Homeostasis

“ Thus far we have spoken of hormones only in connection with their ability to excite those nerve cells by which smooth muscles and glands are controlled. As a matter of fact, their action is much wider than that. They have the power of affecting the metabolism of very many body cells. Some of them appear to have the special function of regulating the rate of metabolism. These we shall talk about in detail, when we return to the study of metabolism in a later chapter. One of the hormones is interesting in connection with the relation of emotions to smooth muscle and gland activity. ”

“ The body converts potential into kinetic energy by metabolism in the body. The potential energy of food is transformed into the actual energy of heat and mechanical labor. In this respect the only difference between man and other vertebrates is the nervous and intellectual processes, which are not yet understood.
Metabolism is anabolic and katabolic. Anabolism is constructive; it includes growth and the act of the tissues in selecting, appropriating, and making substances absorbed from the alimentary canal a part of themselves. The body is never stable ”

“ These, as should be perfectly clear by this time, are the seats of our most active functional metabolism. When the muscles are active, great amounts of oxygen and food are being withdrawn from the blood and large amounts of waste material, including carbon dioxide, poured out into it. Only a very rapid circulation will take care of this situation. At the same time the skeletal muscles are the most compact of our living tissues. The cells are crowded together in making up the very strong muscular machine by which our movements are performed. ”

“ When we come to consider more in detail the results of these actions we find that the various secretions of the body, such as the sweat, gastric juice, bile, milk, urine, &c., may be increased or diminished; that the heart may have its muscular or nervous apparatus stimulated or depressed; that the nerve-centres in the brain, medulla and spinal cord may be rendered more sensitive or the reverse; and that the general metabolism of the body may be altered in various ways. ”

“ When those substances are wanting, whose function in the organism is to support the process of respiration, when the diseased organs are incapable of performing their proper function of producing these substances, when they have lost the power of transforming the food into that shape in which it may, by entering into combination with the oxygen of the air, protect the system from its influence, then, the substance of the organs themselves, the fat of the body, the substance of the muscles, the nerves, and the brain, are unavoidably consumed. ”

“ The increased action of the muscles of the heart and the blood-vessels increases the efficiency of the circulation; the secretion of the adrenal gland causes a rise in the blood-pressure; the increased action of the thyroid gland causes an increased metabolic activity; there is evidence that glycogen is actively called out, this being the most immediately available substance for the production of energy; the increased activity of the respiration is needed to supply the greater need of oxygen and the elimination of the increased amount of waste products ”

“ The cellular tissue exhales a serous fluid, and when it becomes excessive in quantity, general dropsy is produced. Fat is another secretion, which is thrown out, in a fluid state, from the cellular membrane. It is deposited in little cells, and exists in the greatest abundance between the skin and the muscles. Its use seems to be, to form a cushion around the body for its protection; to furnish nutriment for the system when food cannot be taken; to supply the carbon and hydrogen necessary to sustain the generation of heat, when these articles of combustion are not otherwise furnished. ”

“ A careful study of the conditions and processes necessary for both tissue building or nutrition, and tissue waste or disintegration, in all the higher order of animals, will show that neither process can be materially retarded without retarding or preventing the other. Both processes take place only in bioplasm or vitalized matter, supplied with oxygen, water and heat. Neither the assimilation of new material food, nor its use in tissue building can be effected without the presence of free oxygen and nuclein, or corpuscular elements of the blood. ”

“ Endogenous or tissue metabolism. Exogenous or intermediate metabolism. Needs of the body for proteid food possibly satisfied by quantity sufficient to meet the demands of tissue or endogenous metabolism. Bearings of Folin’s views on current theories and general facts of proteid metabolism. Large proteid reserve and voluminous exogenous metabolism probably not needed. Importance of feeding experiments in determining the true value of different views.
As we have already seen, every form of muscular activity begets an increase in the energy exchange of the body. ”

“ They pass into the blood numerous end-products of their metabolism. Further, some cells decay here and there, and partial products reach the blood which are out of harmony with the species, and, of course, entirely so with the plasma and the cell. The whole regulation of tho normal metabolism is seriously injured. The cells of the gut-wall will still be on the watch to prevent any disharmonious material from entering the organism; and the single cells of the body will still struggle to supply the blood only with properly altered substances. ”

“ Under the influence of this regimen a greater quantity of heat is developed and, in a given time, there is a greater absorption of oxygen than during a vegetable one; the respiration is performed more freely, the organs increase in size, but it is then a genuine embonpoint; nutrition is, in reality, more active, it is not a deceptive turgidity; the energy of the secretions and exhalations is redoubled, cutaneous perspiration becomes more abundant, and the glandular apparatus fulfil their functions with greater facility. ”

“ When an organ is exercised properly, there is an increased blood supply to it, and, consequently, stimulated nutrition and growth in various parts, such as in the muscular, nervous or other tissues.
When an organ is disused there is diminished blood supply, and, consequently, diminished growth and functional capacity. In man it is known that certain activities, such as coal-heaving, shoemaking, etc., produce recognizable effects upon the muscular system, the skeleton, and other parts of the body. ”

“ Muscles, nerves, all the wonderful tissues, are in process of formation; and in the strange growth and development of this most helpless yet most precious of all God's creations, there are certain elements which must be had,—phosphates to harden the delicate bones; nitrogen for flesh, which is only developed muscle; carbon,—or sugar and fat, which represent carbon,—for the whole wonderful course of respiration and circulation. Water, too, must be in abundance to fill the tiny stomach, which in the beginning can hold but a spoonful ”

“ We come now to the supreme and all-pervading metabolism which has for its effects the conspicuous manifestations of life—the nervous and muscular activities. Here comes up afresh a question discussed in the edition of 1864—a question to be reconsidered in the light of recent knowledge—the question what particular metabolic changes are they by which in muscle the energy existing under the form of molecular motion is transformed into the energy manifested as molar motion? ”

“ The liberation of energy in the tissues.—In the blood itself, no important chemical transformation occurs. The food fragments are picked out of the blood by the tissues and in the living protoplasms of each tissue, those important changes occur which constitute the most essential processes of life. These are, first, the building up of new protoplasmic matter, namely, growth and tissue repair, and, second, the liberation of energy by further decomposition and final burning or oxidation. ”

“ Food may exert an indirect influence on the pancreatic secretion. The acid in the chyme stimulates the flow of pancreatic juice. One is almost inclined to speak of the physiologic education of the digestive glands, and to conceive them as being trained for fat, protein, or carbohydrate digestion.
Metabolism.—Life consists, so far as material phenomena are concerned, in the transformation of matter into energy. To these transformations the term metabolism is [Pg 99] applied. In the metabolism of matter the changes are chemical; in energy the changes are physical. ”

“ A part of the art of feeding and fasting is scientific, for we get the same results every time, under given conditions.
When we consider the fact that the body is made up of various tissues, such as connective tissue, blood, nerves and muscles; that these in turn are made up of billions of cells, as are the various glandular organs and membranes; that these cells are constantly bathed in blood and lymph, from which they select the food they need and throw the refuse away, we must marvel that an organism so complex is so resistant, stable and strong. ”

“ Now that we have learned something about both muscles and sense organs we are ready to look into the way in which communication between them is carried on. First of all, we must realize that living protoplasm does this. The nerve cells are alive and have their basic metabolism just as do all other living cells. They also have their functional metabolism; but in them, instead of taking the form of forcible motion, as in muscles, or of the manufacture of special materials, as in gland cells, it takes the form of the transmission of a disturbance from one part of the cell to another. ”

“ These ceaseless processes are greatly modified by the activity of the bodily functions. Every movement of a muscle, for instance, involves change in its component cells. And since the loss of every atom of the body is in direct relation to its activity, a second process is necessary to repair this constant waste; else the body would rapidly diminish in size and strength, and life itself would soon end. This process of repair is accomplished, as we shall learn in Chapters VI. and VII., by the organs of nutrition, which convert the food into blood. ”

“ Bodily Control of Energy.—A fact of importance in the supply of energy to the body is that the rate of transformation (changing of potential to kinetic) is just sufficient for its needs. It is easily seen that too rapid or too slow a rate would prove injurious. The oxidations at the cells are, therefore, under such control that the quantity of kinetic energy supplied to the body as a whole, and to the different organs, is proportional to the work that is done. ”

“ It is evident that the amounts of these depend upon the amount of metabolism; the total metabolism is made up of the basic metabolism which is steady, shifting little day in and day out, plus the functional metabolism which depends upon how actively the body works. The main functional metabolism is that of the muscles and it is that which varies from day to day. In the case of children there is the additional metabolism of growth for which energy is required and for which food must be eaten. ”

“ The ex­cit­abil­ity of the muscle is restored after suitable periods of rest, by the opposite metabolic change of assimilation. “Assimilation and Dissimilation must be conceived as two closely interwoven processes, which constitute the metabolism (unknown to us in its intrinsic nature) of the living substance. Excitability diminishes in proportion with the duration of D-stimulus, or, as it is usually expressed, the substance fatigues itself. It is perfectly intelligible that a progressive fatigue and decrement of the magnitude of contraction must ensue. ”

“ Our present task is to see how muscles act; in other words to examine their functional metabolism. One feature that must be in mind from the very beginning is that the functional metabolism of muscle cells is under control; they do not go off at random, but only when started. This is more or less true of the functional metabolism of all the cells in highly organized animals. The agency that starts them off is named a stimulus. To picture how stimuli act we shall have to think for a moment of the state of affairs in cells at rest. As we have tried to make clear, cells at rest are not stagnating ”

“ The red corpuscles contain the oxygen which goes to combine with the superabundant carbon, and develop heat; the fatty matters probably repair the fatty tissues, and glands that are of a fatty nature; and the various salts contribute to the bones, and to the chemical properties of those secretions which are formed by the glands, &c., while the great proportion of water is employed in cleansing, softening, and cooling the whole, or the living edifice, and it is the medium through which all the nutrition of the body is distributed. ”

“ We will first consider the environment necessary for the normal expression of life in the body. Unhindered transmission of mental impulses alone will not give us the processes of metabolism. To have normal metabolism in the body oxygen must be carried to the tissue cells and there must be an uninterrupted transmission of mental impulses. Nutrition is derived from the food taken into the body and oxygen from the air is breathed into the lungs. The mental impulses are transformed in the brain by Innate Intelligence and transmitted by efferent nerves ”