Classification

Placentas are variously classified. It can be done by their macroscopic appearance, as for instance as being discoid (human), cotyledonary (ruminant), diffuse (whales), and zonary (carnivores). Another way is according to the intimacy of fetal-maternal contact. For the latter distinction, the "Grosser classification" is conventionally employed. Grosser (1927) distinguished the epitheliochorial, syndesmochorial, endotheliochorial, and hemochorial types.

Then there is the aspect of the development of the structure of villi that has demanded separate classification such as being of the folded (pig), lamellar (carnivores), trabecular (some primates), labyrinthine (rodents, lagomorphs, insectivores) and villous types (human).

A table that is here placed for the purpose of orientation might be useful:

Placentation (part two)

Birds and other non-mammalian species possess membranes in their embryonic development within the egg that, ultimately, eventuated in the placental structures, as we now know them in mammals. from the analysis of placentas from a variety of mammals, it must be concluded that some of the diverse forms of placentas had separate origins. For instance, clearly the invasive simian placentas derived from prosimian ancestors with noninvasive placentas. The principal difference of simian and prosimian placentas is that, in the latter, the relationship to the maternal organism was appositional, in the former, invasive placentation evolved.

This important change in placental development mentioned above, to become an invasive structure that infiltrates the maternal uterus, must have had major cosequences; for instance, the feature of non-rejection by the maternal organism of a genetically "foreign" genotype had to be accommodated.

Most recently, it has been learned that genetic "imprinting" of placental (trophoblastic) cells differs from that of the imprinting on the genome of embryonic cells. Paternal gene expression predominates in the placenta, while maternal expression dominates in embryo development. The presence or absence of certain enzymes, the presence of some structures (e.g. allantoic sac) and other aspects vary substantially in different animals' placentas, presumably signaling some totally different intrauterine physiologic behaviors of water exchange and its conservation. The regulation of the length of the umbilical cord varies widely, and so on. Thus, knowing the structure of one placenta (e.g. the sheep) is not always helpful for an understanding of the organ in another species…

                              

 The classification of placentas will be presented by the next update

                                               Wish you the best- Dr. MOHSEN SALEHI K ahrizsangi

Hi 

This is my new weblog which is recently opend, I try to write in english here, I hope this would be interesting for you gentel men and ladies.

                                    I  look forward to hereing from you

                                                                  yours sincerely

Placentation ( part one)

Hi every body, I hope things work out for you all.

The study of the placenta is often difficult for pathologists. Mossman (1937) has aptly stated that "the placenta is probably more variable in structure than any other mammalian organ".And Kaufmann (1983) has similarly stated that there is much more variation in the structure of the placenta than is true of any other organ.Placentologists are more concerned with understanding the fine structure of the trophoblast/fetal-maternal interchange. That is not the reason for writing these pages. The reason for presenting these data and the many pictures I have added ( contact me for the pictures) is to enable the pathologist, confronted with an unusual placenta, to undertake a proper examination of this strange structure.While the pathologist is used to using formalin fixation for tissue processing, embryos and placentas are much better fixed in Bouin's solution as they are so delicate and water-laden. So, for optimal fixation, this is a better way to go for routine slides. We would like to know many aspects of the placenta that are not usually considered in texts, such as: the number of cotyledons, their sizes and distribution; how long is the umbilical cord and how many vessels does it contain? Are there ducts that lead to an allantoic sac? Is there inflammation (chorioamnionitis or abscesses)? And is the maternal organism infiltrated by trophoblast, something that can best be established when the placenta is still attached to the uterus. And are there infarcts or other areas of necrosis? Some of these features are essential for our understanding the cause of fetal demise, neonatal infection, and for an understanding of the genesis of fetal anomalies or premature birth. ….

                                                With lots of thanks- Dr.MOHSEN SALEHI Kahrizsangi