Epithelial Tissues م. م. فاطمة سوادي زغير

General Features: Minimum extracellular material. Maximum cell-to-cell contact. Minimum extracellular material. Cell junctions: Several types of junctional specializations unite adjacent epithelial cells (tight junctions, desmosomes and gap junctions). Supported by basement membrane (basal lamella). Avascular: There are no blood vessels within the epithelial layer. Derived from all embryonic germ layers, including endoderm, mesoderm and ectoderm

Classification of Epithelium Number of layers of cells Simple- one layer of cells. Each extends from basement membrane to the free surface Stratified- more than one layer. Pseudostratified- tissue appears to be stratified, but all cells contact basement membrane so it is in fact simple Shape of cells Squamous- flat, scale-like Cuboidal- about equal in height and width Columnar- taller than wide

Classifications of Epithelia

Simple squamous epithelium a single layer of thin, flattened cells look like a fried egg easily damaged common at sites of filtration, diffusion, osmosis; cover surfaces air sacs of the lungs, walls of capillaries, linings of blood and lymph vessels

Simple Squamous Epithelium Figure 4.3a

Simple cuboidal epithelium single layer of cube-shaped cells centrally located nucleus secretion and absorption surface of ovaries, linings of kidney tubules, and linings of ducts of certain glands

Simple Cuboidal Epithelium Figure 4.3b

Simple columnar epithelium single layer of cells that are longer than they are wide nucleus located near basement mem. ciliated or non ciliated some have microvilli goblet cells = secrete mucus absorption, secretion, protection linings of the uterus, stomach, and intestine

Simple Columnar Epithelium Figure 4.3c

Pseudostratified columnar epithelium appear stratified , nuclei are at 2 or more levels NOT stratified b/c all cells touch basement membrane. ciliated goblet cells protection, secretion, movement of mucus linings of respiratory system

Pseudostratified Ciliated Columnar Epithelium Figure 4.3d

Stratified Epithelia Contain two or more layers of cells Regenerate from below Major role is protection Are named according to the shape of cells at apical layer

Stratified squamous epithelium many layers of flattened cells named based on appearance of top layer of cells protection outer layers of skin, linings of oral cavity, throat, vagina, and anal canal Location Keratinized – forms epidermis Non-keratinized – forms lining of esophagus, mouth, and vagina

Stratified Squamous Epithelium Specific types Keratinized – contain the protective protein keratin Surface cells are dead and full of keratin Non-keratinized – forms moist lining of body openings

Stratified Squamous Epithelium Figure 4.3e

Stratified cuboidal epithelium 2 or 3 layers of cuboidal cells protection linings of larger ducts of mammary glands, sweat glands, salivary glands, and pancreas

Stratified columnar epithelium protection and secretion vas deferens, part of the male urethra, parts of the pharynx (throat)

Transitional Epithelium Figure 4.3h