The liver, an essential organ in the human body, performs over 200 vital functions that can be broadly categorized into metabolic, hematological, endocrine regulation, and bile production.

Metabolic Regulation:

The liver is the central organ involved in regulating blood composition. It stabilizes blood glucose levels, maintaining them within the range of 70–110 mg/dL. When these levels drop, the liver breaks down glycogen reserves and releases glucose into the bloodstream. It can also synthesize glucose from other carbohydrates or amino acids through a process called gluconeogenesis. Conversely, when blood glucose levels increase, the liver removes glucose from the bloodstream for storage as glycogen or for lipid synthesis.

In lipid metabolism, the liver regulates levels of triglycerides, fatty acids, and cholesterol. When these levels decrease, the liver breaks down lipid reserves and releases them into the bloodstream. If the levels are high, lipids are removed and stored.

Protein metabolism involves hepatocytes breaking down amino acids through deamination for ATP production or converting them into carbohydrates or fats. The toxic byproduct, ammonia, is converted into urea, which is then excreted in urine.

Detoxification:

The liver plays a significant role in detoxifying substances like alcohol and excreting drugs such as penicillin, erythromycin, and sulfonamides into bile. It absorbs lipid-soluble toxins from the diet and stores them in lipid deposits, preventing disruptions to cellular functions. The liver also removes other toxins from the bloodstream, breaking them down or excreting them in bile. Moreover, it chemically modifies or excretes hormones to regulate their activity.

Hematological Regulation:

The liver's stellate reticuloendothelial (Kupffer) cells phagocytize aged red blood cells, white blood cells, and some bacteria. These cells also recycle iron and other components from hemoglobin.

Endocrine Functions:

The liver plays a significant endocrine role by producing and regulating various hormones and hormone-like substances essential for maintaining homeostasis. It synthesizes insulin-like growth factor 1 (IGF-1) in response to growth hormone, promoting cell growth and repair. The liver also secretes angiotensinogen, a precursor to angiotensin, which is crucial for regulating blood pressure and fluid balance. Additionally, it produces thrombopoietin, a hormone that stimulates platelet production in the bone marrow. The liver contributes to hormonal balance by metabolizing and inactivating steroid hormones such as estrogen and testosterone. It also participates in the endocrine regulation of vitamin D metabolism by converting vitamin D into 25-hydroxyvitamin D, the primary circulating precursor to its active form, which is critical for calcium and phosphate regulation.

Bile Production:

Lastly, the liver synthesizes and secretes bile into the duodenum's lumen.

The liver's diverse functions underscore its importance in maintaining overall health and performing a wide range of tasks, including metabolism, detoxification, nutrient storage, and immune system support.