Paper - On the origin of the pulmonary arteries in mammals 2
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II. On the Origin of the Pulmonary Arteries in Mammals
Harvard Medical School
In 1902 I published a paper on this subject-Z a restnncs of xishich is here given. The pulrnonary arteries in man, rabbit, get, and (·log, appear as symmetrieal vessels, one rising from each tifth, or pulmonary arch. With the growth of the truncus pulmonalis, and its torsion about the bulbus aorta the two pulmorrarszy arches are wound, as it were, around the baulbus, and their walls thus brought into contact are absorbed, so that the truncus pulmonalis grows longer at thcir expense, tl1e point of bifureation moving continually farther from the heart. The left areh, being the outside one in this rolling «·p proeess, reeeivscs the most Full, beeomes the straightkkr and therefore the larger vix-Seel, and is shortenetl more rapidlzn As a resultz the point of bifiireation of the trunous puhnonalis Iseaclies the left puhnonarzs artery vssliile the right pulmonary artery is still seen arising from the right arch some distaiice dorsal to this Feind. (see diagram, page 338). The portion of the right« pulmonary arch betwecii the origin of the pulmonary artery and the dorsal aorta beoomes obliterated, the anterior portion of the arch remains oontinuous with the arter·y, and we then have the oondition described by Rathke,—the two pulrnonary arteries apparently arisiiig together from the left pnhnonary arel1. It should be note-d, hoxsvever, that thc right pulrnonary artery of the fetus includes, beside the hoinologrre of the left puhrionkiry artery, the proximal portion of the right pulmonary sei-eh.
In the Pig, although the pulmonary arteries first appear, as usual, as symmetrieal oHshoots, one from each pulmonary arehz and although the fetal condition is practically the same, the intermediate steps are different. The two arteries, while their points of origin are still far apart, bend toward each other lot-ver down, and soon anastomose to form a long vcsseh eonnected at its upper end vvith both the right and the 1eft pnlmonary Stroh-Es, and forking at its lower end to send a branch to either lang. soon the upper, or proximah part of the right pulmonary artery beeomes ob1iterated, leaving the eommon stem in communieatioir with the left areh only, thns foreing the blood to both lnngs to pas-s» through the lr-ft« pnhnonkxrys areh. Since 1902 I have been ahle, through new aeqtiisitiotis to this. Ilarvarcl Embryologieal Colle-knien, to traee the derelopriieiit of the pulmoiiary arteries in other msansnnals,—opossnrn, sheep, and guinea—pig, and to make a few observations on the eow and deer. In the opossum and sheep the pieture is essentially the same as in man, rabbit, cat, and dog, though in the sheep the two pnlmonary arteries are bronglit to the bifureation at almost the same kirrte, so that very little of the right areh plays a permanent röle in the right pulmonary artery. In the guinea—pig, on the other band, the dexseloprnent of these arteries follows very elosely that cleseribed in the Fig, but with one important different-e. In both animals the arteries originate as symmetrieally placed vessels from the right and left pulmonary arches, in both they bend toward each other and anastornose, and in both the 11pper end of one pnlrnonarys artery, from the arch to the antistmosis, becomes obliterated, leaving the anastoinosis and the lower ends of both arteries connected with only one Hirsch. ln the pig the left- areh remains in oommunieation with the eomhined pulmonary arteries, in the guinea-pig the right; in the pig the entire right pulmonarzs arch from the bifnreation of the truneus pulmonaiis beeomes obliterated in the guinea pig the anteriois part of the arch, as far as the origin of the right pulmonary arter·y, hecsotnes ineorporatecl in the adu1t pulmonary arterztz and only the posterior part is lost.
Fig. 1. — Guinea—pig, 737 nun. (ll. H. C» Series 1512, Sections 190—233.) Dorsal vie-ev. P. A» Dulmonary Hirsches, lett and right; n. a» Hin-notiert· arterzq T. P» trnncus Palmen-Eis. X 125 Atem.
Fig. 2. — Gu1nea—pig. 8.0 nun. (H. E. O. set-les 1513, Sections 277-315.) X 125 Mem.
Fig. 3. — Guinea—pig, 832 nun. (H. E. C. series 770, Sections 230-256.) c-. P. a» rsonjoined pulmonary arteries The lower portjon ok the pulmonary atsteries not eben-n. )( 125 Garn.
Minor differences of development occur in the two anima1s, as may be seen by eomparing the aeeompanying dran-singe xvith the figures of pig enihrzsos in the former paper. The pnhnonaxjy arteries in the gninea—pig are seen to form a meshxvork of eapillaries and to preserve their irregular course even after the uppeis part of the left artery has liscoine oliliteratcd From the beautiful injection of the blood vessels of einbryos made by Dr. II. M. Evans of the J ohns Hopkins Medical Scheel, it is probable that in all embryos the pulmonary arteries, in comnion with all other small arteries, arise at first by a capillarzss network, and that only later the Inain channels become largcr and free from the surrounding capillaries Remnants of this capillarys origin of the pulmonary arteries are not infrequently seen in embryos, as for instance the short vesscl from the right arch in Figure L, loop formations near the pulmonary arch, side twigs from the arteries, even (in one instance in a sheep embryo of 10.0 mm., H. E. C. series 1340, Sections 398-409) an artery which is double throughout most of its course, Inaking a very long loop. In the gninekkpig this early condition Iasts longer than in the pig or the other animals studied, the pulmonary arteries are later in straightening out and beconiing distinct channels
Another minor difference lies in the fact that, although in both pig and guineaspig the two pulmonary archcs are wound about the bulbus aortao as described above, in the guineajiig there seems to be no fusioii (or at least a much tlclayed fnsion) bktwecn the two, So that the truncus puhnonalis is not 1engthene(l, as in other mammals, at the expense of the two arches; the two archos nierely lie one below the other, side by side. This is showii in Figure Z, in which the left arch is seen to overlap the right for a considerable distance; if fusion had taken place, as in the Fig, the pnlmoiiary artery would already seem to spring from the bifurcation instead of (Iistinct1y from the isiglit arch as in the drawing.
In 1904, two years after my first article, Sakurai published a paper in which he dcscribes the growth of the pulmonary arteries in the deer.2 The original starting point is the same, two symmetrical buds, one from each pulmonary arch; but the left pulmonary artery, according to this author, moves toxvaisd the bifnrcation of the truncus pulmonalis, and then continues fartlieis to the right 11nti1 it arises distinctly from the right arch, near to the origin of the right artery.
»Anat. Anzeigeiz Band XIV, No. H, H. 321. 1904. 338 John Lewis Brei-nor.
Dutzend! l.——siiows the originai Szvmtiietry ok the Duhnonary arteries, and, in the second tigure, the result ok the torsion about the bulhus aortæ. A, truncus 1)111n1ona1is. at the point ok the original hihircsutioxu B, point on lekt Duhnonary are-h where the lekt pulmonaisy artery risesz O, same kor right side.
Busen« II.—-(a) ln the Fig; shows the original syn11netry, the pulmonary arcshes less wide spreading, the arteries nearer togethetc In the second Hgura the anastoiiiosis os the arteriekh and in the. third kig11re. the resnlt of torsion. (h) same kor the sahest-Fig.
I feel obliged to doubt, not the iigures in Sakuraks paper, but the interpretation of them. Osertainly in the deer3 in this laboratory I find not-hing that would lead one to suspeet that the deer diifered from man, rabbit, sheep, eat, or dog in the development of its pulmonary arteries In ernbryos up to 9.8 mm. in length the pioture is the usual one, tl1e two pulmonary arteries approaehing eaeh other as the bifureation of the truneus puhrxoxialis is brought farther dorsalz and in an embryo of 18.6 mm. (li. (J., series 1230), xvhose general eharaoteristies show it to be younger thanthe olclest tigured by Sakurai, the left pulmonary artery is seen arising from a short stcsm eon1mon to it and the right pulmonarys arteryx The posterior part of the right pulmonarys areh no long-er exists. The arter— ies are well estab1ished, nsith thiek wal1s, so that any migration would seen1 i1npossible. A short oonnnon stem for the two pulmonary arterjes in the fetns is not 1111eon11s11on, and I should prefer to inter— pret sakuriiPs last fignre as an unusual lengthening of this eommon stem rather than as a niigisatioii of the left artery along the right areh, especially as the landmark the posterior part of the right pulmonary arch, is lacking
If we accept this interpretatioii of sakuraks figures, the different methods of the developmcsiit of the pulmonary aiiteries so far reported fall into two main groups, one of wshieh may be subdivided. (1) In man, eat, dog, rabbit, sheep, eow, deer (?), and opossum the development may be described by Diagisam I. (2) In the pig and guineapig the development differs from that of the other mammals mentioned, and may be shown roughly in Diagram II, (a) representing the pig, (b) the guinea-pig.
In this enrious grouping of the animals studied, generis lines seem to have no influenee In rny former paper it was suggested that the large size of the aurieles in the pig embryo eaused the erowds ing together of the pulmoiiaisy aistexsies and their eonsequent anastomosis, and I again offer this explanation. In the guinea—pig also the aurieles are very large at the time xvlieti the pnlmonary arteries Ver-nie sann-wiss. The laboratory is indebted to Professor Franz Keine! kor the embryos are growingtz but there seems to be no erowding of the tissue sur— rounding the traehea from the sides. The meohanism seems to be sliglitly more eompheatect The large aurieles and large sinus venosns separate the traehea posteriorly from the bulbus aortae and the trnncus pulmonsalis anteriorly more, it seems to« me, than is usual in animals xvithont the large aurie1es. The aortie arehes are straight ened o11t more, the figure they present with the bulbus or trunens beeomes more like a Y than like a tuning fork, and henee the pulmonary arteri-es, starting out at right angles to the pulmonary arehes, point toniard each other instead of haekward, as in other animals This purely meehanieal result of large aurieles seen-is to me to aeeountfor the diiferenee of developtricsnt hetween t-he pig and the guinea pig and all other mammals studied. The cause of the larger anrieles I do not know; nor ean I explain why, after the anastomosis, the left artery in one case, and the right in the other, should remain permanent1y.
Cite this page: Hill, M.A. (2019, June 19) Embryology Paper - On the origin of the pulmonary arteries in mammals 2. Retrieved from https://embryology.med.unsw.edu.au/embryology/index.php/Paper_-_On_the_origin_of_the_pulmonary_arteries_in_mammals_2
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