The Lumleian Lectures on the Muscular Arterioles: Their Structure and Function in Health and in Certain Morbid States

G. Johnson
1877 BMJ (Clinical Research Edition)  
have the honour to deliver, I propose to discuss certain questions relating to the structure of the minute blood-vessels and the forces concerned in carrying on and regulating the-circulation of the blood. Upon this subject modern researches have thrown an entirely new light; and I shall endeavour to show that the increased knowledge of the physiology of the circulation which has been acquired within the last quarter of a century has rendered necessary a revision and correction of some
more » ... on of some pathological doctrines which had gained more or less general acceptance. The chief anatomical discovery relating to the organs of circulation made during the period to which I refer was Henle s demonstration of the muscular elements in the middle coat of the arteries. John Hunter and others, it is true, had on theoretical grounds assumed that the middle coat of the arteries contains muscular tissue; but it was Henle (Wochenschrift fur die gesammte Heilkunde, I840, No. 21, p. 329) who first described the fusiform muscular elements encircling the arterial tube between the outer and the inner coats, and who showed that these have the same characters as the unstriped muscular tissue of organic life. There. are obvious structural differences, corresponding with important diversities of physiological function, between the large and the small arteries. The chief anatomical distinction between the large and the small arteries is to be found in their middle coat. The middle coat of the largest arteries is composed almost entirely of elastic tissue, with a very slight admixture of muscular fibres. As the arteries diminish in size, the proportion of muscular tissue increases, until, in the smallest arteries, the middle coat is composed entirely of muscular tissue. These smallest arteries are commonlv designated "muscular arterioles", to distinguish them from the large elastic arteries. The muscular arterioles, varying in diameter from the onehundredth to the one-three-thousandth of an inch, have their middle coat composed of muscular fibre-cells, without the slightest admixture of connective or elastic tissue. The muscular fibre-cells, which, when separated, are seen to be elongated and spindle-shaped, with an oblong nucleus in the centre, are arranged in a circular manner round the arteries, forming contractile muscular lamelbe. The circular muscular coat in arteries between about the one-hundredth and the one-three-hundredth of an inch in diameter possesses two or three layers of muscular fibres. In the smaller arteries, the muscular coat consists of only a single layer of fibres, whose elements become shorter and shorter until, in the smallest arteries approaching the capillaries, the muscular elements separate from each other and at length completely disappear. The muscular coat has on its inner surface the tunica intima, and on its outer the tunica adventitia. The tunica intima consists of two layers: an inner epithelial layer, and a shining membrane which Kolliker calls the elastic inner coat. The tunica adventitia consists of connective tissue and fine elastic fibres with elongated nuclei, having their long diameter parallel with the axis of the vessel. The tunica adventitia is generally as thick as, and often thicker than, the muScular coat; and it is readily made to swell up under the influence of certain reagents. My colleague Dr. Beale and other microscopic observers nave demonstrated the presence oi minute nervous gangila and extremely delicate nervous fibres ramifying upon the minute arteries and the capillaries. During the last quarter of a century, the physiology of the vasomotor system and the relation between the nervous and the vascula apparatus have been the subject of laborious research by numerous and very able investigators; and the result has been a'large addition to our positive knowledge of the forces which are concerned in regulating the movement of the blood through the minutest subdivisions of the vascular system. M. Vulpian, in his two recently published volumes (Lefons sur l'Appareil Vaso-Moteur, Paris, 1875), has given a very lucid and complete history of these investigations. An able summary of the physiology of the vaso-motor system appeared in the British and Foreign Medico-Chirurgical Review for Odtober I876; and the whole subject of the vascular mechanism has been treated withl great ability by Dr. Michael Foster in his recently published Handbook of Physiology. We have already seen that in the year 1840 Hcnle had demonstrated the muscular tissue of the middle arterial coat. About the same time, Stilling (Recherches Pathologiques et Medico-Pratiques suri l'Irritation SPinale, Leipzig, I840) was led to the conclusion that there are certain nerves which influence the movements of the blood-vessels. For these nerves he invented the term vaso-motor, and he looked upon them as analogous to'the nmusculo-motor nerves. But the starting-point of our present positive knowledge of the vaso-motor nerves was the year I85I, when M. Claude Bernard published his first conclusive experiments (Comptes Rendius de la SociJt de Biologie, I851, p. I63). In his first memoir, Bernard showed that after division of the cervical sym- pathetic, but more especially after removal of the superior cervical ganglion, in the horse, the dog, or the rabbit, there is an increased afflux of blood to the ear and the whole of that side of the face, and with this an elevation of temperature and an increased senisibility. In a second communication, made this time to l'Acade'mie des Sciences (Coinptes Rendus de l'Acad. des Sciences, Mars 29, I852), he described in more detail the facts recorded in his first paper. It was not until towards the end of the year 1852 that Bernard published his explanation of the phenomena which he had discovered. Meanwhile, public attention having been directed to these researches, in the interval between the publication of Bernard's second and third memoirs, Dr. Brown-Sequard had published in America (Philadelphia IMedial Examiner, August I852) the interesting results at which he had arrived. This able experimenter confirmned Bernard's observation of the dilatation of the blood-vessels and the elevation of temperature resulting from division of the cervical sympathetic. He then went on to show that the galvanic stimulus applied to the cut end of the peripheral portion of the nerve caused a constriction of the blood-vessels and a 'lowering of the temperature. He thus proved that the elevation of temperature resulting from division of the sympathetic is directly due to the increased afflux of blood consequent on paralysis of the arterioles. In Bernard's third memoir, published in November I852 (Conmptes Rendus de la Societt de Biologie, Nov. 1852, p. I68), he also records the observation that the increased blood-supply which results from the paralysing influence of dividing the sympathetic is at once arrested by galvanising the divided end of the nerve, when the parts which were previously red and congested become pali and comparatively bloodless. Since this great field of research was opened up by Claude Bernard and Brown-Sequard, numerous experimenters have laboriously entered upon it, and the result has been the accumulation of many interesting facts and the construction of a tolerably consistent though not as yet an entirely complete theory of the vaso-motor system. Time would not permit me now, even if it were necessary or desirable, to enter into the minute details of this extensive subject. I need only refer to such ascertained facts and principles al have relation to some pathological phenomena which we shall presently have to discuss. The vaso-motor nerves may be said, in a general way, to belong to the great sympathetic; but, by means of communicating branches, they are also connected with the spinal nerves and with the spinal cord. In fact, there is reason to believe that all the vaso-motor fibres are derived from the cerebro-spinal axis, from which they pass out chiefly by the anterior roots of the spinal nerves; and that the chief centre of vaso-motor nerve action is the medulla oblongata, near thefloor of the fourth ventricle. Injury to this part of the nervous centre or division of the cord in the upper cervical region, cutting off the communication between the centre above and the vaso-motor nerves, causes general relaxation of the arterioles and a fall of blood-pressure throughout the body. On the other hand, electrical stimulation'of the centre excites general contraction of the arterioles and an increase of blood-pressure. The nerves which, when divided, cause arterial paralysis, and when !ii -I.,iLe+, PA.-iC +.LAr; L ILtrn eLinn -J vp heen deqi-nated vaso.
doi:10.1136/bmj.1.850.443 fatcat:l3esw2lwl5gslk4ridkcyk2ztq