North American porcupine at San Diego Zoo. | ||
2) General gestational data North American porcupines are solitary animals, which produce a single precocious newborn in spring. Without delayed implantation they breed in autumn and have a long gestation of seven months (205-217 days). The ovarian activity is unusual, as is its placenta. Possible positioning into a separate suborder has been entertained (Perrotta, 1959). Depending on the stage of pregnancy, adult females weigh between 4,000 and 7,000 g. Males are much larger; they weigh up to 18 kg (Nowak & Paradiso, 1983). The newborn weight is given as between 340 and 640 g. Shadle & Ploss (1943) observed a normal newborn weighing 480. Later, Shadle (1948) provided new data on the length of gestation. The uterus is described as being "transitional between duplex and bicornuate" by Perrotta (1959) and as having spiraled lumens (Mossman, 1987). The cervix is Y-shaped. The endometrium consists of tubular glands, some of which are branched, in the endocervix. Accessory corpora lutea develop from atretic follicles but persist only on the side of pregnancy. Mossman (1987) made other pertinent remarks on the preservation of corpora lutea. The placental weight at term is around 50 g, including the membranes and the relatively short umbilical cord. An extensive investigation of placenta and reproduction of the porcupine comes from Perrotta's detailed study (1959). 3)
Implantation |
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General situs of placental development of the porcupine. | ||
General situs of placental development of the porcupine. | ||
4) General characteristics of placenta Perrotta's study (1959) relied upon 200 macroscopic and 40 histologic specimens. Despite that commendable effort, very few early stages were identified. This animal has a discoid, labyrinthine placenta with a complex lobular pattern and a hemochorial fetal-maternal relation. The placenta resembles that of the guinea pig. The placenta of the guinea pig, another South American rodent, has been well studied by Kaufmann (1981), and by Enders (1965). The latter preferred the designation of this animal as having a "hemomonochorial" maternal/fetal relationship (Enders, 1965). My specimen measured 6 x 5-x 2 cm. It had abundant membranes. There was an area of marked necrosis and calcification in the center of the maternal surface, which corresponds to the "subplacenta" and that marks the attachment site to the decidua below. Lateral to this central calcified area there was a greenish hue due to fibrin-like material that contained hemosiderin granules in macrophages and in degenerating basal trophoblastic giant cells. Degenerating decidua and trophoblast were present in this hyalinized mass, as well as some specks of dystrophic calcification. The basal giant cell trophoblastic layer that abuts this hyalinized floor is often markedly vacuolated and has occasional pyknotic nuclei. This was previously described by Perrotta (1959). Some cells contain additional hemosiderin, demonstrable by Prussian blue stain. At term, the yolk sac stalk is mesometrially oriented. The inverted endodermal slpanchnopleure lies over the disk and forms a ring that is seen in the macroscopic picture of this placenta. There is a circular ring of vitelline vessels, similar to that in the guinea pig. Invasive trophoblast such as occurs into the myometrium of humans has not been described. Giant cells penetrate the decidua and cause degenerative changes there, which eventuate in calcification. In this area, the peripheral trophoblast forms huge giant cells; many become vacuolated, accumulate iron and subsequently degenerate in the floor. It should be noted, however, that these trophoblastic cells invade in the guinea pig (Nanaev et al., 1995) and we have found it in the pacarana (Dinomys branickii). Moreover, Miglino et al. (2002) studied three other hystricomorph rodent placentas with great similarities of many features seen in porcupines. The most complicated aspect of porcupine placentation is the inversion of the yolk sac. It comes to envelop the outside of the conceptual sac, with yolk sac endoderm located on a connective tissue sheet (the "Splanchnopleure"). We assume that it has absorptive function, but that has not been studied in the porcupine. It is so, however, in other rodents (Please see the chapter on mouse). As this vascularized splanchnopleure comes toward the edge of the placental disk, a fibrovascular "ring" develops that is illustrated here. The original yolk sac atrophies completely, as does the transitory allantois. |
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Delivered placenta at term. | ||
Cross-section of porcupine placenta with the inverted yolk sac membranes above. Calcified subplacenta is yellow in the center and on the maternal surface. Next are the cross-sections of the placental lobules. The luxurious, undulating splanchnopleure membranes are folded on top. | ||
Sections through the edge and center of the placenta with the "subplacenta" located at the bottom. | ||
Sections through the edge and center of the placenta with the "subplacenta" located at the bottom. | ||
Edge of porcupine placenta with villous tissue below, splanchnopleure curving to left top and vascular ring (VR). | ||
One of many complex lobules of the porcupine placenta with maternal (M) and fetal (F) vessels in the center. | ||
Masses of giant cells at the floor of the porcupine placenta. | ||
Masses of giant cells at the floor of the porcupine placenta. | ||
Higher magnification of one lobule of porcupine placenta with maternal (MA) and fetal (FV) blood vessels. | ||
Attachment site of porcupine placenta - so-called "subplacenta". | ||
5) Details of barrier structure The fetal-maternal relationship is hemochorial, in a labyrinthine network of villi with complex maternal and fetal vascularization. Trophoblastic channels contain the maternal blood. Fetal capillaries are present in the ample connective tissue. Thus, there is a typical countercurrent blood flow. The next pictures show the intricacies of the main placental tissue. |
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Highest magnifications of the trophoblastic and vascular arrangement of the porcupine placenta. | ||
Highest magnifications of the trophoblastic and vascular arrangement of the porcupine placenta. | ||
Another view of the complex fetal/maternal relationship. G=Giant cells; F=Fetal blood space. | ||
6) Umbilical cord The umbilical cord of our specimen inserted near the center of the placenta and was 13 cm in length, and 1 cm in width. It had no twists. There were two chorio-allantoic arteries and two umbilical veins, plus a large number of smaller vessels (usually seen in placentas endowed with allantoic sacs). Some of these vessels had thick muscular walls. Others had many capillary-like small vessels without any specific grouping around the remaining parts of the allantoic duct. There was a remnant of allantoic duct and, in a portion of one of the umbilical cords available to me, smooth muscle bundles accompanied the duct remnant. Another umbilical cord that I studied had a patent allantoic duct. The surface of the cord is remarkably more loosely structured than its center. The cord surface has a thin amnion. Except for locations directly beneath the surface, little Wharton's jelly exists. There are no amnionic "callosities". |
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Cross-sections through two umbilical cords of porcupine. | ||
Cross-sections through two umbilical cords of porcupine. | ||
7) Uteroplacental circulation No details have been published and no uterus was available to us. 8) Extraplacental membranes The initial decidua capsularis is described to disappear halfway through gestation; the decidua basalis is sparse. There is no allantoic cavity and amniogenesis is by cavitation. Perrotta (1959) stated that there is fine vascularization of the amnion near the placental disk, clearly an unusual feature in most mammals. Perrotta assumed that these vessels were vitelline blood vessels. More likely, they merely border the amnion and do not provide amnionic vascularization. In any case, they are confined to a small ring. The placenta has a bilaminar omphalopleure; the endoderm extends over a portion of the parietal trophoblast of the blastocyst that then disappears and persists only on the surface of the placental disk. There is no so-called "chorio-vitelline" placenta but the endoderm extends over the periphery with numerous closely approximated villi. The "vascular splanchnopleure" has the complete inversion of the yolk sac. This persists to term, with numerous blood vessels (of vitelline nature) of yolk sac origin. The epithelium, endodermal-yolk-sac-derived, makes up its surface. It lies against the opposite side of the endometrial epithelium where it assumes an epitheliochorial relation between mother and fetus (Kaufmann, 1981). One must assume that much transport can occur here in this rodent placenta as well; certainly this is so in early gestation (King & Enders, 1970a). Protein-rich material locates here in rodents and presumably it is absorbed by the complex epithelial trophoblastic surface (Please see chapter on mouse). For the guinea pig, this has been well illustrated by King & Enders (1970b). Towards the embryo, this inverted yolk sac membrane abuts the connective tissue of the amnion and then the amnionic epithelium. |
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Placental structure at the site of surface chorionic plate with maternal vessel (M), large fetal blood vessel (F.V.) and peripheral trophospongium and giant cells. | ||
9) Trophoblast external to barrier None. 10) Endometrium The endometrium beneath the major placental disk of rodents becomes the decidua, as is also true in Erethizon. It must be cautioned, however, that this tissue differs from the "decidualization" induced by progesterone in human uteri, as Wynn (1965) has made very clear. It is a complex structure and may subserve some nutritional role but is not well studied in the porcupine. Perrotta (1959) showed its hyalinization and degenerative changes towards term, and our placenta had not only hyalinization and degeneration, but much dystrophic calcification within it as well. |
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This is a section through the inverted endodermal (yolk) membrane that apposes the uterine wall with many villi and a cuboidal epithelium. | ||
11) Various features An accessory placenta ("subplacenta") exists in early placentation but disappears gradually later through a process of hyalinization and degeneration. It is confined to the central portion of the disk and is remarkably calcified in my specimen. The location of the subplacenta is essentially similar to that described for the guinea pig (Kaufmann, 1981; see also Kaufmann & Davidoff, 1977). 12)
Endocrinology 15)
Pathological features 17)
Other resources 18)
Other relevant data. |
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Prehensile-tailed porcupine abortus with placenta attached. Note the thick membranes with yolk sac epithelium. At right is the maternal side of this placenta with the light area being the subplacenta. | ||
Prehensile-tailed porcupine abortus with placenta attached. Note the thick membranes with yolk sac epithelium. At right is the maternal side of this placenta with the light area being the subplacenta. | ||
Maternal surface of the aborted prehensile-tailed porcupine. It shows extensive basal degeneration and the villous tissue is undergoing early autolysis. | ||
References CRES at: http://www.sandiegozoo.org/conservation/cres_home.html. Please direct your inquiries to Dr. Oliver Ryder (oryder@ucsd.edu). Benirschke, K.: The chromosome complement and meiosis of the North American porcupine. J. Hered. 59:71-76, 1968. Dodge, W.E.: The biology and life history of the porcupine (Erethizon dorsatum) in western Massachusetts. Ph.D. Thesis, University of Massachusetts, Amherst, 1967. Enders, A.C.: A comparative study of the fine structure of the trophoblast in several hemochorial placentas. Amer. J. Anat. 116:29-68. 1965. Hayssen, V., v. Tienhoven, A. and v. Tienhoven, A.: Asdell's Patterns of Mammalian Reproduction. Comstock Publishing Assoc., Ithaca and London, 1993. Kaufmann, P: Functional anatomy of the non-primate placenta. Placenta (supplement 1) pp:13-28, 1981. Kaufmann, P. and Davidoff, M.: The guinea pig placenta. Adv. Anat. Embryol. Cell Biol. 53:1-91, 1977. King, B.F. and Enders, A.C.: Protein absorption and transport by the guinea pig visceral yolk sac placenta. Amer. J. Anat. 129:261-288, 1970a. King, B.F. and Enders, A.C.: The fine structure of the guinea pig visceral yolk sac placenta. Amer. J. Anat. 127:397-414, 1970b. Luckett,
W.P. and Mossman, H.W.: Development and phylogenetic significance of the
fetal membranes and placenta of the African hystricognathous rodents Bathyergus
and Hystrix. Amer. J. Anat. 162:265-285, 1981. Mossman,
H.W.: Vertebrate Fetal Membranes. MacMillan, Houndsmills, 1987. Perrotta, C.A.: Fetal membranes of the Canadian porcupine, Erethizon dorsatum. Amer. J. Anat. 104:35-59, 1959. Roberts,
C.M. and Perry, J.S.: Placental development , pp. 344-350, in, The Biology
of Hystricomorph Rodents. I.W. Rowlands and B.J. Weir, eds. Academic Press,
N.Y. 1974. Sokolowsky, A.: Der Tierpark als wissenschaftliche Forschungsst@tte. Carl Hagenbeck's Illustrierte Tier- und Menschenwelt. 1(12):259, 1926/27. Wood, A.E.: Porcupines, Paleography, and Parallelism. Evolution 4:87-98, 1950. Woods, C.A.: Erethizon dorsatum. Mammalian Species, # 29, 1973. Wynn, R.M.: Electron microscopy of the developing decidua. Fertil. Steril. 16:16-26, 1965. |
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