Liver and Gallbladder
The liver is a remarkable, essential, and central organ for the healthy functioning of the human body. The liver supports almost every organ in the body and is vital for survival. It is the main chemical and enzyme production "factory" in the body and performs over 500 essential life processes including:
Detoxification, protein synthesis, a major role in metabolism, glycogen storage, decomposition of red blood cells, plasma protein synthesis, hormone production, bile production, and production of biochemicals necessary for digestion. The liver is necessary for survival; there is currently no way to compensate for the absence of liver function in the long term, although new liver dialysis techniques can be used in the short term.
The liver lies below the diaphragm in the abdominal-pelvic region of the abdomen. It produces bile, an alkaline compound which aids in digestion via the emulsification of lipids (fats). The liver's highly specialized tissues regulate a wide variety of high-volume biochemical reactions, including the synthesis and breakdown of small and complex molecules, many of which are necessary for normal vital functions.
The liver is a reddish brown organ with four lobes of unequal size and shape. A human liver normally weighs 1.44–1.66 kg (3.2–3.7 lb), and is a soft, pinkish-brown, triangular organ. It is both the largest internal organ (the skin being the largest organ overall) and the largest gland in the human body. It is located in the right upper quadrant of the abdominal cavity, resting just below the diaphragm. The liver lies to the right of the stomach and overlies the gallbladder.
The liver is connected to two large blood vessels, one called the hepatic artery and one called the portal vein:
- The hepatic artery carries the blood that the liver needs to live and function from the aorta to the liver
- the portal vein carries into the liver, the blood that the liver performs functions upon. This blood arrives directly from the entire gastrointestinal tract, spleen and pancreas and contains digested nutrients and anything else that has got into it. The portal vein subdivides into capillaries, which then lead to a lobule. Each lobule is made up of millions of hepatic cells which are the basic metabolic cells. Lobules are the functional units of the liver.
PRODUCTION OF BILE
Bile or gall is a bitter-tasting, dark green to yellowish brown fluid, produced by the liver of most vertebrates, that aids the digestion of lipids in the small intestine. In many species, bile is stored in the gallbladder and, when the organism eats, is discharged into the duodenum. Bile is 85% water, 10% bile salts, 3% mucus and pigments, 1% fats, and 0.7% inorganic salts.
LIVER FUNCTION IN DETAIL
The liver is thought to be responsible for up to 500 separate functions, usually in combination with other systems and organs.
Further information: Proteins produced and secreted by the liver
- A large part of amino acid synthesis
- The liver performs several roles in carbohydrate metabolism:
- The liver is responsible for the mainstay of protein metabolism, synthesis as well as degradation.
- The liver also performs several roles in lipid metabolism:
- The liver produces coagulation factors I (fibrinogen), II (prothrombin), V, VII, IX, X and XI, as well as protein C, protein S and antithrombin.
- In the first trimester fetus, the liver is the main site of red blood cell production. By the 32nd week of gestation, the bone marrow has almost completely taken over that task.
- The liver produces and excretes bile (a yellowish liquid) required for emulsifying fats and help the absorption of vitamin K from the diet. Some of the bile drains directly into the duodenum, and some is stored in the gallbladder.
- The liver also produces insulin-like growth factor 1 (IGF-1), a polypeptide protein hormone that plays an important role in childhood growth and continues to have anabolic effects in adults.
- The liver is a major site of thrombopoietin production. Thrombopoietin is a glycoprotein hormone that regulates the production of platelets by the bone marrow.
- The breakdown of insulin and other hormones
- The liver glucoronidates bilirubin, facilitating its excretion into bile.
- The liver breaks down or modifies toxic substances (e.g., methylation) and most medicinal products in a process called drug metabolism. This sometimes results in toxication, when the metabolite is more toxic than its precursor. Preferably, the toxins are conjugated to avail excretion in bile or urine.
- The liver converts ammonia to urea (urea cycle).
- The liver stores a multitude of substances, including glucose (in the form of glycogen), vitamin A (1–2 years' supply), vitamin D (1–4 months' supply), vitamin B12 (1–3 years' supply), vitamin K, iron, and copper.
- The liver is responsible for immunological effects—the mononuclear phagocyte system (MPS) of the liver contains many immunologically active cells, acting as a 'sieve' for antigens carried to it via the portal system.
- The liver produces albumin, the major osmolar component of blood serum.
- The liver synthesizes angiotensinogen, a hormone that is responsible for raising the blood pressure when activated by renin, an enzyme that is released when the kidney senses low blood pressure.
- The liver also functions as a blood reservoir, being an expandable organ. Large quantities of blood can be stored in its blood vessels, its normal blood volume in the hepatic veins and that in the hepatic sinuses is about 450ml. During cardiac failure with peripheral congestion, the liver expands, and 0.5 to 1 liter of extra blood is occasionally stored in the hepatic veins and sinuses, due to high pressure in right atrium which causes back pressure in the liver.
The main purpose of the gallbladder is to store bile, or gall. The gallbladder is part of the biliary system and serves as a reservoir for bile, which is produced by the liver. The liver produces the bile and then it flows through the hepatic ducts into the gallbladder. The gallbladder releases the bile in response to a hormone called cholecystokinin, which is released from the small intestine. When the bile is released, it is released into the small intestine and its purpose is to break down large fat molecules into smaller ones. After the fat is absorbed, the bile is also absorbed and transported back to the liver for reuse.
When food containing fat (and amino acids) enters the digestive tract, it stimulates the secretion of cholecystokinin (CCK) from I cells of the duodenum and jejunum. In response to CCK, the adult human gallbladder, which stores about 50 millilitres (1.7 U.S. fl oz; 1.8 imp fl oz) of bile, contracts and releases its contents into the duodenum. The bile, originally produced in the liver, emulsifies fats in partly digested food.
During storage in the gallbladder, bile becomes more concentrated which increases its potency and intensifies its effect on fats.
In 2009, it was proposed that the gallbladder can produce several pancreatic hormones, including insulin.