The parathyroids.

Abstract

In most species the parathyroids are four in number, two superior and two inferior. Each has its own blood supply. The nerve supply is from the perivascular sympatheic plexus. Little is known of the embryology. Jackson (66,67,68), however, has found that their growth energy surpasses that of the thyroid. This author finds that holding animals at a fixed maintenance of body weight the parathyroids increased in size whereas the thyroids suffered reduction.Histologically, the parathyroids present quite a different picture from the thyroid. Colloid is scarce and the cells tend to arrange themselves in columns, separated by bands of connective tissue. Each gland has a well defined capsule (2,8,9,65,96,106,123).It has been held that the thyroid and parathyroids are closely related functionally, that the latter are merely embryonic thyroid tissue (118). The beautiful researches done on parathyroid tetany seem to show conclusively that, although their association is an intimate one from the standpoint of location, functionally the two organs are quite distinct (47,48,51,54,55).Function. The history of parathyroid research is fascinating. The glands were first adequately described by Sandstroom, in 1880, who found them present in both man and animal. No great attention was given to the discovery until Gley (54) in 1891 rediscovered them and showed them to be different functionally from the thyroid. Gley, fortunately, worked with the rabbit in which, as we have previously suggested, the external parathyroids are not in intimate contact with the thyroid. He found that when both thyroid and parathyroids were removed, severe and fatal symptoms ensued, similar to those described by Schiff, Rapp, Horsley (106), and others.Gley, furthermore, showed that when he removed the external parathyroids and left the thyroid no fatal results took place. The same was true when the external parathyroids were left and the thyroid-containing the internal parathyroids-was removed. The explanation seems to be that in many of the vertebrates, the dog, cat, and others, a thyroidectomy means a parathyroidectomy as well.