The Liver: Vital Functions, Metabolic Hub, and Clinical Significance

The liver (1.5 kg, largest solid internal organ) performs >500 functions. It is the body's metabolic, detoxification, synthetic, and immunologic factory.

Core Functions

1. Metabolism:
   • Carbohydrates: Glycogen storage/gluconeogenesis → glucose homeostasis.
   • Proteins: Synthesis (albumin, clotting factors, transport proteins), deamination, urea cycle (ammonia detox).
   • Lipids: β-oxidation, lipoprotein synthesis (VLDL, HDL), ketogenesis, cholesterol synthesis/bile conversion.
2. Storage: Glycogen (100g), vitamins (A, D, E, K, B12), iron (ferritin), copper.
3. Detoxification: Phase I (CYP450 oxidation), Phase II (conjugation) → biliary/renal excretion. Drugs, toxins, hormones, bilirubin.
4. Bile Production (0.5–1 L/day): Bile acids (fat emulsification), bilirubin, cholesterol, phospholipids. Stored in gallbladder.
5. Hemostasis: Synthesizes all clotting factors (except VIII/vWF), anticoagulants (protein C/S, antithrombin), fibrinolytic proteins.
6. Immunity: Kupffer cells (80% body's fixed macrophages) clear gut-derived bacteria/endotoxin. Acute-phase proteins (CRP, fibrinogen). Complement synthesis.
7. Hormone Regulation: Degrades insulin, glucagon, steroids, thyroid hormones. Produces IGF-1, hepcidin (iron), thrombopoietin.

Unique Features

• Dual Blood Supply: Hepatic artery (25% flow, 50% O₂) + Portal vein (75% flow, nutrients).
• Regeneration: Can restore mass after 70% resection (hepatocyte proliferation).
• Zonation: Periportal (oxidative, gluconeogenesis) vs. Pericentral (glycolysis, detox, CYP450).

Clinical Assessment

• LFTs: ALT/AST (hepatocellular), ALP/GGT (cholestatic), Bilirubin, Albumin, INR (synthetic function).
• Imaging: US (first-line), CT/MRI, FibroScan (stiffness).
• Biopsy: Gold standard for etiology/staging.

Liver failure = multisystem collapse. Early detection (screening at-risk) and etiology-specific treatment (antivirals, abstinence, immunosuppression, metabolic) save lives.