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).
Organ cells are specialized and do not replicate. In most all instances a person is born with the number of cells they will have in their lifetime. The exception to that are skin cells and bone cells.
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.
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.
Muscle Tissue is specialized for gross movement by means of cellular contraction. Embryonically, muscle derives from mesoderm or mesenchyme.
Organ cells are specialized and do not replicate. In most all instances a person is born with the number of cells they will have in their lifetime. The exception to that are skin cells and bone cells.
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.
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.
Muscle Tissue is specialized for gross movement by means of cellular contraction. Embryonically, muscle derives from mesoderm or mesenchyme.
