tissue

Tissue is a group of cells that share a common structure and perform a specific function. In multicellular organisms, tissues organize into organs and organ systems, enabling complex processes such as digestion, movement, and support. In plants, tissues form the basic structural and functional units of organs like leaves, stems, and roots.

Animal tissues are typically categorized into four main classes: epithelial tissue lines body surfaces and forms glands; connective tissue supports and binds other tissues and includes bone, cartilage, adipose, blood, and fibrous tissues; muscle tissue contracts to produce movement and is divided into skeletal, cardiac, and smooth types; nervous tissue conducts electrical impulses and encodes information through neurons and supporting glial cells.

Plants also possess organized tissues, grouped into three primary systems: dermal tissue for protection and gas exchange, ground tissue for photosynthesis, storage, and support, and vascular tissue for transport of water, minerals, and sugars (xylem and phloem).

In tissues, cells reside within an extracellular matrix that provides structural support and biochemical communication. The matrix in connective tissue is rich in collagen and other fibers, while epithelial and nervous tissues have less extracellular matrix. Tissues are studied in histology, and normal and abnormal tissue structure underlies diagnostics.

Development and maintenance: Tissues arise from the three germ layers in animals and from meristematic activity in plants; many tissues turn over continuously through stem cells; injury triggers healing and regeneration. Clinically, tissue samples are used in pathology and tissue engineering seeks to create functional tissues for repair.