GENERAL HISTOLOGY

Detailed explanation-1: -Epithelial layers contain no blood vessels (avascular), so they must receive nourishment via diffusion of substances from the underlying connective tissue, through the basement membrane.

Detailed explanation-2: -Tissues that do not contain blood vessels or lymphatic system are referred to as avascular tissues. Examples of avascular tissue include epithelial cells, cornea of the eye and cartilage.

Detailed explanation-3: -So, epithelial cells are tightly packed into one or more layers, held together by a variety of intercellular junctions. The deepest layer sits on a basement membrane, while the surface layer is free. Epithelial tissue is avascular but innervated.

Detailed explanation-4: -Squamous epithelial cells are thin, flat and arranged closely packed. Outer lining of intestine is made up thin muscle cells and connective tissue cells.

Detailed explanation-5: -Epithelial tissues are nearly completely avascular. For instance, no blood vessels cross the basement membrane to enter the tissue, and nutrients must come by diffusion or absorption from underlying tissues or the surface. Many epithelial tissues are capable of rapidly replacing damaged and dead cells.