Makindo Medical Notes.com

Overview of Liver Physiology

The liver is a vital organ that plays a central role in metabolism, detoxification, and synthesis of essential proteins and biochemicals. It is involved in the regulation of various physiological processes critical for maintaining homeostasis.

Key Concepts

• Anatomy of the Liver:
  • Located in the upper right quadrant of the abdomen.
  • Composed of four lobes: right, left, caudate, and quadrate.
  • Functional units: Liver lobules, containing hepatocytes, bile canaliculi, and sinusoids.
• Blood Supply:
  • Dual blood supply: Hepatic artery (oxygenated blood) and portal vein (nutrient-rich blood from the gastrointestinal tract).
  • Blood exits through the hepatic veins into the inferior vena cava.
• Metabolic Functions:
  • Carbohydrate Metabolism:
    • Gluconeogenesis: Synthesis of glucose from non-carbohydrate sources.
    • Glycogenesis: Storage of glucose as glycogen.
    • Glycogenolysis: Breakdown of glycogen to release glucose.
  • Lipid Metabolism:
    • Synthesis of cholesterol and triglycerides.
    • Production of lipoproteins (e.g., VLDL, LDL, HDL).
    • Beta-oxidation of fatty acids to produce energy.
  • Protein Metabolism:
    • Synthesis of plasma proteins (e.g., albumin, clotting factors).
    • Urea cycle: Conversion of ammonia to urea for excretion.
    • Transamination and deamination of amino acids.
• Detoxification:
  • Biotransformation of drugs and toxins into less harmful compounds.
  • Phase I reactions: Oxidation, reduction, hydrolysis (primarily via cytochrome P450 enzymes).
  • Phase II reactions: Conjugation with glucuronic acid, sulfate, glutathione.
• Bile Production and Secretion:
  • Bile is produced by hepatocytes and stored in the gallbladder.
  • Contains bile acids, cholesterol, and bilirubin.
  • Essential for the digestion and absorption of fats in the small intestine.
• Storage Functions:
  • Storage of glycogen, vitamins (A, D, B12), and minerals (iron, copper).

Detailed Processes

• Carbohydrate Metabolism:
  • Gluconeogenesis:
    • Synthesis of glucose from lactate, glycerol, and glucogenic amino acids.
    • Occurs mainly during fasting and intense exercise.
  • Glycogenesis:
    • Conversion of excess glucose into glycogen for storage in the liver.
    • Regulated by insulin.
  • Glycogenolysis:
    • Breakdown of glycogen to release glucose during periods of low blood sugar.
    • Regulated by glucagon and adrenaline.
• Lipid Metabolism:
  • Cholesterol Synthesis:
    • Cholesterol is synthesized from acetyl-CoA.
    • Essential for cell membrane structure and synthesis of steroid hormones and bile acids.
  • Triglyceride Synthesis:
    • Formation of triglycerides from glycerol and fatty acids for storage or transport.
  • Lipoprotein Production:
    • Synthesis of VLDL, LDL, and HDL to transport lipids in the blood.
• Protein Metabolism:
  • Plasma Protein Synthesis:
    • Production of albumin, clotting factors, and other plasma proteins.
  • Urea Cycle:
    • Detoxification of ammonia by converting it to urea for excretion by the kidneys.
  • Amino Acid Metabolism:
    • Transamination: Transfer of amino groups to form new amino acids.
    • Deamination: Removal of amino groups, producing ammonia and keto acids.
• Detoxification:
  • Phase I Reactions:
    • Oxidation, reduction, and hydrolysis reactions, often catalyzed by cytochrome P450 enzymes.
  • Phase II Reactions:
    • Conjugation with molecules like glucuronic acid, sulfate, or glutathione to increase solubility for excretion.
• Bile Production and Secretion:
  • Hepatocytes produce bile, which is transported to the gallbladder for storage.
  • Bile is released into the small intestine to aid in digestion and absorption of dietary fats.

Clinical Relevance

• Hepatitis:
  • Inflammation of the liver caused by viral infections, alcohol, or toxins.
  • Can lead to liver damage and impaired function.
• Cirrhosis:
  • Chronic liver damage leading to scarring and liver failure.
  • Caused by chronic alcohol use, hepatitis, or other liver diseases.
• Fatty Liver Disease:
  • Accumulation of fat in liver cells, often associated with obesity, diabetes, and alcohol use.
  • Can progress to inflammation and cirrhosis.
• Drug-Induced Liver Injury:
  • Liver damage caused by medications or toxic substances.
  • Monitoring liver function is crucial when administering potentially hepatotoxic drugs.
• Liver Cancer:
  • Primary liver cancer (hepatocellular carcinoma) or metastatic cancer from other organs.
  • Risk factors include chronic hepatitis and cirrhosis.

Summary

Liver physiology encompasses vital functions in metabolism, detoxification, bile production, and storage. The liver plays a central role in maintaining metabolic homeostasis and detoxifying harmful substances. Understanding liver physiology is crucial for diagnosing and treating various liver diseases and conditions that impact overall health.