Epithelia Cells

Epithelia Cells Objectives • Define Epithelia Cells • Identify the location of Epithelia Cells • Classify types of Epithelia Cells Epithelial Tissues • Epithelial tissues cover body surfaces. – Outer layer of skin and the lining of organs – Also found in glandular tissue – Play roles in absorption, filtration, secretion, and protection against foreign substances Special Characteristics of Epithelium • Usually fit closely together in continuous sheets • Exception: glandular epithelium • Avascular (Have no blood supply of their own) • How do they get nutrients? • If well nourished, epithelial cells regenerate themselves easily. Special Characteristics of Epithelium • Have one free (unattached) surface or edge called the apical surface – Exposed to body’s exterior or to the cavity of an internal organ • Lower surface of an epithelium rests on a basement membrane – Structureless material secreted by both the epithelial cells and the connective tissue cells Classification of Epithelium • Each epithelium is given 2 names • First: indicates relative number of cell layers – Simple (one layer of cells) – Stratified (more than one cell layer) Classification of Epithelium • Second: describes the shape of cells – Squamous (cells flattened like scales) – Cuboidal (cube-shaped) – Columnar (shaped like columns) Simple Squamous Epithelium •Simple squamous (SS) tissue is composed of flat, scale-like cells that usually forms membranes •It lines the walls of blood vessels, pulmonary alveoli (shown here), and the lining of the heart, lung, and peritoneal cavities. Simple Cuboidal Epithelium •This tissue is composed of a single layer of cubelike cells. •It lines the walls of kidney tubules, covers the surface of ovaries, and is common in glands and their ducts. Simple Columnar Epithelium • This tissue is composed of a single layer of tall cells. • It often includes mucus-producing goblet cells. • It often lines the digestive tract. Pseudostratified Columnar Epithelium • Although this tissue appears stratified, it is actually composed of a single layer of cells of different types. • Although their nuclei are found at different levels, each cell adjoins the basal membrane (BM). • This tissue lines the larger respiratory passageways. • It is often ciliated (arrows). Pseudostratified Columnar Epithelium • Main functions: absorption and secretion • Ciliated variety lines respiratory tract – Mucus produced by goblet cells traps dust and other debris – Cilia propel mucus upward and away from the lungs Stratified Squamous Epithelium • The term “stratified” refers to the layered arrangement of cells. • The outer layers of cells appear flat, but the inner cells vary in shape from cuboidal to columnar. • Stratified squamous epithelium serves as a barrier to the outside environment in locations such as the skin, mouth, and esophagus. Stratified Cuboidal Epithelium • Stratified cuboidal epithelium (SC) is found in the ducts of sweat glands and surrounds Graafian follicles of ovaries (shown below). Transitional Epithelium • Shape of cells depends upon the amount of stretching • It lines organs of the urinary system. Ciliated Epithelium • Some epithelial membranes are made up of cells with cilia, tiny projections that beat in unison to move mucus along the surface. • Ciliated epithelia in the trachea, for example, sweep debris out of the respiratory tract. Glandular Epithelium • A gland is defined as one or more cells responsible for secreting a particular product • Two major gland types – Endocrine gland • Ductless since secretions diffuse into blood vessels • All secretions are hormones • Examples include pituitary, pancreas, ovaries, testes – Exocrine gland • Secretions empty through ducts to the epithelial surface • Include sweat and oil glands