Chapter 4: Tissues Chapter 4: Tissues

Epithelial TissueEpithelial Tissue

Covers exposed surfacesCovers exposed surfaces– Example: The skinExample: The skin

Lines internal passageways Lines internal passageways – Example: The intestinesExample: The intestines

Forms glandsForms glands– Example: Sweat glandsExample: Sweat glands

KEY CONCEPTKEY CONCEPT

Tissues are collections of cells and cell Tissues are collections of cells and cell products that perform specific, limited products that perform specific, limited functionsfunctions

4 tissue types form all the structures of the 4 tissue types form all the structures of the human body: human body: – epithelial, connective, muscle, and neuralepithelial, connective, muscle, and neural

Epithelial TissuesEpithelial Tissues

EpitheliaEpithelia: : – layers of cells covering internal or external layers of cells covering internal or external

surfacessurfaces

GlandsGlands: : – structures that produce secretionsstructures that produce secretions

Characteristics of EpitheliaCharacteristics of Epithelia

1.1. Cellularity (Cellularity (cell junctionscell junctions))

2.2. Polarity (Polarity (apicalapical and and basalbasal surfaces) surfaces)

3.3. Attachment (Attachment (basal laminabasal lamina))

4.4. Avascularity Avascularity

5.5. RegenerationRegeneration

Functions of Epithelial TissueFunctions of Epithelial Tissue

1.1. Provide physical protectionProvide physical protection

2.2. Control permeabilityControl permeability a. Move fluids a. Move fluids overover the epithelium (protection) the epithelium (protection)

b. b. Move fluids Move fluids throughthrough the epithelium (permeability) the epithelium (permeability)

3.3. Provide sensationProvide sensation

4.4. Produce specialized secretions (Produce specialized secretions (glandular glandular epitheliumepithelium))

a. Produce a. Produce secretionssecretions (protection and messengers) (protection and messengers)

Free Surface and Free Surface and Attached SurfaceAttached Surface

Polarity:Polarity: – apical and apical and

basolateral basolateral surfacessurfaces

Increasing Surface AreaIncreasing Surface Area

MicrovilliMicrovilli increase absorption or secretion increase absorption or secretion

-respiratory tract, digestive tract-respiratory tract, digestive tract CiliaCilia (ciliated epithelium) move fluids (ciliated epithelium) move fluids

-injury to cilia – smoking, abrasion-injury to cilia – smoking, abrasion

Effective BarriersEffective Barriers

Physical integrity is maintained by:Physical integrity is maintained by:– intercellular connectionsintercellular connections– attachment to basal laminaattachment to basal lamina– maintenance and repairmaintenance and repair

Intercellular ConnectionsIntercellular Connections

Support and Support and communicationcommunication

Large ConnectionsLarge Connections

CAMsCAMs (cell adhesion molecules): (cell adhesion molecules):– transmembrane proteinstransmembrane proteins

Intercellular cementIntercellular cement

Cell JunctionsCell Junctions

Form bonds with other cells or extracellular Form bonds with other cells or extracellular material:material:– tight junctionstight junctions– gap junctionsgap junctions– desmosomesdesmosomes

Tight JunctionsTight Junctions

Between 2 cell Between 2 cell membranesmembranes

Prevents passage Prevents passage of water and solutesof water and solutes

Gap JunctionsGap Junctions

Allow rapid Allow rapid communicationscommunications

Allows ions and Allows ions and small molecules to small molecules to pass throughpass through

Held together by Held together by channel proteinschannel proteins

DesmosomesDesmosomes

CAMsCAMs,, dense dense areasareas, and , and intercellular intercellular cementcement

Ties cells Ties cells together, together, helps to helps to stabilize cell stabilize cell shapeshape

Attachment to Basal LaminaAttachment to Basal Lamina

Hemidesmosomes – half of a desmosome, Hemidesmosomes – half of a desmosome, attaches cell to basal laminaattaches cell to basal lamina

Repairing and Repairing and Replacing EpitheliaReplacing Epithelia

Epithelia are replaced by division of Epithelia are replaced by division of germinative cellsgerminative cells ( (stem cellsstem cells))– Continuous Continuous

Near Near basal laminabasal lamina

Glandular EpitheliaGlandular Epithelia

EndocrineEndocrine and and exocrineexocrine glands glands

Endocrine GlandsEndocrine Glands

Release hormones:Release hormones:– into into interstitial fluidinterstitial fluid– no ductsno ducts

Exocrine GlandsExocrine Glands

Produce secretions:Produce secretions:– onto onto epithelial surfacesepithelial surfaces– through through ductsducts– Tears, milk, enzymes into digestive tract, Tears, milk, enzymes into digestive tract,

perspiration on skinperspiration on skin

Modes of Secretion – Exocrine Modes of Secretion – Exocrine Glands Glands

Merocrine secretion – produced in Golgi Merocrine secretion – produced in Golgi apparatus, released by vesicles (exocytosis)apparatus, released by vesicles (exocytosis)

Modes of SecretionModes of Secretion

Apocrine secretion – produced by Golgi apparatus, Apocrine secretion – produced by Golgi apparatus, released by shedding cytoplasmreleased by shedding cytoplasm

Modes of SecretionModes of Secretion

Holocrine secretion – released by cells burstingHolocrine secretion – released by cells bursting

Types of Secretions – Exocrine Types of Secretions – Exocrine GlandsGlands

Serous glandsSerous glands::– watery secretionswatery secretions

Mucous glandsMucous glands::– secrete mucinssecrete mucins

Mixed exocrine glandsMixed exocrine glands::– both serous and mucousboth serous and mucous

Gland Structure – Exocrine GlandsGland Structure – Exocrine Glands

Exocrine glands can be classified as:Exocrine glands can be classified as:– unicellular unicellular glandsglands– multicellularmulticellular glands glands

Unicellular GlandsUnicellular Glands

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

Structure of Multicellular Exocrine Structure of Multicellular Exocrine GlandsGlands

Structural classes of exocrine glandsStructural classes of exocrine glands

Structure of Multicellular Exocrine Structure of Multicellular Exocrine GlandsGlands