11/07/2026
Human Physiology of the Liver
The liver is the largest internal organ and the body's central metabolic factory. It performs over 500 vital functions that maintain homeostasis, process nutrients, detoxify harmful substances, and produce essential proteins.
1. Carbohydrate Metabolism
The liver regulates blood glucose levels by:
Glycogenesis: Converts excess glucose into glycogen for storage.
Glycogenolysis: Breaks down glycogen into glucose when blood sugar falls.
Gluconeogenesis: Produces glucose from amino acids, glycerol, and lactate during fasting.
Importance: Maintains a stable blood glucose level.
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2. Protein Metabolism
The liver:
Synthesizes plasma proteins such as albumin and clotting factors.
Converts ammonia (a toxic waste product) into urea through the urea cycle.
Metabolizes amino acids.
Importance: Maintains blood volume, clotting, and removes toxic nitrogen waste.
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3. Lipid (Fat) Metabolism
The liver:
Produces cholesterol and phospholipids.
Synthesizes lipoproteins.
Converts excess carbohydrates and proteins into fat.
Oxidizes fatty acids to produce energy.
Produces ketone bodies during prolonged fasting.
Importance: Provides energy and supports hormone synthesis.
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4. Bile Production
The liver produces 600–1000 mL of bile daily.
Functions of bile:
Emulsifies fats.
Helps absorb fat-soluble vitamins (A, D, E, and K).
Excretes bilirubin and excess cholesterol.
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5. Detoxification
The liver detoxifies:
Drugs (e.g., paracetamol)
Alcohol
Environmental toxins
Metabolic waste products
Hormones
This function mainly occurs through liver enzymes such as the cytochrome P450 system.
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6. Storage Function
The liver stores:
Glycogen
Iron
Copper
Vitamin A
Vitamin D
Vitamin B12
Vitamin K
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7. Bilirubin Metabolism
Old red blood cells are broken down, producing bilirubin. The liver:
Converts unconjugated bilirubin into conjugated bilirubin.
Excretes it into bile.
Failure of this process leads to jaundice.
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8. Immune Function
Specialized liver macrophages called Kupffer cells:
Remove bacteria.
Destroy old blood cells.
Filter toxins from portal blood.
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9. Blood Clotting
The liver synthesizes clotting factors including:
Fibrinogen
Prothrombin
Factors V, VII, IX, and X
Without adequate liver function, bleeding risk increases.
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10. Endocrine Functions
The liver:
Activates vitamin D.
Produces IGF-1 (Insulin-like Growth Factor-1) in response to growth hormone.
Metabolizes hormones such as insulin, estrogen, and cortisol.
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Summary Table
Function Role
Carbohydrate metabolism Maintains blood glucose
Protein metabolism Produces albumin and clotting factors; converts ammonia to urea
Fat metabolism Produces cholesterol, lipoproteins, ketone bodies
Bile production Digests fats and removes waste
Detoxification Removes drugs, alcohol, toxins
Storage Glycogen, vitamins, iron, copper
Bilirubin metabolism Prevents jaundice
Immune defense Kupffer cells remove pathogens
Blood clotting Produces clotting factors
Endocrine Activates vitamin D and produces IGF-1
Clinical Correlation
When liver function is impaired (e.g., hepatitis or cirrhosis), patients may develop:
Jaundice
Low blood sugar
Bleeding disorders
Ascites
Hepatic encephalopathy
Reduced albumin causing edema
The liver is essential for metabolism, detoxification, digestion, immunity, and maintaining the body's internal balance.
