The Liver
The liver is the largest internal organ, functioning as the body’s primary metabolic hub. It is organized into functional units called hepatic lobules.
Microscopic Organization (The Portal Triad)
At the corner of each hexagonal lobule is the portal triad, consisting of:
- Portal Vein: Carries nutrient-rich blood from the GI tract (75% of liver blood supply).
- Hepatic Artery: Carries oxygenated blood (25% of supply).
- Bile Duct: Collects bile from hepatocytes.
Functional Zones (Rappaport Classification)
| Zone | Key Characteristic |
|---|---|
| Zone I (Periportal) | Highest oxygenation; most active in oxidative metabolism and gluconeogenesis. |
| Zone II (Intermediate) | Intermediate metabolic activity. |
| Zone III (Centrilobular) | Lowest oxygenation; most prone to ischemia and toxin-induced injury (e.g., CYP450 metabolism of alcohol/drugs). |
High-Yield Exam Pearl:
Zone III (centrilobular) contains the highest concentration of cytochrome P450 enzymes. This is why centrilobular necrosis is the classic finding in cases of acetaminophen (paracetamol) toxicity or severe ischemic injury (shock liver).