Tissues - group of cells.

 In biology, tissues are the standard for cellular alignment between cells and complete tissue. Tissue is a group of identical cells and their outer matrix from the same origin that combine to perform a specific function. The structures are then made up of a functional collection of many tissues.

The English word "tissue" is derived from the French word "tissue", meaning something "woven", from a past participle of the verb, "weave".

The study of human and animal tissues is known as histology or, in relation to disease, as histopathology. In plants, discipline is called plant anatomy. Old-fashioned tissue study tools are a paraffin block in which tissue is inserted and disassembled, a histological stain, and a visible microscope. Advances in electron microscopy, immunofluorescence, and the use of expanded tissue components have increased the potential for tissue damage. With these tools, the normal appearance of the tissues can be evaluated in health and disease, enabling greater screening and treatment.

Animals

PAS diastase showing fungus Histoplasma

Animal tissues are organized into four basic types: connective tissue, muscle, nervous and epithelial. [1] A collection of units assembled into units to serve the same organ function. While all animals can be thought of as having four types of tissue, the expression of these tissues can vary depending on the type of meat. For example, the origin of the cells that make up a particular type of tissue may vary from one species to another.

The epithelium in all animals is found in the ectoderm and endoderm, with a small contribution from the mesoderm, which forms the endothelium, a special type of epithelium that forms the vasculature. In contrast, the true epithelial tissue exists only in a single layer of cells held together by cohesive joints called solid junctions, creating a selective barrier. This tissue includes all living organisms that come in contact with the external environment such as the skin, airways and digestive tract. It performs protective functions, fluids, and absorption, and is isolated from other tissues below by the basal lamina.