Paper - Morphology of the tubules of the human testis and epididymis
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Bremer JL. Morphology of the tubules of the human testis and epididymis. (1911) Amer. J Anat. 11: 393-416.
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Morphology of the Tubules of the Human Testis and Epididymis
John Lewis Bremer
Harvard Medical School, Boston, Mass.
Twelve Figures (1911)
The intention of this paper is to show accurately the form of the seminiferous tubules of the testis and of the tubules of the epididymis, and to trace their development in man, especially in the late embryonic and fetal stages With this study the blood vessels are so intimately associated that a description of them is added.
Many attempts have been made heretofore to decide whether the tubules are single with blind ends, or anastomosing or merely branching, but the methods used gave contradictory results, and were unsatisfactory teasing methods are not convincing, because, in spite of the particularly tough reticular tissue described by Hill as encircling them, the tubules are easily broken; and injections are never complete, as the injection mass is forced through the walls of the tubules before the resistance of the many convolutions is over-come. The method employed as a basis of this paper is the study of serial sections, from which usually wax reconstructions have been made. The material is human, though freiquently the many embryos of pig, sheep, cat, rabbit, etc., in the Harvard Embryological collection have given valuable assistance in interpreting the human material.
Allen has given us an account of the origin of the seminiferous tubules, of the rete testis, and of the connections of this latter with the tubules of the Wolfiian body on the one hand and the testis tubules on the other. His resu1ts, obtained by studying pig and rabbit, I have confirmed, with slight variations in man. Briefly stated, Allen’s factsare these; the testis tubules originate as cords of epithelial ce1ls containing germ cells, which grow inward from the peritoneal epithelium covering thegmiddle third of the genital ridge; the rete is formed of similar cords growing inward from the anterior third of the same ridge Both sets soon lose their attachments to the peritoneum, so as to 1ie free within the ridge. The rete cords, forminganetwsorh grow into the mediastinum, extending caudally to reach the inner or central ends of the testis cords, with which they become joined. On theirway, the rete cords unite with the glomeruli of the Wolflian body, thus coiiipleting the passages by spwhich the products of the seminiferous tubules are later carried away from the gland. The testis cords Allen described as anastomosing and branching, and occasionally growiiig parallel to the surface.
Further detailed study of these testis cords gives rather surprising results. Instead of branching and anastomosing irregularly, as suggested by Allen’s descripition, the cords form a complete network, evcry cord anastomosing wsith others, leaving no free ends except those at the periphery and those near the mcdiastinum. The bases of the cords, at the periphery of the gland, form free ends when they have lost their connection vvith the peritoneal epithelium from which they grewz and the distal ends of the cords, which, since growth is centripetal are found near the mediastinum, are also usually free ends, though occasionally two may join at their tips. Otherwise all the oords are joinod by anastomosing branches As a whole this netvsxork is crescentic in cross Section, occupying a peripheral Zone of the genital ridge, of which the mediastinum is the eccentric core; this brings the Central ends of the cords nearer together and accounts for the occasional anastomosis of their tips.
Although this network (Fig.5) seems at first sight to be quite irregular, a more critical study shows that each of the cords has three (occasionally four) sets of branches, so that there« are three sets of cross connections joining the radial1y disposed cords. 0ne set of branches is given off a little distance from the peritoneal epithelium, and the branches run more or less parallel to the surface, as described by Allen; the second and third sets are given off respectively nearer the mediastinum. Beyond the thircl set« of branches the cords grow centripetally without further branching The Hgure or pattern thus produced, which is given in a very much simpliiied and idealized form in Iigure l, results apparently from the fact that the testis cords possess a normal rate of branching, and are moreover limited in length by the thickness of the genital ridge. Three, or possibly four, sets of manches, a certain distance apart, are all that each cord produces.
Fig 1 Diagram of testis network of human embrzso of 20 mm. Outer dotted 1ine represents germinal epitheliunn solid lines represent testis cords.
The cords forming this network vary in diameter, and, though usually approximately round, in certain places they are flattened, forming plate-like structures, often where three or four cords join. sometimes these plates are pierce(:l, malcing larger or smaller rings.
This network is comp1eted shortly after the cords have become detached from the peritoneal epitheliu1n, and before the central tips have joined the rete cords; in the human embryo this corresponds to a length of about 2() mm. to 22 mm. Further growth takes place in two ways ; by the increase in diameter of the cords, and by the increase in thickness of the genita1 ridgc, caused by the lengthening of the radially disposed cords, not at their ends, but throughout their whole extent, so that the cross connections are more widely separated. No more branches are produced. With this there occurs, apparently, an absorption of the peripheral free ends into the network, leaving the outer set of cross connections as a series of arches, joining the ends of the radial cords (flg. 6). Also, since the cross connections do not lengthen so much as the radial cords, the network assumes a distinctly radial appearance. if T There now occurs a partial destruction of the network. kAls though there is a general increase in the diameter of the cords, certain ones, usually, but not exclusively, those forming cross connections, remain of their original size or even become smaller. Many of these attenuated connections soonbecome severed, strand after Strand, and the loose ends are, absorbed into the network. This partial destruotion of the network goes on for a long time, in the human embryo certainly from 22.8 mm. to 9.1 cm., perhaps longer; in the later stages, when the cords have become more established, the loose ends are not usually retractedor absorbed, but remain as short knobs or as long branches with blind ends. The results of this process may be, seen by comparing the models of tubules from embryos of 37.0 mm. and 9.1 cm. (figs. H, 7, 8 and 9), a full description of which will be given later. At a glance, the destruction of the network and the consequent isolation of certain cords can be easily traced, as the figures are still uncomplicated by convo1utions.
During this time the inner or central ends of the radial cords have come into contact with the rete cords, which also have formed a network. The rete network, the Tceimdriisenneta of Miha1kowicz and other older writers, is quite irregular, of small mesh, and persists throughout life. It occupies the mediastinum testis, and in the lower two—thirds of this spreads out in a fanshape, fills ing the space enclosed by the mass of the testis cords, which is itself cresentic in Section. A single testis cord may come directly in contact and join with the rete network, or peripheral rete cords may extend far into the area of the testis network, so that the boundary line between rete network and testis network is irregular and wavy (fig. 6). These extensions probably indicate the position of the septa of the adult testis, along which the tubuli recti often run for some distance before joining the seminiferous tubules Frequeritly two testis cords anastomose just before joining a rete cord; on the other hand, one testis cord may be connected with several rete cords.
In regard to the age at which the testis and rete cords join, I find such differences between my findings in man and Allen’s in pig and rabbit that they seem worthy of note. Allen gives the time of junetion as about 13.0 cm. in the Fig, and y21 days in the rabbit; in both cases the rete cords were already hollow before joining. In man the development of this connection is much more rapid, though there seem to be quite wide individual variations At 16.0lmn1. there is no extension l of the rete cords dovvnvwsarch while at 23.0 mm. the cords have already grown past the upper glomeruli into the mediastinum , and in embryos of 32.0 mm. have already United with the testis cords. (In one embryo, H. E. C» no. 819, of «19.0 mm., this union has taken place.) For Some time after joining, the rete cords in man remain solid, without lumen. This precocious development of the rete cords inman may be correlated with the small size and rapid degeneration of the mesonephros, as compared with that of pig and r«abbit. In the sheep, another embryo with large mesonephros, the rete again develops late; whereas in the cat, vvhose mesonephros is small, the rete cords and testis cords have nearly joined at 24.0" mm. o (H. E. C» no. 467).
By the end of the third month or the middle of the fourth the rapid destruction of the testis network probably ceases, though many connections may be sevsered much later; mylpreparations give no information on this point. The cords become so long that they are forced into convolutions, which increase progressiveljy till puberty; on the other hand the cords decrease in diameten becoming more and more slender until at seven months they are of about ones-half as great diameter as at three months. From scven months on there is a gradual increase in calibre. This reduction in Size may be due to a rearrangement of the eells to allow for the rapid increase in length The convolutions are in short, stiff curves, which remain within a small area, condensing the Connective tissue around them. It thus happens that different parts of the same tubule are isolated from each other, and lie in comparts ments, which can be easily reeognized in the adult testis, marlcing subdivisions of the parenchyma between the septa.
The greatest complexitv of convolutions is in the peripheral part of the gland, and apparently in the oross connections, not in the radial cords, vvhieh latter may frequently be seen in the adult running from the rete with only a slightly wavy course to a convoluted portion situated near the outer surfaee of the gland. The diagrarn (fig;. 2) gives the approximate course of several tubules in a fetus of seven months and suggestss from what part of the original network they have been derived, while the model (Fig. 11) shows the aetual form of some of the tubules at the same age. In the adult I have been unable to follow completely any single tubule but from the portions studied I feel convinced that, except for the greater number of oonvolutions, the oonditions are similar to those found at seven months.
Fig. 2 Diagram of the course of several tubules in testis of seven knonths fetus, made by noting their eonnections and the positions of the various branches in the gland. The original network is represented by fine lines, the permanent portions of the tubules by heavzs lines; rete eonnections at bottom of figure
From the diagram Iwe see that there are to be found tubules with no connections whateven except that with the rete, ending blindly ; others with several branches which end blindly ; others anastomosing with their neighbors In one a short blunt knob, m, was seen (found also in the adult testis) such as has been described as oommonly present by Some authors. But to me the most interesting part of the diagram is the preservat-ion, at seven months and probablyin the adult, of the course, connections, and position of each tubule as determined for it by the original network of the testis cords.
The Blood Vessels
Hill has described the development of the blood vessels of the testis in the pig, and in a later work has apparcntly taken for granted that, although the adult arrangement in pig and man differ widely, the early development is similar in each case. In the pig the SperInatic artery arises as a separate vessel from the dorsa1 aorta, caudal to the last mesonephric arterzz or rarely as a branch of the latter. It makes its way horizontally to the mesial bordcr of the Wolflian body, and then turns upward, toward the head, passing mesial to the mesonephric arteries, and orossing over the last five or six of them, to reach the genital gland ; it thus approaches the testis from the oaudal end. In man there is no such vessel formed. The arteries to the WolfHan glomeruli in the region of the future testis send branches to supply the gland directly, so that at first there are many spermatic arteries, which enter all along the attachment of the testis to the Wolffian bodzk 0n examining embryos of other mammals in regard to the origin of their spermatic arteries, I Hnd that in sheep, rabbit, cow, and deer (ce1vus capreolus) a separate vessel is formed to supply blood to the genital glancL whether it be testis or ovary; while in the cat the arteries to the glomeruli send branches directly to the gland. In sheep, the new artery is more apt to arise as a branch of the last mesonephric artery than as a direct outgrowth from the aorta, and in one deer embryo of 19.6 mm. (H. E. C» no 1230) one ovarian artery is a branch of the mesenteric arterzn I find here, then the same grouping of animals that occurred when the time of junction of rete cords and testis cords was under considep ationz species with large Wolflian bodies (so far as my limited studies show) provide a new vessel for the genital glands, while those with small Wolflian bodies utilize branches from the nearest arteries.
In man and cat the mesonephric arteries anastomose freely with each other before entering the glomeruli, and with the early degeneratsion of the glomeruli the number of mesonephric arteries diminishes gradually, until one only is left ; this one is, however, oonnected wsith all the arteries of the testis, and so becomes the single spermatic artery. The factors in this deorease in number of the Wolfkian arteries seem to be the descent of the testis, which stretches them into long parallel vessels, and theingrowth of the cords which are to form the cortex of the suprarenal body, which occurs directly in the course of these vessels, and presses upon them. Incidentally it may be mentioned that small pieces of this suprarenal tissue are often carried down with the lengthening arteries, and left as the small aberrant glands not infreqiiently found on the posterior wall of the abdominal cavitxz along the course of the spermatic arterzN In a human embrzso of ,37.0 mm. (H. E. C» no. 820) there are two complete spermatic arteries in each side, and four or five arterial stems parallel to the main arteries either joining them or sending blindly, evidently recently obliterated. In an embryo of 44.3 mm. (H. E. C. , no. 293) one artsery on each side remains, Iwith two or three obliterated pieces beside it. Inboth embryos suprarenal tissue appears along the course of the arteries. This method of arriving at a single sperms atic artery on each sidein man aceounts for the wide range in its point of origin in the adu1t, as described in the text-books of anatomy.
The veins of the testis in all the mammals examined arise as simple offshoots from the sinusoids of the Wolflian body in the neighborhood of the genital gland.
The blood vessels of the testis in man, then, arise as two capillary networks, one from the branches of the efferent arteries of the glomeruli of the mesonephros, the other from the sinusoids. Both sets interdigitate with the netvvork of eords, and extend beyond the the outer cross eonnections of the network so as to lie just underneath the peritoneal epithelium. The flow of blood is in two directions from the hilus or mediastinum testis toward the periphery, and from the periphersy toward the centerz the veins also return the blood in both directions There are at first, then, no terminal arteries or veins. As certain cords beeome destroyed, the capillaries lying near them are alloxved to assume a straighter course; they then beoome the more favored vessels, grow larger and are established as main arteries or veins. Since the eross connections of the network are those most frequently Hevered, the radial tressels are the most favored, and hence the main arteries and veins of the testis run radiallzn But not infrequentlzg as we have seen, the radial cords are severed, and this factiiacoounts for the few main vessels which, though not iigured by Hi1l, are commonly present in the adult testis, running diagonally or even for some distance parallel to the surface of the gland, quite deep swithin the substance. Another curious arrangement of vsessels not mentioned by Bill, is found in the testis ; three or four arteries run parallel to one another for long distances to supply an area which would usually be served by a single arterzz with short branches. To explain this it is only neeessary to imagine that certain cross eonneetions of the cord netvrorlc vvhieh may at first have separated the different vessels quite widely, were destroyed late, after each vessel was vvell established, and that subsequent radial grsowth drew the vessels together.
The terminal arteries are at their first appearance probably portions of the capillary network not favored by a direct course. 1n the fourth month three sets of terminal arteries can be made out, one set situated betswseen the outer and second sets of eross connections of the testis cords, another bettveen the second and inner sets of eross eonnections, and a third set nearer the rote. At seven months new arteries have grown from these, and also apparently from the main stems of the radial and peripheral arteries, so that the pieture is much con1plieated;yot even inthe adult, the embrys onic arrangement of three main branches from each radial artery can be traced in some places. (Hill, flgn 12.) In both the fourth and the seventh months a vascular unit can be made out, as the veins are arranged in a network around the terminal arteries in the usual manner. Hill mentions «vascular units which correspond to units of structure and which repeat themselves similarly throughout the Organs« but does not state what these units of structure are; I have found in the testis of seven months and in the adult that the structural unit corresponding to the vascular unit consists of a number of coils of a single tubule enclosed in a compartment, as described earlier in this paper. The border veins of the unit lie in the connective tissue which surrounds the- convolutions, the terminal artery pierces the compartment It is probable that the terminal artery is the causative factor in this unit ; the portion of a tubule situated nearest to the artery would be more favorably placed for growth and consequent convolution, than the portions of the tubule further from the blood supply ; the convolutions would therefore form around the arteries, one set for each terminal artery. These units are quite large, readily visible to the naked eye; the capillaries surrounding the tubulcs are therefore of considerable length. As structural units they are not typicah like the unit of the lung or of the salivary glands, since they only very occasionally represent the terminal, blind ends of the secreting or active portion of the gland, and since there is no constant relation between the ter1ninal artery and the channel through which the secretion leaves the unit. One tubule passes through several units, but all the convo1utions within a unit belong to the same tubule.
The peripheral layers of the original capillary networks, both arterial and venous, interdigitate vvith the peripheral portions of the cords, while these portions are still attached to the peritoneal epithelium from which they grew. When this connection is lost and the peripheral ends of the cords have been absorbed into the network, the peripheral vascular networks remain, and become incorporated in the vascular layer of the tunica albugineaz the main vessels are given their prominence by their direct connections with the main radial vessels within the testis. In the ovary, this same peripheral layer of the vaseular network is buried within the Organ, and becomes the System of arched vessels found between the medulla and eortex. For in the ovaryz the original or medullary eords degenerate, and new eords (Pfliiger’s oords) grow from the surface, earrying before them the vessels whieh lay just beneath the surfaoe From these new vessels grow peripherally, while the network, which supplied the medullary eords for the most part is lost. The terminal arteries of the ovary, then, like the real sexual eords, are seoondary affairs when eompared xvith similar structures in the testis.
The preeursors of the epididymis are the anterior mesonephrio tubules, which form the duetuli efferentes, and the anterior portion of the mesonephrie duet, wh0se eonvolutions form a large part of the head and the tail of the epididymis, vvhile the posterior part remains uneonvoluted and forms the duetus deferens As in the case of the testis tubules, this paper deals with the more detailed morphology of the epididymal tubules in man, especially in the late embryonie and fetal stages
Perhaps the most aeeurate aoeounts of the Wolflian tubules are those of MaeCallum, who studied pig, and, less th0rough1y, man, and Grafe, who worked with ehick Material. Aeeording to MaoCallum the tubule of a fully formed Wolfkian body, in the pig, is a long affair, running from the glomerulus in svveeping our-see, from mesial to lateral border of the organ (see his textckigure no. 8). Some of these tubules were seen to branch soon after leaving the Wolf-Plan duot, others just before entering the glomeruli. «Evidenees of anastomosis and the formation of networks of tubules were also made 0ut,« particularly in the region of the dorsal border. hilaccallum made models from serial Sections and also injeeted fresh material ; the anastomoses and netvvorks were found by the latter method. Grafe also found branehes of the tubules, and aflirms that they indieated new tubules which have grown by buddingn He also made a point of the faet that some of the tubules enter the duct on its dorsal aspect, Some on its ventral In the chick the tubules are not so long nor so convoluted as in the pig.
1n man also the tubules seem to be of two more or less distinct groups, one entering the mesonephric duct on then ventral, one on the dorsal side, and these two groups run vvith few oonvoluss tions along the ventral and dorsal borders of the gland respectively to the glomeruli, which lie far dorsallzn The tubules of the ventral set thus approach nearer to the genital anlage than their respective glomeruli, but this is not true of the dorsal set of tubules. None of the tubules in man ever attain the extreme length found in pig, sheep, rabbit, and other animals which retain functioning Wolflian bodjes to an advanced embiryonic age. MacCaL lum found the full formation of the Wolflian body in the pig at between 40 mm. and 95 mm., while in man he noted a reduction of the number of tubules after 12 mm. This latter statement, however, I cannot reconcile with what I have found in the embryos of man in the Harvard Erhbryoligical collection, unless very wside individual differences occur. MacCallum oounted 27 tubules in one Wolffian body in a human embryo of 12 mm., 20 in one of 14 mm., and 9 in one of 20 mm.; while, as the following table shows, I have found no constant reduction in the number of tubules up to 44 mm.
Miit-Haber of tabules in oisxe Woljliasa body
LENGTH of Einen-ro H.B.C. No. Tonnen-s 4.0 714 23 7.5 256 34 8.0 817 28 9.1 734 35 9.4 529 37
10.0 1000 34 11.5 189 30 12.0 816 27 16.0· 1322 30 19.0 819 25 22.8 871 31 37.0 820 33 44.3 293 32
These numbers are not akfected to any appreciable extent by the formation of new branches, as in no case have I found more than five or six of these in one WolfHan body. That the tubules must remain as functioning and useful parts of the embryo longer than is suggested by Maccallumwill be evident when vve consider that the kindey in man is only beginning to be provided with glomeruli and convoluted tubules in an embryo of 20 mm.; but there seems to be no constant relation between the size of the Wolflian body and the growth of glomeruli in the kidney, since the kidney in pig is fu1ly as far advanced at 20 mm. and in later stages as in man, in spite of the much larger and longer lasting Wolfkian body. Hill agrees with Pohlman, that the vascularization of the human kidney takes place between 25 and 30 mm., a little later than the presence of gloIneru1i would indicate, and gives the size forpig embryos as 28 mm. The cause of the continued growth and activity of the mesonephros in the pig and several other animals, even after the kidney is apparently able to act as an excretory Organ, is a subject which I shall have to leave for future investigation.
Of these mesonephric tubules the 6th to the 20th in pig, the 12th to the 20th in rabbit lie, according to Allen, opposite the rete region, and presumably (though it is not so stated by him) join with the rete cords. In man the rete region is more cephalad, opposite the first eight or nine glomeruli; but the rete cords anastomose not only with these but with many others in their course down the mediastinum. 0ccasionally the first one or two glomeruli do not join the rete, and remain as small cysts, losing their tubules (fig. 3). Such isolated glomeruli would give rise to the appendix epididymis, described by Toldt as being present in 27 per cent of cases examined The disconnected tubules of such glomeruli would end blindly, as shown in fig. 3 and 4, and in Hg. 12, and would ordinarily lie inconspicuously among the convolutions of the epididymal duct; if the upper glomerulus and its tubule were separated by a considerable distance from the others, as I have seen it in two of the embryos studied, this blind tubule might form the infrequent lovver paradidymis of Toldt, a single tubule in a connective tissue sheath lying behind the head of the epididymis.
The number of mesonephric tubules which join vvith the rete, as described by Allen and others, varies in the speeimens examined from eleven to nineteen or twenty. The rete cords do not always meet the glomeruli, but in man not infrequently conneot with the proximal part of the mesonephric tubule. This is the result of the course taken by the ventral tubules in the human mesonephrost as described above, for the rete seems to join with the neares, part of the tubule. Tubules thus tapped along their course are, by a rearrangement of their parts, brought to seem like two tubules each arising from the rete, one running to the duct, the other ending blindliy, usually vvith an expanded ensiL Such a blind tubule may be seen in Fig. 4, I, and in a fetus of seven months I have traced five or six simi1ar tubules. It is probable that these are the tubules of the appendages of the rete testis, as described by Roth and Poirier, and also the upper, shorter ducttilus aberrana described by other writers as opening into the rete and ending blindly. Roth and Poirier regarded them as tubules which, after aoquiring a union with the Rete, lost their connection with the WolfHan duetz but the presence of the blind tubu1es I have described renders unneoessary such an unlikely supposition as the separation of the tubule and the duct after a new ohannel has been formed These tubules may lie inconspicuously among their neighbors or, as in the seven months fetus, be grouped together in a separate sheath of conneetive tissue.
Fig. 3 Jiagratn of epididymal tubules of a fetus of 10 ern. To show slight branching and disconnected upper glomerulus many glomeruli have entirely disappeared rete not indicated.
Fig. 4 Diagram of opididymal tubules of a seven mont-hs’ fetus Junctions with rete indicatod by fine lines
In several embryos and in a fetus of three months and another of seven months I have found tubules lying in the rete region and yet unconneeted with the rete cords (kig. 4, 4 and l O. In the older fetus such tubules are of smaller diameter than the duetus epidjdymis, but have a similar epithelium.t If separated from their neighbors, these tubules would form the lower ductulus aberrans. The upper paradidymis of Toldt (organ of Giraldes) is probably correctly described by him as mesonephric tubules lying below the rete region but maintaining then« connections with the duct.
While not dealing in this paper with the histological differentiation of the epithelium lining these tracts, I may mention that this differentiation seems to depend not on the portion of the mesonephric tubules or duct which gives rise to any tubule in the adult. but on the connections which are permanently established. At three months the epithelium of the tubules and duct is similar all trace of former differentiation having disappeared; at about seven months a new differentiation takes placez but this time all the tubules conneeted with the rete show a similar epithelium, all tubules connected with the duct have duct epithelium. Thus tubules of like origin may at seven months and later be lined by different kinds of epithelium. The similarity of the epithelium in the duct and the blind tubules emptying into it seems to me to point distsinctly toward a secretory function of this eoiled tube.
As will be seen from the diagrams, (which have been eompiled after carefully following each tubule in serial Sections of theorgans, and which have been offered instead of models or actual reconstructions, as showing more clearly the courses and connections of the different tubules), there are several cases of branehing in each epididymis, as found by MacCallum and Grafe in the Wolffian body. In only one fetus was an vanastomosis found (Hg. 4, l and B, and the formation of a more considerable network was nowhere seen. It is probable that tubule Z, in the same diagrann originally lanastomosed with tubule 4 or some other, since in this way the Position-of the persistent glomerulus may be explained, by imagining two tubules running to the same glomerulus, only one of which joined with the rette. But anastomoses among the vasa efferentia of man must be considered as of rare occurrence Convolutions of the vasa efferentia and the ductus epididymis begin to appear at about the fourth month of feta1 life, as was found to be the case with the testis tubules. Here also the convelutions are in short, stiff cum-es, and here also certain portions of the tubules form groups of coils, joined by unconvoluted Portions, each group ultimately developing a vascular unit of its own. In the case of the coni vascu1osi, sing1e vasa efferentia are usually separated by connective t1ssue, though occasionally two or Inore may be intertwinedz each eonus contains several units. In position the coni are of two distinct groups, lying mesial and Iateral respectively to the convolutions of the ductus epididymis. This arrangement, not described in the text-denke, seems to be due to the two sets of mesonephric tubules which enter the duct on its ventral and dorsa1 aspect respectively, as described above; the ventral tubules form the lateral group of coni vasoulosi The head of the epididymis thus shows three main lobes, more or less distinct, the middle lobe containing the duetus epididymis.
- The testis cords, growing from the germinal epithelium of the genital ridge, form a network with three sets of anastomosing branches. After completion, this network breaks down partiallzy leaving certain cords as persistent stems. The tubules of the adnlt show,t in their course, conneotion, and position in the testis, traces of this network. Testis tubules may be single, ending b1ind1y, may brauch, or may anastomose.
- The unit of the testis is a considerable number of coi1s of one tubule, enclosed within a sheathz there are many units for each tubule, connected by less convoluted portions.
- The spermatic artery is not a Special vessel, as in the pig, etc» but the survivor of the mesonephricfarteries in the genital regionF The others were obliterated by stretching and by the growth of the cortex of the suprarenal gland. Pieces of this latter are common along the course of the spermatic artery.
- The mesonephric tubules in man join the duct on either its dorsal or ventral side.. The dorsal ones run dorsallzz so that the Isete tubules join their glomeru1i; the ventral ones take a more ventral course, so that. the tubules before reaching the glomeruli pass by the mediastinum testis, and are joined by the rete tubules. The glomerular ends of the ventral tubules form the appendages of the rete testis, (Roth and Poirier),h and the upperductulus abei«rans.
- The rete tubules in man develop opposite the first eight or nine mesonephric glomerulh but are eonnected with many more in their course downward in the mediastiinum. The first one or two may remain unattaiched, forming the appendix epididymis their tubules making the lower paradidymis (To1dt). Tubules below the junction of the rete form the lovver ductulus aberrans and the Organ of Giraldes.
- The small percentage of cases in which these appendages are found is due to thefact that the tubules involved frequently lie inconspicuously among the convolutions of the normal ducts.
- The epithelium lining these appendages depends upon their final connections, not upon their origin.
FULL, E. C. 1909 The vascularization of the human testi«s, Am. Jour Anat. vol. 9-, no. 4.
1907 On the gross development and vascularization of the testis, Am. Joutu Anat. vol..«6, no. 4,»·
ALLE-N, B. M. 1904 Theembryonie development of the ovary and« testiscin mammale, Am. Jouic Anat» vol 3,.no..2,.
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Fig. 5 Modelz testis of human embryo of 22.8 mm. (H.B.C., no. 871). Ä Segment of a transverse slice is shown; the Iimit of the genital riclge and the outer border of t-he Inediaetinuirx testie are indicated bzs dotted litt-es. The proximal or Peripheral ends of the corde have already lost their attachment t-o the peritoneuny the distal or central ends are seen reaching toward the mediastinunn in one case Uniting at their t-ips. Except for these tswo eets there are no free ends, each branch fort-Hing an anastornosis vvith others; the cut surfaees represent connections beyond the extent of the modeL The arrangement of three cross oonneetions shown best at the two cut edges of the modelz plates and ring kormation are also to be seen. X 180 diagn. · ·
Fig. 6 Nlodelz testis of human embryo 0f 37.0 mm. (I«1. E. C. , no. 820). Orientxxtion same as in Hg. 4. Peripheral ends of cords have been absorbech leaving a series of arehes as the outer border of the kigure The rete network has alreadyjoined the geistig, and rete cords can be roeognized by their Srna-l! diametetsz the lower dotted line indieates their irregular extensiork Other eut ends represent, as before, anastomoses beyond the limit of the modeL Fewer cross conneetions, more radial disposition of got-de. X 180 diagn.
Figs. 7, 8 and 9 lNIodels; human fetais of 9.1 ern» age given as three Inonths. Tubules from different part-s of same testis; Hgs. 8 and 9 two views of saine InodeL The rete cords are slender with out ends. The large out ends represent a11a.sto1nc)ses with tubules not modcled Loops formed by radial tubules and eross Connections are seen, so1ne including the peripheral set of cross eonneotions, Some the second set; while short-er" oonneetions of the Central set oan be n1ade out nearer the mediastinujn In Fig. s, at ex, a peripheral loop is just breaking apart; in iig. 7, at X, another has just been several. At l) and c, in figsu 8 and J, the tubules are very small and will probably part in a short while. Tubule A is uneonrieoted exeept near the rete, and oonsists of a radial oord ivith the greater part of a peripheral loop. Tubule B has a short anastomosing braneh representing the inner- set (at e) and a Iooped end consisting of the outer two sets of conneotions and the part of the radial tubule between them, the rest of which has been Iost. Tubule C« has all t-hree sets of eonneotions representecL Ring forination can be seen at r. D( 90 dianr
Fig. 10 Model; hurnan fetus of about 10.0 cm., age given as 106 days. lonvolkk tions have begun, ehieiizs in the eross eonneotions; the tubules have beeome of nearly even diarr1eter. The only blind ends are at it: and F. Tubule A is eonnected with three rete tubules, and extends only to the inne-r cross eonneotion, which ean be traoed through a few eonvolutions to another radial Iimb, also without branehes till near the rete; a separate short loop is thus made. Cross oonneetsions belonging to the other ttvo sets are reeognizablkx and can be traeed easily in the actuai modeL X 90 diam.
Fig. 11 Modelz hurnan fetus of seven months Two tubules of the testis with their eonneetions. The tubules are colored red and yellow, (tubuIes Jl and B). Cross eonneetions between them, of which there are two, are eoIored two shades of Orange and represent the outer and middle sets. From the outer eross eonnection eorne two branehes, one anastomosing with other tubules, not modeled, the other ending b1indly at m. From the other eross eonnection there is also an anastomosing brauch, a; while other branches from tubule B, which should be eonsidered as belonging to the middle set, are seen at l) and c. The inner set of eross conneetions is represented by branches z» and S, of which je; ends blindly. T ubule B joins another before meeting the rete tubule (fig. 5) while two rete tubules connect with tubule A. The group of tubules in yell0w, between the middle set of cross connections and the periphery, form a unit; a single artery supplies them, and a network of veins surrounds them, lying partly between them and the tubu1es in Orange. At r a ring is seen in the course of tubule A. X 90 die-m.
Fig. 12 Reeonstruetionz epididymis of human fetus of about 10 ern» age given at 106 days. The Wolflian duet is shown with fifteen Wolkkian tubules opening into it one of which is traced to the rete (shown by the fine 1ine), the others represented as eut short. The upper end of the duet is probablythe first tubule which has f ailed to unite with the rete. The eonnections of all the tubu1es is shown in Hg. 4. X 40 diam.
Cite this page: Hill, M.A. (2020, November 1) Embryology Paper - Morphology of the tubules of the human testis and epididymis. Retrieved from https://embryology.med.unsw.edu.au/embryology/index.php/Paper_-_Morphology_of_the_tubules_of_the_human_testis_and_epididymis
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