Epithelial Tissue covers body surfaces (epi, on + thelium, surface). Epithelial tissue consists of cells attached to one another to form an uninterrupted layer of cells that separates the underlying tissues from the outside world. The body's epithelium not only covers its obvious surfaces (such as the epidermis of the skin and the linings of respiratory, urinary, and digestive tracts) but also extends into all of the complex invaginations which form lungs, kidneys, sweat glands, digestive glands, liver, etc. Epithelial tissue provides the essential functions of protection; containment of body fluids; and transport in and out across body surfaces (absorption and secretion). Embryonically, most epithelial tissues are derived either from ectoderm (e.g., epidermis) or endoderm (e.g., epithelium of trachea and lung). [More] [Examples]
Connective Tissue supports other tissues. Connective tissue consists of several cell types and extracellular products which, together, provide essential functions of mechanical reinforcement, immune surveillance, transport/diffusion of nutrients and wastes, and energy storage (fat). Embryonically, connective tissues derive from mesoderm or mesenchyme. [More] [Examples]
Nervous Tissue is responsible for rapid long-distance signalling, coordination, and "thinking". Nervous tissue consists of highly specialized nerve cells and support cells which are derived from embryonic neuroectoderm and neural crest. [More]
Muscle Tissue is specialized for gross movement by means of cellular contraction. Embryonically, muscle derives from mesoderm or mesenchyme. [More]
A note on pathology nomenclature: The names of neoplasms reflect the fundamental nature of their source tissues. Thus a carcinoma is a cancer of epithelial origin, while a sarcoma is a cancer of mesenchymal (connective tissue or muscle) origin.
Parenchyma / Stroma: The parenchyma of an organ consists of that tissue which conducts the specific function of the...