RESUMEN
The platypus kidney shows morphological similarities to those of other mammals. Macroscopically, the cortex is easily distinguishable from the fairly wide medulla. Within the medulla, no clear border is observed between the inner and outer zones. Light and transmission electron microscopically, the glomeruli show quite similar architecture to those of other mammals; however, the glomerular lobulation is very clear. The glomerular tufts are rather simple, but capillary lumen varies widely in size, which is one of the unique features of the platypus kidney. The urinary tubule is generally similar to that of human and other mammals in shape and segmentation; however, the staining specificities of histochemical reactions and the shape of epithelial cells of the Henle's loop differ from those of other mammals. The most conspicuous features are: 1) although no protein casts are found in the tubular lumina, epithelial cells of the proximal convoluted tubule (PCT) have numerous electron-dense vesicles as in human nephrotic kidneys; and 2) the platypus Henle's loop consists of the thick epithelial cells similar to the mammalian type nephron of birds. As compared to those of other mammals such as humans and rats, our observations suggest that the platypus kidney is less developed, in terms of evolution.
Asunto(s)
Riñón/anatomía & histología , Ornitorrinco/anatomía & histología , Animales , Aves , Femenino , Aparato Yuxtaglomerular/anatomía & histología , Riñón/ultraestructura , Glomérulos Renales/anatomía & histología , Glomérulos Renales/irrigación sanguínea , Glomérulos Renales/ultraestructura , Túbulos Renales Colectores/anatomía & histología , Túbulos Renales Colectores/ultraestructura , Túbulos Renales Distales/anatomía & histología , Túbulos Renales Distales/ultraestructura , Túbulos Renales Proximales/anatomía & histología , Túbulos Renales Proximales/ultraestructura , Masculino , Mamíferos , Microscopía Electrónica , Nefronas/ultraestructura , ReptilesRESUMEN
The morphological features of the intestinal mucosa and intra-abdominal lymphoid tissues of the platypus were examined. The mucosal surface of the intestine was characterized by the formation of large folds instead of the finger-like villi found in placental mammals. The lamina propria of the mucosal fold was well developed and contained numerous lymphocytes, expressing the lymphoid nature which is characteristic of the lamina propria of mammalian intestines. Although numerous well-developed Peyer's patches were observed in the ileum, solitary lymphoid nodules could not be found anywhere in the small intestine. Other intra-abdominal lymphoid tissues, particularly mesenteric lymphoid nodules, were well developed. However, each nodule represented a single follicle in contrast to the mammalian mesenteric lymph node which is composed of numerous follicles fused together. On the basis of the above findings, the tissues in question are considered to be at an evolutionary level preceding that of placental mammals.