I am quite confused because some sources distinguish between 5 types: folded, lamellar, villous, trabecular, labyrinthine (e.g. Book Benirschke's Pathology of the Human Placenta
;Article Evolution of the mammalian placenta revealed by phylogenetic analysis
); whereas some sources distinguish only 3 types: villous, trabecular, labyrinthine (e.g.Article Phylogenetic Evidence for Early Hemochorial Placentation in Eutheria
;Article The evolution of fetal membranes and placentation in carnivo...
).So, who is right? Why the folded and the lamellar types do not appear in some sources? In the sources where they appear, Suidae are said to have folded interdigitations, but trabecular in sources where they do not appear. Carnivora are said to have lamellar interdigitations, but their interdigitations are referred as labyrinthine in sources where the word "lamellar" is not even mentioned. Is the distinction between folded and trabecular spurious? As well as the distinction between lamellar and labyrinthine? This seems odd, because on textbook's diagrams these types are very different.
Fetomaternal interdigitations in placentas refer to the intricate connections between fetal and maternal tissues that facilitate nutrient and gas exchange during pregnancy. There are several types:Villous interdigitation: This occurs at the microscopic level within the placental villi, where fetal chorionic villi project into maternal blood spaces, increasing surface area for exchange.Decidual interdigitation: Involves the maternal decidua, which is the lining of the uterus during pregnancy. Decidual cells extend between fetal villi, contributing to the structural integrity of the placenta.Placental barrier interdigitation: This refers to the physical and biochemical barriers between maternal and fetal circulations within the placenta, ensuring selective exchange of nutrients, gases, and waste products while preventing direct mixing of blood.
Muhammad Umar I am sorry, this does not answer my question. You are describing the structure of human interdigitation. These structures are quite different in other mammals. For example, there are no chorionic villi projection maternal blood spaces in species with epitheliochorial or endotheliochorial placentation. There are also species without decidua. My question is about the structural classification of different types of interdigitations in different mammal species. Please, see the inconsistent classifications schemes used in the linked papers and books.
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