Anatomy and Physiology | hepatitisliver

Gross Anatomy

The liver has four primary lobes. The largest, the right lobe,

is visible on all liver surfaces and separated from the smaller

left lobe by a deep fissure. The posteriormost caudate lobe and the quadrate lobe, which lies inferior to the left lobe, are visible in an inferior view of the liver.

A mesentery, the falciform ligament, separates the right and left

lobes anteriorly and suspends the liver from the diaphragm and anterior abdominal wall. Except for the superiormost liver area (the bare area), which touches the diaphragm, the entire liver is enclosed by the visceral peritoneum.

A ventral mesentery, the lesser omentum, anchors the liver to the lesser curvature of the stomach. The hepatic artery and the hepatic

portal vein, which enter the liver at the porta hepatis, and the common hepatic duct, which runs inferiorly from the liver. The gallbladder rests in a recess on the inferior surface of the right liver lobe.

The traditional scheme of defining liver lobes (outlined

above) has been criticized because it is based on superficial features

of the liver.

Bile leaves the liver through several bile ducts that ultimately

fuse to form the large common hepatic duct, which travels

downward toward the duodenum. Along its course, that duct

fuses with the cystic duct draining the gallbladder to form the

bile duct

Microscopic Anatomy of Liver

Microscopically, the liver consists of several components:

1. Hepatocytes: These are the major functional cells of the liver; they perform metabolic, secretory, and endocrine functions.

2. Bile canaliculi: These are small ducts between hepatocytes that collect bile produced by the hepatocytes. From bile canaliculi, bile passes into bile ducts. The bile ducts merge and eventually form the larger right and left hepatic ducts, which

unite and exit the liver as the common hepatic duct. The common hepatic duct joins the cystic duct (cystic bladder) from the gallbladder to form the common bile duct. From here, bile enters the hepatopancreatic duct to enter the duodenum of the small intestine to participate in digestion.

3. Hepatic sinusoids. These are highly permeable blood capillaries between rows of hepatocytes that receive oxygenated blood from branches of the hepatic artery and nutrient-rich deoxygenated blood from branches of the hepatic portal vein.

Functions of the Liver

Carbohydrate metabolism. The liver is especially important in maintaining a normal blood glucose level. When blood glucose is low, the liver can break down glycogen to glucose and release glucose into the bloodstream. The liver can also convert certain amino acids and lactic acid to glucose, and it can convert other sugars, such as fructose and galactose, into glucose. When blood glucose is high, as occurs just after eating a meal, the liver converts glucose to glycogen and triglycerides for storage.
Lipid metabolism. Hepatocytes store some triglycerides; break down fatty acids to generate ATP; synthesize lipoproteins, which transport fatty acids, triglycerides, and cholesterol to and from body cells; synthesize cholesterol; and use cholesterol to make bile salts.
Protein metabolism. Hepatocytes remove the amino group (–NH2) from amino acids so that the amino acids can be used for ATP production or converted to carbohydrates or fats. They also convert the resulting toxic ammonia (NH3) into the much less toxic urea, which is excreted in urine. Hepatocytes also synthesize most plasma proteins, such as globulins, albumin, prothrombin, and fibrinogen.
Processing of drugs and hormones. The liver can detoxify substances such as alcohol or secrete drugs such as penicillin, erythromycin, and sulfonamides into bile. It can also inactivate thyroid hormones and steroid hormones such as estrogens and aldosterone.
Excretion of bilirubin. Bilirubin, derived from the heme of aged red blood cells, is absorbed by the liver from the blood and secreted into bile. Most of the bilirubin in bile is metabolized in the small intestine by bacteria and eliminated in feces.
Storage of vitamins and minerals. In addition to storing glycogen, the liver stores certain vitamins (A, D, E, and K) and minerals (iron and copper), which are released from the liver when needed elsewhere in the body.
Activation of vitamin D. The skin, liver, and kidneys participate in synthesizing the active form of vitamin D.

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