart Failure and Liver Necrosis / 635 Folder 18.3 Insulin Production and Alzheimer’s Disease / 655 Folder 18.4 Functional Considerations: Insulin Synthesis, an Example of Posttranslational Processing / 655
The liver is the largest mass of glandular tissue in the body and the largest internal organ, weighing approximately 1,500 g and accounting for nearly 2.5% of adult body weight. It is located in the upper right and partially in the upper left quadrants of the abdominal cavity, protected by the ribcage. The liver is enclosed in a capsule of fibrous connective tissue (Glisson’s capsule); a serous covering (visceral peritoneum) surrounds the capsule, except where the liver adheres directly to the diaphragm or the other organs.
The liver is anatomically divided by deep grooves into two large lobes (the right and left lobes) and two smaller lobes (the quadrate and caudate lobes; Fig. 18.1). This anatomic division has only topographic importance because it relates lobes of the liver to other abdominal organs. Division into functional or surgical segments that correspond to the blood supply and bile drainage is more clinically important.
In the embryo, the liver develops as an endodermal evagination from the wall of the foregut (specifically the site that will become the duodenum) to form the hepatic diverticulum. The diverticulum proliferates, giving rise to the hepatocytes, which become arranged in cellular (liver) cords,
FIGURE 18.1 • Anatomic structure of the liver. This diagram shows the gross view of the diaphragmatic and visceral surfaces of the liver, with labeled anatomic landmarks found on both surfaces. The enlarged cross-sectional area of the liver (bottom) shows the general microscopic organization of the liver into lobules. Note the presence of hepatic portal triads at the periphery of each lobule, with the terminal hepatic venule (central vein) in the center of the lobule.
thus forming the parenchyma of the liver. The original stalk of the hepatic diverticulum becomes the common bile duct. An outgrowth from the common bile duct forms the cystic diverticulum that gives rise to the gallbladder and cystic duct.