Epithelial Tissue Department of Biology, WCU

Introduction Unicellular versus multicellular Tissue definition Tissue types epithelial (skin, villi) connective (between muscles) muscle (skeletal, smooth, cardiac) nervous (CNS, PNS) Histology

Epithelium 1. Covering and lining 2. Glandular skin, pericardium, digestive tract 2. Glandular Mucus, oil, sweat, goblet cells Epithelium forms boundaries Internal, external

Functions of epithelium Protection Absorption Filtration Excretion Secretion Sensory reception

Characteristics of epithelium Cellularity Simple, stratified Cell contacts Tight junction, desmosome, gap junction Polarity Microvilli, flat, rounded

Characteristics of epithelium Innervated but avascular Nutrients and O2 diffuse from blood vessels Regeneration Abrasion (lower GI, skin)

Classification of epithelium 1. Number of cells in layer

Classification of epithelium 2. Shape squamous cuboidal columnar transitional

Simple epithelium Simple squamous diffusion, filtration e.g. lungs, glomerulus of kidney

Simple epithelium Simple cuboidal Secretion and absorption e.g. kidney

Simple epithelium Simple columnar Secretion and absorption e.g. GI tract

Simple epithelium Pseudostratified columnar Secretion and absorption One layer Ciliated (trachea)

Stratified epithelium Stratified squamous most abundant named after cells on surface lining skin, mouth, esophagus

Stratified epithelium Stratified cuboidal ducts of glands

Stratified epithelium Stratified columnar Male urethra, some gland ducts

Stratified epithelium Transitional epithelium Basal cells cuboidal/columnar, apical cells distendable

Surface modifications 1. Microvilli Increase surface area (intestine, kidney brush border)

Surface modifications 2. Cilia Longer than microvilli Unidirectional particle movement (trachea)

Glandular epithelium Cell or group of secreting cells Covering and lining epithelium Secretion water based, contains protein Types exocrine, endocrine

Exocrine glands Numerous e.g. surface - sweat, cavity - intestine Types unicellular: goblet cell

Exocrine glands Types Multicellular Duct and secretory unit Simple- unbranched Compound - branched

Exocrine glands

Exocrine glands Modes of secretion Merocrine (exocytosis) Holocrine (rupturing)

Glands 3. Apocrine - apex of cell pinching Endocrine glands mammary gland Endocrine glands ductless secretions enter blood stream pancreas (insulin and glucagon)