Diseases associated with a change in phosphorus-calcium metabolism occur in people of both sexes, regardless of age. Phosphorus and calcium are vital chemicals essential for full human health. Surely, each of us knows that bone tissue contains more than 90% calcium and about 80% of the phosphorus reserves from the entire body. In small quantities, these components are found in ionized blood plasma, nucleic acids and phospholipids.
Metabolism of calcium and phosphorus at an early age
During the first year of life, the risk of metabolic disturbances is highest, which is associated with the rapid growth and pace of development of the baby. Normally, the baby in the first 12 months triples the body weight given from birth, and from 50 average centimeters at birth the one-year-old baby grows to 75. In children, calcium-phosphorus metabolism is manifested by a relative or absolute deficiency of useful minerals and substances in the body.
Numerous factors lead to the appearance of such problems:
- lack of vitamin D;
- violation of its metabolism due to immaturity of enzyme systems;
- deterioration of intestinal absorption and renal reabsorption of phosphorus and calcium;
- endocrine system diseases.
Hypercalcemic conditions, which are an excess of calcium and phosphorus, are much less often diagnosed. An excessive amount of chemicals in the body is no less dangerous for the health of the child and requires medical correction. However, to achieve this state with a normal diet is almost impossible. So the daily need for calcium in infants is equal to 50 mg per 1 kg of body weight. Therefore, a child who weighs about 10 kg should receive about 500 mg of Ca daily. 100 ml of mother's milk, which is the only source of nutrients, contains about 30 ml of Ca, and in cow - more than 100 mg.
Biochemistry of phosphorus-calcium metabolism
After these chemicals enter the body, they are absorbed in the intestine, then the exchange between blood and bone tissue, followed by the release of calcium and phosphorus from the body with urine. This stage is called reabsorption, which occurs in the renal tubules.
The main indicator of a successful exchange of Ca is its concentration in the blood, which normally varies between 2.3โ2.8 mmol / L. The optimal content of phosphorus in the blood is considered to be 1.3โ2.3 mmol / L. Important regulators of calcium-phosphorus metabolism are vitamin D, parathyroid hormone and calcitonin, produced by the thyroid gland.
Half of the calcium in the blood has a direct connection with plasma proteins, in particular albumin. The rest is ionized calcium, which seeps through the capillary walls into the lymphatic fluid. Ionized calcium is a regulator of many intracellular processes, including the transmission of impulses through the membrane into the cell. Thanks to this substance, a certain level of neuromuscular excitability is maintained in the body. Calcium bound to plasma proteins is a kind of reserve reserve for saving the minimum level of ionized calcium.
The reason for the development of pathological processes
The predominant fraction of phosphorus and calcium is concentrated in inorganic salts of bone tissue. Throughout life, hard tissues are formed and destroyed, due to the interaction of several types of cells:
- osteoblasts;
- osteocytes;
- osteoclasts.
Bone tissue is actively involved in the regulation of phosphorus-calcium metabolism. The biochemistry of this process ensures the maintenance of their stable levels in the blood. As soon as the concentration of these substances drops, which becomes clearly in terms of 4.5-5.0 (it is calculated by the formula: Ca multiplied by P), the bone begins to rapidly decay due to increased activity of osteoclasts. If this indicator significantly exceeds the specified coefficient, salts begin to be deposited in bones in excess.
All factors that negatively affect the absorption of calcium in the intestine and worsen its renal reabsorption are direct causes of the development of hypocalcemia. Often in this condition, Ca is washed out of the bones into the bloodstream, which inevitably leads to osteoporosis. Excessive absorption of calcium in the intestine, on the contrary, entails the development of hypercalcemia. In this case, the pathophysiology of calcium-phosphorus metabolism is compensated by the intense deposition of Ca in the bone, and the remaining part leaves the body with urine.
If the body is unable to maintain a normal level of calcium, a completely logical consequence is a disease caused by a deficiency of a chemical element (usually manifestations of tetany) or its excess, which is characterized by the development of toxicosis, Ca deposition on the walls of internal organs, and cartilage.
The role of vitamin D
Ergocalciferol (D2) and cholecalciferol (D3) are involved in the regulation of calcium-phosphorus metabolism. The first type of substance is present in small quantities in oils of plant origin, wheat germ. Vitamin D3 is more popular - everyone knows about its role in the processes of calcium absorption. Cholecalciferol is found in fish oil (mainly salmon and cod), chicken eggs, dairy and sour-milk products. A person's daily requirement for vitamin D is approximately 400-500 IU. The need for these substances increases in women during pregnancy and lactation, therefore, it can reach 800-1000 IU.
The full intake of cholecalciferol into the body can be ensured not only by the consumption of these products or vitamin food supplements. Vitamin D is formed in the skin under the influence of UV rays. With a minimum duration of insolation in the epidermis, the necessary amount of vitamin D is synthesized by the body. According to some reports, ten minutes in the sun with open hands is enough.
The reason for the lack of natural ultraviolet insolation is, as a rule, the meteoclimatic and geographical conditions of the locality, as well as domestic factors. Vitamin D deficiency can be offset by eating foods high in cholecalciferol or taking medications. In pregnant women, this substance accumulates in the placenta, which guarantees the newborn protection against rickets during the first months of life.
Since the main physiological purpose of vitamin D is to participate in the processes of biochemistry of calcium-phosphorus metabolism, we cannot exclude its role in ensuring the full absorption of calcium by the intestinal walls, the deposition of trace mineral salts in bone tissues, and phosphorus reabsorption in the renal tubules.
In conditions of calcium deficiency, cholecalciferol starts the processes of bone demineralization, enhances the absorption of Ca, thereby trying to increase its level in the blood. As soon as the concentration of the trace element reaches the norm, osteoblasts begin to act, which reduce bone resorption and prevent its cortical porosity.
Scientists were able to prove that the cells of the internal organs are sensitive to calcitriol, which is involved in the systemic regulation of enzyme systems. The launch of the corresponding receptors through adenylate cyclase causes the interaction of calcitriol with the protein-calmodulin and enhances the transmission of momentum to the entire internal organ. This relationship produces an immunomodulatory effect, provides for the regulation of pituitary hormones, and also indirectly affects the production of insulin by the pancreas.
The participation of parathyroid hormone in metabolic processes
No less significant regulator is parathyroid hormone. This substance is produced by the parathyroid glands. The amount of parathyroid hormone that regulates calcium-phosphorus metabolism increases in the blood with a lack of Ca, leading to a decrease in plasma ionized calcium. In this case, hypocalcemia becomes an indirect cause of damage to the kidneys, bones and digestive system.
Parathyroid hormone provokes an increase in calcium and magnesium reabsorption. At the same time, reabsorption of phosphorus is markedly reduced, which leads to hypophosphatemia. In the course of laboratory studies, it was possible to prove that parathyroid hormone increases the likelihood of penetration of calcitriol into the kidneys and, as a result, increased intestinal absorption of calcium.
Calcium present in the bone tissue under the influence of parathyroid hormone changes its solid form to soluble, due to which the chemical element is mobilized and enters the blood. The pathophysiology of calcium-phosphorus metabolism explains the development of osteoporosis.
Thus, parathyroid hormone helps to save the right amount of calcium in the body, participating in the homeostasis of this substance. At the same time, vitamin D and its metabolites are endowed with the function of constant regulation of phosphorus and calcium in the body. Parathyroid hormone production is stimulated by low blood calcium.
What is calcitonin used for?
Phosphorus-calcium metabolism needs a third indispensable participant - calcitonin. It is also a hormonal substance produced by thyroid C cells. Calcitonin acts as an antagonist of parathyroid hormone on calcium homeostasis. The rate of production of the hormone increases with an increased concentration of phosphorus and calcium in the blood and decreases with the lack of adequate substances in the body.
The active secretion of calcitonin can be provoked with the help of a diet rich in calcium-containing products. This effect is neutralized by glucagon, a natural stimulant of calcitonin production. The latter protects the body from hypercalcemic conditions, minimizes the activity of osteoclasts and prevents bone resorption by intensive accumulation of Ca in bone tissue. โExcessโ calcium, due to calcitonin, is excreted in the urine. The possibility of an inhibitory effect of the steroid on the formation of calcitriol in the kidneys is suggested.
In addition to parathyroid hormone, vitamin D and calcitonin, other factors are also able to influence calcium-phosphorus metabolism. For example, trace elements such as magnesium, aluminum, and strong can interfere with the absorption of Ca in the intestine, replacing calcium salts of bone tissue. With prolonged treatment with glucocorticoids, osteoporosis develops, and calcium is washed out into the blood. In the process of absorption in the intestines of vitamin A and vitamin D, the first has an advantage, therefore, it is necessary to use products containing these substances at different times.
Hypercalcemia: consequences
Hypercalcemia is considered the most common violation of phosphorus-calcium metabolism. Elevated serum Ca (more than 2.5 mmol / L) is a characteristic feature of hypersecretion of the parathyroid glands and hypervitaminosis D. In analyzes of phosphorus-calcium metabolism, an increased calcium content may indicate the presence of a malignant tumor in the body or Itsenko-Cushing's syndrome.
A high concentration of this chemical element is characteristic of patients with peptic ulcer of the gastrointestinal tract. Often the cause is excessive consumption of dairy products. Hypercalcemia is an ideal condition for the formation of calculi in the kidneys. Phosphorus-calcium metabolism affects the functioning of the entire urinary system, reduces neuromuscular conduction. In severe cases, the likelihood of developing paresis and paralysis is not ruled out.
In a child, prolonged hypercalcemia may result in stunted growth, regular stool disorders, constant thirst, and muscle hypotension. With violations of phosphorus-calcium metabolism in children, arterial hypertension develops, the central nervous system is affected, which is expressed by confusion, memory lapses.
What threatens calcium deficiency
Hypocalcemia is diagnosed much more often than hypercalcemia. In most cases, it turns out that the cause of a lack of calcium in the body is hypofunction of the parathyroid glands, active production of calcitonin and poor absorption of the substance in the intestine. Calcium deficiency often develops in the postoperative period as a response of the body to the introduction of an impressive dose of alkaline solution.
In patients with impaired calcium-phosphorus metabolism, the symptoms are as follows:
- there is an increased excitability of the nervous system;
- tetany develops (painful muscle contractions);
- the feeling of โgoosebumpsโ on the skin becomes constant;
- seizures and respiratory dysfunctions are possible.
Features of the course of osteoporosis
This is the most common consequence of disorders associated with phosphorus-calcium metabolism in the body. This pathological condition is characterized by low bone mass and a change in the structure of bone tissue, which leads to an increase in its fragility and brittleness, and hence an increase in the risk of fracture. Doctors almost unanimously agree that osteoporosis is a disease of modern man. The risk of developing osteoporosis is especially high in old age, however, with the negative impact of technological progress, reduced physical activity and the impact of a number of adverse environmental factors, the proportion of mature patients increases.
Every year, osteoporosis is diagnosed in 15-20 million people. The vast majority of patients are menopausal women, as well as young women after removal of the ovaries and uterus. About 2 million cases of fractures annually are associated with osteoporosis. These are fractures of the femoral neck, spine, limb bones and other parts of the skeleton.
If we take into account information from WHO, then the pathology of the skeleton and bone tissue in prevalence among the world's population is second only to cardiovascular, cancer and diabetes. Osteoporosis can affect various parts of the skeleton, so any bones can undergo fractures, especially if the disease is accompanied by significant loss of body weight.
Metabolic diseases of the skeleton, in particular osteoporosis, are characterized by a significant decrease in the concentration of trace elements, in which the bone is resorbed much faster than it forms. Thus, bone mass is lost and the risk of fracture increases.
Rickets in children
This ailment is a direct consequence of failures in calcium-phosphorus metabolism. Rickets develops, as a rule, in early childhood (up to three years) with a lack of vitamin D and impaired absorption of trace elements in the small intestine and kidneys, which leads to a change in the proportion of calcium and phosphorus in the blood. It is worth noting that adults living in the northern latitudes often experience problems with phosphorus-calcium metabolism due to a lack of ultraviolet radiation and a short stay in fresh air for a year.
At the initial stage of the disease, hypocalcemia is diagnosed, which starts the parathyroid glands and causes hypersecretion of parathyroid hormone. Further, as in a chain: osteoclasts are activated, the synthesis of the protein base of the bone is disrupted, mineral salts are deposited in insufficient quantities, leaching of calcium and phosphorus leads to hypercalcemia and hypophosphatemia. As a result, the child has a delay in physical development.
The characteristic manifestations of rickets are:
- anemia;
- irritability and irritability;
- leg cramps and development of muscle hypotension;
- increased sweating;
- digestive system disorders;
- frequent urination;
- X-shaped or O-shaped tibia;
- belated teething and a tendency to rapidly progressive carious infections of the oral cavity.
How to treat such diseases
With metabolic disorders, complex complex treatment is required. - , , - . , . , .
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The first substance stimulates intestinal absorption by improving the permeability of epithelial membranes. Basically, vitamin D3 is used to prevent and treat rickets in babies. Available in water-soluble ("Aquadetrim") and oil forms ("Vigantol", "Videin").
Ergocalciferol is absorbed in the intestine with the active production of bile, after which it binds to alpha globulins of the blood, accumulates in the bone tissue, and remains as an inactive metabolite of the liver. Widely used in the recent past, fish oil is not recommended today by pediatricians. The reason for refusing to use this drug is the likelihood of side effects from the pancreas, but, despite this, pharmacies still offer fish oil in the form of dietary supplements.
In addition to vitamin D, in the treatment of disorders of phosphorus-calcium metabolism use:
- Monopreparations of calcium containing the necessary chemical element in the form of salts. Instead of the previously popular Calcium Gluconate, which is poorly absorbed in the intestines, Calcium Glycerophosphate, Calcium Lactate, and Calcium Chloride are now used.
- Combined drugs. Most often, complexes that combine calcium, vitamin D and other trace elements to facilitate the absorption of calcium ions (Natekal, Vitrum calcium + vitamin D3, Orthocalcium with magnesium, etc.
- Synthetic analogues of parathyroid hormone. Used injection or in the form of nasal sprays. In tablets, such drugs are not available, since when administered orally, the active substances are completely destroyed in the stomach. This group includes the sprays "Miacalcic", "Veprena", "Osteover", powder "Calcitonin".