Basic concepts and terms

General histology

General histology is a part of the histology course devoted to the study of development patterns, tissue structure, and tissue functioning in multicellular organisms

Basic concepts and terms

Tissue

• is a distinct system of the body, which developed during the evolution; it fits the intermediate level of body structural organization (molecules – cells – tissues – organs)
• contains cells that are the principal elements of tissues, as well as cell derivatives: intercellular substance, supracellular structures (symplasms, syncytia), and structures derived from single cells
• involves one or several cell lineages
• exerts its own specific functions due to collaboration of all tissue elements

Tissue philogeny

• in the course of evolution, tissues have been formed with properties resulting from divergence: diversity of features caused by cell adaptation to certain environmental conditions in primary multicellular organisms
• similar basic functions (interaction with the external environment, homeostasis, motility, body part integration) led to a development of similar tissues in animals of different evolutionary groups whereas these similar tissues first appeared independently and simultaneously with almost the same structure

Ontogenetic tissue development (histogenesis)

• occurs in embryogenesis (embryonic tissue development) and during the following period (postembryonic tissue development)
• repeats (recapitulates) general tissue development patterns in phylogeny
• results from cell determination and differentiation, as well as from their reproduction, death, migration, and mutual interaction

Embryonic tissue development

• non-tissue organism step: it corresponds to the stages of cleavage and gastrulation when various cells emerge though tissue systems are not formed yet
• step of tissue-specific differentiation: it begins with formation of embryonic rudiments from the germ layer material. The step is marked by a development of specialized cells to constitute certain tissue types

Postembryonic tissue development

• is a continuation of embryonic tissue development
• is simultaneous with the processes of constant renewal, adaptive rearrangement, and tissue repair after damage