Changes in physiological calcium and phosphate concentrations in non-bone-related body fluids

2021-06-07 04:29 PM

At the plasma calcium concentration halved, the peripheral neuromuscular becomes excitable, becomes spontaneously contracted, impulses form, which then propagates to the peripheral neuromuscular causing Typical tetany contraction.

The change in the level of extracellular fluid phosphate from very low from normal values ​​to 2-3 times the normal value does not cause immediate changes in the body. In contrast, even just 1 change Small changes in calcium in the extracellular fluid can cause immediate physiological effects.

In addition, chronic hypocalcaemia and hypophosphatemia produce a dramatic decrease in bone mineralization, which will be explained in the next chapter

Low calcium stimulates the nervous system and Tetany

When the extracellular fluid calcium ion concentration falls below normal, the nervous system becomes more excitable due to increased permeability of the neuronal membrane to Na ions, allowing the emergence of action potentials. easily. At the plasma calcium concentration halved, the peripheral neuromuscular becomes excitable, becomes spontaneously contracted, impulses form, which then propagates to the peripheral neuromuscular causing Typical tetany contraction. Therefore, hypocalcaemia causes tetany. It also sometimes causes convulsions by making brain cells excitable

Hand tetany often appears first before tetany occurs in other parts of the body. It is called a carpopedal spasm.

Tetany occurs when serum calcium levels fall from the normal range of about 9.4 mg/dl to about 6 mg/dl and can be lethal at about 4 mg/dl.

In animals, severe hypocalcaemia can cause effects that are rarely seen in humans, such as marked dilation of the heart, alteration of cellular enzyme systems, and increased membrane permeability in certain cells (such as neurons), and damage the blood-clotting system.

Figure. Image of tetany in the hand, also known as carpopedal spasm

Hypercalcemia reduces the activity of the nervous system and muscles

When the concentration of calcium in the body fluids increases, the nervous system becomes sluggish and the motor reflexes of the central nervous system become sluggish. Furthermore, increased calcium levels decrease cardiac QT time and cause loss of appetite and constipation, possibly due to decreased contractility of the gastrointestinal tract wall muscles. The above effects begin to appear when the serum calcium level rises above 12 mg/dl, and it becomes more pronounced above 15 mg/dl. When the serum calcium level rises above 17 mg/dl, calcium phosphate crystals may be present. potential for precipitation throughout the body, which will be discussed later in the section on parathyroid toxicity.