An original histological method for studying the volar skin of the fetal hands and feet.

AIMS: The human fetal period of life is when there is complete development of the dermatoglyphic pattern. However, to date not enough is known about the differentiation of the papillary terrain during prenatal life and which mechanisms are involved in this differentiation. The aims of the present study are to contribute to the clarification of the embryogenesis of the papillary ridges and to compare their development on the hands and feet. METHODS: The hands and feet of 35 human embryos and fetuses were examined in the present study. We used a new and original method of orientation. The right hand with right foot or left hand with left foot of each embryo/fetus were placed together into one paraffin block. Three different planes of orientation were used. RESULTS: Volar pad development and papillary ridge formation are identical on hands and feet, but the developmental stages on feet lag one week behind those of hands. Papillary ridge embryogenesis follows the cranio-caudal developmental direction. After developmental week 14 the configuration of the future dermatoglyphic pattern has already ocurred at the dermo-epidermal junction. We consider the 6(th) month of prenatal development to be the gestational age when the papillary ridge development is completed. CONCLUSION: Our observations lead to the conclusion that the increased vascularization of dermis considerably affects papillary ridge formation.

Morphologic heterogeneity of human thymic nonlymphocytic cells.

The thymus is the central organ of the immune system. It is essential for the development and maintenance of normal immune system, especially cell-mediated immunity. From the morphological point of view, the thymus is divided into two main compartments, cortex and medulla. The thymic microenvironment consists of a network of reticular epithelial cells and other fixed and free cells. The microenvironment of thymus is very important for the selection and maturation of T cells. T cell differentiation occurs via T cell receptors. The major histocompatibility complex participates in interactions between T cells and thymic epithelial cells, in addition to interactions between T cells and dendritic cells, macrophages and myoid cells. The neuroendocrine system regulates early T cell differentiation by the transcription of neuroendocrine genes in the stromal network and expression of cognitive receptors by immature T cells. This work briefly summarizes morphological and ultrastructural characteristics of thymic epithelial cells, dendritic cells, macrophages and myoid cells. It is accompanied by the authors' own photomicrographs and electronmicrograph from a transmission electron microscope. All of these cells play a critical role in the proliferation, differentiation and selection of precursor cells in the T-cell lineage, but the precise mechanisms not well understudood.

The phylogenesis and ontogenesis of the human pharyngeal region focused on the thymus, parathyroid, and thyroid glands.

The pharyngeal (branchial) region represents a classic example where the relationship between ontogenesis and phylogenesis has been demonstrated. It is a region where the development of gills during ontogenesis of all chordates has been recapitulated. In the process of evolution the pharyngeal region has undergone marked changes. While it functioned to ensure blood oxygenation and regulation of a constant internal environment in aquatic animals, it had to adapt to new and more complex functions in terrestrial vertebrates. The lungs have taken on the main role of blood oxygenation and the salivary glands now regulate ionic balance. The immune organs in mammals such as the thymus and the palatine tonsil, endocrine organs such as the parathyroid glands and the parafollicular cells of the thyroid gland, which produces calcitonin (originally as independent ultimobranchial bodies), as well as a part of the ear developed from the pharyngeal region. This article briefly summarizes the current knowledge regarding the phylogenesis and development of the human thymus, parathyroids, and the thyroid gland with a focus on the influence of neural crest cells during development.