Physiology of fatty liver disease

2021-04-28 02:09 PM

In general, the clinical presentation is usually inconspicuous and the progression is usually mild, since the fat is not a toxic substance, it only causes the mechanical impact of the liver to be slightly large.

Definitions

Normally, the amount of fat in the liver is about 4-6%, mainly triglycerides. Called fatty liver when the amount of fat in the liver is over 13%, in most cases, it is due to increased storage of triglycerides, if microscopy of the liver can usually detect fat droplets inside the cytoplasm of the cells. liver cells. These fat droplets push the nucleus of the liver cells close to the cell membrane.

Mechanism

Normally, triglycerides, after being synthesized inside liver cells, are rapidly transported out of the liver in the form of VLDL. Therefore, fatty liver can be divided into two groups: (1) due to increased synthesis of triglycerides inside hepatocytes, (2) by reducing the transport of triglycerides from the liver.

Fatty liver results from increased synthesis of triglycerides inside liver cells beyond its ability to transport it out of the liver

May be encountered in the following cases:

(1) Increased macronutrients due to high lipid intake. When eating a lot of fat, increase the nourishing seeds to the liver, including many fatty acids. Under the effect of lipoprotein lipase in the blood, nourishing seeds release many free fatty acids into the liver. Fatty acids are activated inside liver cells to acyl-coenzyme A and then combine with glycerol phosphate into many triglycerides.

(2) Increased free fatty acid in the blood due to increased mobilization from stored adipose tissue in diabetes or starvation. In these cases, there is an increase in the mobilization of free fatty acids from fatty tissue into the blood, from which the liver increases the absorption of free fatty acids and then converts to more triglycerides.

(3) Diet is too high in calories. When the diet is too high in calories, excess acetyl coenzyme A samples cannot be converted back to pyruvic acid because of the unidirectional reaction, so these samples go into the synthesis of acyl-coenzyme A and combine with glycerol phosphate into triglycerides.

(4) Alcoholism. In alcoholism, ethanol causes increased NADH in liver cells, thereby stimulating fatty acid synthesis leading to increased synthesis of triglycerides in liver cells. Alcoholism is the most common cause of fatty liver in Western countries.

Fatty liver results from decreased transport of triglycerides from the liver

Once synthesized, triglycerides must be combined with cholesterol, apolipoprotein and phospholipids to be transported out of the liver cells as very low molecular weight VLDL lipoprotein. This transport may be disturbed by:

(1) Reduced apolipoprotein synthesis in hepatocytes. Hepatocytes decreased protein synthesis due to lack of materials such as malnutrition, especially Kwashiokor in children in underdeveloped countries, or because hepatocytes were poisoned with substances such as tetra chlorocarbon (CCl4), phosphorus, or because liver cells are inhibited by antibiotic resistance to Protide synthesis such as tetracycline.

(2) Lack of elements needed to make phospholipids. Factors needed to create phospholipids are choline, methionine (amino acid providing methyl group to create choline), lecithin (containing choline). In the absence of these factors, the combination of phospholipids with triglycerides is reduced for transport out of the liver. These are called adipose-oriented factors.

Clinical manifestations and progressions vary depending on the cause. In general, the clinical presentation is usually inconspicuous and the progression is usually mild, since the fat is not a toxic substance, it only causes the mechanical impact of the liver to be slightly large. Fatty liver is usually reversible if the cause is removed. However, in some severe cases such as acute phosphorus poisoning, tetra chlorocarbon, serious liver dysfunction can lead to hepatic encephalopathy syndrome (also called hepatic coma). Chronic fatty liver can lead to cirrhosis of the liver due to compression, death of some liver cells and is replaced by fibrous tissue

 

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