Chapter 4: The Tissue Chapter 4: The Tissue

Level of OrganizationLevel of Organization

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

Epithelial TissueEpithelial Tissue

Covers exposed surfacesCovers exposed surfaces– ExamExample: ple: The skinThe skin

Lines internal passageways Lines internal passageways – Example: Example: The intestinesThe 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

What are the special structures and What are the special structures and functions functions

of epithelial tissues?of epithelial tissues?

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 CiliaCilia (ciliated epithelium) move fluids (ciliated epithelium) move fluids

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

Gap JunctionsGap Junctions

Allow rapid Allow rapid communicationscommunications

DesmosomesDesmosomes

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

Attachment to Basal LaminaAttachment to Basal Lamina

HemidesmosomesHemidesmosomes

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

Classes of EpitheliaClasses of Epithelia

Based on shape and layersBased on shape and layers

LayersLayers

Simple epitheliumSimple epithelium: : – single layer of cellssingle layer of cells

Stratified epitheliumStratified epithelium::– several layers of cellsseveral layers of cells

Cell ShapeCell Shape

Squamous epitheliaSquamous epithelia::– Thin, flat, irregular shaped (fish scale)Thin, flat, irregular shaped (fish scale)

Cuboidal epitheliaCuboidal epithelia::– square shaped (cube)square shaped (cube)

Columnar epitheliaColumnar epithelia::– tall shaped (column)tall shaped (column)

Simple Squamous EpitheliumSimple Squamous Epithelium

Stratified Squamous EpitheliumStratified Squamous Epithelium

Cuboidal EpitheliaCuboidal Epithelia

Simple cuboidal epithelium: Example – Kidney tubulesSimple cuboidal epithelium: Example – Kidney tubules– secretion and absorptionsecretion and absorption

Cuboidal EpitheliaCuboidal Epithelia

Stratified cuboidal epithelia: Sweat gland ductsStratified cuboidal epithelia: Sweat gland ducts– sweat and mammary ductssweat and mammary ducts

Transitional EpitheliumTransitional Epithelium

Urinary bladderUrinary bladder

Columnar EpitheliaColumnar Epithelia

Simple columnar epithelium: Intestinal LiningSimple columnar epithelium: Intestinal Lining– absorption and secretionabsorption and secretion

Columnar EpitheliaColumnar Epithelia

Pseudostratified columnar epithelium: TracheaPseudostratified columnar epithelium: Trachea– cilia movementcilia movement

Columnar EpitheliaColumnar Epithelia

Stratified columnar epithelium: Salivary Gland DuctStratified columnar epithelium: Salivary Gland Duct– protectionprotection

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

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

Merocrine secretionMerocrine secretion

Modes of SecretionModes of Secretion

Apocrine secretionApocrine secretion

Modes of SecretionModes of Secretion

Holocrine secretionHolocrine secretion

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