Biochemistry

Selenium is found in the retina of humans and animals (mammals and birds). Lack of selenium leads to the emergence of animal necrosis of the liver or alimentary hepatitis, as well as muscle dystrophy or white muscle disease. With the lack of selenium in the human body, the occurrence of certain diseases of the cardiovascular system is associated. Boron. Its content in the earth's crust is 3-1 O ’ 4 % by weight. In nature, boron is found in the form of borax Na 2 B 4 O7-10H 2 O, natural boric acid H 3 BO 4 and some other compounds. In biological environments, boron does not form bioorganic compounds, however, this element has a significant effect on the activity of parathyroid hormone, which affects the exchange of calcium, magnesium and phosphorus in the animal and human body. Boron deficiency greatly inhibits the formation of nucleic acids. The physiological role of boron is very noticeable in plants, which is associated with its effect on the activity of phytohormones - auxins, cytokinins and gibberellins. Boric acid H3BO3 (in the form of an alcoholic solution) is often used as an external antiseptic. Silicon is the second most abundant element after oxygen (29.5% of the mass of the earth's crust), one of the main elements of inanimate nature. Its compounds - silicates and aluminosilicates - make up 75% of the mass of the earth's crust. Quite a lot of silicon contains some representatives of the plant and animal world. In the form of silicic acid esters, this element is involved in the “ crosslinking ” of polysaccharide chains. Especially silicon-rich tissues of the trachea, tendons, large blood vessels, which gives them strength and elasticity. The daily human need for silicon is 20-30 mg. Fluorine, chlorine, bromine and iodine are collectively called halogens (Greek gals - salt, give birth to genes). In nature, they are in the form of salts - fluorides, chlorides, bromides and iodides, which determines their common name. Fluorine is quite widespread in nature (content in the earth's crust of 6.25% of the total mass). Fluoride refers to trace elements. Its content in the body of vertebrates and humans is only a few milligrams. The bulk of fluoride is concentrated in the teeth, to a lesser extent in the bones and nails. Fluorine is part of the teeth in the form of sparingly soluble fluorapatite Ca 5 F(PO 4 ) 3 , which mainly determines its value for vertebrates and humans. Deficiency of this element is one of the main causes of dental caries. In contrast, an excess of fluoride in the body causes a disease calledfluorosis. Dark spots appear on the tooth enamel. In addition, the patient experiences headache, weakness, cramps, sensation of fever, itching, general exhaustion. In the 11