Comprehensive Anatomy Notes: Liver
1. Introduction
The liver is the largest internal organ of the human body and serves as a vital hub for
metabolism, detoxification, nutrient storage, and synthesis of plasma proteins. Located
in the upper right quadrant of the abdominal cavity, the liver extends across the midline
into the left upper quadrant. It lies inferior to the diaphragm, superior to the stomach,
right kidney, and intestines. The liver is a highly vascular organ with a unique dual blood
supply and remarkable regenerative capacity, which makes it essential for maintaining
homeostasis and overall health.
2. External Anatomy
The liver is roughly triangular or wedge-shaped, weighing approximately 1.2–1.5 kg in
adults. Its diaphragmatic surface is smooth and convex, lying against the diaphragm.
The visceral surface is irregular and contacts multiple organs, including the stomach,
duodenum, right kidney, and colon.
Lobes of the Liver:
● Right Lobe: Largest lobe, occupies most of the right hypochondrium.
● Left Lobe: Smaller, extends into the epigastrium and left hypochondrium.
● Quadrate Lobe: Situated between the gallbladder and round ligament.
● Caudate Lobe: Located posteriorly near the inferior vena cava.
Important Landmarks:
● Falciform Ligament: Separates the right and left lobes anteriorly; contains the
ligamentum teres (remnant of the umbilical vein).
● Coronary Ligaments: Attach liver to the diaphragm.
● Porta Hepatis: Transverse fissure on the visceral surface where vessels and
ducts enter or exit the liver.
3. Internal Anatomy
Internally, the liver is divided into functional units called lobules, which are hexagonal
structures centered around a central vein. Each lobule consists of hepatocytes arranged
in plates, separated by sinusoids through which blood flows. The portal triad, located at
each corner of the lobule, contains:
1. Hepatic artery branch (oxygenated blood)
2. Portal vein branch (nutrient-rich, deoxygenated blood from the intestines)
3. Bile duct (collects bile produced by hepatocytes)
Hepatic Zones:
● Zone 1: Closest to portal triad, first to receive blood, most oxygenated
● Zone 2: Intermediate zone
● Zone 3: Closest to central vein, most susceptible to hypoxia
4. Blood Supply
The liver has a dual blood supply, which is unique among organs:
● Hepatic artery proper: Supplies 25–30% of blood flow; oxygen-rich.
● Portal vein: Supplies 70–75% of blood flow; nutrient-rich but less oxygenated.
Blood drains through the central veins into the hepatic veins, which empty into the
inferior vena cava. This arrangement allows the liver to process nutrients and detoxify
substances absorbed from the gastrointestinal tract before they reach systemic
circulation.
5. Biliary System
The liver produces bile, a greenish fluid essential for fat digestion. Bile is secreted by
hepatocytes into bile canaliculi, which merge into intrahepatic bile ducts. These
converge into the right and left hepatic ducts, forming the common hepatic duct, which
joins the cystic duct from the gallbladder to form the common bile duct. The common
bile duct empties into the duodenum at the ampulla of Vater, regulated by the sphincter
of Oddi.
Functions of Bile:
● Emulsification of dietary fats
● Excretion of bilirubin and cholesterol
● Facilitation of fat-soluble vitamin absorption (A, D, E, K)
6. Liver Ligaments and Peritoneal Attachments
The liver is suspended in the abdominal cavity by several ligaments:
● Falciform ligament: Anterior, divides left and right lobes
● Coronary ligament: Superior, connects liver to diaphragm
● Triangular ligaments (right and left): Lateral extensions of the coronary ligament
● Round ligament (ligamentum teres): Inferior free edge of falciform ligament,
remnant of fetal umbilical vein
● Ligamentum venosum: Remnant of ductus venosus
7. Functional Segmentation
Clinically, the liver is divided into 8 functional segments (Couinaud classification) based
on portal vein and bile duct distribution. Each segment has its own vascular inflow,
outflow, and biliary drainage, allowing segmental resections in surgical procedures
without affecting remaining liver tissue.
Segments:
● Segment I: Caudate lobe
● Segments II–IV: Left lobe
● Segments V–VIII: Right lobe
8. Metabolic Functions
The liver has diverse metabolic roles:
● Carbohydrate metabolism: Glycogenesis, glycogenolysis, gluconeogenesis
● Lipid metabolism: Synthesis of cholesterol, triglycerides, and phospholipids
● Protein metabolism: Synthesis of albumin, clotting factors, and urea from amino
acids
● Detoxification: Biotransformation of drugs, alcohol, and ammonia
● Storage: Glycogen, vitamins (A, D, B12), and minerals (iron, copper)
9. Endocrine and Exocrine Functions
● Endocrine: Produces insulin-like growth factor (IGF-1), angiotensinogen,
thrombopoietin
● Exocrine: Secretes bile into biliary ducts for digestion
Additional Roles:
● Converts inactive vitamin D to active form
● Processes bilirubin from hemoglobin breakdown
10. Clinical Relevance
● Liver Diseases: Hepatitis, cirrhosis, fatty liver, hepatocellular carcinoma
● Surgical Considerations: Knowledge of segments is essential for hepatectomy
● Transplantation: Liver can regenerate after partial hepatectomy; donor and
recipient surgeries are guided by vascular and segmental anatomy
● Imaging: Ultrasound, CT, MRI, and Doppler studies assess liver structure and
blood flow
11. Conclusion
The liver is a complex organ with vital roles in metabolism, detoxification, synthesis,
storage, and bile production. Its anatomical divisions, vascular architecture, and
functional segmentation are crucial for medical practice, including surgery, hepatology,
and diagnostic imaging. Maintaining liver health through a balanced diet, limiting
alcohol, and avoiding hepatotoxic drugs is critical for overall well-being.
