As I delve deeper into my nutritional therapy studies I am discovering the many mechaisms our body has to maintain homeostasis - stability. In this article discover the fascinating way in which our bones help regulate blood acidity levels through the tight and controlled release of stored calcium.

The body’s skeletal system serves a multitude of functions far in excess of providing structural support. One of they key functions of the skeleton is to act as a storage facility for our body’s mineral supply and through this serve as a key regulator in our blood pH range. Minerals make up roughly about 4% of the body and are essential, meaning they must come from our food. We require a range of macro and microminerals for healthy bone structure, metabolic function and cellular health, and an excess or deficiency even on a small scale can have significant health consequences. This article specifically discusses the way in which the skeleton and mineral levels, which help control blood pH, interact.

Mineral reserves are stored in the bones

Our skeleton is the primary storage facility for minerals in the body, which is where these mineral reserves are most heavily concentrated. Many different mineral salts are deposited into the extracellular matrix of the bones, which then hardens or calcifies to form hard bone. Bone formation is referred to as ossification. Calcium is by far the most abundant mineral in the body, and 99% of our calcium reserves are stored in our bones. These calcium reserves are a key player in regulation of the pH in the blood. Calcium is an alkalising mineral and is balanced by phosphorous, an acidifying mineral.

Blood pH balance

pH refers to how acidic or alkaline something is, a critical measure throughout the body for maintaining homeostasis. Our body regulates pH in every tissue and organ very tightly, as a fluctuation either way (ie: becoming to acidic or too alkaline) can be deadly. Blood pH regulated by the mineral stores in our bones, particularly calcium, which is an alkalising (de-acidifying) mineral.

Blood pH is tightly controlled through the release of stored calcium from our bones. If blood pH falls as a the result of some kind of stimulus (ie blood becomes too acidic) then the bones release calcium reserves in order to bring the pH back up (ie re-alkalise the blood). If the pH rises and the blood becomes slightly too alkaline, then calcium will be deposited into the bone to bring the acidity of the blood. This bone/blood pH feedback loop is a critical mechanism for maintaining blood homeostasis. Like all homeostatic functions in the body, calcium is balanced by phosphorous, which is a key acidifying mineral. If the blood becomes too alkali then it is phosphorous that is released from the extracellular matrix of the bones.

Our bones play a critical role in regulating blood pH levels by releasing stored calcium when levels become low.

Bone remodelling

As mentioned, bone is like any other tissue in our body and is continuously regenerating as minerals are deposited and released from the extracellular matrix. This process is called bone remodelling and involves three different bone cells types.

  1. Osteoblasts: are the bone forming cells that turn cartilage into new bone;
  2. Osteocytes: our primary bone cells responsible for the maintenance of bone structure; and
  3. Osteoclasts: cells responsible for the breakdown of calcium and reabsorption into the blood.

Additionally, osteogenic cells are bone stem cells and are the only bone cells that undergo cell division. It is these cells that become osteoblasts, which go onto form new bone.

From the list above we see that osteoclasts are responsible for the release of calcified minerals into the bone when the blood pH begins to drop, and head towards acidic. This process is regulated by the Parathyroid gland, which is responsible for detecting changing levels of pH in the blood.

When slight changes occur (as the result of any kind of stimulus) in the blood pH levels, the parathyroid gland (which is part of the thyroid gland) releases parathyroid hormone. Parathyroid hormone signals to the osteoclasts to get to work breaking down bone cells, thereby releasing the stored calcium into the blood. This ultimately brings the pH back up (re-alkalises) towards neutral and restores homeostasis. In addition to extracting stored calcium from the bones, parathyroid hormone also reduces calcium excretion through urine and pulls it from digestion.

Osteoclasts are the bone cells involved when blood pH tends towards acidic and calcium stores are broken down and released. If the blood becomes more alkali (ie pH rises) for some reason, then it is the osteoblast cells that are involved. These cells are responsible for depositing minerals into the extracellular matrix where they are hardened/calcified and become bone.

Calcium co-factors

There are a number of co-factors that influence our body’s ability to store calcium and then access these stores again as required. Vitamin D is a particularly important co-factor as it works with parathyroid hormone to increase calcium levels in blood serum in response to the signal from the parathyroid gland. In addition to the bone centric calcium buffering system, Vitamin D helps regulate the level of calcium absorption in the small intestine (where the bulk of our nutrients are absorbed), kidneys (where most calcium is excreted).

Exercise also plays a role in the strengthening of bone because stress on the cellular matrix causes more minerals to be deposited, in turn strengthening the area.

Final words on bone remodelling and blood pH

Like many other systems the pH in our blood is tightly controlled by a feedback loop, which is regulated by the brain. The thyroid gland plays a critical role in signalling to our bone cells when it is time to breakdown and release stored calcium. To support this important regulatory system it is important to consume a wide range of minerals from whole food sources that will provide the body with the supplies it needs to regulate blood pH and maintain healthy, strong bones.

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