Hepatic System肝脏 · 化学工厂

Lobule · dual blood supply

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肝小叶 · 双血供

The liver's position in the body is unusual: 1.2-1.5 kg (~2.5% body weight), runs 500+ known chemical reactions, regenerates 70% in 6 months. Only one organ combines all three.

It's also one of few organs with a dual blood supply:

Portal vein provides ~75% of flow — nutrient-rich, draining stomach, intestines, pancreas, spleenHepatic artery provides ~25% — oxygen-rich, from the heart
The two streams converge in hepatic sinusoids, flow slowly past hepatocytes, then exit via central vein → hepatic vein → IVC → heart.

This architecture means almost everything you eat (except some fat that bypasses via lymph) passes through the liver first — the first-pass effect. Several clinical phenomena follow:

Oral drugs typically have lower bioavailability than IV — a fraction is metabolized in the first passIn liver disease, blood ammonia rises (intestinal bacterial NH3 is normally cleared by liver)Postprandial glucose peaks are buffered by liver first — the liver grabs 50-70% of portal-vein glucose for glycogen
The functional unit is the lobule, a ~1 mm hexagonal structure: central vein at the center, six corners each holding a portal triad (portal vein branch + hepatic artery branch + bile duct), hepatocytes arranged in plates, sinusoids between them. Kupffer cells, resident macrophages, sit along sinusoids phagocytosing gut-derived debris and senescent red cells.

Hepatocytes also show zonation from portal triad to central vein, Zones 1-3. Zone 1 is oxygen-rich and handles gluconeogenesis, β-oxidation, detox; Zone 3 is hypoxic, runs glycolysis, fat synthesis, alcohol and drug metabolism — which is why alcohol and drug injury always damage Zone 3 first.

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Hepatic System肝脏 · 化学工厂

Lobule · dual blood supply

Stop 1/6

肝小叶 · 双血供

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