MEDICAL BIOLOGY, ANATOMY, HUMAN PHYSIOLOGY AND PATHOLOGY - Ya.I. Fedonyuk 2010

BIOLOGY

SECTION 1. BIOLOGICAL BASES OF HUMAN VITAL ACTIVITY

1.2. CELL. TISSUES. CONCEPT OF AN ORGAN, ORGAN SYSTEM, AND ORGANISM

General characteristics and classification of tissues

A tissue is a phylogenetically established System of the Organism consisting of Cells and non-cellular structures that share a common origin, Structure, and function. The Structural components of Tissues include cells, Cell derivatives (symplasts, syncytia, post-cellular structures), and Extracellular matrix.

Cells are the main elements of any tissue, determining its fundamental properties.

Post-cellular structures are cell derivatives that, in the course of their development, have lost certain cellular components (nucleus, some Organelles) but acquired A number of properties necessary for performing specialized Functions. Human post-cellular structures include erythrocytes and Blood Platelets (formed elements of blood), cornified scales of the epidermis, Hair, and Nails.

A symplast is a multinucleated structure consisting of a large volume of Cytoplasm with numerous nuclei. It is formed As a result of Cell Fusion or nuclear division without subsequent cytoplasmic division. An example of a symplast is a Skeletal Muscle fiber.

A syncytium is a structure formed as a result of incomplete cytokinesis during Cell Division (development of Male Germ Cells, pulp of the enamel organ).

The extracellular matrix consists of ground substance and fibers (Collagen, elastic, reticular). In its physicochemical state, the ground substance is a gel of a certain viscosity and composition, which can be mineralized (Skeletal Tissues).

Throughout the life of the organism, tissues undergo wear and tear, death of cells and non-cellular elements, and their replacement by new ones (physiological regeneration). The restoration of tissues following injury is called reparative regeneration.

The Human Body contains various tissues grouped according to similarities in their Structure and function (morphofunctional principle) or based on a common developmental origin (histogenetic principle). The following morphofunctional types of tissues are distinguished: 1) epithelial; 2) Tissues of the Internal Environment (Connective Tissue, blood, and Lymph); 3) muscle; 4) nervous.

Epithelial Tissue and tissues of the internal environment are grouped into general-purpose tissues. Nervous and Muscle Tissues belong to special-purpose tissues.