MATERS AL CIRCULATION OF THE TORPIN OVUM FOUR 7F.ST PIGIJKES A X D OiiE PLATE ( F O U R F I G U R E S ) I n 1890 Waldeyei. and others were active in establishing the iiidependence of the human maternal and f eta1 circulations. Since that time iiumerous investigators have contributed developn~entaldata which have aided in a better untlerstanding of the anatomy and ph~-siologyof the maternal and fetal cii-culatory relationship. H o u ~ c Ttlicre ~ ~ ,is a s yet no unanimity of opinion concerning many of tlie details of this complex problem. Reinsteiii-nto~ilowa (1891) studied the maternal vascular structures in three young ova in which she gave n clear description of the lacunae mid sinuses but expmssed some doubts regarding the arterial components. Rumm (1893) coiifirmed a portion of the former writer's work but also failed to find the source of the arterial supply to the circuit. In 1923, Boerner-Paltzelt and Schwarzacher pointed out, in their vesy young ovum, the abundance of capillary branches arising from the spiral arteries which gain entrance into the lacunar spaces. Sticve ('26) favorably commends these author's observations but in his own studies lie was unable to confirm the capillary connections with the lacunae in an O Y U of ~ 1.33 clays. Falkiner ( '32), in a wax reconstruction of tlie periemhryonic vascular structures of a 15-day ovum, sliows capillary branches arising from the spiral arteries which pass directly into the lacunae. Wislocki and Streeter ('38) mention thch role of the capillaries in the maintenance of the lacunar blood suppl:r in the macaque arid Ortmann ('38) puhlished a study from wax reconstructions 265 of tlie matcrnal circulation of the Veit ovum in which he gave good figures sl10~7i11gcapillaries entering tlie lacunae. Johnston’s Imblicatioii ( ’41) failed to show any evitleiice of irit erconncction hctwceii the arterial and V C I ~ O U S clianiicls in tlic periembryoiiic region. The present investigation \viis carried out as a port ion of a stud:- of a 13-day ovum. Since thc histoi’y, clinival data, method of preparation, determination of tlie age, arid description have been given by Krafka (’41) they need not be repeated here. This study will he limited to an aiialomical descriptioii arid to possible inteqwctatioii of the \Tilhcultir strnctuiw surrounding the embryo. Employing the Boi-nc method of wax reconstruction, two models wcre mw(k at a magnification of 165 diameters to show the capillary connections with the vciious sinuses and thc lacmiar spaces, a i d another at ti magriification of 120 diameters demoiistrating the lacunae, venous sinuses, and tlie venous drainage of these channels. These observations were supplcmeiited 1))- a dctailed study of complcite ant1 uiiinterrupted serial sections of the ovum. OHRERVA TTONS While some attciitioii has lwen given to s t i m t u r e s :is deep as the muscularis, this study lins been confined chiefly to the circulation in the compactum. The ovum is situated in an endometrial hillock ~ l i i c hprojects into the uterine lumeii with the base of tlic ovum lying only slightly below tlic general level of the endornetrial epithelium. The vascular structures surrounding the ovum, consequently, a r e not deepl? embedded in the decidua. The vascular structures and blood spaces are divided somewhat arbitrarily, for descriptivch purposes, into lacunae, venous sinuses and veins, and arteries and capillaries. LACUNAE: These Mood spaces form a pttrivillous, iatratroplioblastic, shell surrounding the embryonic sphere. They have direct or indirect intercommuiiicatioiis with one another and theii. inner and outer walls are formed by the sync!-tiotrol~lioblast. The rdaf ive thickness of the lacuiiar system varies in differcii t rcgioiis-the opercular pole being almost devoid of lacunae while the abopercular pole is well supplied with them (fig.2). The advanced state of development of the villi varies clirectlv with the sizc of the lacunae. A t the region where tlic t the villi a r e most ~ ~ u m c r o utlic s body lacunae arc l a ~ g e s and stalk is attached to the trophoblast. The w r y small lacuiiae, seen in isolatetl sections, appear as syncytial vacwoles but wlien they a r e traced t1u.oug.h serial sections they are found to liave direct connection with the larger lacunae. It is quite possible that these small s p e c s have been looked up011 i n many casm as lacuiiac formation hy vacuolization of the spcaytium, a theory discussecl and discounted hp Teacher ( ’25). The erythrocytes of the lakes are v-ell prcservcd in most regions and the leucocytes are in about normal proportion. The red 1)lood cells a r e pale and somewhat laked in the opcrcular regioii with gradual transition to strongly staincd cells a t slightly deeper levels. Such lakcd cells suggest a general conditioii of the lacunar erythrocytes which 1i:ive bee11 described in several embryos and this condition appears to 1)tl tlie subjcct of the lengthy discussion of the “lacunar detritus ” of Kiss (’21). Tn this author’s discussion the detritus was interpreted as disintegration of the syncytium, a nietliod by which the s;vncytium gives rise to the lacunar spaces. Thcsc lakcd cells of the Torpiri ovum a r e intcrprcted ae hcirig tlic result of fixation difficulties or perhaps to less adequate circulation in the opercnlar region. No thrombi were fomid in any of tlie lacunae. Pel-haps not a part of the lacunae, but associated b~ adjacent position are small pools of bloocl apparently Ij-ing free in the compactum. Since these pools a r e surrouncled neither by eridotlielium nor syiicytium, they a r e the source of confusion in following the srnaller capillaries as they enter the lacunae. It is this fact that probably accounts f o r the failure of Reinstein-Mogilowa (1891) to observe this important interconnection of tlie arterial a i d venous channels. Oi*trnann 268 J . D. COMBS ( '38) lias called attention to these apparently extrarascular aggregates of erythrocytes. Whether this condition is the result of the inefficieiicp of the syncytiotrophoblast as an '' endothelial substitute, '' f rorn the rupturing of surrounding vascular channels by a rapidly growing embryonic sphere, or from other causes, it was not determineg. hi some regions outside the syiicytial layer, particularly a t the abopercular pole, some fibrinoid is present. These masses of fibrinoid are probably the same a s those described by Greenhill ( '27) which he iiiterpreted as degeneration products of the dccidua resulting from pressure exerted by the expanding ovum. For the most part, they appear a s flattened cells with pale nuclei, into which leucocytes and occasionally syiicytial cells have migrated. Evidence of active opcning of the laciinar spaces into the venous sinuses was observed in many regions. One such case has been photomicrogi.ap1ied (figs. 5 and 6 ) to show a probable stage of the process. The endothelium of the sinus has been disrupted by the invading syncytium which can be seen bulging into the sinus. It would appear that the intralacunar pressure is somewhat high e 1- than t 11e in t r a si 1111s p re ssure. This fact has also suggested that the lacunar spaces are probably more closely coiiiiccted to the arterial side of the circulation than the sinuses. Other regions show tlic endothelium released by the inratling syricytium from its normal substructures thereby allowing the eiidothelium to float f rce in the sinus. The nuclei of this detached endothelium are swollen and paler than those of normal endothelium. VENOUIS SINUSES The large vtiscular spaces lying subjacent to the blastocyst are perhaps the most conspicuous components of the mateinal circidation. They are in all probability the vessels which were so plainly seen i n the gross specimen radiating outward from the embryonic papilla. The sinuses are so arranged, as a group, to form a cap over the abopercular pole of the blastocyst. Figures 1 and 2 suggest that tlie inward 269 Fig. 1 The ~ : I C U I I : I C ,sinuses and venulcs in the rcgion of the ein1)ryo :is shown by a drawing of R wax reconstruction. Tlie spiiericiil lncunnr shell is sccn in the lower half of the figure. These blood spaces have nuttierous connections with the arched, overlying sinuses. At the uppermost part of the figure, the wnules are roursing deep in the endometrium from whirh they finally pass into the reins of the muscularis. Magnification X 42. 3iO J . 1). COMBS growth and cxpaiisiori of the embryonic tissue has encroached upon tlic area previously occupicd by the siiiuses arid caused them a arch themselves over the blastocyst. Deep in the compactum, smaller chaiinels lead from tlie siiiuses as venules tlirectecl toward tlic larger veins of the muscularis. There is considerable ii~tei~communicatioiibetween the siiiuscs, a s is also true of the venulcs arid w i n s which drain Fig. 2 T h c h wax inoticl in figure 1 has hren scrtioned through the o1)rrcularahopercular axis i n order t o show the wlationship of the emhryo t o the lacunae. Within the lncunar sliell one sees the embryo situated almost in the center of the vascular sphere. Here again, as i n figure 1, communications between the laciinac and the sinuses arr secn. The inset is :I riew of figure 1 f r o m tlie oprrcular pole to show the relative absence of 1:icuiuir hcncath the opeiculurn. Within the Iwunar splicre of the insect is found the smsll embryo. Itlapifiration X 42. MATEBSAL ClRCULATION O F TORPIN OVUM 271 the sinuses. No constant feature marks the mode of communication except the direct continuity of the eiidothelial structures. T1iei.e a r e no valves or other structures which appear t o influence the direction of blood flow. C~ommunicatioiibctwcen thc lacunae arid sinuses has already been mentioned. 111 general, i t may be said that the lacunar syricytial walls make rather abrupt transitions to the endothclial lined sinuses. However, the syncytium frequently shows some undermining of the endothelium at the sinuIwcuiiar junctions. Of these communications, Rcinst einXogilowa (1891) mentioned as many as thirten or more f o r one of 1 i c ~young specimens. Tlie Torpin ovum probably has fifty to scvcnty-fivc such communications. The greatest numbei- of intcrlacunar-sinus junctions a r e at the abopercular pole of the ovum but some elongated lateral sinuses reach the lacunae as far as at the equatorial region of the blastocyst. The sinuses a r e often YO expansive that thcy approach the uterine glands arid the uterine lumen with very little i i i t e i ~ e n i n gcompactum between. Tn the c a w of the glands, the sinuses were found i n some instances to have only 8-10 p of tissue btltwcen them and the gland lumina. Likewise, there was one sinus with only 12 p of compactum between it and tlic uterine lumen. It is evident that the sinuses a r e not structures whose singular function is the drainage of the intervillous spaces. Figure 3 is prcsentcd to show that these sinuses also receive capillary hranches from the spiral arteries of the deeper uteiiiie niucosa. A microphotograph (fig. 7) is givcn to show how- the capillaries from the spiral artcries enter thc sinuscs. Such commuiiications are quite abundant arid it is possible that they may bc tlic precursors of the spiral arteriolcs of the mature placenta a s have been dcscribed by Bumm (1893) and Sticre (’26). A KTERTES A N ) C A P I I ~ T ~ A R I E S These s t iwctni-es, while conf 11 sing when studictl di r cc tl y from serial sections, were found to bc relatively easily followctl bv w.as reconstruction. T~’igures 3 mid 4 show the 272 J. D. COMBS F i g . 4 This is a drawing from a wax reconstruction of a segment of the lacurtar sphere with the overlring w n o u s sinuses a n d two spiral arteries and their capillaries. The comrnunieations lretwern thc lacunae and sinuses domoltstrate the presence of numerous channels through whicdli drainagr may occur. Thr effects of the growth of the blastocyst a r e reflectcd in the displacement of thc sinus, the lateral deviation of the interlacunnr-sinus contmuiiicatic~its and the lateral deviation of t h r spiral arteries. The spiral artery gires off many capillaries which open into the lacunae. One of the spiral arteries appears to he less advanced in growth than the other. There is less coiling of this artery and the capillaries have not yet cstnblished connections with the venous or lncunar structures. Magnification X 58. 273 274 J. I). CONBS course of the syii*alarteries and their capillary branches. At least fifteen such spiral arteries were found in the region near the ovum. They lose their muscular coat at some distance from the embryo after which they break up into capillaries. Figure 7 is a photograph of a capillary entering into a sinus. At the upper right portion of this figure is a part of the spiral a r t e r r from which the capillary is derived. The compactum through which the capillaries pass is frequently edematous and cdcma lakes 50-75 p i n diameter a r e often found. Those capillnries leading to the intcrvillons spaces ha\-e their origiii from spiral arteries in much the same maiiner as those supplying the sinuses. The description of the entraiice of the capillaries into the lacunac as given by Teacher (’24) applies pai*ticulai.ly ell to those of the lateral regions of the Torpin ovuni. Quoting him: “The blood vessels a r e of capillary size tind run around the periphery of the ovum. As a conscqucnce, they usually appear as slit-like cavities lined by the ti-oplioblast on the ovum side and by cndothelium on the decidual side, and they open obliquely into the cavity.” I n other cases, the description of this process is similar to that given by Brewer (’37) in x11ic:h lie says: “Invasion of the capillary w d l s by the trophoblast is an active and an extensive pi.occss and has been noted in all specimens studied. Fetal cells are found penetrating the eiidotliclial walls and lying free within the blood vessel lumiiia. ” The lateral deriation of some of the spiral arteries woiild seem to indicate that they a r e being mechanically forced outward by the expanding embryonic mass. Aside from the previously mentioned authors who have dcscribed the entrance of the capillaries into the laeunar spaces, many others h a r e given quite adequate and convincing evidence of similar occurrences. Among those miglit be mentioiled Koerner-T’altzalt and Schwarzacher ( ’23), Falkiiicr ( ’32)’ and Oi*tmaiin ( ’38). Mention should be made of the numerous syncytiril cells which appcar to be isolated in the decidua surrounding the trophoblast. Many of these cells a r e rather closely associated lvitli capillaries and it appears that they frequently hiwe followed centripetally aloiig these minute vcsscls. Unless these cells and vessels a r e studied in serial section it is rarelv possible to uiicleidmid tlieii. i*clationship to oiie ailother. 1)I S('T'SS1ON 'Plic Torpin ovum presciits maternal artcrinl i-lnd veiioiis elements which a r e common to the usual vascular circuit of niost tissues and organs. Resides these structures, the trophoblastic lacunae and tlie widened venous sinuses a r e iiitcrposccl into the system in a m a n n ~ rquite peculiar to the human placenta. Tlie origin and development of tlie venous siiiuscs w3uld seem to be of initial importance in tlie establishmcnt of the ear17 circulation. Whether these sinuses are originally portionh of venous channels of the prcmenst r i d endometrium a h tlesci*ibcci by Bartelrriez ( '31), can only be conjectured; yet, they appear to occupy about tlie same depth of the endometrium and it is possible that their ultiinate fate in the c11~111gefrom tlie progriivicl to a gravid eiidomctrium is 1 ) ~ ciselj7 for the rapid convwsion into dilated venous sinuses. After reviewiag the literature related to tlie piwelit investigation, it would appear that the meclinnical effects of ii rapidly growing spherical ovum, essentially eiiclosed in a slower growing mass of endometrial tissue, has received very little consideration. Mention has been made of the fairly dircct coui-se of the younger arterioles and capillaries toward the implaiitation cavity. Once tlicse structures liavc (1stal)lislicd conncetioiis with the periblastic vascular chnnne1~, they arc subject to lateral shifting as the blastocyst enlarges. The older arterics a r c quite spiral aiid can probably withstand shifting by extension of their coils. On tlie other hand, vessels are interpreted as the straighter vessels tlic ~-oungcr+ and they a r c probably subjected to considerable stress from the same process. This l a t e i d shift of the vascular channels may acconnt for froqucnt ~ ~ x - t ~ ~ a v a s aoft i o1)lood a cells ncar 5 6 J. D. COMBS the implantation cavity. The effect of coritiiiued and increasing pressure of the blastocyst on the adjacent endometrium has been suggestcd as the maniicr in which the maternal fibriiioid develops (Greenhill, '27). Still another effect of the incrcasing embryonic mass is the occlusion of the neclr 's of the endometrial glands d i i c h a r e still in the secretory phase with a resulting dilatioii of the fundus of these glands. One can p s t i i l a t c the coui-sc of tlic \TiiSc;ular circwlation in tlic maternal rcssels only oil the basis of the knowledgc of circulation as it is applied to other tissues; l1o~\7evcr7it woiild seem piwbable that the intervillous S ~ P A C C Sils , \\.ell as the veiious sinuses, are directly supplied by the spiral arteries and their capillary branches. The lacunae hare rather direct and ahnclant drainage to the rcnous sinuscs at the emhryonic pole and thcre arc a few veins which drain tlie lacuiiae at the equatorial zone by passing tlirough the compactum after which they filially empty into some remote venous channel. The intimate interconnections of the lacunae themselves necessarily serve a n important functioii for those lacunae having no direct opciiings into the w n o w siiluscs or venous clianncls. From thc sinuses tlic hlood may pass into the rciinles and \-eins which leiid to the arcuatc vessels of the utcrus. Such a s)xtcm would sccm to be csta1)lishcd in this 13-dwy cmbr;c-o. The manner in which i t has heeii so f a r established can be, at the present time, hardly morc than speculative; and its fatc in the mature placenta likewise, must he based upon hypothetical conccpts until sufficient materiid is available for liiikiiig many gaps in the prcsent knowledgc of tlie devdopmciit of the human placenta. SVMMARY 1. Wax reconstructions of the maternal vascular structnrrs around near a 13-day Il~mi111embryo have been made from serial sections. 2. Capillaries from the spiral arteries were found to empty chiefly into the lacunae; a few were fourid to empty into the venous sinuscs . MATERNAL CIRCULATION OF TOKPIN O Y U N 277 3. The lacunae were fouiid t o have direct or indirect conncxtions with one another and also with the venous sinuses. 4. The renous sinuses have connections with the veins which coiinect with the deeper uterine vessels. LITERATL’RE CITED RARTELXEZ,G. W. 1931 The human uterine mucous nicnibranc (luring nicnstruation. Am. J. Ob. & G y . , rol. 21, pp. 623-643. T<OERI\’ER-PALTZELT, n., A N D w. kk’IIWARZA(’HER 1923 Ein jUiIgeF4 111~nS~~h~iCh~S Ei in situ. Zeitsch. f. d. gesamt. Anat., Bd. 68, S. 204-229. J. 1. 1937 A riormiil hunian ovum in a stage preceding the primitive HAEWER, streak. Am. J. Anat., vol. 61, pp. 429-481. B u b l M , F,. 1893 Urher die Entwicklung des miitterlichen Blutkreislaufc in mrnsclilic~henPlacenta. Arrh. f . Gynack., Rd. 43, S. 181-195. I’ALKINER, N. 1933 A description of a human ovuni 15 d a > s old with y w i a l refrrenre t o tlie vascular ;irrangements and to the morpliology of the trophoblast. J. Ob. and Gyn. Brit. Emp., vol. 39, pp. 4il-506. GREENHILL, J. P. 1927 A young ovum in situ. Am. J. Anat., vol. 40, pp. 315-354. JOHNSTON, T. B. 1941 The chorion and cndonietrium of the cnil)ryo H. R. 1. .T. Anat., rol. 75, pp. 153-163. Kiss, F. 1921 Ein Junges niensclilichcs Ei. Zeitsdir. f . Anat. u. Entwicklungsgesch., Rd. 62, S. 519-535. RRAFKA, J., JR. 1941 The Torpin Ovum. A presomitc human rnil~ryn. (‘cintrih. Einbryol. Carnrgie Pub. ( I n prcss.) ORTMANN,R. 1938 Uehcr dir Placrnta einrr i n situ fixirrtcn mensehlichen Keinb1:ise aus der 4. Woehe. Zcitschr. f. Anat. u. Ent~~icklungsgcsrlr., Bd. 108, S. 425-458. REINSTEIN-MOGIILOWA, A 1891 Ueher die Brtheiligung der Xrllschiciit dca Cliorion an drr Bildung der Scrotina und Reflew. Arch. f. h t h . Anat., Hd. 124, 5. 1-27. X‘I‘IIWE, H. 1926 Ein 13if Tage altes in der Gebiirmutter erhaltenrs uml (lurch Eingriff gewounenes menschliches Ei. Zcitschr. f. Mikr. Anat. Forsch., Hd. 7, S. 295-402. ’I’EA(TER, J . H. 1924 On the implantation of the human ovum and the r:irly development of the trophohlast. J. 01,. & Gyn. Brit. Emp., rol. 31, pp. 166-210. 1925 On the implantation of the human ovum and the early dcrelopment of the trophohlast. Zeitschr. f. Anat. Entwieklungsgcs., Bd. 76, S. 360-383. YER, H . 1890 Bemerkungcn iihcr den Bau der Mensvhen- und AffenWALDB placenta. Arch. f. Mikr. Snat., Bd. 35, S. 1-52. Wlsr.ocK1, G. B., AND G. L. STREETER 1938 On the placentation of the niacnqur (Macaca niulatta), Contrib. Einbryol. Carnrgie P u h . 27, pp. 1-84. 3 A ~ihotoiiiic.rogralihshowing a pni'tioii of tlir lacunar splicre and tlic 01 crlying sinuses. A t n i i c rrgion t h r plasmotrc~~iliol~last r a n he seen inwding the sinus wall. A portion of the s)neytium is bulging into t h e sinus. JIagnilication X 3i. 6 A portion of figurr 6 showing i n grcater detail that portion of thc sjxic.\ t i u i i i which is liulgiiig into thcl sinus. Magnificatioii X 335. T A photomirrogiaph of :I large sinus showing :I capillary penetratiiig the sinus wall. 111 tlir uppw r i g h t of the figure is a section of the spiral artrry from d i i c h the capillary arises. I'lasnin lakes i i i the rrgion of the cnpiI1:try mag I K srm. The stronin surrounding the spiral artery is quite compact. hlagnificxtion x 50. 8 A pliotoiiiicrograph showing a portion of the large spiral artery shonn i n figure 1. Many sniall capillaries hare arisen from thc~a r t e r y a n d they m i ? I)r seen in t h e region of the 1;icun:ie. Magnifiutioii x 37.