The human liver is a crucial organ situated in the upper right quadrant of the abdomen, playing a central role in various bodily functions such as metabolism, detoxification, digestion, and nutrient storage. Structurally, it is the largest internal organ and gland, weighing about 1.4 kg (3 pounds), and is divided into two primary lobes, the right and left lobes, which are further segmented into smaller lobes. The liver receives blood from the hepatic artery, providing oxygenated blood, and the portal vein, supplying nutrient-rich blood from the gastrointestinal tract. Its basic structural unit is the lobule, a hexagonal arrangement of hepatocytes, the liver cells that radiate around a central vein.

 

In metabolic processes, the liver maintains blood glucose levels by storing excess glucose as glycogen through glycogenesis and breaking it down to release glucose via glycogenolysis. It also converts non-carbohydrates into glucose through gluconeogenesis. In lipid metabolism, the liver synthesizes, stores, and breaks down fats, producing triglycerides, cholesterol, and phospholipids, and converts excess carbohydrates and proteins into fatty acids and triglycerides. Protein metabolism involves the synthesis of most plasma proteins, including albumin, clotting factors, and globulins, and the deamination of amino acids to produce urea, which the kidneys excrete.

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The liver detoxifies various metabolites, drugs, and toxins through enzymatic processes, notably involving cytochrome P450 enzymes, making these substances more water-soluble for excretion via urine or bile. It also breaks down and removes excess hormones from the bloodstream. Bile production is another critical function, with the liver producing bile, a greenish-yellow fluid essential for digesting and absorbing fats. Bile contains bile salts, cholesterol, bilirubin, and water, and is stored in the gallbladder, released into the duodenum to emulsify fats.

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Storage functions of the liver include storing glycogen, fat-soluble vitamins (A, D, E, K), vitamin B12, and minerals such as iron and copper. Additionally, the liver plays a significant role in blood filtration, processing blood from the digestive tract before it enters systemic circulation. Kupffer cells, specialized immune cells in the liver, engulf and break down old red blood cells, bacteria, and other particulate matter, contributing to the body’s immune defense.

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The liver also regulates blood clotting by synthesizing most of the proteins required for this process, including fibrinogen, prothrombin, and clotting factors V, VII, IX, and X, as well as producing anticoagulant proteins like heparin and antithrombin. It plays a substantial role in hormone metabolism, breaking down insulin, glucagon, thyroid hormones, and steroid hormones such as estrogen and cortisol.

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Various pathological conditions can impair liver function, including hepatitis (inflammation often caused by viral infections or toxins like alcohol), cirrhosis (chronic liver damage leading to scarring and impaired function), fatty liver disease (accumulation of fat in liver cells, which can be non-alcoholic or alcoholic), liver cancer (malignant tumors often secondary to chronic liver diseases), and liver failure (a severe decline in liver function due to acute injury or chronic disease). Understanding the liver’s complex functions is crucial for recognizing and managing liver-related diseases, which can significantly impact overall health and quality of life.