Functions of the liver.
Functions of the Liver
The liver, a vital organ strategically located in the abdominal cavity, receives a significant portion (25%) of the cardiac output, primarily through the portal vein, which carries blood from the gastrointestinal tract. This strategic positioning enables the liver to efficiently process absorbed nutrients and detoxify potentially harmful substances like drugs and toxins. The liver performs a wide array of functions essential for maintaining homeostasis and supporting various physiological processes.
Metabolic Functions
- Carbohydrate Metabolism:
- Glycogenesis: The liver converts excess glucose into glycogen for storage. This process is stimulated by insulin, the hormone of "abundance," ensuring glucose levels are regulated during periods of high glucose availability.
- Glycogenolysis: The liver breaks down stored glycogen into glucose when blood glucose levels drop. This process is stimulated by glucagon, the hormone of "starvation," maintaining glucose supply during fasting or low glucose conditions,
- Gluconeogenesis: The liver synthesizes glucose from non-carbohydrate sources, such as amino acids, lactate, and glycerol, particularly during prolonged fasting or carbohydrate deprivation. This process is crucial for maintaining blood glucose levels and supplying energy to the brain and other glucose-dependent tissues.
- Protein Metabolism:
- Amino Acid Synthesis: The liver synthesizes non-essential amino acids, providing the building blocks for protein synthesis.
- Plasma Protein Synthesis: The liver is the primary site for the synthesis of most plasma proteins, including albumin, clotting factors, and transport proteins.
- Albumin is crucial for maintaining plasma oncotic pressure, preventing edema, and transporting various substances in the blood.
- Clotting factors, like prothrombin, are essential for blood coagulation. Liver dysfunction can lead to impaired clotting and bleeding disorders.
- Transport proteins carry lipids, hormones, and other molecules in the blood.
- Ammonia Detoxification: The liver converts ammonia, a toxic byproduct of protein metabolism, into urea, which is then excreted by the kidneys.
- Lipid Metabolism:
- Fatty Acid Oxidation: The liver breaks down fatty acids for energy production, particularly during fasting or low carbohydrate availability.
- Lipoprotein Synthesis: The liver synthesizes lipoproteins, such as VLDL (very low-density lipoprotein), LDL (low-density lipoprotein), and HDL (high-density lipoprotein), responsible for transporting lipids in the blood.
- Cholesterol Synthesis: The liver synthesizes cholesterol, which is used for cell membrane structure, hormone production, and bile acid synthesis.
- Bile Acid Synthesis: The liver converts cholesterol into bile acids, essential for lipid digestion and absorption.