LIVER

Origin: evagination of the wall of the foregut.

Location: upper right quadrant of the abdominal cavity.

Function:

• Protein synthesis and secretion (albumin, prothrombin, fibrinogen)
• Bile formation and secretion
• Metabolism of lipid-soluble drugs (including detoxification) and steroids (including cholesterol synthesis)
• Lipoprotein synthesis and secretion
• Carbohydrate metabolism
• Urea formation from ammonium ion (urea cycle).

Anatomic features

• The largest mass of glandular tissue in the body and also the largest internal organ.
• About 75% of the blood supply it receives from hepatic portal vein, which carries venous blood from the digestive tube, pancreas, and spleen. Remaining 25% of the blood supply provides the hepatic artery with oxygenated blood. Blood from the two sources is mixed as it perfuses the hepatocytes of the liver parenchyma.
• The "classic" liver lobule is the sixsided polyhedral prism with portal triads (hepatic artery, portal vein, and bile duct) at each of the corners. The vessels of the portal triads send distributing branches along the sides of the lobule, and these branches open into the sinusoids. The long axis of the lobule is transversed by the central vein, and this vessel receives blood from the sinusoids. Interconnecting sheets of hepatocytes are disposed in a radial pattern from the central vein to the perimeter of the lobule.
• The portal lobule - its morphologic axis is the interlobular bile duct of the portal triad of the "classic" lobule. Its outer margins are imaginary lines drown between the three central veins that are closest to that portal triad. The portal lobule emphasizes the exocrine function of the liver - bile secretion.
• The liver acinus is described as diamond or lozenge shaped. Its short axis is defined by the terminal branches of the portal triad that lie along the border between two "classic" lobules. The long axis is the line drown between the two central veins closest to the short axis. It allows interpretation of patterns of degeneration, regeneration and toxic effects in the liver parenchyma relative to the degree of vascular perfusion of the hepatic cells.

Composition:

• Hepatocytes, organized as plates of cells
• Connective tissue stroma
• Blood vessels (venules, small arteries and arterioles), nerves, lymphatic vessels, and bile ducts that travel in the stroma - the portal triad.
• Sinusoidal capillaries (sinusoids) between the plates of hepatocytes

HEPATOCYTES

Function: constitute about 80% of the cell population, large polygonal (20 - 30 mkm in diameter).

Composition and functions:

• Nucleus - in the adult liver are tetraploid, genetic information
• Rough endoplasmic reticulum and free ribosomes - protein synthesis and secretion
• Numerous mitochondria (as many as 800-1000 per cell) - energy generation, urea formation from ammonium ion
• Large deposits of glycogen - energy and metabolic storage, carbohydrate metabolism
• Lipid droplets - energy and metabolic storage, lipoprotein synthesis and secretion
• Several Golgi complexes - protein and lipoprotein synthesis and secretion
• Peroxisomes - (as many as 200-300 per cell) - gluconeogenesis, metabolism of purins, alcohol, and lipids
• Smooth endoplasmic reticulum - detoxification of drugs and conjugation of other noxious substances
• Lysosomes - storage site for iron

PORTAL TRIAD

Location: at each of the corners of the "classic" lobule, in the loose stromal connective tissue designated as portal areas or portal canals. Between stroma and hepatocytes is a small space called space of Mall - one of sites where lymph originates.

Composition: portal vein, hepatic artery  - interlobular vessels, bile duct, lymphatic vessels.

SINUSOIDS

Location: between the anastomosing plates of hepatic cells. They receive mixed portal and arterial blood from the smallest portal triads and lead to the venous network - central vein.

Function: provide for the exchange of substances between the blood and the liver cells.

Composition: discontinuous capillaries

• discontinuous sinusoidal endothelium with discontinuous basal lamina
• stellate sinusoidal macrophage -Kupffer cells

• perisinusoidal space ( space of Disse )

• Canaliculi are the small canals formed by grooves in neighboring hepatocytes.
• Canals of Hering - small ductules that constitute a network with cuboidal epithelium and basal lamina.
• Intralobular bile duct - a part of the portal triad, 15 - 40 mkm in diameter.

• Right and left lobar ducts