Human Anatomy and Physiology - I. V. Gayvoronsky 2011

Metabolism and Energy
Vitamins

Structure/19.html">The Importance of vitamins. Vitamins are BIOLOGICALLY ACTIVE SUBSTANCES required in small quantities for metabolic processes and the maintenance of normal physiological Functions. The term "vitamin" is derived from the Latin vita meaning life, and "amines," a group of chemical compounds containing a nitrogen atom. The first vitamins discovered belonged precisely to this chemical group. However, substances that do not belong to amines but still perform vitamin functions in the body were subsequently discovered.

Most Vitamins are essential for the normal progression of enzymatic processes. Many of them act as Coenzymes—substances that bind to the protein molecule of an enzyme, enabling it to carry out its function. The body requires only small amounts of vitamins for normal functioning, measured in milligrams per day. They are obtained through food, while some are produced by intestinal Bacteria or synthesized within the body. To preserve the maximum amount of vitamins in food, it is necessary to minimize cooking time and ensure proper storage. It should be noted that contact with metals inactivates most vitamins, a factor that must be considered when choosing cookware for food storage.

When vitamins are ingested in amounts that do not meet the body's needs, Metabolic Disorders and related diseases occur. An insufficient intake leads to hypovitaminosis, a condition frequently observed in late winter and early spring due to a decreased consumption of fresh, vitamin-rich fruits and vegetables. If essential vitamins are entirely absent from the diet, avitaminosis develops. Metabolic disorders associated with an excessive intake of vitamins are known hypervitaminosis. These are extremely rare; for hypervitaminosis to occur, the intake of a particular vitamin must exceed the normal level by thousands of times. Such conditions have become possible due to The Development of the pharmaceutical industry and are typically linked to the excessive use of various vitamin supplements.

All vitamins are classified into fat-soluble and Water-soluble. Fat-soluble vitamins enter the body alongside dietary fats, which are necessary for their absorption. These include vitamins A, D, E, and K. Water-Soluble Vitamins comprise the B-complex vitamins and Vitamin C.

Fat-soluble vitamins. Vitamin A (retinol) is a structural component of the visual pigment rhodopsin. In addition, it influences the regeneration of the Skin and corneal epithelium. A deficiency in this vitamin leads to a condition known as night blindness (nyctalopia), which impairs twilight Vision—the loss of The ability to see in low-light conditions. Over time, the epithelium of the skin and the Cytology/practical/76.html">Cornea of the eye becomes affected.

Retinol is found in the form of provitamin A (carotene) in carrots, bell peppers, spinach, and several other plant-based foods. Vitamin A itself is present in the Liver, eggs, butter, and milk. The recommended daily allowance of this vitamin is 2.5 mg.

Vitamin D (calciferol), the antirachitic vitamin, participates in The regulation of Calcium and phosphorus METABOLISM in the Body and promotes normal Bone tissue development. A deficiency of calciferol causes Rickets, a disease that primarily affects children and is characterized by the softening and deformation of bones, as well as Nervous system dysfunctions.

Vitamin D is found in fish oil, eggs, butter, and milk. Its active forms can also be synthesized in the skin under The Influence of ultraviolet sunlight. Therefore, mild forms of hypovitaminosis can be treated by taking sunbaths. The daily requirement for vitamin D is 2.5 µg.

Vitamin E (tocopherol) is an antisterility vitamin; its deficiency in animals causes Infertility, and in humans, it also plays a vital role in reproductive function. Vitamin E has been shown to counteract Aging, reduce Lipid Peroxidation in Cell membranes (antioxidant effect), lower cellular oxygen demand, and enhance cellular tolerance to elevated carbon dioxide concentrations (antihypoxic effect). This vitamin is found in grains, vegetable oils, and green vegetables. The daily requirement for vitamin E is 15 mg.

Vitamin K represents a group of substances sharing the common designation of phylloquinones. They are essential for the synthesis of numerous Blood-clotting factors. A deficiency in vitamin K impairs blood clot formation; consequently, cases of avitaminosis and hypovitaminosis are frequently marked by unexpected bleeding. Vitamin K is found in vegetables (such as spinach and cabbage) and liver, and it can also be synthesized by the intestinal microflora. The daily requirement for vitamin K is 1 mg.

Water-soluble vitamins. Vitamin C (ascorbic acid), the antiscorbutic vitamin, participates in The formation of Collagen, the primary protein of Connective Tissue. It is necessary for strengthening vascular walls, maintaining healthy skin, and fortifying cell membranes. Vitamin C increases the body's resistance to infections. Its deficiency leads to scurvy, a disease characterized by severe vascular damage, significantly weakened vessel walls, frequent minor hemorrhages, bleeding Gums, and tooth loss. Furthermore, the body's Resistance to Infectious diseases drops, and wounds heal poorly. This vitamin is found in fresh fruits, berries, and vegetables, being particularly abundant in rose hips, black currants, cranberries, and citrus fruits. The daily requirement for vitamin C is 50–100 mg.

Vitamin B₁ (thiamine), the antineuritic vitamin, is necessary for the normal functioning of enzyme systems responsible for carbohydrate and fat metabolism. A deficiency in this vitamin causes beriberi, which manifests as dysfunctions of The Nervous System, Cardiovascular system, and gastrointestinal tract. This vitamin is found in cereal grains, legumes, liver, eggs, and brewer's Yeast.

Vitamin B₂ (riboflavin) is a component of Enzymes involved in tissue Respiration. A deficiency in this vitamin leads to visual impairments, stunted growth (in children), Hair loss, inflammation of mucous membranes, and muscular weakness. Vitamin B₂ is present in cereal grains, legumes, liver, eggs, milk, and brewer's yeast.

Vitamin B₃ (pantothenic acid) is a constituent of coenzyme A, which plays a crucial role in virtually all metabolic processes. Hypovitaminosis of this vitamin is extremely rare, as it is found in almost all PLANT AND ANIMAL foods.

Vitamin B₅ (nicotinic acid), also known as the antipellagric vitamin or Vitamin PP, is essential for the synthesis of enzymes involved in tissue respiration, oxidation-reduction reactions, and protein, fat, and Carbohydrate Metabolism. Avitaminosis of vitamin PP results in pellagra, accompanied by skin inflammation, Central Nervous System disorders, and gastrointestinal tract dysfunctions. This vitamin is found in meat, liver, eggs, fish, brewer's yeast, and certain cereal grains and legumes.

Vitamin B₆ (pyridoxine) is utilized by the body as a coenzyme for numerous enzymes involved in Protein metabolism and is required for normal hematopoiesis. Avitaminosis leads to anemia, skin lesions, and central nervous system dysfunctions. This vitamin is present in the majority of animal and plant foods.

Vitamin B₈ (biotin), also known as vitamin H, acts as a coenzyme for numerous enzymes involved in the metabolism of CARBOHYDRATES and Fatty acids. It is found in milk and liver, and is also synthesized by the intestinal microflora. Avitaminosis primarily manifests as skin lesions.

Vitamin B₉ (folic acid), also known as vitamin B_c, participates in the Synthesis of purine NUCLEOTIDES and influences the formation of DNA and RNA. Avitaminosis disrupts normal hematopoiesis, resulting in anemia. Sources of vitamin B₉ include liver and leafy greens, and it can also be synthesized by the intestinal microflora.

Vitamin B₁₂ (cyanocobalamin). The primary function of this vitamin is its involvement in hematopoiesis. It should be noted that the absorption of vitamin B₁₂ is only possible after it binds to Castle's intrinsic factor, which is produced by the gastric glands. Consequently, cyanocobalamin deficiency arises from two main causes: an insufficient Dietary intake of the vitamin or inadequate production of intrinsic factor (resulting from surgical removal of The Stomach or Chronic gastritis). A deficiency in vitamin B₁₂ leads to pernicious (malignant) anemia, characterized by the appearance of giant red Blood Cells (megaloblasts) in the blood that are inefficient at Oxygen transport. This vitamin is found in most animal products, particularly the liver. The daily requirement for B-complex vitamins is 20–25 mg.