Tissues Groups of cells performing specialized roles

4 Major Tissue Types Epithelial tissue Connective tissue Muscle tissue Nervous tissue

Epithelial tissue Widespread throughout the body Lines all body surfaces inside and out Major tissue of glands Lacks blood supply (avascular) Reproduces quickly Tightly packed—good barriers Control permeability

Classification of Epithelium Tissue 1. Shape of the cells Squamous Cells are thin and flat Often display many angular outlines when viewed from above Cuboidal Cells are approximately as tall as wide Columnar Cells are definitely more taller than wide

2. The number of cell layers present Simple Only one layer of cells All cells touch the basement membrane Stratified There is more than one layer of cells Only the lowest cells rest on the basement membrane Other cells are stacked upon each other in various configuration making up the "layers"

Simple Squamous Epithelium Single layer of thin flattened cells Functions in diffusion Lines air sacs of lungs and blood vessels

Simple Cuboidal Epithelium Single layer of cube shaped cells Covers ovaries, lines ducts of glands, kidney tubules Functions in secretion & absorption

Simple Columnar Epithelium Single layer of elongated cells Functions in protection, absorption & secretion May have microvilli which increase surface area for absorption May have goblet cells scattered among the columnar cells to secrete mucus Lines stomach & intestines

Pseudostratified Columnar Epithelium Appears stratified (layered) but is not Cells may possess cilia (hair-like projections) May have goblet scattered throughout Lines respiratory tract Helps to move mucus

Stratified Squamous Epithelium Many layers of cells thick Cells reproduce in deep layers and push older ones out Forms outer layer of skin (epidermis) Lines mouth, throat, vagina Functions in protection

Transitional epithelium Specialized to undergo changes in response to increased tension Expands and contracts Forms lining of urinary bladder & ureters stratified