Calcium metabolism is ultimately controlled by a portion of the brain called the hypothalamus. In a case of gross oversimplification, the hypothalamus tells the pituitary gland what to do by way of hormones. The quantity of those hormones tell the pituitary gland to produce other hormones, which then go into the bloodstream to target other organs, which, in turn, tell other endocrine organs what to do.
Whew! Are you tired yet? Fortunately, all of this goes on automatically throughout the day.
Even though we are today talking about calcium and phosphorous metabolism and their interpretation in the chemistry profile, the hypothalamus and pituitary glands are actually in charge of several hormones at once. We will discuss those hormones in future articles.
Calcium is crucial to nearly every bodily function, from nerve information transmission to the contraction of every muscle. Its levels in the body are monitored in the bloodstream, although its actions are at the cellular level. If serum quantities vary beyond a narrow range, a signal is sent to the hypothalamus, which contacts the pituitary gland, which contacts the parathyroid gland, which produces a hormone that raises or lowers the amount of calcium in the bloodstream.
Bones act as the main reservoir of calcium in the body. We think of our bones as reaching adulthood, then becoming static. Nothing could be further from reality. In fact, our bones are constantly being remodeled from the day we are born until we pass away. Therefore, it is easy for calcium metabolism to call on the already-active bone cells to send some calcium out for use.
Under normal circumstances, bones have plenty of calcium and they can spare all the body needs. However, bones may run out of calcium in a condition called Renal Secondary Hyperparathyroidism. In this condition, occurring in kidney failure, calcium is sapped from the bones over an extended period of time until the bones become soft. The condition is also known as rubber jaw.
Phosphorous metabolism essentially follows calcium levels. If serum calcium rises, the body seeks to keep calcium and phosphorous in balance with each other. Elevated levels of phosphorous occur most commonly in renal failure and food contamination.
Low calcium levels occur when albumin levels drop in the body, because calcium is bound (chemically attached) to albumin in circulation. Low albumin can happen because of poor production in the liver, or losses through the intestine and/or kidneys.
Calcium also drops in eclampsia, a condition in nursing female dogs in which calcium is not mobilized to the bloodstream as fast as it is lost in milk. Eclampsia is an emergency condition that starts with tremors, progresses to seizures and can result in death.
Calcium also becomes low in hypoparathyroidism. In dogs, this is believed to be an autoimmune condition, in which the body attacks the gland, resulting in poor production of parathyroid hormone, or parathormone.
Pseudohypoparathyroidism is similar, except that the parathyroid glands produce sufficient hormone, but the body is unable to respond to it.
Calcium levels tend to increase in certain kinds of cancer and in hyperparathyroidism, a condition in which the parathyroid glands produce too much parathormone. Tumors in the parathyroid gland(s) are the most common cause. Excessive administration of Vitamin D can also raise calcium levels.
“The kneebone is connected to the thighbone.” Nowhere in the body is this principle more evident than in the study of hormone-related diseases. Everything is interconnected.
See you tomorrow, Dr. Randolph.
