chapter 4.1: tissues. epithelial tissue epithelia—layers of cells that cover internal or external...

Chapter 4.1: Tissues

Epithelial Tissue Epithelia—layers of cells that cover internal or

external surfaces Glands—secreting cells of epithelia Characteristics Cells very close together Apical surface—exposed to

outside/environment Basement membrane—attaches epithelia to

connective tissue Avascular—no blood vessels Continually replaced

Figure 4.3a

Functions of Epithelia Protection from abrasion and dehydration Controls permeability Sensation (especially touch) Secretions Exocrine—secrete onto surface Endocrine—secrete into blood Ex: Hormones—regulate and coordinate

Intracellular Connections Cell Adhesion Molecules (CAMS) Hold together epithelial cells Cell Junction—where 2 cells meet Tight Junction—tightly bound No passage of water/solutes Ex: Stomach—prevent HCl acid from harming body Gap Junction—forms channel between cells Allows small molecules and ions to pass Ex: Cardiac and Smooth muscles Desmosome—bendable connection Ex: Skin

Figure 4.2

Figure 4.2c

Figure 4.2d

Epithelial Surface Microvilli Increase surface area by 20x Cilia Beat together to move substances forward

Figure 4.3b

Epithelial Renewal and Repair Stem cells—unspecialized cells Found near basement membrane

Cell Layers Simple Epithelium—one layer of cells Thin and fragile Line internal compartments Good for secretion and absorption Stratified Epithelium—2 or more layers of cells Surface of skin