The Spleen ofZaedyus pichiy, (Mammalia, Dasypodidae): a Light and Electron Microscopic Study

Abstract

Armadillos are ancient mammals important as models for biomedical, evolutive and ecological studies, because they have adaptive and primitive morpho-physiological characteristics. In this work we study the splenic microarchitecture of the 'Patagonian Piche', Zaedyus pichiy, as an attempt to understand the relationship between the organizational plan of the organ and the particular features of this species. The organ samples were classically processed for light and electron microscopic study. The microanatomy of the organ as well as its different cell types are studied. The spleen is non-sinusoidal, with the typical arrangement for storage functions. White pulp is well defined. Red pulp is a meshwork of circulating, immunocompetent and haemopoietic cells. The general structure of the organ agrees with the semi-fossorial habit and the adaptability of the species. Comparative aspects with other armadillos or other less specialized groups are discussed. Persistence of haemopoietic spleen activity in the adult suggests the existence of specific inductive functions of the stroma. Better knowledge of spleen structure and function in ancient mammals may give important information about their phylogeny.

The Spleen of a Specialy Adapted Mammal: The Little Hairy Armadillo Chaetophractus vellerosus, (Xenarthra, Dasypodidae). A Light and Electron Microscopic Study

“…This fact agrees with the splenic structure observed in D. novemcinctus (Hayes, 1970) and D. hybridus (Galíndez et al, 2000) and differs from the observed in Z. pichiy, which shows isolated smooth muscle cells and myofibroblasts interposed between filtrant beds (Galíndez et al, 2003). An indirect proof of adaptive remodelling of the splenic microarchitecture in armadillos, is the fact that new-borns of C. villosus, have a myeloid spleen without trabeculae .…”

“…The size of the organ is similar to the one of other member of the genus, C. villosus and greater than the one of the other studied Euphractini, Z.pichiy (Galíndez et al, 2003). Nevertheless, because of the scarce number of studied exemplars, the morphometric data are offered only with informative purpose.…”

“…The intermediate zone has narrow borders than the other studied Euphractini (Galíndez et al, , 2000(Galíndez et al, , 2003, and differs from rabbits and rodents (Blue & Weiss, 1981). The presence of macrophages Perls (+), ellipsoids and a discrete amount of vasculature, make this structure very similar to that present in the ancestral group Insectivora (Tanaka, 1990) and is, probably, the place for blood clearance.…”

The blood-storing ability of the spleen

“…Apart from this, it is striking to note that they developed a type of spleen specialized to store blood similar to the ungulate one. A bi-layered capsule and the presence of a wide muscular network in the pulp cords have been reported in all the species studied until now: Myrmecophaga tridactyla, Tamandua tetradactyla, Choloepus hoffmanni, Cabassous unicinctus, Chaetophractus villosus, Euphractus sexcinctus (Claussen, 1969), Dasypus novemcinctus (Hayes, 1968), Dasypus hybridus (Galindez et al, 2000), Zaedyus pichiy (Claussen, 1969;Galindez et al, 2003).…”

Zaedyus pichiy(Cingulata: Dasypodidae)

“…Both red and white pulp are present. Its hemopoietic activity persists in adult individuals (Galindez et al 2003).…”