May 7th, 2012
Tissues: groups of similar cells and extracellular products that carry out a common function, such as providing
protection or facilitating body movement. Tissues are formed from the three primary germ layers (ectoderm,
mesoderm, and endoderm). The 4 tissue types vary in structure, function of their specialized cells and the
presence of the ECM.
Histology: the study of tissues and their relationships within organs.
THE 4 primary TYPES OF TISSUES ARE:
Structure of Epithelial Tissue
Basement Membrane: A thin extracellular layer that
physically separates the epithelial tissue from the
underlying connective tissue. Made of both the Basal
Lamina and Reticular Lamina.
acts as a regulator for movement of molecules to the
deeper connective tissue
acts to anchor epithelium to the underlying
connective tissue Functions: Epithelia may have several functions, although no single epithelium performs all of them. These
Physical Protection/Barrier: Epithelial tissues protect both exposed and internal surfaces from dehydration,
physical, mechanical or chemical injury. i.e. skin - in severe burns, dehydration is a primary concern
Selective permeability: All epithelial cells act as “gatekeepers,” in that they regulate the movement of materials
into and out of certain regions of the body. All substances that enter or leave the body must pass through an
epithelium. Sometimes an epithelium exhibits a range of permeability; that is, it may be relatively impermeable to
some substances, while at the same time promoting and assisting the passage of other molecules by absorption or
secretion. The structure and characteristics of an epithelium may change as a result of applied pressure or stress.
i.e. walking around without shoes may increase the thickness of calluses on the bottom of the feet, which could
alter or reduce the movement of materials across the epithelium.
Absorption: Regulates the passage of substances into the body. i.e. absorption occurs in the organs such as the
small intestines, which is lined with epithelial tissue. i.