tkanivá

Tkanivá (tissues) are groups of cells that cooperate to perform specific functions within an organism. They are the structural and functional building blocks of organs, and their composition includes both cells and the extracellular matrix that surrounds them. During embryonic development, tissues arise from the three germ layers—ectoderm, mesoderm, and endoderm—and become specialized for diverse roles in growth, protection, movement, signaling, and metabolism.

The four principal tissue types are epithelial, connective, muscle, and nervous tissue. Epithelial tissue lines surfaces and cavities, forms glands, and provides protection and selective exchange. It can be organized as simple (one cell layer) or stratified (multiple layers), with specialized forms such as glandular epithelium. Connective tissue supports and binds other tissues, and includes loose and dense forms, as well as cartilage, bone, and blood. It contains cells embedded in an extracellular matrix rich in fibers and ground substance. Muscle tissue contracts to generate movement and is classified as skeletal (voluntary), smooth (involuntary), and cardiac (heart). Nervous tissue transmits electrical signals and coordinates body activities, consisting of neurons and supporting glial cells.

Tissues also integrate with organs and organ systems to produce organ function. The extracellular matrix in connective tissue, along with cell adhesion and matrix remodeling, determines tissue properties such as strength, elasticity, and resilience. Regeneration and turnover vary by tissue type; some tissues renew rapidly (epithelium and blood), while others renew slowly or with scar formation after injury.

Histology is the study of tissues using microscopy, and advances in tissue engineering and regenerative medicine aim to repair or replace damaged tissues.