Epithelial Tissue Epithelial tissues in the body line body cavities, cover the body surface (skin) and form glands. Functions include:  protection of body parts (skin)  absorption of materials (stomach lining)  filtration (kidneys)  secretion (mucus cells)

Epithelial Tissue Characteristics of epithelial cells/tissue:  fit closely together  free surface that doesn’t attach to anything  bottom cells sit on a basement membrane  avascular (no blood supply)  regenerate easily

Epithelial Tissue Classification: each epithelial tissue has two names that indicate (1) the number of layers and the (2) shape of the cells. Number of layers:  Simple - one layer of cells resting on the basement membrane  Stratified – more than one layer of cells

Epithelial Tissue Classification: each epithelial tissue has two names that indicate (1) the number of layers and the (2) shape of the cells. Shapes of the cells:  squamous – flat, platelike cells  cuboidal – cube-shaped cells  columnar – column-shaped cells

Epithelial Tissue: Exceptions Pseudostratified:  single layer of columnar cells of different size  all cells rest on the basement membrane  some cells do not reach the free surface  modified versions have cilia (free surface)

Epithelial Tissue: Exceptions Stratified squamous:  basal cells are cuboidal or columnar  surface cells are squamous

Epithelial Tissue: Exceptions Stratified cuboidal & columnar:  only two cell layers  outermost cells are the indicated shape

Epithelial Tissue: Exceptions Transitional:  basal cells are cuboidal or columnar  cells at the free surface are various shapes that stretch to accommodate liquid volume (bladder)

Epithelial Tissue: Glandular Glandular tissue: epithelium that makes up glands (secretions) Two types:  Endocrine (ductless glands that secrete hormones directly into the blood stream)  Exocrine (attached to ducts; secretions empty into ducts)