Basic concepts and terms

Special hystology

Special hystology — is the section of the histology course dedicated to the study of microscopic structure of organs and organ systems along with the pattern of tissue interactions in processes of development, functioning, reactive and age-realted organ changes.

Organ:

• a specialized system of interacting tissues formed in evolution, isolated from the surrounding structures of the body;
• characterized by:
  • the patterns of development in ontogenesis — organogenesis is a result of histogenesis complex during which forms structural and functional units of organs;
  • the relative constancy of the position in the body, shape and size, internal structural organization, sources of blood supply and innervation;
• has a complex of specific functions implementing through the interaction of the tissues forming it.

Structural and functional unit of the organ:

• is a part of organ represented by its smallest structural unit that ensures basic organ functions;
• includes cells of different tissue nature, united by a common blood supply and innervation;
• corresponds to the concepts of: functional element, microdistrict, region, module, lobule, acinus, etc.;

By structure internal organs are divided into hollow and parenchymal.

Hollow organs:

• are tubular or bag-shaped in shape, characterized by the presence of a cavity and its surrounding wall;
• the wall consists of shells, the number of which and the tissue composition depend on the organ belonging to the corresponding apparatus and its departments;
• examples: blood vessels, digestive tube organs, etc.

Parenchymal organs:

• compact in structure, they consist of parenchyma and stroma:
  • parenchyma:
    • is the defining organ element;
    • is formed by a particular tissue that provides specific organ functions (epithelial, nervous, lymphoid, myeloid, muscular);
  • stroma:
    • is formed by connective tissue, which determines the spatial organization of parenchymal components;
    • includes an organ capsule and intra-organ layers (septa, trabeculae, interstitium) containing vascular and nerve structures;
• examples: kidneys, liver, spleen, etc.

Parenchymal organ and hollow organ

Organ systems — are a combinations of organs that jointly participate in one significant body function (blood supply, respiration, digestion, excretion, reproduction, regulation of vital activity) and form a single and systematically constructed whole — the apparatus of organs