Chapter 4: The Tissue

Level of Organization

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

Epithelial TissueCovers exposed surfacesExample: The skinLines internal passageways Example: The intestinesForms glandsExample: Sweat glands

KEY CONCEPTTissues are collections of cells and cell products that perform specific, limited functions4 tissue types form all the structures of the human body: epithelial, connective, muscle, and neural

Epithelial TissuesEpithelia: layers of cells covering internal or external surfacesGlands: structures that produce secretions

What are the special structures and functions of epithelial tissues?

Characteristics of EpitheliaCellularity (cell junctions)Polarity (apical and basal surfaces)Attachment (basal lamina)Avascularity Regeneration

Functions of Epithelial TissueProvide physical protectionControl permeability a. Move fluids over the epithelium (protection) b. Move fluids through the epithelium (permeability)Provide sensationProduce specialized secretions (glandular epithelium) a. Produce secretions (protection and messengers)

Free Surface and Attached SurfacePolarity: apical and basolateral surfaces

Increasing Surface AreaMicrovilli increase absorption or secretionCilia (ciliated epithelium) move fluids

Effective BarriersPhysical integrity is maintained by:intercellular connectionsattachment to basal laminamaintenance and repair

Intercellular ConnectionsSupport and communication

Large ConnectionsCAMs (cell adhesion molecules):transmembrane proteinsIntercellular cement:

Cell JunctionsForm bonds with other cells or extracellular material:tight junctionsgap junctionsdesmosomes

Tight JunctionsBetween 2 cell membranes

Gap JunctionsAllow rapid communications

DesmosomesCAMs, dense areas, and intercellular cement

Attachment to Basal LaminaHemidesmosomes

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

Classes of EpitheliaBased on shape and layers

LayersSimple epithelium: single layer of cellsStratified epithelium:several layers of cells

Cell ShapeSquamous epithelia:Thin, flat, irregular shaped (fish scale)Cuboidal epithelia:square shaped (cube)Columnar epithelia:tall shaped (column)

Simple Squamous Epithelium

Stratified Squamous Epithelium

Cuboidal EpitheliaSimple cuboidal epithelium: Example Kidney tubulessecretion and absorption

Cuboidal EpitheliaStratified cuboidal epithelia: Sweat gland ductssweat and mammary ducts

Transitional EpitheliumUrinary bladder

Columnar EpitheliaSimple columnar epithelium: Intestinal Liningabsorption and secretion

Columnar EpitheliaPseudostratified columnar epithelium: Tracheacilia movement

Columnar EpitheliaStratified columnar epithelium: Salivary Gland Ductprotection

Glandular EpitheliaEndocrine and exocrine glands

Endocrine GlandsRelease hormones:into interstitial fluidno ducts

Exocrine GlandsProduce secretions:onto epithelial surfacesthrough ducts

Modes of Secretion Exocrine Glands Merocrine secretion

Modes of SecretionApocrine secretion

Modes of SecretionHolocrine secretion

Types of Secretions Exocrine GlandsSerous glands:watery secretionsMucous glands:secrete mucinsMixed exocrine glands:both serous and mucous

Gland Structure Exocrine GlandsExocrine glands can be classified as:unicellular glandsmulticellular glands

Unicellular GlandsGoblet cells are the only unicellular exocrine glands:scattered among epitheliae.g., in intestinal lining

Structure of Multicellular Exocrine GlandsStructural classes of exocrine glands

Structure of Multicellular Exocrine Glands

Histology the study of tissuesCellularity tightly packed cellsPolarity top and bottomAvascular no blood vessels

Physical protection =abrasion, dehydration, destruction from chemicals or biological agentsPassive = without energyActive = with energyPermiability can be affected by hormones or stress (calluses)Sensation = large sensory nerve supplyProtection = surfaceMessengers = surrounding interstitial fluid and bloodApical = exposed surfaceBasolateral = base and sides of cell to cellExample=lining the respiratory tract mucous from lungs and toward the throatInjury to cilia = smoking, abrasionIn order for epithelium to be a barrier it must have a complete coveringAdhesion belt attaches to terminal webPrevents passage of water and solutes Isolates wastes in the lumen- the space inside a tube, Example- keep waste, digestive juices, enzymes, acids from leaving the digestive tract and entering other tissue where it would cause damage.

Held together by channel proteins (junctional proteins, connexons)Allow ions and small molecules to pass Coordinated contractions in heart muscle

Button desmosomes small discs =stabilize cell shapeTies cells together Allow bending and twisting, stretching, and compressionGet strength from dense areaSuperficial area of skin has lots of dense desmosomes = peeling from a sunburn comes off in sheetsHemidesmosomes = half of a desmosome = attach cell to basal laminaHemidesmosomes = half of a desmosome = attach cell to basal laminaHemidesmosomes = half of a desmosome = attach cell to basal lamina

Lamina lucida: thin layer secreted by epitheliabarrier to proteinsLamina densa: thick fibersproduced by connective tissuestrength and filtration

Protects against attacksKeratin proteins add strength and water resistance

Tolerates repeated cycles of stretching and recoil without damageRelease into bloodstreamExamples = thyroid and pituitaryExamples=tears, milk, enzymes into the digestive tract, perspiration on the skinAre produced in Golgi apparatusAre released by vesicles (exocytosis) Most commonMucous salivary glandse.g., sweat glands

Are produced in Golgi apparatusAre released by shedding cytoplasme.g., mammary gland

Are released by cells bursting, killing gland cellsGland cells replaced by stem cellse.g., sebaceous gland hair follicles oily hair coatingStructure of the duct:simple (undivided)compound (divided) Shape of secretory portion of the gland:tubular (tube shaped)alveolar (blind pockets)acinar (chamberlike)Relationship between ducts and glandular areas:branched (several secretory areas sharing 1 duct)