ANATOMY&PHYSIOLOGY FOR NURSES

FUNCTIONS OF EPITHELIAL TISSUE Protective. The epithelial tissue which forms the covering of the body, the skin and the lining of the cavities which open on to the surface is mainly protective. It prevents injury to the underlying tissues, prevents the loss of fluid from these tissues and also prevents the passage of fluid into the structures which are covered by skin.  Micro- organisms cannot pass through healthy skin but they can and do pass through abraded skin. Secretory.  Most of the secreting glands and their ducts are composed of columnar epithelium. Very often the epithelium lining the gland and its duct is continuous with that of the surface in which the glands lie. Simple tubular and simple saccular glands are just involutions from the surface such as thesimple tubular glands of the intestine as shown in When these involutions branch, the structure becomes more complicated , as in the formation of compound tubular glands such as those of the kidney, and compound racemose or saccular glands  such as the salivary glands and the pancreas.         The endocrine glands are also composed of epithelial cells which may be massed together or may line hollow vesicles as occurs in the thyroid gland where the vesicles are lined by columnar epithelial cells, cubical in shape. These cells produce their secretion-colloid- but there is no duct from these glands and therefore the secretion reaches the blood stream either directly or through the lymphatics.