Test Questions

1. List the function of blood plasma proteins.

2. How can the level of albumin in plasma change at liver damage? Why?

3. On what basis are enzymes of blood plasma classified? Which of them have important diagnostic value?

4. When does productive azotemia develop?

5. What are the major buffer systems of blood?

6. What diseases cause metabolic acidosis?

7. Describe current understanding of blood coagulation.

8. How important is vitamin K in the synthesis of clotting factors?

9. What mechanisms lead to the activation of enzymes of the cascade of blood clotting? What is anticoagulative pathway?

10. Describe the functioning of the anticoagulation system of blood. What causes of A and B hemophilia? What are the differences?

12. Liver biochemistry

12.1. Main functions of the liver

It is impossible to find a link in metabolism, which anyway would not be associated with the processes in the liver. Liver enzymes is varied, and accordingly the metabolic transformations of substances.

The most important functions of the liver:

1. The biosynthesis of substances "for export". These include plasma proteins, glucose, lipids, ketone bodies, and others.

2. Biosynthesis of urea as the end product of nitrogen exchange in the body.

3. The digestive function associated with the synthesis of bile acids, the formation and secretion of bile.

4. Neutralization of toxic substances formed in the body or coming from outside.

5. The excretory function is a secretion of some metabolic products of the bile into the intestine. This is the only way to remove excess cholesterol from the body and bile acids formed from it with feces. Heme degradation products (bile pigments) and many of the products resulting from neutralization of substances in the liver are excreted with the bile.

Approximately 80% of liver cells have on hepatocytes; approximately 15% are epithelial cells, 44% of which are Kupffer cells. In addition to hepatocytes and Kupffer cells there is a small amount of connective stroma in the liver. It consists mainly of collagen. About 1.2 liters of blood goes through the liver per minute, and 70% of its passes through the portal vein that collects blood from the digestive tract. Despite the fact that the absorption of nutrients from the intestine into the bloodstream occurs intermittently, not constant (and therefore in the portal circulation can undergo changes in the concentration range of substances: glucose, amino acids, etc.) in the general circulation changes in the concentrations of these compounds are insignificant, due to the important role of liver in the maintenance of constant internal environment. Under certain pathological processes (cirrhosis), the relative content of connective tissue in the liver is greatly increased, which has a pressor effect on blood vessels and breaks the flow of bile, particularly strong suffers especially the portal circulation is influenced in this case.

About 70% of liver weight is water, which content is subject to considerable fluctuations, both in normal and pathological conditions, indicating on the active involvement of the liver in the regulation of water and salt homeostasis. In edema water amount can be up to 80% by weight of the body; with excessive deposition of fat in the liver the amount of water can significantly decrease. About half of the dry residue of the liver account for proteins, most of which are globulins. The remaining proteins are albumin, nucleoproteins and collagen. Among the proteins specific to the liver, the spleen and bone marrow, chromoprotein ferritin, which contains iron, should be noted.

The liver is very rich in various enzymes. Along with the enzymes available in other organs, the liver contains the enzymes unique to it. These include enzymes that catalyze the synthesis of urea, removal of phosphoric acid from glucose-6-phosphate, the formation of glucuronic acid esters, etc. A number of other enzymes involved in the metabolism of various substances in the liver (proteins, fats, carbohydrates, pigments) are of great diagnostic value in clinical biochemistry.

The liver is a depot for the polysaccharide glycogen. In severe parenchymal liver damage amount of glycogen in the liver cells is significantly reduced. Conversely, when different types of glycogen disease (glycogen storage disease) it is increasing, reaching 20% or more by weight of the liver.

In the chemical composition of the liver such lipids as neutral fats (triglycerides), phospholipids, cholesterol, etc. takes a special place. In obesity, lipid content can reach 20% by weight of the body, and with fatty degeneration of the liver up to 50%. Under certain pathological processes in the liver the content of products of lipid metabolism increases. Thus, with the Niemann-Pick disease sphingomyelin is deposited in the liver and the spleen, as in Gaucher’s disease there is an accumulation of cerebroside kerasine.

The liver is extremely rich in various vitamins, especially vitamins A, C, PP, pantothenic acid, to a lesser extent - in vitamins В₆, E and В₂. The liver plays a key role in the formation of vitamin D₃ metabolite. It is its transport form 25-hydroxycholecalciferol (25-ОН-D₃). Mineral composition of the liver is various. It contains Na, K, Ca, Mg, and a number of micro elements: Fe, Zn, Cu, Mn, As, etc. The amount of iron, copper, manganese and arsenic exceed the concentrations of these elements in other organs. With a number of pathological processes, content of these elements can vary considerably.