Definition:
The liver is the largest internal organ in the human body, located in the upper right quadrant of the abdomen. It performs a wide range of vital functions essential for metabolism, digestion, detoxification, and immune defense.
Anatomy of the Liver:
1. Location: The liver is situated beneath the diaphragm, primarily on the right side of the body. It extends across the midline and partially into the left upper quadrant of the abdomen.
2. Structure:
– Lobes: The liver is divided into two main lobes, the right lobe and the smaller left lobe. These lobes are further subdivided into functional units called lobules.
– Segments: Each lobe is further divided into segments based on vascular and biliary structures, allowing for surgical resection and anatomical localization of liver lesions.
– Vascular Supply: The liver receives dual blood supply from the hepatic artery (oxygenated blood) and the portal vein (nutrient-rich blood from the gastrointestinal tract). These blood vessels branch into smaller vessels within the liver lobules, supplying oxygen and nutrients to hepatocytes (liver cells).
3. Histology:
– Hepatocytes: The liver consists predominantly of hepatocytes, specialized epithelial cells responsible for performing metabolic functions, detoxification, and bile production.
– Sinusoids: Blood flows through sinusoidal capillaries within the liver lobules, allowing exchange of nutrients, oxygen, and metabolic waste products between hepatocytes and blood.
– Bile Ducts: Bile produced by hepatocytes drains into small bile ducts within the liver lobules, which eventually coalesce into larger bile ducts that exit the liver and transport bile to the gallbladder and small intestine.
4. Gallbladder and Biliary System:
– The gallbladder is a small, pear-shaped organ located beneath the liver, which stores and concentrates bile produced by the liver. Bile is released from the gallbladder into the duodenum to aid in digestion and absorption of fats.
Functions of the Liver:
1. Metabolism:
– Carbohydrate Metabolism: The liver plays a central role in regulating blood glucose levels by storing glucose as glycogen (glycogenesis) and releasing glucose into the bloodstream as needed (glycogenolysis and gluconeogenesis).
– Lipid Metabolism: Hepatocytes synthesize and metabolize lipids, including fatty acids, cholesterol, and triglycerides. The liver also produces bile salts, which emulsify fats in the digestive tract to facilitate their absorption.
– Protein Metabolism: The liver synthesizes plasma proteins, including albumin, clotting factors, and complement proteins. It also deaminates and metabolizes amino acids, converting ammonia into urea for excretion by the kidneys (urea cycle).
2. Detoxification and Biotransformation:
– The liver metabolizes and detoxifies endogenous and exogenous substances, including drugs, alcohol, toxins, and metabolic byproducts. Hepatocytes contain enzymes (e.g., cytochrome P450) and conjugation pathways that facilitate the breakdown and elimination of harmful substances from the body.
3. Bile Production and Secretion:
– Hepatocytes synthesize bile, a complex fluid composed of bile salts, cholesterol, phospholipids, bilirubin, and electrolytes. Bile is secreted into bile canaliculi, transported through bile ducts, and stored in the gallbladder before being released into the duodenum to aid in fat digestion and absorption.
4. Storage:
– The liver serves as a storage organ for essential nutrients, vitamins, and minerals, including glycogen, fat-soluble vitamins (A, D, E, and K), iron, and copper. These stored substances are released into the bloodstream as needed to maintain metabolic homeostasis.
5. Immune Defense:
– Kupffer cells, specialized macrophages located within the liver sinusoids, play a crucial role in immune defense by phagocytosing pathogens, foreign particles, and damaged cells. The liver also produces acute-phase proteins and cytokines involved in the immune response to infection and inflammation.
6. Hematopoiesis (Fetal Development):
– During fetal development, the liver is a major site of hematopoiesis, producing red blood cells (erythropoiesis) and immune cells. However, this function declines after birth as hematopoiesis shifts to the bone marrow.
Understanding the anatomy and functions of the liver is essential for diagnosing and managing liver diseases, as well as for developing therapeutic strategies to support liver function and promote overall health. Advances in medical imaging, diagnostic techniques, and treatment modalities continue to enhance our understanding and management of liver disorders.
