Paper - The lobule of the spleen (1898)
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The Lobule of the Spleen
By Franklin P. Mall.
From the Anatomical Laboratory, Johns Hopkins University.
When the whole vascular system of the spleen is studied in connection with the trabecular system, it is found that the two together outline distinct masses of spleen pulp about one millimeter in diameter. These may easily be likened to the liver lobules, and for this reason I name them the lobules or the anatomical units of the spleen.
If a piece of fresh spleen is washed out by crushing it between the fingers in flowing water, it is found that the trabeculse and veins outline spaces which were filled with pulp. They are best demonstrated by macerating the whole spleen in water at ordinary room temperature until the pulp is very soft. Then, by cutting off the small end of the organ, the debris may be washed out, leaving the capsule, larger veins and trabeculffi. A specimen obtained in this way may then be stained with acid fuchsin, washed with alcohol, distended and dried. Then with transmitted light the lobules are plainly seen as vesicles immediately below the capsule. By first injecting the spleen with either colored celloidin or agar-agar before macerating, the relation of the arteries and veins to the lobules can be determined. This is possible because neither the celloidin nor agar-agar is destroyed by the process of maceration. Thick sections made from such specimens may be immersed in xylol or mounted in Canada balsam.
It is found by studying numerous specimens of this sort, as well as those made by injecting cinnabar into the arteries and ultramarine blue into the veins, that the artery always penetrates the lobule and passes along its center, while the vein is intimately related to the trabecule and remains on the periphery of the lobule. In the case of the lobules lying immediately below the capsule, the artery enters the side as far away from the capsule as possible, as shown in the figure. The end of the lobule at which the artery enters I shall term the proximal side, while that opposite will be designated the distal side of the lobule. The deeper lobules of the spleen, then, have a distinct relation to the artery and not to the capsule. The Malpighian corpuscle usually lies in the proximal end of the lobule, but, in case it is very large, it may distend the lobule and cause it to bulge.
On an average there are 80,000 lobules in the spleen of a dog weighing 10 kg. In smaller spleens there may be as few as 25,000, while in larger spleens there may be 200,000. In all cases they are clustered together around the terminal branches of the artery in the same manner as the lobules of the lung are around the bronchus and the lobules of the liver around the hepatic vein. In order to understand the structure of the spleen it is necessary to study one lobule only, and for its anatomy the relations of the lobules to one another.
Fig. 1 Diagram of the Lobule of the Spleen. A, artery in the centre of the lobule; r, interlobular vein within the interlobular trabeculie ; Tr, intralobular trabecula- ; L, JIalpiijhian follicle ; C, intralobular collecting vein ; P, intralobular vein plexus which surrounds the pulp cords or histological units; Am, ampulla of Thoma.
The accompanying figure is a diagram of an average lobule drawn to scale. In no case can a picture like this be gotten from a single section, as the artery and two veins are never in the same plane. Moreover, the branches from the artery, as well as those from the vein, radiate from the main stem and pass in all directions. Practically all of the interlobular veins are covered by interlobular trabeculse, but tbere are numerous interlobular trabeculse which are solid. In the periphery of each lobule there are three main interlobular trabeculag, each of which sends three branches into each of the three surrounding lobules. The intralobular trabecule communicate with one another within the lobule, thereby dividing the lobule into about ten compartments. The relation of the veins to the lobule is much like that of the trabeculas. In fact, it is the relation of the trabecule to the veins which makes the lobule. The large veins of the spleen cannot be said to lie within the trabeculse, although their walls are thick, are continuous with the trabeculas and give rise to them. The points which mark the separation of the smaller veins from the trabeculse mark the boundary of the lobule (see diagram). As the venous branches leave the lobule they are at first independent of the intralobular trabecule, but near their exit they are related to them. The intralobular collecting veins also aid to divide the lobule into the ten parts, spoken of above. Of course the artery is distributed to the lobule from a direction opposite to that of the veins. The tendency is for veins and arteries of the same order to remain as far separated from one another as possible. The central artery of the lobule gives rise to .about ten branches, each of which passes into one of the ten compartments of the lobule and through its centre. All of the above can be demonstrated best with granular infections, thick sections and low magnification.
If an interstitial injection of the spleen is made with an aqueous solution of Prussian blue, or if the blue is injected into the vein, it is found in either case that the venous plexus of the lobule is completely filled. This plexus is indicated in the figure giving its relation to the surrounding structures. It divides the spleen pulp into small areas or the histological units as I call them. In fact, however, these areas are not isolated, but communicate with one another as do the cavities of a sponge. Since the histological units run together to form cords of spleen tissue, I term them collectively pulp cords. Thick sections which leave the venous plexus intact show the optical section of the pulp cords or the histological units, while very thin sections cut the venous plexus and demonstrate the pulp, cords. The terminal arteries ramify in the pulp cords and along their course, give off numerous small branches which end in a dilatation, the ampulla of Thoma. The beginning of the ampulla always lies in the centre of a pulp cord. As a rule a number of the minute branches arise from each terminal artery and radiate in all directions. I have been able to obtain complete injections of the vascular system of the spleen only after the organ has been distended to its maximum by ligating the vein half an hour before killing the animal or by making an artificial oedema with gelatin by injecting it into the veins. By both methods all the intercellular spaces within the pulp cords become enormously distended. In spleens prepared in either of the above ways the ampulla? and their communications with the veins may be filled by injecting an aqueous solution of Prussian blue into the artery. If carmine or some such fluid is used it will only add another color to the fluids in the pulp spaces. The blue, however, precipitates easily and with it, it is often easy to obtain complete injections. The specimen is made still better if the venous plexus is marked by injecting chrome yellow into the vein before injecting the blue into the artery. The gelatin-spleens are best cut on the freezing microtome and mounted in glycerine, as alcohol causes too much shrinkage of the gelatin. The injections show that the ampullffi have a tendency to communicate with amptillje from neighboring arteries, while other branches comnnmicate directly with the veins. Yet judging from the amount of extravasation which is always present the walls of the ampullar must be very porous.
Carmine gelatin injected into either the artery or vein will cause an CBdema of the pulp; in case it is injected into the artery it will ultimately run out of the vein, while when injected into the vein it will never run out of the artery. When cinnabar is injected into the artery, the greater part of it passes directly over into the vein, while a small portion of the granules pass into the tissues. When it is injected into the vein a considerable quantity passes into the intercelltilar spaces of the ptilp cords, showing that the walls of the vein are pervious. Solutions of nitrate of silver injected into the artery show that the endothelial coat becomes incomplete at the beginning of the ampulla. The first two-thirds of the amptilla are lined with spindle-shaped cells lying upon a delicate framework of reticulum. Throughout the last third, at the junction with the vein, no cell boundaries can be demonstrated, nor can this portion of the amptilia be injected from the vein. In fact it appears as if this portion of the ampulla were cut up by fibrils of reticulum passing across it. Silver injected into the veins shows that the complete layer of cells ends at the point of junction of the intralobular plexus with the intralobular collecting veins. Throughout the plexus the cell walls are incomplete and the endothelial cells are spindle-shaped, the space between them being large enough to allow cinnabar granules to pass easily, tiltramarine blue granules with difficulty, and chrome yellow granules not at all. The openings in the veins are largest in the neighborhood of the Malpighian follicles.
The reticulum extends throughout the lobule, supplies the framework for the ampullse and the venous plexus, and is continuous with the reticulum of the lymph follicles surrounding the arteries. Its arrangement is such that an cedema distends the lumina of the veins out of proportion to those of the pulp spaces. The reticulum is very delicate and elastic. It can be stretched to double its length and when relaxed it will return to its former shape. It is easily destroyed with acid or with alkali, and is digested with pancreatin. This last reaction makes of it a new variety of reticulum. While this reticulum is so delicate and easily destroyed, the reticulum of the trabeculse and capsule is most resistant. In fact, it is more resistant than that of the lymphatic gland or of the mucosa of the intestine. We have therefore within the spleen two extremes of reticulum, the most resistant and the least resistant.
The microscopic anatomy shows that the ampulla} and venous plexus have very porous walls which permit fluids to pass through with great ease and granules only with difficulty. In life the plasma constantly flows through the intercellular spaces of the pulp cords, while the blood corpuscles keep within fixed channels. Numerous physiological experiments which I have made corroborate this view.
A more detailed account of the facts enumerated above, together with illustrations, is being prepared for publication.
Cite this page: Hill, M.A. (2020, September 28) Embryology Paper - The lobule of the spleen (1898). Retrieved from https://embryology.med.unsw.edu.au/embryology/index.php/Paper_-_The_lobule_of_the_spleen_(1898)
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