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Liver & intrahepatic bile ducts

General

Anatomy

Author: Komal Arora, M.D.

Last author update: 1 April 2012

Last staff update: 8 July 2022

Copyright: 2002-2024, PathologyOutlines.com, Inc.

PubMed Search: Anatomy liver

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Table of Contents

Cite this page: Arora K. Anatomy. PathologyOutlines.com website. https://www.pathologyoutlines.com/topic/livernormalanatomy.html. Accessed April 24th, 2024.

Definition / general

1,200 - 1,600 g
Dual blood supply of portal vein (2/3) and hepatic artery (1/3) via porta hepatis (common hepatic bile duct exists in same region)
Blood exits liver via left and right hepatic veins to inferior vena cava
Divided into right and left lobes by Cantlie line projecting between gallbladder fossa and vena cava and defined by middle hepatic vein
Right lobe is divided into anterior and posterior segments by right hepatic vein
Left lobe is divided into medial and lateral segments by left hepatic vein
Intrahepatic biliary tree: classified into intrahepatic large bile ducts (grossly visible with fibrous ductal wall and peribiliary glands) and small bile ducts
Regional lymph nodes: hilar, hepatoduodenal ligament, caval

Embryology

Arises at embryonic junction (septum transversum): where ectoderm of amnion meets endoderm of yolk sac (externally) and where foregut meets midgut (internally); mesenchymal structure of transverse septum provides support so blood vessels and liver can form in underlying splanchnic mesoderm (UNSW Embryology: Gastrointestinal Tract - Liver Development [Accessed 23 October 2017])
Hepatic diverticulum buds from ventral foregut at end of third week, grows into primitive septum transversum
Liver forms from endodermal cells of diverticulum, termed hepatoblasts and mesenchyme
Blood supply primarily from umbilical vein; also portal vein and hepatic artery
Placenta clears wastes in bile and absorbs nutrients and umbilical vein blood bypasses liver via ductus venosus
All elements of the biliary tree are recognizable by week 5, although bile duct system not complete until after birth; derived from endoderm (large ducts) and embryonic ductal plate (smaller intrahepatic ducts) (Dig Surg 2010;27:87)
Hematopoietic cells are present in embryonic / fetal liver but absent at term

Physiology

Bile:

Liver produces about 500 ml/day of bile
Promotes dietary fat absorption via detergent action of bile salts; eliminates waste products (bilirubin, excess cholesterol, xenobiotics) that are insufficiently water soluble to be excreted into urine

Bile acids:

Carboxylate steroid molecules, derived from cholesterol, that promote bile flow and secretion of phospholipid and cholesterol
Primary bile acids are cholic acid and chenodeoxycholic acid, secreted as taurine and glycine conjugates; two secondary ones (deoxycholic and lithocholic acid) are formed in the colon by bacterial action

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Bile acids

Bile acid circulation:

All bile acids are reabsorbed via sodium bile acid cotransporter in apical membrane of ileal enterocytes and transported back to liver
Enterohepatic circulation of bile acids maintains a large endogenous pool of bile acids for digestive and excretory purposes

Jaundice:

Also called icterus
Discoloration of skin and sclera due to disruption of bile formation by either retention of pigmented bilirubin or block in bilirubin secretion (cholestasis)

Bilirubin:

End product of heme degradation
200 mg produced daily from old red blood cells broken down via monocyte phagocytic system in spleen, liver, marrow
Also from turnover of P450 cytochromes and premature destruction of marrow red blood cells (with ineffective erthyropoiesis)
Red blood cells are broken down and produce hemoglobin
Globin proteins are removed, leaving heme molecule
Heme is converted to biliverdin via heme oxygenase
Biliverdin is converted to bilirubin via biliverdin reductase
Bilirubin is bound to serum albumin since it is insoluble in blood at physiologic pH; the % unbound increases in severe hemolytic disease or if protein binding drugs displace bilirubin
Hepatocytes take in bilirubin at sinusoidal membrane, conjugate it with glucuronic acid using bilirubin uridine diphosphate glucuronosyltransferase (UGT) in endoplasmic reticulum, then bilirubin is excreted into bile
Bacteria have beta glucuronidases which deconjugate and degrade bilirubin to colorless urobilinogens, excreted in feces as stercobilin, a brown pigment that colors stools
20% of urobilinogens are reabsorbed in ileum / colon, returned to liver, reexcreted into bile
Some urobilinogen is reabsorbed and excreted by the kidney, oxidized to urobilin - a pigment that gives amber color to urine

Accessory lobe

May appear clinically as hepatic mass
Anterior abdominal wall defects are frequently associated with accessory hepatic lobes
Can present with torsion (Surg Radiol Anat 2011;33:819)

Diagrams / tables

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