Hello! I have been a doctor for 21 years. My name is Georgy Olegovich Sapego. In this article I will discuss how calcium is retained in the blood.
We have calcium in our blood. It swims there in different forms. About 40% of calcium is bound to the blood protein albumin. Another 15% is in the form of any citrates, phosphates and other sulfates. The remaining calcium floats in the blood ionized, that is, free naked and with proudly protruding plus signs.
Usually in the laboratory all calcium is determined at once. This is sufficient because both bound and free calcium often change in parallel.
It is clear that only a small part of all our calcium floats in the blood.
Special hormones have a very powerful effect on the level of calcium in the blood. Guess which type of calcium they act on? Right! For naked calcium. They drive it in all directions: they let it into the body through the intestines, pack it into bones or pick it out from the bones, and can also drain through the kidneys.
Food
Calcium is absorbed from food in two ways.
The first way - active absorption in specially designated places at the very beginning of the intestine. There are doors for calcium.
Second way - This is a primitive self-propelled absorption throughout the intestine.
In terms of absorption, calcium is very picky. It is not like other ions. He needs vitamin D. Without it, calcium refuses to be absorbed.
It is also important that calcium is not bound to salts. The bound calcium will transit out of the intestine. Sometimes it's even useful. If there are oxalates in the intestine, then calcium will bind to them. It will not be absorbed by itself, but oxalate will not be absorbed either. Usually, oxalate produces kidney stones, so calcium from food protects us from stones.
An adult can eat about 1,000 milligrams of calcium per day. From this thousand, 400 - 500 milligrams will be absorbed. Then, about 300 milligrams of calcium will be released back into the intestines along with the digestive juices, and 100-200 milligrams will be released through the kidneys. The result is a perfect balance.
Bones
Almost all of the calcium in our body is stored in the bones. There it is packaged as hydroxyapatite.
There are two types of special cells in bones. Some pack calcium into bones, while others pluck it out of the bones. This maintains a stable concentration of calcium in the blood.
Kidney
Free calcium is constantly filtered through the kidneys. In this case, 98% of the filtered calcium is immediately absorbed back into the blood. It turns out that the kidneys are continuously juggling with ionized calcium. They play with him like a cat and a mouse - let go and immediately catch him.
Parathyroid hormone
It is secreted by the parathyroid glands. Parathyroid hormone regulates calcium levels in three different ways:
- activates vitamin D, and that already draws in calcium from the intestines;
- commands special cells in the bones that begin to scoop out calcium from the bones;
- prevents the kidneys from releasing calcium.
Vitamin D
It is rather not even a vitamin, but a hormone. Vitamin D opens the door for calcium in the intestines, and calcium enters.
If there is little calcium in the blood, then vitamin D causes the bones to release calcium. They still don't understand how he does it.
Well, vitamin D also knows how to prevent the kidneys from excreting calcium.
My own calcium
Calcium and without any hormones knows how to negotiate with the kidneys and other ions like potassium and sodium. If someone strenuously expels sodium from the blood with diuretics, then calcium remains in the blood. This is their mutual assistance.
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