Chapter 4: Tissues

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

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 -respiratory tract, digestive tract  Cilia (ciliated epithelium) move fluids -injury to cilia – smoking, abrasion

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  Prevents passage of water and solutes

Gap Junctions  Allow rapid communications  Allows ions and small molecules to pass through  Held together by channel proteins

Desmosomes  CAMs, dense areas, and intercellular cement  Ties cells together, helps to stabilize cell shape

Attachment to Basal Lamina  Hemidesmosomes – half of a desmosome, attaches cell to basal lamina

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

Glandular Epithelia  Endocrine and exocrine glands

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

Exocrine Glands  Produce secretions: –onto epithelial surfaces –through ducts –Tears, milk, enzymes into digestive tract, perspiration on skin

Modes of Secretion – Exocrine Glands  Merocrine secretion – produced in Golgi apparatus, released by vesicles (exocytosis)

Modes of Secretion  Apocrine secretion – produced by Golgi apparatus, released by shedding cytoplasm

Modes of Secretion  Holocrine secretion – released by cells bursting

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