- Citado por SciELO
versión On-line ISSN 0717-9502
Int. J. Morphol. v.22 n.1 Temuco 2004
ANATOMICAL ASPECTS OF THE PLACENTA OF THE SLOTH,
Bradypus variegatus, SCHINZ, 1825
ASPECTOS ANATÓMICOS DE LA PLACENTA DEL PEREZOSO Bradypus variegatus, SCHINZ, 1825
AMORIM, A. L. M. J. A.; AMORIM JÚNIOR, A. A.; MESSIAS, J. B.; SILVA JÚNIOR, V. A. & BERINSON, M. K. Anatomical aspects of the placenta of the sloth Bradypus variegatus, Schinz, 1825. Int. J. Morphol., 22(1):9-18, 2004.
SUMMARY: Sloth plows euterians mammals, belonging to the order Edentata, sub-order Xenarthra, infra-order Tardigrada, family Bradipodidae, which comprehend three specimen, Bradypus tridadctylus, Bradypus variegates and Bradypus torquatus. They plows few work found in the literature related to the anatomy of the placenta of this specimen.
The material used in this research was consisted of 3 placentas of Bradypus variegatus of adult females (Briton, 1941) original of the Forests of the City of Recife and Zone of the Forest of the State of Pernambuco with average weight 4,2 Kg. Placentas were fixed in buffered glutaraldehyed 4%, pH 7,4, 0,1M and processed goes optical microscopy.
Macroscopically was observed that the placenta of the sloth is composed of discoidal lobes and had the fundal position of the uterine cavity. The fetal membranes identified were chorium, applied on the uterine surface and, amnion adherent to inner face of chorium. In the specimen examined presented vestige of allantois sack and vitelline sack in these gestational phase. Anatomically, placenta of Bradypus variegatus could be classified like chorium-amniotic. Microscopic analysis of the placenta showed endothelial cells of maternal vessel hypertrophied and fetal components without cellular limits identified. The fetal tissue presented an epithelioid aspect with fetal vessel surrounded to connective tissue and epithelioid cells or next to maternal vessel. According our description, Placenta of Bradypus variegatus could be classified microscopically in syndesmochorial and endotheliochorial.
KEY WORDS: 1. Placenta; 2. Sloth; 3. Anatomy; 4. Bradypus variegatus.
The toothless ones plows one of the most characteristic groups of the mammals of America of the south.
The sloth of three fingers and of brown neck of Brazil, in the museum of Frankfurt, was described by Schinz (1825) the Bradypus variegatus, "Geflecktes Fautthier". The Bradypus variegatus is commonly the recent name used goes the sloth of brown neck B. infuscatus Wagler (Wetzel, 1973)
They plows many the work accomplished in this research line in several species; however, it needed better investigation, given the odd importance of this subject. The sloth of the species Bradypus variegatus, typical representative of our fauna, belongs one to them.
The present work have the objective to obtain anatomical dates of the placenta and fetal membranes of
sloth, in your morphologic aspects, classifying like this the placenta of this toothless one. This classification can be made ours to see: 1) with relationship to your format, 2) with relationship to the arrangement of your maternal fetal relationship areas, 3) with relationship to the arrangements of the fetal membranes, 4) with relationship to the aspect of the inter hematic membrane, in other words, the invasive capacity of the trophoblastc, associated the destruction of the maternal tissue.
The dates to be obtained can contribute to the explanation of certain existent gaps on the morphology of this organ in this animal group and to supply subsidize goes subsequent studies on ethnology, reproduction, handling and clinical parameters and/or pathologic of this organ of these animals alone representative of the Brazilian fauna, whose biology stays still ignored, facts that woke up our interest significantly, seeking the morpho-functional study of the placenta and your fetal enclosures of the Bradypus variegatus and we participate like this of the effort of your preservation. Britton (1941) it describes that the sloth didactylus plows considered adult when they reach weights between 6.5 and 7.5kg, while tridactylus weigh between 3.5 and 4.5kg.
Few plows the work found in the literature related to the anatomy of the placenta of this specimen and, most of them turns on the microscopical light. With relationship to the macroscopic anatomy and ohters aspects these plows rare and antiquate. The beginning of the formation of the placenta vary, in agreement with several authors' criteria.
Simon (1902) studying the anatomical conditions of the placenta of Bradypus, demonstrated the placenta of discoid format with "lobes" of different sizes, adds presenting cubic form, other oval ones.
The placenta of the sloth Bradypus tridactylus is considered deciduouse, composed of " lobes " that form the maze. The macroscopic and microscopic study, and development of the placenta of sloth due to the research of series of embryos accomplished by Wislocki (1926, 1927, 1928a).
Wislocki (1928a) revised contributions the one of Becher, 1921; The Lange, 1926, it goes placentation understanding in this species and the sloth didactylus (Turner, 1873). This still concludes that the placenta of the sloth was the transitory form between the type syndesmochorial and endotheliochorial.
The De Lange (1926) apud Wislocki (1928a) studying Bradypus, affirmed that the placenta of Bradypus shows an intermediate phase between the types endotheliochorial and hemochorial. Comparative studies of placentation classify the placenta the endotheliochorial (Mossman, 1937; Ramsey, 1975).
Heuser & Wislocki (1935) emphasized that the fetal membranes of these animals plows remaining of the primates' similar apprenticeships, particularly the man. It exists in the sloth the rudimentary allantoids. The amnion and the vitelline sack exhibit characteristics which plows almost close to the conditions found in the primates.
Enders (1960) in your eletromicroscopical observations of placenta villous and hemochorial of the Armadillo (Dasypus novemcinctus), told that the placenta barrier seen in eletromicrografy, is composed of the syncytiotrophoblastc, mesodermic crest and vascular villous.
King et al. (1982) studied the maze of the placenta of two fetuses of sloth Bradypus tridactylus, in electronic microscopy. The observations of the placenta of the embryo of 55mm CRL revealed areas where adds components of maternal conjunctive tissue stayed classifying her them placenta syndesmochorial. In other areas where it existed juxtaposition of the endothelial maternal and the trophoblastc of the placenta could be classified the endotheliochorial. The bad preservation of the oldest specimen impeded lives detailed analyses of the structural changes in the several layers.
Benirschke & Powell (1985) examining placenta to term of Bradypus tridactylus and Choloepus hoffimanni in the electronic microscope, they observed that the placenta was formed approximately of 20 nodules disks. They also identified the placenta of sloth them placenta endotheliochorial. The placenta according to them resembles each other in both families of sloth with the invasive chorium and it could be classified like this usually them placenta endotheliochorial (Gilmore et al., 1998).
MATERIAL AND METHOD
The material used goes research it consisted of 3 placentas of Bradypus variegatus (Fig. 1), of adult females (Britton), weighing 4.2 kg on average, original of the forests of the city Recife and Carpina, Zone of the Forest of the State of Pernambuco. The female 1 and 3 was donated frozen and 2 acquired live goes the researchers of the Center of Researches cardio-lung of the Department of Physiology of the Federal University of Pernambuco. These animals were acquired in the months of August of 1998 (animal 1); September of 1999 (animal 2) and January 1999 (animal 3).
| ||Fig. 1. Membrane fetais of sloths (animal 1), where we visualize the corium (C), this in contact with amnion (A). Itis noticed intense vascularization of the uterine wall. The embryo presenting itself previously in abdominal position ventro.|
In Recife-foot, the animals stayed in the dependences of the preguicario of the Department of Physiology of the Federal University of Pernambuco, with relative movement freedom, where adds conditions of your natural habitat were offered. The supplied feeding was constituted of leaves of Cecropia adenops (Imbaúba), renewed daily and water ad libitum. Constant evaluations of the rigidity state through physical exam and observation of your behavior gestation were accomplished through ultra-sounds exams and X ray, accomplished in the Department of Veterinary Medicine of the Federal Rural University of Pernambuco, areas of animal Reproduction and Radiology.
The female 1 and 3 was thawed, only that we processed the material regarding the pregnant uterus. After the opening of the abdominal cavity, the abdominal aorta and we injected latex Neoprene 650 (*Du Pont do Brasil S/A Chemical Industry) red-faced with specific pigment of red color. Soon after we fastened the material in aqueous solution of formol to 10%. After 48:00, with the animal in number decubitus on surgical table the dissection was accomplished in the abdominal area, identifying the uterus, incised sagital and middling this organ, with cares gone back to identification of the fetal membranes and morphology of the placenta. Soon after it was retired the only fetus, still connected to the placenta, through the umbilical string. The fetus was identified and soon after we measured the fetal length (distance cefalococcigea - CR = Crow-Rump"). Later we took the length of the umbilical string (ASS) attn the level of your connection with the abdominal fetal wall. It goes the procedure we used paquimeter. Where the anatomical configurations didn't allow the direct uses of this instrument, we used the thread of cotton line and soon after we transported the values is the ruler. With aid of the paquimeter, we measured the length and width of the lobes of the placenta, being taken them base the vascular pedicle and in the hilo of the placenta. Soon after we counted the lobes of the placenta.
The female 2, was submitted to fast of 24 hours. It was previously anesthetized with xilazina to 2mg/kg of corporal weight, administered by intramusculary way, being positioned soon after in number decubitus on the surgical table. We preceded like this the cesarean operation, with aid of the team of the Department of Surgery of the Federal Rural University of Pernambuco, with the intention of preserving the mother and the neonate. The same previous procedures were accomplished with objective of the identification of the fetal membranes and morphology of the placenta. Once retired the fetus, took place the retreat of the placenta. This, already isolated, it was washed with paraformolaldehyde to 4% to 0,1 m. to follow the piece it was distended on the paraffin plate, and maintained immersed in the fixer, in order to we accomplish cuts of the lobes of the placenta with the purpose of preparing material the goes histology. We accomplished like this the fixation and schematic drawings of the organ, goes identification ends. Soon after, we cut 0,5cm fragments approximately, which were identified and conditioned in flasks containing paraformolaldehyde and glutaraldehyed 4%, pH 7,4, 0,1M and processed goes optical microscopy.
The cut of 5 mm of thickness were obtained of the placenta and they were red-faced goes the methods of Hematoxiline and Eosine (H. E.) and Tricromic of Masson (Lillie, 1954) and photographed in picture microscope (Axiophot, Zeiss ®), magnifying glass of Vasconcelos S. A.
The terminology goes us used followed the determinations of " International Commitee on Veterinary Gross Anatomical Nomeclature ", Veterinary Anatomical Nomina, Nomina Histologic, Nomina Veterinary Embryologic, 1994.
Macroscopic aspects: The retired fetuses of the laziness 1 and 2 were covered by a membrane flat, white and without vessels, the epitriquic (Fig. 1). However, in the less advanced gestation, the fetus (3) unprovided of hair, didn't possess evidences of epitriquial membrane (Fig.2). During the operation Cesarean operation intense blood exit was observed, in the displacement of the fetal and maternal placentas.
| ||Fig. 2. Fetais membranes of sloths (animal 3), where we visualize two fetais membranes joined. Most superficial, the chorium (C); is contacted with the amnion (A): We observe the simpe uterus with the presence only of an embryo.|
The analysis of the macroscopic aspects of the placenta of Bradypus variegatus will be appreciated in this chapter in the following order: I. Placenta; II. Hilo of the palcenta and III. Fetal membranes.
I. Placenta. The placenta was studied with relationship to your morphologic aspect in the three pregnant animals. The first of them contained a fetus (animal 1) measuring 14cm of length (CR) and other (animal 2) measuring 19 cm of length (CR) and the third measured 7.5 cm of length (CR).
It was observed that the placenta of the sloth is composed by lobes of discoid formats. The number of lobes varied in agreement with the age of gestation. These were counted in number of 18 in the animal 1. 25 in the animal 2 (Fig. 3) and 80 in the animal 3. (Fig. 2) The lobes occupied the chorium in a diffuse way in the uterine cavity. They possessed fractions that separated the mass of the placenta surrounded by the membranes, through which walk vessels that established connection with the main mass. Other lobes came entirely isolated of the main mass. In this case the vessels established direct connection with the umbilical string (Fig. 3). In the animal 3, where the gestation was less advanced, the lobes of the placenta came of spherical formats of the size of dispersed peas, occupying the chorium almost entirely, except in the cervical area of the uterus. The placenta still presented your discoid format, occupying with your main mass the bottom of the uterus.
| ||Fig. 3. Placenta (animal 2) presenting 25 lobes of polygon format. These lobes (L) occupied the chorium of diffuse form. The placentaria mass increased of size in the fundic region of the uterus. The fetais membranes (chorium and amnion) were proven here, through which walk sanguineous vases.|
The lobes measured in the animals 1, 2 and 3 respectively 21mm of diameter and 38mm of length (larger wolf) and 8mm of diameter and 10mm of length (smaller wolf), 17mm of diameter and 30mm of length (larger wolf) and 4mm of diameter and 5mm of length (smaller wolf), 7mm of diameter and 11mm of length (larger wolf) and 2mm of diameter and 4mm of length (smaller wolf). The chorium presented membranous areas (Fig. 3), becoming flat however, evidencing visible supply of blood fetal vessels (animal 2).
We observed that these lobes crowded round and increased of size in the bottom of the uterus. In another area of the chorium these lobes came with irregular formats, and smaller as they stood back of the bottom of the uterus, becoming discoid (Fig. 4). This discoid format was visualized in the three cases, however more sharply in the animal a, in which these they were limited to the area lateral back of the bottom of the uterus.
II. Hilo of the placenta. The Hilo of the placenta is the area of implantation of the umbilical string, or pedicles of the string in the fetal surface of the placenta, similar to what happens with vascular pedicles of some organs. The area hilar varied of 3cm (animal 1), 4 cm (animal 2) and 2cm (animal 3) of diameter and it was placed in the margin of the placenta, area that was characterized by the presence of larger lobes (Fig.4).
| ||Fig. 4. Placenta of sloths(animal 2) presenting discoidal format. Funicule umbilical if inserts in the placenta in form of Y. The area of placentario hilo (H) measured 4 cm of diameter and was situated in the edge of the placenta, region that if characterized for the preence of bigger lobes (L).|
III. Fetal membranes. In the studied animals, the fetal membranes were identified. After the uterine incision, we visualized the first fetal membrane, together with the lobes of the placenta and your respective vessels. These were shown membranaceas mainly in the ventral cervical area of the uterus, and in the bottom of the uterus this placenta mass took a discoid format. The membrane chorium (Figs.1 and 2) interfered in the margin of the placenta, being in contact with the whole uterine area.
The chorium, externally to the placenta of the side mesometrial comes as an applied thin membrane in the uterine surface on a side (Fig.1), adherent for the delicate and thin amnion in your other face (fetal). The junction chorium-amniotic was made the small distance of the uterine wall, leaving the same flat (Fig.1).
The second visualized membrane, the amnion located stuck to the first, which surrounded the fetus completely. It presented an appearance flat, very fine and unprovided by blood vessels in the surface of the placenta (Figs. 1 and 2).
No specimen presented vestige of a membrane allantois and of a vitelline sack evident.
Microscopic aspects. 1. Microscopic analysis of the placenta. The lobe of the placenta is divided in lobes of dimensions and irregular formats, separated to each other by septs constituted by an abundant fetal mesenquima. These septs contain numerous vessels that invade the maze of the placenta. Of the interlobes septs (Fig. 5), they break thinner septs (septules) that subdivide the maze in very irregular units.
| ||Fig. 5. Placenta of fetus of lazines Bradypus variegatus (animal 2) where he sees himself the division of a lobe in lobes of dimensions and irregular formats, separate for septs constituted by abundant fetal mesenquima. Starting from the interlobes septs, they break thiner septs (septula) that subdivide the maze in irregular units. Tricromic of Masson. 20 x.|
The fetal face is covered for the amniotic epithelium, that presents a typical structure (simple plane epithelium). This amniotic epithelium (Fig.6) leans on in the parietal mesoderm, which for your time, it is obscure, and it constitutes the chorionic mesoderm. Inside this mesoderm they are arteries and fetal veins (chorionic vessels), that are dependents of the umbilical vessels. These chorionic vessels eventually are projected for the amniotic cavity, being always covered for the amnion. They are typical chorionic vessels, because, to example of the umbilical vessels, they also present a muscular layer that constitutes the medium tunic, with bunches of muscular cells disposed longitudinally (intern subtunic) and in a circular way (external subtúnica). Besides, great spaces exist filled out by the intercellular substance of the mesenquima. Among the fibers that constitute these bunches.
| ||Fig. 6. Placenta of fetus of lazines Bradypus variegatus (animal 2) where he sees could be seen the fetal face covered again by the amniotic epithelium, that leans on in the parietal mesoderm, which is obscure for your time; it constitutes the chorionic mesoderm. H. E. 40 x.|
The labyrinth of the placenta. The maternal element is represented for capillary with quite defined morphology. The endothelial cells come hypertrophied, with very abundant cytoplasm so that the distance among your nuclei is very small, differing largely of a capillary one ordinary. Of this it sorts things out, to the light microscopy this endothelium becomes visible discreetly. Around the endothelium, it was possible to identify a thin layer of matrix extra cellular that is very probably treated of a tunic subendothelial. These capillary ones maternal perpendicularly are disposed in the maternal-fetal interface, exhibiting, per times some tortuosity. The diameter of these vessels is big, having variations. It was possible to surprise some anastomitics communications among these vessels. The placenta of the Bradypus variegatus can be classified like this as endotheliumchorial and syndesmochorial.
The fetal components of the placenta understand: the trophoblast, the mesenquima and the capillary ones. The trophoblast is a continuous and irregular mantle, always in contact with the capillary ones maternal. He is of syncytial nature and it didn't show possible cellular limits of they to be identified (Figs. 7 and 8). Associated to this mantle trophoblastic there is a mesenquima (Fig. 8) reduced with very little material intercellular, in such a way that the all-fetal tissue presents an aspect epithelioid. The capillary ones fetal present very reduced diameter when compared to the capillary ones maternal and for that they are typical (Figs. 7 and 8). They form a net around the capillary ones maternal and with great frequency they are had parallel way to these. In a transverse section, these capillary ones fetal can gives considered " satellites " in relation to the existent gaps. It was possible to observe about from 3 to 10 sections of these capillary ones of a capillary one maternal.
Fig. 7. Placenta of fetus of sloth Bradypus variegatus (animal 2) where could be seen the labyrinth of the placenta. The materal vessels (CM) do they present your endothelial cells hypertrophied. The trophoblast (T) is a continuous and irregular mantle, always in contact with the capillary ones maternal. Associated to this trphoblastic mantle that i a reduced mesenquima, with very little intercellular material, in a such a way the fetal tissue presents and epitheliod aspect. H. E. 40 x.
Fig. 8. Placenta of fetus of sloth Bradypus variegatus (animal 2) where we see ourselves the maternal capillary (CM) hypertrophied, presenting the endotelial cells () hipertrophophyd, so that, the distance among the nuclei of this cell is very small and is their cytoplasm abundant. About of this endothelic a thin layer of head office extracellular is visalized (·) being treated of the tunic subendothelial. The maternal capillary diameter (CM) it is big; the capillary ones fetal (CF) they come typcally and your diameter is smaller than the materal. Tricromic of Masson. 100 x.
In the consult to the literature, we verified adds work referring to the morphologic aspects of the edentate placenta, particularly armadillos and anteaters and with smaller frequency the sloth. We still cam across an insufficient documentation of these discoveries, which plows per teams accomplished with pathological material or badly preserved. Face to the exposed, the dates obtained in our work will be confronted with those that integrate the order edentate.
The methodology used in our research, regarding the uses of adds techniques had the parameter the classic technology countersigned in the study of the anatomy and histology of the organs. In our comments we emphasized mainly the aspects anatomical macro and microscopic of the placenta of sloth with views information that will be goes the enrichment of the comparative anatomy to discuss.
The number of studied animals is constituted of an enough biological sampling to evaluate the anatomical results. Being treated of the wild animal of solitary habits with the long gestation period (6 months), and birth of only nestling, can be considered animal of uncertain future now, meeting in the list of threatened Brazilian mammals of extinction (Fadda, 1989) and strictly controlled by Ibama.
It i still worth to point out, the existent controversy in the zoological classification of the species in appreciation, since we found in the work of King et al., the uses of the same animals, focused in our work, that, originating from of the same area, and classified the Bradypus tridactylus. It is worth to say that this fact diverge of the consulted literature, since this species classified the Bradypus variegatus, Schinz (Wetzel & Kock). The species Bradypus tridactylus, Linnaeus,1758 have your geographical distribution according to Gardner, (1993) in Guyana, Surinam, French Guiana, Venezuela and North of Brazil (area of the river Solimões - Amazon) while the species Bradypus variegatus, Schinz found in the areas of Honduras to Colombia, Ecuador, West of Venezuela, Peru, Bolivia, Paraguay, North of Argentina, Brazil (areas of the Atlantic forest - Northeast to the Southeast).
Wislocki (1926 and 1928 ); King et al. (1982); Benirschke & Powell (1985), studying the placentation of the sloth classified the same the endotheliocorial. In fact the placenta of the Bradypus variegates the research can be considered with relationship to the histological aspects of the membrane inter-hematic, or be to the invasive capacity of the trophoblast the typical endotheliocorial placenta. Still Wislocki (1926; 1928 the); King et al. they increase the importance of the acts of the development of the placenta, since these they classified it in the beginning of the gestation, the transition between the types syndesmochorial and endotheliochorial. However, the transitions between the types syndesmochorial and endotheliochorial affirmed by these authors cannot be compared with the dates obtained in our research, because we examined placentas to term. The most immature placenta of the fetus of animal the 3, didn't allow microscopic analysis in our investigation. Though, the observations done goes of Lange (1926) apud Wislocki (1928a), studying the placenta of Bradypus, describes an intermediate phase between the types endotheliochorial and hemochorial. This statement doesn't corroborate with the results seen by Wislocki (1926 and 1928); King et al. (1982), Benirschke and Powell the well the with our discoveries.
Enders (1960; 1965a and 1965b) classifies the placenta of the armadillo the villous, hemomonochorial. Already Strahl (1906) apud Wislocki (1928b); Walls (1939) using the model the anteater classified to the deciduous, hemochorial and villous. Before the exposed, we still ratified the difference of the placenta of animals of the same order. In fact analyzing the evolution of the fetal membranes and comparing it with the evolution of the body, we still verified the link faulty of explanation of the why species alone fellow presents such different placentas and such several species show the same placentation type.
Wislocki (1928) studying the placenta of the sloth comments the morphologic similarity of the labyrinth of the placenta among the species Choloepus and Bradypus in the certain phase, since in this period it i noticed the presence of the clearer vascular tunic around the maternal vases in Bradypus, characterizing the invasive activity of the trophoblast (Gilmore et al., 1998).
Wislocki (1927, 1928); King et al. and Benirsche & Powell describes that the trofoblastic maze presents separate blood vessels goes strips of the fetal mesenquima. Cells and cellular layers separate the maternal and fetal circulation in the maze of the placenta. Our dates show the presence of the hypertrophy equally in the maternal endothelium, whose cells have very abundant cytoplasm, only that the distance among your nuclei very small, differing of the capillary ordinary; the layer of syncytial trophoblast, associated the basal membrane, it i shown evident, the well the fetal capillary endothelium.
According to King et al. this trophoblast of syncytial nature. In fact, it was not possible to identify cellular limits in the light microscopy in our research. The maternal element i represented goes capillary with pays off defined morphology.
King et al.; Wislocki (1928a) still mark, that the trophoblast layer was characterized by an uncommon configuration, with lacy aspect, the sponge, however another uncommon characteristic of the placenta of sloth one of the epithelioid evidences of the fetal estroma. In our results, we didn't visualizes this uncommon characteristic of the trophoblast in your cytoplasm, the sponge. Perhaps this fact have been visualized better in the electronic microscopy of transmission, technique not used in our work. Though, referring the epithelioid characteristic of the fetal estroma of the placenta of the sloth seen by King et al. and Benirschke & Powell; in the armadillo goes Enders (1960 and 1965a) and in the anteaters (Walls), we can affirm that this can be considered the characteristic common of the edentates, since in our results they plows added to the these observations.
Considering the macroscopic anatomical aspect of the placenta of the sloth now, Bradypus variegatus saw that the armadillo and the anteater demonstrate peculiar differences, the one that allows weave us comparative comments. The placenta of the anteater described by Walls; Wislocki (1928b) shows anatomical aspect that allows you classify it with relationship to your format them placenta diffuse nodular (immature placenta) and placenta discoid or bidiscoid (placenta to term). Already, Newman & Patterson (1910) apud Walls tell that the morphology express of the placenta of the armadillo subjects to marked transformations. This characteristic also evident in our results, meantime to the format bidiscoid it was not visualized. Therefore, we can affirm that the placenta of other edentate resembles each other anatomically to the sloth, in your format discoid, receiving the classification with relationship to your format of placenta discoid.
Simon (1902); Wislocki (1926); Klinkowström (sd) apud Simon (1902) researching the placenta of an embryo of Bradypus 110mm, verifies that the placenta was composed by adds " spherical lobes " of the size of dispersed peas on the whole surface of the chorium. The author described the placenta of the sloth composed of numerous " polygonal lobes " that appears in the lumen of the uterine cavity. In the youngest phase (37mm CR) these lobes occupy the whole chorium being diffused in the uterine cavity. With moving forward of the gestation, this chorium in your cervical portion became flat, only that, in the oldest specimen (60 to 76mm CR), the cervical portion of the chorium became membranous. These lobes degenerations in the chorium resulted of the reabsorption of the " lobes ". While this, the " lobes " that were destined to persist, the one of the area functionally active of the placenta increased slowly. Our results plows added to these, still increasing, that in the Bradypus variegatus, the spiritual medium number of lobes was the same to 41. This fact, it was not evidenced in the consulted literature. The relative nomenclature to the anatomical structures that integrate the placenta deserved repairs to moves away confusions, to facilitate the designation of morphologic aspects and to clear the lobe meaning and " lobe ". Lobe - of the Greek: lobes, it means the round and convex part of any organ. Lobe - it means the division of the lobe; the authors invert these concepts and they use the term indiscriminately.
Wislocki (1926) measured the " lobes " that plows destined to persist, those found functionally in the area active of the placenta. These increase slowly, only that in the fetus (60 mm CR) this structure measures from 4 to 9 mm of diameter; in the fetus (76 mm CR) measures from 5 to 14 mm of diameter. In the Bradypus variegatus the lobes measured (animal 1) 21 mm of diameter and 38 mm of length (larger wolf) and 8 mm of diameter and 10 mm of length (smaller wolf); animal 2: 17 mm of diameter and 30mm of length (larger wolf) and 4 mm of diameter and 5 mm of length (smaller wolf); animal 3: 7 mm of diameter and 11 mm of length (larger wolf) and 2 mm of diameter and 4 mm of length (smaller wolf). We could end like this that the lobes that persist, that i, they don't deteriorate, they increase of size the measure that the placenta ripens and they concentrate on the bottom of the uterus determining the format discoid of the placenta to term of the sloth.
In relation to the fetal membranes, Walls tells the difficulty of identifying the fetal individual membranes in the anteater embryo. According to him, the amnion covers the embryo completely. To the margin of the placenta the chorium becomes evident. It goes Heuser and Wislocki (1935) in young apprenticeships of development of the placenta of Bradypus the amnion and the vitelline sack also exhibit characteristics, which plows almost close to, the conditions found in the primates. Of this analogy, it results the evolutionary convergence undoubtedly between two groups of mammals without connection. To the likeness of our discoveries, Walls, affirms that the amnion surrounds the embryo completely, and he links with the chorium which in intimate relationship with the endometrious in the face, and with the amnion, in the other, classifying the placenta of the sloth, with relationship to the arrangement of the fetal membranes them placenta chorium-amniotic, just the it i the human placenta. It worth to point out that in agreement with the consulted literature in the animal shows this characteristic.
Relating biological aspects of the species in appreciation, it was possible to verify the similarity that the "bug laziness " presents in morphologic terms with the human species, especially biological of the reproduction. The uterus of the sloth simple; the placenta discoid, chorium-amniotic, labyrinthine. Placenta of Bradypus variegatus could be classified microscopically in syndesmochorial and endotheliochorial
Another important aspect to be studied in future inherent researches the placenta of the sloth is the presence of the membrane epitriquial, well placed by Simon; Wislocki (1926; 1928); Walls involving the fetus of sloth. It i worth to say that this structure, only characterized in the sloth and in the man, protects the fetus, it appears evident with the birth goes the protection the uterus and infiltrate-senas corporal fetal depressions, being shown continuous with the mucous membrane of the pseudocloaca of the sloth. In the one donate refer to the evolutionary aspects what your meaning would be? This and many other subjects, such the because the allantoids and the vitelline sack only plows the little developed? When of the they appear, do how long donate it last? Why? We concluded like this our task accomplishing part of our proposal, because this research should have sequence the line to be developed federal Rural University of Pernambuco and the Federal University of Pernambuco close to, aiming attn to establish enough and appropriate dates to the reproduction and preservation of the species.
AMORIM, A. L. M. J. A.; AMORIM JÚNIOR, A. A.; MESSIAS, J. B.; SILVA JÚNIOR, V. A. & BERINSON, M. K. Aspectos anatómicos de la placenta del perezoso Bradypus variegatus, Schinz, 1825. Int. J. Morphol., 22(1):9-18, 2004.
RESUMEN: El mamífero euterion perezoso, perteneciente al orden Edentata, sub-orden Xenarthra, infra-orden Tardigrada, familia Bradipodidae, comprende tres especímenes, Bradypus tridadctylus, Bradypus variegates y Bradypus torquatus. Pocos trabajos fueron encontrados en la literatura relacionados con la anatomía de la placenta de este especimen.
Usamos 3 placentas de hembras de Bradypus variegatus (Briton, 1941) provenientes de la Floresta de la ciudad de Recife y Zona de la Floresta del Estado de Pernambuco, Brasil. Las placentas tenía un peso promedio de 4,2 Kg y fueron fijadas en glutaraldehido tamponeado al 4%, pH 7,4, 0,1M y procesadas para microscopía óptica.
Macroscópicamente se observó que la placenta del perezoso estaba compuesta por lóbulos discoidales y ocupaba una posición en el fondo de la cavidad uterina. Las membranas fetales identificadas fueron el corion, aplicado en la superficie uterina y amnios adherido a la cara interna del corion. El especimen examinado presentaba vestigios de sacos alantoideo y vitelino en esta fase gestacional. Anatomicamente, la placenta de Bradypus variegatus puede ser clasificada como corion-amniótica. El análisis microscópico de la placenta mostraba células endoteliales de vasos maternos hipertrofiados y componentes fetales sin límites celulares identificados. El tejido fetal presentaba un aspecto epiteliode con vasos rodeando al tejido conectivo y células epiteliales próximas a los vasos maternos. De acuerdo con nuestra descripción la placenta del Bradypus variegatus puede ser clasificada microscópicamente como sindesmocorial y endoteliocorial.
PALABRAS CLAVE: 1. Placenta; 2. Perezoso; 3. Anatomía; 4. Bradypus variegatus.
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Prof. Dra. Marleyne José Afonso Accioly Lins Amorim
Universidade Federal Rural de Pernambuco
Departamento de Morfologia e Fisiologia Animal
Rua Dom Manuel de Medeiros, S/N Dois Irmãos
Received : 18-07-2003
Accepted : 08-12-2003