Hyperthyroidism and Its Surgical Treatment.

By E. Gordon Anderson, M.B., F.R.C.S.E.

Of all the endocrine glands, we know more about the thyroid and its function than of any other gland.

Of tremendous help in the investigation of the functions of this gland is the fact that thyroid given by mouth (unlike many other glandular substances) is not destroyed within the gastrointestinal tract, but its essential component or components are absorbed into the circulation in an active condition.

This is explained by the theory that the thyroid originally secreted its hormone into the pharynx, and thus into the alimentary canal ; since in the early embryo it is developed from a median entodermic invagination of pharynx between the second and third bronchial arches in the region of the foramen cæcum of the tongue, and thence grows down as a hollow tube piercing the hyroid bone and on front of the upper trachea divides into its lateral lobes and isthmus.

The importance of this gland to the human economy can be gauged anatomically by the fact that, although of normal weight of some 1½oz., its blood supply is such that the whole blood of the body is believed to pass through the gland every hour ; and, such is the intricate arrangement of its blood supply (which is estimated to be some five times that to the kidneys and almost thirty-four times that to the brain), it does not matter which vessels to the gland are ligated it still can get a sufficient blood supply.

On viewing a microscopic section of normal thyroid tissue it is found to consist of series of tubules lined with cubical cells, and these tubules are filled with a colloid substance. These tubules are supported in a fibrous stroma, which also supports a plexiform arrangement of vessels and lymphatics, but, in addition, lying scattered within this stroma, are a few disjointed cells precisely like those lining tubules, but of apparent irregular arrangement.

The thyroid cells elaborate a hormone, termed thyroidin or thyroxin, into the manufacture of which iodine enters and forms a main constituent, and this thyroidin is stored within the colloid substance, where it remains inert, only to be paid out into the blood stream as is found necessary for the human economy, where it plays a most important part in metabolism.

Its chief function seems to be as a catalytic agent enabling the tissues to take up oxygen, and thus it acts as a draught or fan to the human flame.

Various investigators have, from experiments on thyroidectomised animals and from thyroid feeding experiments, assigned to the thyroid the government of sexual development, particularly in the female ; growth ; detoxicating function ; and an important relationship with immunity processes. But the consensus of opinion seems to be that these functions are affected indirectly, rather than directly, by the altered general metabolism brought about by the decrease or excess of thyroid within the animal.

The mass of research findings tends to the belief that almost all diseases of the thyroid are due at the outset to an actual or relative shortage of iodine ; the relative shortage being manifest at puberty, pregnancy, during infections, and particularly when food, although containing the requisite amount of iodine, is contaminated by fæcal derivatives.

I believe that here lies the explanation of the apparent discrepancies between the work of McCarrison and that of Marine.

Experimenters seem to have proven beyond question that, of animals kept on iodine-free diet, those confined within a limited space whose kennels are not kept strictly clean develop goitres more rapidly and of greater size than those given more freedom and kept under better conditions. The confined animals are fed from the floor, and their food must of necessity become contaminated with urinary and fæcal discharges. It seems that these ingested fæcal derivatives have either the power of fixing the iodine and preventing it becoming of use to the animal, or that the handling of these ingested impurities necessitates an over-supply of thyroidin.

This iodine deficiency seems to cause the body to cry out for thyroidin and stimulates the thyroid to work overtime. Thus its blood supply increases ; its follicular cells increase, forming not only more follicules, but filling the follicules with cells several layers deep, obliterating the cavity, and causing a disappearance of the contained colloid. Whether this increase is the result of stimulation in order to produce more thyroidin, or whether it enables the gland to filter the blood more thoroughly so as to pick out the minutest quantity of iodine present, we do not know—probably both.