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Last updated: September 15, 2021

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The liver is a wedge-shaped organ that is located underneath the diaphragm in the right upper abdominal quadrant. It is covered by a capsule and connected to surrounding structures via ligaments. The porta hepatis structures are found in a fissure between two of the four liver lobes. The hepatic artery proper and the portal vein provide the liver with a dual blood supply. Microscopically, the liver is divided into lobules, each with a central vein and a portal triad. Each portal triad consists of an artery, vein, and bile ductule, and is accompanied by lymphatic vessels and a branch of the vagus nerve. Liver parenchyma consists of hepatocytes and hepatic sinusoids. Hepatic sinusoids drain into the central vein of each lobule. The liver is responsible for energy metabolism, synthesis of various substances (e.g., glucose, ketones, bile acid), glucose homeostasis regulation, nutrient storage, and the clearance/excretion of toxins (e.g., ethanol) and waste products. In fetuses, the liver is the site of erythropoiesis from 6 weeks' gestation until birth. During embryogenesis, the liver originates from the endoderm. The ligamentum teres forms from the obliterated umbilical vein and is located in the free edge of the falciform ligament.

General structure

  • Largest gland in the body
    • Weight: ∼ 1.2–1.5 kg in adults (2.6–3.3 pounds) [1][2]
  • Wedge-shaped
  • Consists of four lobes:
    • Right (largest)
    • Left
    • Quadrate
    • Caudate
  • Typically divided into 8 segments
  • Surrounded by the hepatic capsule (two layers)
    • Outer serous layer derived from peritoneum, which covers the entire liver (except the bare area of the liver)
    • Fibrous inner layer (the Glisson capsule) that covers the entire liver (including the bare area of the liver), the hepatic artery, portal vein, and bile ducts
  • Porta hepatis structures




Vasculature of the liver
Type of vessel Vessels

As part of the liver's dual blood supply, the portal vein allows tissue to remain oxygenated and preserve function in the event of an obstructed hepatic artery.


Distention of the capsule results in well-localized, sharp pain, as seen in ascites, inflammation, or hepatic cancer.


Zone I is first and zone III is last to receive O2.

Zone II is affected in yellow fever.


Functions of the liver
Function Related biochemical pathways
Energy metabolism
Detoxification and clearance/excretion

For laboratory parameters for each of the functions, see “Parameters of hepatocellular damage,” “Parameters of cholestasis,” and “Parameters of hepatic synthesis” in “Liver function tests.”


Breakdown of ethanol

Example of zero-order elimination (for alcohol dehydrogenase); : A constant amount of alcohol is metabolized per unit time (∼ 1 ounce of alcohol/hour). NAD+ is the limiting reactant for this pathway.

  1. Oxidation of ethanol to acetaldehyde by alcohol dehydrogenase
  2. Oxidation of acetaldehyde to acetate by acetaldehyde dehydrogenase
  3. Ligation of acetate and coenzyme A to acetyl-CoA by thiokinase under ATP consumption

When large quantities of alcohol are consumed, acetaldehyde builds up faster than it can be metabolized by acetaldehyde dehydrogenase. Excess acetaldehyde plays a major role in hangover symptoms.

FOMEpizole: For Overdosing on Methanol or Ethylene glycol!

It is DISgusting to drink alcohol when taking DISulfiram!

Metabolic consequences of heavy ethanol consumption

When ethanol is metabolized, there is an increase in the NADH/NAD+ ratio in the liver. Heavy ethanol consumption and consequently excess NADH result in:

  • The main purpose of all the metabolic alterations during fasting and starvation is to provide energy to supply vital organs (e.g., the brain) and cells (especially the RBCs) to guarantee their function and protein preservation
  • The metabolic processes during fasting and starvation are primarily regulated by
  • The amount of stored substrate (e.g., adipose tissue) determines the survival time.
Energy sources during fasting and starvation
Time Biochemical reactions and substrates
Fasting (in between meals)
Starvation days 1–3
Starvation after day 3

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