Chapter 4: The Tissue Level of Organization

There are 4 types of tissues – We will only study epithelial now.

Epithelial Tissue  Covers exposed surfaces –Example: The skin  Lines internal passageways –Example: The intestines  Forms glands –Example: Sweat glands

KEY CONCEPT  Tissues are collections of cells and cell products that perform specific, limited functions  4 tissue types form all the structures of the human body: –epithelial, connective, muscle, and neural

Epithelial Tissues  Epithelia: –layers of cells covering internal or external surfaces  Glands: –structures that produce secretions

 What are the special structures and functions of epithelial tissues?

Characteristics of Epithelia 1.Cellularity (cell junctions) 2.Polarity (apical and basal surfaces) 3.Attachment (basal lamina) 4.Avascularity 5.Regeneration

Functions of Epithelial Tissue 1.Provide physical protection 2.Control permeability a. Move fluids over the epithelium (protection) a. Move fluids over the epithelium (protection) b. Move fluids through the epithelium (permeability) b. Move fluids through the epithelium (permeability) 3.Provide sensation 4.Produce specialized secretions (glandular epithelium) a. Produce secretions (protection and messengers) a. Produce secretions (protection and messengers)

Free Surface and Attached Surface  Polarity: –apical and basolateral surfaces

Increasing Surface Area  Microvilli increase absorption or secretion  Cilia (ciliated epithelium) move fluids

Effective Barriers  Physical integrity is maintained by: –intercellular connections –attachment to basal lamina –maintenance and repair

Intercellular Connections  Support and communication

Large Connections  CAMs (cell adhesion molecules): –transmembrane proteins  Intercellular cement:

Cell Junctions  Form bonds with other cells or extracellular material: –tight junctions –gap junctions –desmosomes

Tight Junctions  Between 2 cell membranes

Gap Junctions  Allow rapid communications

Desmosomes  CAMs, dense areas, and intercellular cement

Attachment to Basal Lamina  Hemidesmosomes

Repairing and Replacing Epithelia  Epithelia are replaced by division of germinative cells (stem cells) –Continuous  Near basal lamina

Classes of Epithelia  Based on shape and layers

Layers  Simple epithelium: –single layer of cells  Stratified epithelium: –several layers of cells

Cell Shape  Squamous epithelia: –Thin, flat, irregular shaped (fish scale)  Cuboidal epithelia: –square shaped (cube)  Columnar epithelia: –tall shaped (column)

Simple Squamous Epithelium

Stratified Squamous Epithelium

Cuboidal Epithelia  Simple cuboidal epithelium: Example – Kidney tubules –secretion and absorption

Cuboidal Epithelia  Stratified cuboidal epithelia: Sweat gland ducts –sweat and mammary ducts

Transitional Epithelium  Urinary bladder

Columnar Epithelia  Simple columnar epithelium: Intestinal Lining –absorption and secretion

Columnar Epithelia  Pseudostratified columnar epithelium: Trachea –cilia movement

Columnar Epithelia  Stratified columnar epithelium: Salivary Gland Duct –protection

Glandular Epithelia  Endocrine and exocrine glands

Endocrine Glands  Release hormones: –into interstitial fluid –no ducts

Exocrine Glands  Produce secretions: –onto epithelial surfaces –through ducts

Modes of Secretion – Exocrine Glands  Merocrine secretion

Modes of Secretion  Apocrine secretion

Modes of Secretion  Holocrine secretion

Types of Secretions – Exocrine Glands  Serous glands: –watery secretions  Mucous glands: –secrete mucins  Mixed exocrine glands: –both serous and mucous

Gland Structure – Exocrine Glands  Exocrine glands can be classified as: –unicellular glands –multicellular glands

Unicellular Glands  Goblet cells are the only unicellular exocrine glands: –scattered among epithelia –e.g., in intestinal lining

Structure of Multicellular Exocrine Glands  Structural classes of exocrine glands

Structure of Multicellular Exocrine Glands