1. CARBOHYDRATE METABOLISM: As you know, the liver regulates the blood glucose level. Excess glucose is converted to glycogen in a process known as glycogenesis when blood glucose is high; the hormones insulin and cortisol facilitate this process. During hypoglycemia or stress situations, glycogen is converted back to glucose in a process known as glycogenolysis to raise the blood glucose level. Epinephrine and glucagon are the hormones that facilitate this process. The liver also changes other monosaccharides to glucose. Fructose and galactose, for example, are end products of the digestion of sucrose and lactose. Because most cells, however, cannot readily use fructose and galactose as energy sources, they are converted by the liver to glucose, which is easily used by cells.
2. AMINO ACID METABOLISM: The liver regulates blood levels of amino acids based on tissue needs for protein synthesis. Of the 20 different amino acids needed for the production of human proteins, the liver is able to synthesize 12, called the non essential amino acids. The other eight amino acids, which the liver cannot synthesize, are called the essential amino acids. In this case, “essential” means that the amino acids must be supplied by our food, because the liver cannot manufacture them.
3. LIPID METABOLISM: The liver forms lipoproteins, which as their name tells us, are molecules of lipids and proteins, for the transport of fats in the blood to other tissues. The liver also synthesizes cholesterol and excretes excess cholesterol into bile to be eliminated in feces. Fatty acids are a potential source of energy, but in order to be used in cell respiration they must be broken down to smaller molecules. In the process of beta-oxidation, the long carbon chains of fatty acids are split into two-carbon molecules called acetyl groups, which are simple carbohydrates.
These acetyl groups may be used by the liver cells to produce ATP or may be combined to form ketones to be transported in the blood to other cells. These other cells then use the ketones to produce ATP in cell respiration.
4. SYNTHESIS OF PLASMA PROTEINS: The liver synthesizes many of the proteins that circulate in the blood. Albumin, the most abundant plasma protein, helps maintain blood volume by pulling tissue fluid into capillaries. The clotting factors are also produced by the liver. These, include prothrombin, fibrinogen, and Factor 8, which circulate in the blood until needed in the chemical clotting mechanism. The liver also synthesizes alpha and beta globulins, which are proteins that serve as carriers for other molecules, such as fats, in the blood.
5. FORMATION OF BILIRUBIN: This is another familiar function: The liver contains fixed macrophages that phagocytize old red blood cells (RBCs). Bilirubin is then formed from the heme portion of the hemoglobin. The liver also removes from the blood the bilirubin formed in the spleen and red bone marrow and excretes it into bile to be eliminated in feces.
6. PHAGOCYTOSIS BY KUPFFER CELLS: The fixed macrophages of the liver are called Kupffer cells (or stellate reticuloendothelial cells). Besides destroying old RBCs, Kupffer cells phagocytize pathogens or other foreign material that circulate through the liver. Many of the bacteria that get to the liver come from the colon. These bacteria are part of the normal flora of the colon but would be very harmful elsewhere in the body. The bacteria that enter the blood with the water absorbed by the colon are carried to the liver by way of portal circulation. The Kupffer cells in the liver phagocytize and destroy these bacteria, removing them from the blood before the blood returns to the heart.
7. STORAGE: The liver stores the fat-soluble vitamins A, D, E, and K, and the water-soluble vitamin B12. Also stored by the liver are the minerals iron and copper. You already know that iron is needed for hemoglobin and myoglobin and enables these proteins to bond to oxygen. Copper (as well as iron) is part of some of the proteins needed for cell respiration, and is part of some of the enzymes necessary for hemoglobin synthesis.
8. DETOXIFIFICATION: The liver is capable of synthesizing enzymes that will detoxify harmful substances, that is, change them to less harmful ones. Alcohol, for example, is changed to acetate, which is a two carbon molecule (an acetyl group) that can be used in cell respiration. Medications are all potentially toxic, but the liver produces enzymes that break them down or change them. When given in a proper dosage, a medication exerts its therapeutic effect but is then changed to less active substances that are usually excreted by the kidneys. An overdose of a drug means that there is too much of it for the liver to detoxify in a given time, and the drug will remain in the body with possibly harmful effects.
RELATED;
1. CORTISOL
2. GLUCAGON
3. EPINEPHRINE
6. HEPATITIS
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