Functions of the liver
introduction
The liver is the largest and most important metabolic organ in the body. It takes on a wide range of tasks, from breaking down harmful substances and utilizing food components to synthesizing new enzymes and proteins that are essential for the body to survive. A failure of the liver function can lead to life-threatening imbalances in the metabolism.
general tasks
About the Portal vein (Port vein) substances that have been absorbed by the intestine into the blood enter the liver. Depending on the needs of the body, the components are used differently. In this way, the liver always ensures that the other organs are adequately supplied with nutrients before it stores them itself. If there is enough in the body, the liver stores sugar in the form of, for example Glycogen. If the blood sugar level falls, the liver can get out of it depot release glucose again.
Also Fat, vitamins and Protein building blocks (amino acids) can be stored in the liver. The liver can then use different amino acids produce vital proteins. These include, for example Clotting factorsthat for the Blood clotting are important, or that too C-reactive protein, which plays an important role in inflammation and also in the blood count as Inflammation parameters applies. It also represents the liver Proteins that can transport fat-soluble substances (fats, hormones) in the blood. Also the body's own cholesterol is largely formed in the liver, which is also part of the Bile which is also produced in the liver.
But the liver is not only responsible for the formation of substances, but also for the Breakdown of harmful substances (detoxification). This is how the liver builds, for example ammonia and instead forms the harmless urea from it. Also Alcohol and medication, as other poisons (Toxins) are broken down in the liver by various enzymes. This includes the Alcohol dehydrogenase and the Cytochrome P450. Another important job the liver does is Degradation of aged or defective cells (for example old erythrocytes). The general excretion of substances via the intestines and kidneys is also coordinated by the liver. For example, water-insoluble substances are excreted through the bile, which reaches the gastrointestinal tract, and water-soluble substances are excreted into the blood, which is then filtered through the kidneys. The liver therefore has important functions in many different areas.
- Alcohol breakdown
- detoxification
Digestive tasks
The most important function of the liver for digestion is Formation of bile. Every day are in the liver about 700 ml Bile is produced, which is then sent via the bile ducts Gallbladder get there and there saved become. The bile consists Lecithin, bile salts, cholesterol, coupled with glucuronic acid (conjugated) Hormones and Bilirubin (Part of the blood pigment, gives the bile its yellow-green color). The bile is released from the gallbladder with meals and is used for Digestion of fats and the Neutralization of acidic gastric juice. It also excretes various substances such as cholesterol and bilirubin.
If fats enter the small intestine with food, they stimulate the production of the hormone cholecystokinin in the mucous membrane of the small intestine. This ensures that the gallbladder tightens and the bile is released into the intestine. The Form bile salts so-called Micelles (spherical lumps) with the fat-soluble components the food, such as free fatty acids, vitamins and cholesterol. In this way, these substances can be transported in the blood and are thus available to the body. These substances can now be absorbed from the blood in all organs and thus used to generate / provide energy or to produce enzymes and other important substances.
In addition, the bile ensures that the Stomach acidwhich gets from the stomach to the duodenum with the chyme, neutralized is used to protect the lining of the intestines. The bile also causes the Promotes the secretion of pancreatic fluidwhich in turn is important for digestion. The pancreatic fluid contains enzymes that can break down fats, proteins and carbohydrates so that they can be absorbed through the intestinal mucosa. The liver is therefore very important for digestion, because without the bile it would be difficult to absorb the fat-soluble food components.These are essential for many functions of the body (hormone production, enzymes).
Tasks for detox
The liver is one of the most important tissues for that Biotransformation. By that one understands the Conversion of non-excretable substances in excretable substances. This is particularly important for substances that are harmful to the body so that they do not accumulate in the body. Many such substances are converted in the liver. These include, for example Alcohol, medicines, pollutants and toxic metabolic waste products. They reach the liver via the blood vessels and are converted or excreted there.
The conversion reaction involves two steps. In the first step, a functional group, for example -OH or -SH, is attached to the substance (Conversion reaction) and in the second step, the molecules are attached to water-soluble substances via the functional group (Conjugation reaction). The important enzymes for these reactions are Cytochrome 450 oxygenases. You are for one Phase 1 reaction responsible and are only slightly substrate-specific. This means that they can convert many different substances. Once the substances have been converted into water-soluble substances in the liver, they can be released into the blood and excreted via the kidneys (for example Ammonia to urea). Other substances cannot be released into the blood, but are excreted in the bile. This includes, for example, the Blood pigment hemoglobin. It gets in the liver degraded to bilirubin. This is then conjugated (coupled) and bound to bile salts in the bile and transported in order to be excreted via the intestine. This also applies to many drugs.
alcohol is also broken down in the liver. For this, however, there is specific enzymes. In the first step, the alcohol is through the Alcohol dehydrogenase converted into a harmful intermediate, the aldehyde. Now this must have another enzyme that Aldehyde dehydrogenase, converted into acetic acid. People who do not have sufficient availability of this second enzyme experience increased nausea and severe headaches. So the liver is that central organ for the detoxification of various substances through biotransformation. If the reactions of the biotransformation no longer work or if the liver is no longer functional, the body can be seriously damaged by the accumulation of these harmful substances (medication, alcohol, waste materials).
- Liver disease
- Jaundice
Absorption phase
In the absorption phase (directly after ingestion) the nutrients are absorbed from the intestine into the liver and there, into the Storage products and energy suppliers transformed. The energy suppliers are then transported to the various organs, where they are available for the metabolic processes of the individual organs. As soon as all organs are taken care of, the excess glucose in glycogen converted and stored in the liver, or in high amounts also into fat transformed. The Fatty acids are converted into triacylglycerides (Fats) are converted and stored in adipose tissue and the Amino acids are made into proteins and enzymes rebuilt and made available for the corresponding functions. Some of them can also be stored in storage vesicles (small, rounded vesicles) in various end organs (e.g. insulin, thyroid hormones). In this way, the liver builds up a supply in times of excess, which then serves to supply all vital organs and functions in times of hunger. Only with these storage possibilities can we do vigorous sport and sometimes not eat anything for hours without our body having to restrict functions.
- carbohydrates
- Fats in the human body
Tasks for the metabolism
The liver is the body's central metabolic organ. She regulates that Metabolism of protein, fats and sugars but also Minerals, vitamins and hormones. The nutrients pass through the portal vein from the intestine to the liver and are absorbed there. The liver can then divide up different steps. In this way, the substances can be converted into others or excreted. At the same time, the liver can also build up new substances that are important for the metabolism. This includes Proteins, coagulation factors, sugar, fatty acids and of course cholesterol.
All of these substances are needed to transport other substances (proteins), to build membranes (cholesterol), to synthesize hormones (cholesterol, proteins), to build up energy reserves (fatty acids, sugar) and to release energy (sugar, fatty acids, proteins ). Most of the substances that get into the liver are passed on to the other organs as needed. Only the excess substances are kept in the liver and stored there as a reserve so that they can be given back to the other organs when needed. In particular, sugar (glycogen), fat-soluble vitamins and minerals (iron) are stored in the liver.
