Observations on the propulsion of lymph through the mesenteric lymphatic vessels of the living rat.код для вставкиСкачать
OBSERVATIONS ON THE PROPULSION O F LYMPH THROUGH T H E MESENTERIC LYMPHATIC VESSELS O F THE LIVING RAT RICHARD L. WEBB Department of A n a t o m y , College of Medicine, Unimersity of Illinois, Chicago ONE FIGURE A study of the mesenteries of the white rat revealed the feasibility of making a microscopical examination of the large lymphatic channels which accompany the mesenteric blood vessels. Consequently, the present investigation was undertaken in an attempt to study these vessels in life under conditions which were as little altered as possible from the normal. The body wall of the anesthetized rat was opened along the linea alba, a distance sufficient to permit the withdrawal of a segment of the gut with its mesentery. The rat was then placed on an animal board and the mesentery exposed for microscopical examination. It was soon observed that in order to study the lymphatics, the surrounding fat must be reduced. As a result, most of the animals used in this study have undergone a period of inanition extending from 5 to 8 days. Approximately fifteen animals were studied before an attempt was made to obtain permanent records of the changes which take place in the living lymphatics as they propel their fluid. Permanent records were made by taking photomicrographs of successive stages of activity. F o r this purpose, a Leitz ‘Miflmca’ camera and Eastman ‘Superpanchromatic’ film were used. In general, low magnification ( X 24) was employed, and the time of exposure ranged from 1/125 second t o 1/25 second, depending on the type of filter. 345 346 RICHARD L. WEBB I n their study of the growth of lymphatics as seen in the transparent chamber introduced into the rabbit’s ear, Clark and Clark ( ’32)l describe the movement of lymph in these vessels “to be a bobbing back and forth, synchronous with the heart beat or respiration, with only a sluggish, jerky, f o r ward progression. ” These observations do not conform with the well-known fact that in all laboratory animals a definite progressive flow of lymph can be observed in the larger channels-especially the thoracic duct. In the human, under certain pathological conditions, this definite, regular flow of lymph is observed. The movement that Clark and Clark describe may be the result of the lack of valves within the lymphatic vessels that grow into the chamber, which, because of their nature as terminal radicles, possess a sluggish current. Other authors have confined their study to fixed material, and from observations of the presence of muscle fibers and their innervation, they have assumed logically that the lymphatics contract. The first animals t o be studied during the course of this investigation were healthy, well-nourished rats. Although it was impossible to take photographs of the vessels because of the surrounding fat, certain advantages of making a study o f these were evident. These vessels were protected by the fat from external environmental conditions introduced by the exposure of the mesentery. Due to difference in light refraction, their course could be seen. Contractions were observed at intervals along the line of the vessel which were evidenced by the movement of the fat cells surrounding the particuIar lymphatic. I n a rat having a respiration rate of 74 and a heart rate of 168 per minute, it was found that the rate of contraction of a lymphatic vessel was 12 per minute. In portions of such a vessel not deeply embedded in fat, cells could be seen passing through it at an even rate of speed, making continual progress toward the more central lymphatics. ‘Clark, E. R. a n d E. L. Clark. 1932. Observations on the new growth of lymphatic vessels as seen in the transparent chambers introduced into the rabhit ’s ear. Am. J. Anat., vol. 51. PROPULSION O F LYMPH 347 A continuation of this study on rats which had undergone a period of inanition revealed more clearly the lymphatics which were contracting. Their valves were discernible. A wave of contraction usually originated in the region of the valve sinus. The entire contraction was divided into two phases : the first, a slow movement concerned chiefly with the eradication of the space of the sinus, and a second, more rapid movement which continued centrally almost obliterating the lumen of the vessel. This was followed by a relaxation of the walls. These contractions were segmental, confined to the portions between valves. Each segment of the lymphatic seemed to be timed with the neighboring segments so that the contractions served to propel the fluid within the vessel as a whole (fig. 1). This is the type of movement observed within the lymphatics, the segments of which were contracting at a rate between twelve and eighteen times per minute. Such a picture was seen in nearly all vessels which had received a minimum of manipulation and exposure. It was possible to make a more leisurely study of the movements of these vessels after the mesenteries had been exposed for a period of time. Although the circulation of blood remained almost normal, lymphatic circulation became much slower. The movement was sluggish, quite similar to that described by Clark and Clark. A noticeable increase in blood cells occurred within the lymph. Frequently the contracting segments of the vessels were no longer in time with each other. As a consequence, the lymph was churned back and forth making only occasional progress toward the central vessels, I n such a vessel, it was possible to study the effectiveness of valve flaps. Their action seemed to be purely passive. I n the event of a reversal in the flow of lymph, part of the fluid at first streamed back through the opening between the two valve flaps, while the more peripheral parts of the current exerted pressure on the walls of the valve sinuses, tending to distend them (fig. 1C). The pressure of the fluid within these sinuses soon became great enough to force the mid-portions of the flaps together, thus obliterating 348 RICHARD L. WEBB the channel and preventing further regurgitation through. the valve (fig. 1 D). Ordinarily, during the circulation of the lymph the valves along the regular channels act apparently as an emergency mechanism. As shown by actual observations, the same cannot be said of the valves which protect the tributaries at their point of junction with the larger channels. The larger vessel usually has a valve located just peripheral to the opening f o r the smaller. The valve of the smaller vessel is located almost at its point of entrance into the larger. Under this arrangement both valves are called upon to assert their functional activity continually. Realizing the inadequacy of descriptive terms in giving a complete picture of the activity of living lymphatics, the writer is now making cinematographic records of these vessels, as a supplement t o this work. Certain aspects of the investigation are being continued. Sufficient data have not been collected to determine whether o r not peristalsis of the gut has any effect on the movement of the lymph in this region. Some evidence has been obtained which indicates that the rate of the circular contractions is not synchronous with the movement of the lymphatic walls. I n conclusion, it can be said that the lymph within the lymphatic vessels of the mesentery of the rat is propelled by means of contractions of their walls. These contractions are segmental, occurring in sections of vessels between valves. Fig. 1 Photomicrographs a d explanatory sketches of a series of changes occurriiig in the walls of a portioii of a meseiiteric lymphatic during a wave of contraction. X 60. Contractions in this vessel were slow, taking place at a rate of three times per minute. As indicated by the position of the valves ( 1 and Z ) , flow of lymph i n this vessel was normally from right to left. A) entire portion of vessel partially relaxed. Valves 1 and 2 are open. B) peripheral segment contracting, forcing lymph through valve 1. Wave of contraction coutinues through segment, 1-2, propelling lymph through valve 2. C ) reversed current of lymph has closed valve 2. Segment 1-2, only partially relaxed. Pressure from the reversed flov of lymph is begiiiniiig to disteiid the sinuses of valve 1. D ) valve 1 completely closed, preventing further regurgitatioii of lymph. Peripheral segment completely relaxed and distended. E ) entire portion of vessel distended. Movement of lymph ceases uiitil a new wave of contraction is initiated. 349 THE AN.4TOMICAL RECORD, VOL. 5 7 , N O . 4, A N D SUPPLFIv1E:NT 350 R I C H S E D L. \X7EBB The rate at which the movements take place is twelve to eighteen times per minute, which indicates that it is in no way related to respiration or to the heart beat. The flow of the fluid is a rapid progression toward the central vessels. The action of the valves in preventing regurgitation of lymph is a passive one, depending entirely upon the force of the reversed stream to approximate the valvular flaps. APPENDIX After this paper was accepted for pxhlicatioii, the author found that Florey ('27) had published the results of a similar iiircstigatioii. (Olnscrvations on the coiitracti1it~-of lacteals. ,J. I'hyiol., vol. 62.) Altliougli Florcy did not illustrate his paper witli fignrcs, our descriptions of the movements of the lymphatics are ill agreement.