By Peter Wooding, Graham Burton
Technological know-how produces attention-grabbing puzzles: why is there the sort of diversity of placental constructions while different mammalian organs are so structurally uniform ? Why and the way did the various placental constructions evolve ? Comparative placental experiences can facilitate the id of the typical elements in placental development, differentiation and serve as and their relevance to attainable evolutionary pathways. Comparative Placentation is the one ebook offering updated facts illustrating the good number of constitution yet uniform functionality of vertebrate placentas from fish to guy. this data is vital for number of appropriate types to enquire specific functional difficulties of impaired or anomalous progress in human and animal placentation. the original selection of the simplest gentle and electron micrographs from the final thirtyfive years which accurately illustrate the structural variety in each one taxon, make the publication the main authoritative book during this box and a necessary resource of knowledge for someone on reproductive body structure, anatomy and medication.
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Extra info for Comparative Placentation: Structures, Functions and Evolution
7) (Metz et al. 1976, 1978). The tight junctions may be remnants of those which linked the cells from which the syncytium formed and the desmosomes are needed to maintain the relationship between the layers. Gap junctions are normally considered to function by allowing the unimpeded passage of molecules below a certain size and thus to link cells electrically for synchronous activity (uterine smooth muscle, for example). 6 Types of Chorioallantoic Placentation 29 has been suggested that in this placental context the gap junctions facilitate metabolite transfer across the layers.
3). 2 Trilaminar Yolk Sac (Trilaminar Omphalopleure or Choriovitelline Placenta) The central mesoderm is richly vascularized and the external trophoblast usually forms an intimate apposition with uterine tissues so a true placenta is formed. This arrangement is found in certain fish (Figs. 2), reptiles (Fig. 3) and marsupials (Fig. 1) as the major placental structure. Eutherians frequently develop an area of this structure which may be important at early stages of development following implantation but never persists as a functional structure to term (Fig.
1 Cyto- and Syncytiotrophoblast All trophoblast is initially cellular. In endotheliochorial and haemochorial placentas this cytotrophoblast produces a continuous mantle of syncytiotrophoblast by division and fusion of some of its daughter cells into an overlying syncytium. Subsequent division of the residual cytotrophoblast provides one cell for fusion into the syncytium and the other persists as a stem cell for the syncytium. In haemochorial placentas the daughter cells may develop into individual giant cells which can migrate into the maternal tissues; in synepitheliochorial placentas they may differentiate into binucleate cells which form fetomaternal syncytia with uterine epithelial cells throughout pregnancy.