Thus, the skeletal bone is a huge bank to allow the rapid and large as needed release of in this case calcium carbonate and other substances to neutralize the excess acid. Which maintains a neutral Ph. This release through the vitamin D3’s activated-fast hormonal pathway is body’s main way to accomplish this acid neutralization.
To summarize the blood levels of the active form of vitamin D3 in the blood are increased or decreased depending on calcium blood level and calcium bicarbonate needs. This to activate the active-fast state. This to meet rapid needs concerning calcium blood levels and to neutralize acid.
For completeness it is the activated-slow state which I will discuss in a different set of blog posts that replenishes bones, think prevents osteoporosis. That only occurs under perfect conditions or at optimal blood levels. Ideally in replenishing the bones other vitamins and minerals are needed.
The body adjusts calcium blood levels as I have explained by acting on special cells in the small intestine, kidney and the osteoclasts in skeletal bone. As hopefully I made clear the body is constantly adjusting the blood calcium and calcium carbonate levels. The next question is how? How does the body determine the calcium blood levels and how does it affect the amount of the active form of vitamin D3 to adjust the blood level of calcium and calcium carbonate?
In the area of the thyroid and in fact attached to it are typically four glands call the parathyroid glands. They have receptors that constantly monitor the blood calcium levels. If too low, they secrete parathyroid hormone (PTH) into the blood and if normal or too high they stop. The PTH acts to cause the blood form of vitamin D3 to be converted into the active form.
This occurs in the kidneys. I believe it does this here as there is the most important area to act to prevent excess excretion of calcium. Also, PTH is important in directly activating the osteoclasts and osteoblasts in skeletal bone.
Both act to free up calcium and calcium carbonate in the short term. Only osteoclasts are important for raising the blood calcium on long term. Again, to keep this as short and to the point I will not go into more detail than this.
The action first in the kidneys is to prevent loss of calcium. See, if the osteoclasts and osteoblasts were to be turned on but it took excess time for enough of the active form of vitamin D3 to get to the kidneys to act, then much of the calcium freed from the bones but also that absorbed in the small intestines would be excreted.
Thus, wasted before the kidney’s reabsorption was turned on. As there is no other reason, I see for this process, activating the vitamin D3 from blood form to active form, to not otherwise occur in the liver. In the liver the vitamin D form we make in our skin and found in supplements is converted from that form-cholecalciferol to the blood form-calcifediol.
Thus, as the blood form of vitamin D3 is already created in the liver it would be convenient to convert it there to active form. But it is not. It is formed in the kidneys. In the kidneys, it does this through the PTH which controls the function of the enzyme 1-alph-hydroxolase. This is the enzyme that converts the blood form of vitamin D3 to the active form.
As vitamin D3 is hard to come by and it takes a lot of energy to produce it makes sense the two systems would be separated. It is like in Maslow’s hierarchy. First water then food shelter etc. In the human body first make sure it stays alive then worry about great sleep, optimal immune system and such.
In most animals where this system at least mimics what we concerning vitamin D3 effects, they don’t live long enough to worry about diseases of old age. Their lives are to short term and survival comes first. Until recently neither did humans. That is live long enough that the effects of inadequate especially sub optimal blood levels of vitamin D3 negatively affected us. That is in the distant past humans typically died earlier in life, from causes like trauma not disease like atherosclerosis.
*The information posted above is for educational purposes only. Always check with your doctor before initiating any changes in your medical treatment. If you do not, then The Two-Minute Health Fact, Dr. Judson Somerville, nor The Optimal Dose is responsible!