The liver, which is the largest organ in the human body, weighs about 3 pounds and is located in the upper right part of the abdominal cavity. It has two lobes, which are separated by a ligament. It plays a wide variety of roles in the functioning of the human body, which include helping to build muscle, storing energy, stopping cuts from bleeding (blood coagulation) and killing germs and fighting disease. While it is a powerhouse that performs over 500 functions in the body, its role as an excretory organ is of primary importance, since it serves as a filter that removes toxins and unusable materials from the blood before they can reach and affect the rest of the body.
The human body’s excretory system includes the skin, the eccrine or sweat glands, the kidneys and the large intestine. As a whole system, it has four main functions: to get rid of wastes, to eliminate useless by-products excreted from cellular metabolism, to eradicate harmful chemical buildups and to maintain homeostasis, or a steady, balanced chemistry.
The liver plays a unique part in maintaining this balanced chemistry. When proteins are digested, ammonia, which is a toxin, is produced in the body as a by-product. This ammonia enters the liver’s circulatory system (portal circulation), and is converted to urea, which is then excreted by the kidneys in the form of urine. This function of the liver is crucial because, if ammonia is not removed quickly from the body, it will cause permanent damage to the central nervous system.
The liver also manufactures bile. Bile is a fluid containing salts, electrolytes, bilirubin, cholesterol and other organic molecules. It is responsible for the digestion and absorption of fats and fat-soluble vitamins in the small intestine. It is another product of the liver that also aids in excretion because many waste products of the body are secreted into bile and then eliminated in the feces.
Products of red blood cell metabolism are added to bile in the liver in order to be excreted. Bilirubin and biliverdin are both waste products from red blood cell metabolism. When the liver is not functioning properly, bilirubin can build up in the blood, which causes the yellow skin color known as jaundice.
The conversion and elimination of various toxins, such as environmental contaminants, drugs, hormones and other poisons, is another important function of the liver. Because of modern farming techniques and industry, much of the meat, poultry, fish, produce and water consumed today contains hormones, antibiotics, heavy metals and pesticides. Various human vices, such as the over-consumption of alcohol and caffeine, also upset the metabolic balance. Many of these toxins are rich in carbon, similar to the nutrients that are commonly used by the body, and they “hitchhike” into the blood and digestion along with those nutrients. The urinary and the digestive systems, however, are mainly designed to deal with carbon compounds that are water-soluble, like urea, and they are not equipped to deal with these more-complicated toxins. For that reason, these poisons must be converted into a more manageable form before they can be excreted.
This is where the cytochrome p450 system comes into play. The cytochrome p450 is a system of enzymes that are embedded mostly in the lipid part of the endoplasmic reticulum of the hepatocytes, or liver cells. The endoplasmic reticulum is a network of sacs and tubules connected by a continuous membrane, found in all plant and animal cells. It manufactures, processes and transports all sorts of biochemical compounds inside and out of the cells. Because of all the folds, its area makes up a very large portion of the cell itself.
The cytochrome p450 enzymes detoxify poisons that enter the body by finding unusual molecules (poisons) and adding oxygen atoms to them. Most of the time, this has the effect of making the molecule more soluble in water so that it can be more readily excreted by the kidneys. The added oxygen also enables other detoxifying enzymes to aid in converting the poisons to forms that are more easily excreted.
The human liver is one of the few organs in the body that can regenerate itself from as little as 25 percent of its tissue. Although the exact reasons for this are not known, it is indeed fortunate, since the liver and all of its functions are essential for human life. No one can survive without a liver.