Calcium Metabolism and the Parathyroids

Abstract

422CALCIUM METABOLISM AND THE PARATHYROIDS outline. This.lady also had a rounded swelling in the subcutaneous tissues of the back of the neck, for which the favourite label was a lipoma. It is only the subfascial lipomas that are really smooth; those in the subcutaneous tissues always show some lobulation. THE discovery of the control over calcium metabolism exerted by the parathyroids and by vitamin D has led to a renewal of interest in the subject. Calcium had been regarded as a very inert substance, as it is deposited in the largest amounts in normal tissues with a sluggish metabolism, or in any dead tissue wlhich is not infected, but it is so large or so situated that it cannot be absorbed. The replacement of elastic tissues by calcareous material is a characteristic feature of growing old. But all the activities of calcium cannot be disposed of so summarily, for calcium salts are essential to the heart beat, and, indeed, if they were simply inert, no bad results would follow their removal from the diet, which we know is not the case.For a comprehensive view of the recent additions to our knowledge on this subjectwe are indebted to the work of Donald Hunter, and in this brief retsume of the present position I freely acknowledge that indebtedness. In the first place, I should like to say a few words on the association between the thyroid gland and calcium metabolism.In hyperthyroidism the output of calcium may be increased two to eightfold, and out of all proportion to the increase in the basal metabolic rate. In this condition, much of the calcium is excreted by the bowel, and that without any excess of calcium in the blood. This inicreased output cannot be due to the thyroid stimulating the parathyroid, or the blood-calcium would be high. Yet like the parathyroid, the thyroid appears to mobilize the calcium from the bones-in less than half the cases, osteoporosis occurs-but it can be prevented by an adequate calcium diet. It is produced by progressive bone absorption by osteoclasts.But it is naturally in connection with the parathyroids that the question of calcium metabolism has recently come to excite special interest. I want to contrast the effects of parathormone and vitamin D on calcium metabolismn and then to apply this to certain clinical conditions.Although the r6le of the red bone-marrow in the formation of red corpuscles has been known for over sixty years, and for more than half that time it has been recognized that the amount and distribution of blood-forming marrow was not fixed, but fluctuated according to the needs of the organism, it is only recently that we have known that the same applies to the calcified structures of the bone as well. In the skeleton we have a great calcium bank where deposits are continually being paid and withdrawals made. Although from the earlier days of the experimental study of total removal of the thyroid, tetany was connected in inany people's minds with the coincident removal of by copyright.