Anatomy of the Liver Flashcards
Liver Topography
Largest gland in body except skin (1.4-1.6kg)
Wedge-shaped reddish brown organ
Located below diaphragm; mostly in right hypochondrium & epigastrium
Main functions: detoxification, protein synthesis, production of bile (lipid digestion), glycogen storage
Highly vascularised
Pliable to touch (easily lacerated)
Gross anatomy
Diaphragmatic upper surface blunt, dome-shaped/sharp inferior border
Anterior view: divided into 2 main lobes (left and right)
Posterior view: two other lobes (quadrate and caudate)
Surface covered by peritoneum except bare area, where it touches the diaphragm
Falciform (ant) and lesser omentum (post) ligaments separate right and left lobes
Porta hepatis divides the quadrate and caudate lobes
Peritoneal Folds & Lesser Omentum
Falciform ligament: links anterior abdominal wall to liver; ligamentum teres (round ligament) at lower end (round ligament obliterated left umbilical vein extends to umbilicus); coronary ligaments links diaphragm to liver; lesser omentum links liver to stomach
Lesser omentum: from lesser curvature of stomach to porta hepatis; has a free margin (ventral mesentery); encloses hepatic artery, portal vein, bile duct, lymph vessels; close to stomach and encloses gastric arteries and veins
Blood Supply
Coeliac Artery: 3 main branches - left gastric; splenic; hepatic; exits aorta at T12/L1 level; also supplies duodenum and pancreas.
Liver: hepatic artery, a branch from the coeliac trunk, brings from the heart; portal vein, formed by coming together of the superior mesenteric and splenic veins, brings deoxygenated blood from the gut, carrying nutrients/drugs…
Hepatic artery variations: seen in 40-60% of people; causes: right hepatic artery replaced to SMA; left hepatic artery replaced to left gastric artery replaced to left gastric artery;; trifurcation of common hepatic artery (right and left hepatic and gastroduodenal artery - critical test done prior to any surgery on liver)
Porta Hepatis
At the hilum of liver - visceral surface
Deep fissure - 5 cm
Entry/exit point for: hepatic portal vein, hepatic artery proper, common hepatic duct, nerves and lymphatics
Once in: branching of vessels and ducts –> division of the liver into lobes and segments
Functional Anatomy (inc segments)
Metabolism - portal system
Production and secretion of bile
Each lobe contains several lobules (functional unit), which are hexagonal and contain hepatocytes (which secrete bile and are 60% of liver cell population). Each hexagon has a portal triad at each corner
Lobes are divided into segments (Coinaud) according to how hepatic artery and portal vein subdivide; branches of hepatic artery and portal vein carry blood into sinusoids; tributaries of bile ducts accompany the two, but carrying bile in opposite direction
The three structures together are called the portal triad
Hepatocytes - metabolic function
Synthesis and release plasma proteins into blood e.g. albumin and clotting factors
Deaminates amino acids, creating ammonia which is then converted into urea
Converting bilirubin into bile pigment
Production of bile salts to emulsify fats
Venous drainage of liver
Mixed blood from 2 sources (portal and hepatic) in sinusoids passes through hepatocytes, and from there into central vein
Central vein found at centre of hepatic lobule
Several central veins then drain into interlobular (sublobular) vein
Inter/sublobular veins then drain into hepatic veins
Finally, hepatic veins drain into inferior vena cava
Hepatic Portal System
Drains the GI tract towards the liver (distinct from systemic venous system)
Toxins/drugs that are absorbed from GI tract have to pass through the liver before reaching the heart
Anastomosis: communications between some branches of the portal and systemic systems is crucial for survival - known as portocaval anastamosis; this anastamosis is particularly important if the portal vein becomes blocked or passage via the liver meets resistance - portal hypertension. Blood is can travel collateral to the liver returning to the heart
Examples: abdominal part of oesophagus (left gastric tributaries w/ oesophageal branches azygos), anal canal (superior rectal anastamoses with middle and inferior rectal), umbilicus (paraumbilical veins w/ epigastric veins), veins of colon, duodenum, pancreas, liver, with renal lumbar and phrenic
Portal Hypertension
Fairly common clinical condition
Any obstruction to portal vein
Common presentation signs include varicoses, caput medusa; oesophageal varices
Portacaval shunt
Shunts were typically employed to ameliorate hypertension
It is effectively diverted blood from portal vein to IVC, however this has largely been abandoned since invention of TIPS (trans-jugular intrahepatic portosystemic shunting)
Role of Liver in Bile Production
Bile is secreted by hepatocytes into bile canaliculi, at rate of 40ml/hour
Bile canaliculi join to form 2 main hepatic ducts - left and right - that drain the respective lobes
Emerge from porta - unite to form common hepatic duct
Although bile flows continuously towards the duodenum, it is prevented entry by a closed sphincter of Oddi, located at the end of the biliary tree
Lymph drainage
Liver produces vast amounts of lymph that drain into lymph nodes located in the vicinity of the porta hepatis
These nodes are termed coeliac to match coeliac artery
Coeliac nodes in turn drain into the cisterna chyli
Liver Trauma
Closely related to lower ribs
Fracture ribs/penetrating wounds
High vascularisation -> severe haemorrhage
Remove portions due to segmental nature liver and vessels/ducts supplying it - liver biopsies, metastatic spread, cirrhosis
