2013 histology review-1

7/30/2019 2013 Histology Review-1

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NATIONAL BOARD

HISTOLOGY REVIEW

DEN 6416C 2012


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MEMBRANE-BOUND ORGANELLESNucleus euchromatin (active), heterochromatin (silent)

Mitochondrion inner membrane folded into cristae, increaseSA, produce ATP and heat, oxidize fatty acids (muscle cells,hepatocytes cells that require lots of energy)

Lysosome contains hydrolytic enzymes, acidic interior

Peroxisome forms and utilizes hydrogen peroxide, catalase,

involved in lipid synthesis (e.g. hepatocytes)Smooth ER lipid synthesis, transport & storage, detox. ofmetabolites, hormones & drugs, Ca2+ storage/release (steroidhormone-producing cells)

Rough ER ribosomes attached to cytoplasmic face of

cisternae, protein synthesis and modification, entrance tosecretory pathway

Golgi apparatus polarized, modifies, packages & sortsmaterials from rER intracellular use or secretory vesicles


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NON MEMBRANE-BOUND STRUCTURES

Nucleolus ribosomal RNA synthesis

Ribosome large and small subunits, assemble into functionalribosome outside nucleus, fixed (to rER) or free (synthesizeintracellular components, e.g. cytoskeletal protein subunits)

Lipid droplet energy storage depot, large unilocular (white fat)

or small multilocular (brown fat)

CELL SURFACE MODIFICATIONS

Microvilli core of actin microfilaments, anchor into terminal

web, inc. SA for absorption (e.g. small intestine)

Cilia - core of microtubules, may be motile (e.g. conductingportion of respiratory tract)

Stereocilia core of actin, found in male reproductive tract


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Simple

Squamous Cuboidal Columnar

Stratified

Pseudostratified

Relaxed Distended

EPITHELIUM

Transitional(Respiratory-

pseudostrat.

ciliated with

goblet cells)

(Urinary)


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EPITHELIUMSkin stratified squamous keratinized epithelium

(stratum basale stem cells,spinosum stellate, lamellar

bodies, desmosomes, granulosum keratohyaline granules,

breakdown of organelles begins, lucidum breakdown of

nuclei and organelles complete, corneum anuclear flattened

bags of keratin)

Mucosa of vestibule, alveolar mucosa, interdental papilla, soft

palate - stratified squamous NON- keratinized epithelium

Mucosa of hard palate, free gingiva and attached gingiva -

stratified squamous keratinized / parakeratinized (also known

as orthokeratinized epithelium)

Stratified protection Keratinized waterproofing

(Esophagus stratified squamous non-keratinized epithelium,

rest of digestive tract simple columnar epithelium)


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GLANDSExocrine secrete onto free surface

Sebaceous gland Mammary gland Pancreas

Goblet cell unicellular gland, multicellular glands havegroups of cells (acini) secreting into ducts

Endocrine secrete into blood stream


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CONNECTIVE TISSUE COMPONENTSCELLS: fibroblasts

immunevascular

EXTRACELLULAR MATRIX:

Fibers - collagen, elastic,reticular (type III

collagen)

Ground substance -glycosaminoglycans

proteoglycans

adhesive proteins

Tissue fluid

LOOSEconnective tissue many cells, few large bundles offibers (e.g. lamina propria of intestine, papillary dermis of skin)

DENSEconnective tissue appear to be fewer cellsinterspersed between larger bundles of fibers ( IRREGULAR

reticular dermis of skin; REGULAR tendon, ligament)


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COLLAGEN

Most abundant protein in body, can be fibrillar or non-fibrillar Fibers are flexible, unbranched and have very high tensile

strength (> stainless steel). They consist of bundles of threadlike

fibrils bound together by non-fibrillar collagen and proteoglycans

Fibrils are composed of arrays oftropocollagen building blocks.Tropocollagen consists of three chains (same or different)intertwined to form a triple helix

chains consist of repeating amino acid triplets: Gly-X-Y (left).X & Y are commonly proline, hydroxyproline or hydroxylysine. -chains are modified and then assemble into procollagen

molecules within rER

Procollagen is secreted - ends are cleaved extracellularly byprocollagen peptidases to form mature tropocollagen

Tropocollagen molecules cross-link in a staggered arrayresulting in a 68nm periodicity


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ELASTIN

Long (~750 a.a.), hydrophobic protein rich in glycine andproline - favor a compact folded conformation

Synthesized and secreted asproelastin,cleaved totropo-elastinin extracellular space

Contains uniquedesmosine & isodesmosineresiduesformed by covalent bonds between 4 lysines from different

elastin chains

Deposited initially within scaffoldings of microfibrils(composed largely of fibrillins) called oxytalan fibers.(Marfans syndrome fibrillin mutation)

As tropoelastin is deposited, elaunin fibers are formed. As elastin accumulates and occupies the center of the

elaunin fiber, an elastic fiber is formed.

Elastin can occur as discrete, thin, branching fibers or asfenestrated sheets (lamellae) in the walls of large vessels

(e.g. aorta)


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Fibroblasts(inc. reticular cells) synthesize procollagen and

proelastin and ground substance components

Adipocytes - specialized for storage and release of energy

Macrophages -differentiate from monocytes, phagocytose &

destroy dead cells & other foreign material, present antigens toplasma cells for antibody production

Plasma cells not present in blood, differentiate from B

lymphocytes, synthesize and secrete antibodies

Mast cells many large granules containing histamine, growth

and inflammatory factors, heparin, and other proteins.

Degranulation triggered by antigens, leads to vasodilation, inc.

vascular permeability, bronchiolar constriction, attraction of

other WBC

RESIDENT CONNECTIVE TISSUE CELLS


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Neutrophil most common WBC in blood, multilobed nucleus,

neutral-staining specific granules, survive 1 - 4 days in CT,

phagocytose bacteria, when dead form pus

Eosinophil bilobed nucleus, eosinophilic (red) specific

granules, release major basic protein which targets walls of

parasites, phagocytose and destroy antigen-antibody complexes

Basophil least common WBC, basophilic (blue) specific

granules, secrete heparin and histamine that initiate, maintain

and control inflammation

Lymphocyte large nucleus, little cytoplasm, no visible

granules, involved in innate and specific immune responses,

many different types (B cells give rise to plasma cells)

TRANSIENT CONNECTIVE TISSUE CELLS


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CARTILAGESurrounded by a perichondrium, matrix secreted bychondroblasts, mature cells (chondrocytes) are surrounded bymatrix. Cells sit in spaces called lacunae. Cells are arranged inisogenous groups. Grows appositionally and interstitially.Avascular & aneural.

Hyaline most common, found in mostjoints, growth plates & tracheal rings,collagen type II, smooth glassy matrix

Elastic found in pinna of ear andepiglottis, contains collagen type II,many elastic fibers

Fibro - intermediate between denseirregular CT and hyaline cartilage, containscollagen types Iand II, no perichondrium,Forms disc and covers articular surfaces ofTMJ, found in IV discs, pubic symphysis


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BONECompact (outer) and spongy (inner, trabecular) bone. Surroundedby a periosteum (many cell layers), lined by endosteum (single cell

layer). Grows only appositionally. Can form intramembraneously(from mesenchyme) orendochondrally (erosion of a cartilagemodel and deposition of bone).


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COMPACT BONE

Arranged incylindricalunits (calledosteons orHaversian

systems) ofconcentriclamellae ofmineralizedmatrix andosteocytessitting inlacunae.

Central canals (Haversian canals) contain blood vessels, nerves

and lymphatics and are lined by endosteum.


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BONE CELLS

OSTEOPROGENITOR cells derived from mesenchyme,differentiate into osteoblasts, comprise the inner layer of theperiosteum and line Haversian canals and medullary cavity(endosteum)

OSTEOBLASTS synthesize and secrete organic

components of bone matrix, found adjacent to matrix theyhave secreted

OSTEOCYTES individual mature bone cells that reside inlacunae (no cell nests/isogenous groups), surrounded bymatrix, cells processes sit in canaliculi allow for

communication between, and nourishment of, cells

OSTEOCLASTS - large, motile, multinucleate cells, derivedfrom monocytes, lie close to bone in Howships lacunae,involved in bone resorption


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ENDOCHONDRAL OSSIFICATION

Resting / reserve zone

Zone of proliferation

Zone of hypertrophy

Zone of calcification

Zone of vascular invasionEpiphyseal

plate


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SKELETAL MUSCLE ORGANIZATIONEach skeletal muscle has

thousands of fibers huge,long multinucleate cells

formed by the fusion of

hundreds of embryonic

cells.

Each fiber is surroundedby a fine connective

tissue sheath called

ENDOMYSIUM.

Several fibers are groupedtogether in a fascicle by

collagenous PERIMYSIUM.

Fascicles are bound by a dense fibrous connective tissue layer

called EPIMYSIUM.


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1 SKELETALMUSCLE FIBER = 1 CELLSkeletal muscle fibers

contain MYOFIBRILS,long rods which fill 80%

of the sarcoplasm.

Myofibrils are long rows

of repeating contractilesegments called

SARCOMERES.

Sarcomeres - are

composed of regular

arrays of thin (actin)

and thick (myosin)

filaments whose

calcium-dependent

interaction is the basis

of contraction


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INTERACTION BETWEEN ACTIN AND MYOSIN


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SKELETAL MUSCLE CONTRACTION1. Nerve impulse travels down axon, Ach is released into the

synaptic cleft, binds to receptors on the sarcolemmacausing voltage gated Na+ channels to open & Na+ toenter the muscle cell

2. Depolarization is passed via t-tubules (sarcolemmainfoldings) to the sarcoplasmic reticulum resulting in therapid release of Ca2+

3. Ca2+ binds to the TnC subunit of the troponin complex

a) Troponin shifts tropomyosin deeper into groove, exposingthe myosin binding site on actin

b) the ADP-Pi-myosin complex binds to active site on actin

c) Pi is released

d) myosin has conformational change and actin is pulledtoward M-line, releasing ADP

e) ATP binds to myosin releasing it from actin

f) ATP hydrolyzed into ADP and Pi

4. Ca2+

is sequestered into the sarcoplasmic reticulum


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CARDIAC MUSCLEStriated, involuntary, centrally

located nuclei. Fibers are short,fat, branched and interconnected.

Cells are linked by intercalated

discs, function as a syncytium.

Purkinje fibers large, rich in glycogen & mitochondria,

responsible for conducting contractile impulses

INTERCALATED DISC

Longitudinal portion Gapjunctions and desmosomes

Transverse portion Fascia

adherens and desmosomes


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CONTRACTION OF SMOOTH MUSCLE


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NERVE

EPINEURIUM

CT sheatharound several

fascicles of

axons

PERINEURIUMthin, protective

CT sheath

around each

fascicle

ENDONEURIUM

delicate

strands of CT

between

individual axons


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SCHWANN CELLS, NODES OF RANVIER

& SCHMIDT-LANTERMAN CLEFTS

External lamina


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AXONAL TRANSPORT

Internal transport system designed to move materialssynthesized in cell body (neurotransmitters, proteins)

Transport occurs along microtubules and requires motorproteins (kinesins, dyneins)

microtubule

Anterograde

Retrograde

ANTEROGRADE & RETROGRADE TRANSPORT


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CONDUCTING & RESPIRATORY

PORTIONS OF THE RESPIRATORY TREE


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Alveoli

(surrounded byfine elastic fibers)

Bronchus (cartilage

& smooth muscle in

wall, )

Bronchiole ( no

cartilage, just

smooth muscle in

wall, lined withciliated cells &

Clara cells)

Terminal bronchiole

Respiratory

bronchiole

(alveoli off walls)

Alveolar duct

Alveolarcapillarynetwork


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CELLS LINING BRONCHIOLES

Ciliatedcell

Basalcell

Clara

cell

Clara (bronchiolar) cells columnar cells with domedapices and short blunt microvilli. Apical cytoplasm filled

with secretory granules containing surfactant-like material

that reduces surface tension and faciliates patency of

bronchioles. Cells also degrade inhaled toxins.


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Resp. bronchiole

Alveolar duct

Alveolar sac

RESPIRATORY REGION OF THE LUNGSmooth muscle

Alveolus

Type II

Type I cells (squamous alveolar cells) - highly attenuated, cover 97% ofsurface area of alveoli, basement membrane fuses with that of endothelial cell

to minimize thickness of respiratory membrane.Type II cells (septal cells) account for 60% of alveolar cells but only 3% ofsurface area, produce surfactant that lowers alveolar surface tension, divideto form new Type II and type I cells.

Alveolar macrophages (dust cells) derived from monocytes

Type I


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NASAL CAVITY & PARANASAL AIR SINUSES

Respiratory area -pseudostratifiedciliated columnar epithelium with goblet

cells, highly vascularized

Olfactory area(roof of nasal cavity and superior concha)

olfactory epithelium specialized bipolar (sensory) neurons with

sustentacular (supporting) cells and basal cells (stem cells)

SAGITTAL VIEW CORONAL VIEW

O

R


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OLFACTORY EPITHELIUM

Olfactory cells bipolar neurons, apical dendrite ends in olfactoryvesicle from which non-motile cilia with receptors for odiferous

substances arise. When a threshold level of receptors are occupied anaction potential is generated and transmitted to the olfactory bulb viaaxon which passes through cribiform plate to synapse in olfactory bulb.Sustentacular cells tall columnar cells with microvilli. Providephysical support, nourishment & electrical insulation for olfactory cells.Basal cells stem cells to replace olfactory and sustentacular cells.Bowman

s glands provide serous fluid to refresh olfactory cilia.

Olfactory cell

Sustentacular

cell

Bowmansgland

Dendrite

Olfactory vesicle

Basal cell

Olfactory cilia


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CA

RDIO

VASCULA

R

VEINS ARTERIES

CAPILLARIES


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BLOOD VESSELSElastic arteries large arteries (e.g. aorta), have sheets /lamellae of elastin synthesized by smooth muscle cells in

their tunica media

Muscular arteries regulate blood flow to organs, mediamainly comprised of smooth muscle but have prominentinternal and external elastic lamellae (KNOW CELIAC

TRUNK)

Arterioles 1- 3 layers of smooth muscle in walls, regulateflow to capillary beds and modulate pressure

Capillaries sites of exchange, may be continuous orfenestrated

Veins have valves to prevent backflow, large lumenrelative to wall thickness, little muscle in tunica mediacompared to companion arteries, tunica adventitia is mostprominent layer (KNOW VEINS OF UPPER LIMB)


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BLOOD COMPONENTSAll leukocytes have primary granules (lysosomes)Granulocytes have secondary granules (neutrophils,eosinophils, basophils)

Neutrophil most common, multilobed nucleus, secretemyeloperoxidase, form pus

Eosinophil - major basic protein makes holes in walls ofparasites, ingest antigen-antibody complexesBasophil rare, histamine (vasodilation, bronchioleconstriction), heparin (anticoagulant) , leukotrienes

Lymphocyte T-cells (thymus), B-cells (bone marrow,plasma cells) NK cells destroy virus-infected /

transformed cellsMonocyte only found in blood, transform intomacrophages in tissues

Platelets (thrombocytes) fragments of megakaryocytes,adhere and aggregate on exposed CT surfaces, contribute

to clot, removed by plasmin


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REPRODUCTION

All follicles arrested inprophase I until just beforeovulation one completes

meiosis I and is released

from Graafian follicle

Empty Graafian folliclebecomes corpus luteum

Degenerating follicle iscalled atretic follicle

Zona pellucida glycoprotein surroundingoocyte through which spermmust penetrate to fertilize

ovum


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REPRODUCTION

Male germ cellsprogress from

spermatogonia to

spermatocytes to

spermatids to

spermatozoa.Sertoli cellssupport germ

cells, form bloodtestis barrier

Leydig cells insurrounding CT

producetestosterone


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BASIC STRUCTURE OF DIGESTIVE TRACT

WALL

Layers: mucosa, submucosa, muscularis, serosa/adventitia

Each region has identifying characteristics related to function

()

Mucosa

Mucosa

Subucosa

Muscularis

ExternaAdventitia


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OESOPHAGUS


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CELLS OF STOMACH EPITHELIUM

(HCl, intrinsicfactor)

(pepsinogen)


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CELLS OF STOMACH EPITHELIUM

MUCOUS CELLS - surface mucous cells and mucous neckcells, large mucous cup at apical surface of cells, mucous

protects epithelium from low pH and pepsin in stomach lumen

PARIETAL (oxyntic) CELLS - produce HCl and intrinsic factor

(vitamin B12 absorption), many mitochondria, intracellular

canaliculi

CHIEF (zymogenic) CELLS - secrete pepsinogen (inactive

precursor), which is converted into pepsin (acid protease) by

low pH. Also secrete rennin and gastric lipase.

ENTEROENDOCRINE (APUD,DNES) CELLS - secrete gastrin

(stimulates parietal cells) & glucagon (stimulates glucose

release from liver). Located throughout epithelium of GI tract

and secrete different hormones in different locations


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AMPLIFICATION OF ABSORPTIVE

SURFACE OF SMALL INTESTINE

PLICAE CIRCULARES transverse folds of mucosa andsubmucosa, most prominent in jejunum ( SA 2-3 fold).

VILLI 0.51.5 mm long epithelial-covered projections ofthe lamina propria. Core contains capillary loops,

lymphatic channel, few smoth muscle cells embedded inloose connective tissue ( SA 10 fold).

MICROVILLI striated border on apical surface of cells,covered in enzyme-containing glycocalyx ( SA 20 fold).

Total increase in surface area ~ 600 fold


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VILLI & INTESTINAL GLANDS

DUODENUMLeaf-shaped villi,

*mucus-secreting

Brunners glands

in submucosa*

JEJUNUMFinger-shaped

villi, no glands

in submucosa

ILEUMVilli shorter than in

jejunum. Peyerspatches in lamina

propria & submucosa


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COLON

Lumen

Longitudinal m

Circular m

Submucosa

Tenia coli

Mucosa

Absorbs water and ions from chyme it receives from the small

intestine and compacts chyme into feces for elimination.

Large intestine has NO villi but has Crypts of Lieberkuhn.


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EPITHELIAL CELL RENEWAL

Stem cells undifferentiated, capable of self renewal

Stomach stem cells found in neck of gland

Small intestine stem cells found in Crypts of Lieberkuhn

Large intestine stem cells found in lower half of glands


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MUCOSA: Wet membrane that opens to the outside

Small intestine

Hard palate andgingiva:

masticatory mucosa

Small intestineCheeks, soft palate,floor of mouth, lips:

lining mucosa

Type CT depends on functional forces exerted on mucosa

Consists of epithelium and underlying CTForms an impenetrable barrier

DCT


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Skin

Mucosa

(Non-keratinized SSE)

Para-k

MC Junction

Parakeratinized region of skin

Skin(Keratinized SSE))

MUCOCUTANEOUS JUNCTION


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COMPONENTS OF A SALIVARY GLAND

Striated duct

Serous acinus

Serous demilune

Submandibular gland

Mucous cells


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ACINUS & DUCT SYSTEM OF A SALIVARYGLAND

Striated duct(Intralobular) Excretory duct(Interlobular)

Intercalated duct

(Intralobular)

Outside of lobuleWithin lobule

HypotonicSalivaCl-

Striated duct

Na+

K+

Interlobular duct

HCO3

Acinus Intercalated duct

LUMEN


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Parotid- 25% of saliva, largest gland,predominantly serous, secretes into

Stensons duct, well developed striatedducts, synthesizes amylase and

transports secretory IgA synthesized byplasma cells into saliva prevents

adhesion of bacteria and viruses to oral

mucosa

Sublingual (5% of saliva), smallestgland, secretes into ducts of Rivini

(plicae sublingulares), predominantly

mucous secreting, poorly developed

striated ducts

Submandibular (70% of saliva),mixed gland, secretes into Whartonsduct, well developed striated ducts,

makes lysosyme which hydrolyses

walls of bacteria

Serous demilune


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BUD STAGE

RECIPROCAL INDUCTION

Condensedectomesenchyme

Epithelialtooth bud

Dental lamina

Bone


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CAP STAGE

Dental lamina

Supporting

structures

Dentin

& pulp

Enamel

Dentalfollicle

Dentalpapilla

Enamelorgan


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CAP - BELL STAGE

Dentalpapilla

Oral cavity

Outer dentalepithelium

Dental lamina

Stellatereticulum

Stratum

intermedium

Inner dentalepithelium

Cervicalloop


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LATE BELL EARLY

APPOSITION

Collapsed

enamel organ

Pulp

Cervical loop

ODESR

Dentin

Odontoblasts

Enamel

AmeloblastsStratum

inter-

medium

Pulp

Predentin

SR


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SECRETORY AMELOBLAST

DISTAL END

Formsinterrod

substanceProximal portion

Formsenamel rod

Forms rodsheath

Junctionalcomplex

Stratum intermedium Ameloblast body Tomes process


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Rod

T.E.M. OF ENAMEL

Cylindrical rods are composed of long crystals that run parallel to the

longitudinal axis of the rod. Rods are embedded in interrod enamelwhose crystals run in a different direction. Rod and interrod enamel

are separated by a thin rod sheath containing organic material.

Mineralization may be nucleated by apatite crystals in dentin. Non-

amelogenins regulate mineralization, amelogenins regulate growth in

thickness and width of the crystals.

Rod sheath


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ENAMELMost highly mineralized tissue in the bodyComposed of 96% hydroxyapatite crystals, 4% proteins & H2OCovers anatomical crownExtremely brittle, supported by underlying resilient dentinSynthesized by ameloblasts which are lost after eruptionIncapable of repairLong crystals arranged in rods separated by interrod enamelInner and outermost layers of enamel are aprismaticPartially mineralized (30%) enamel deposited first, followed byreplacement of organic material by additional mineral.Enamel proteins (amelogenins (bulk), tuftelin (just at DEJ), enamelin(2%), ameloblastins (5-10%)) play important role in regulation of

mineralization. Crystallites are formed almost immediately within

enamel proteins; no equivalent of predentin or osteoid


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STRIAE OF RETZIUS &

CONTOUR LINES OF OWEN

Striae of Retzius (B)Series of dark lines extending from the

dentino-enamel junction (DEJ) to the tooth

surface (where they end in perikymata).

Caused by metabolic changes that occur

while enamel is being deposited that result

in hypomineralization. The thickest,darkest one, the neonatal line, reflects the

physiological changes which occur around

the time of birth.

Contour Lines of Owen (A)

Analagous to Straie of Retzius but formedin dentin. Both formed at the same stage

of development and meet at the DEJ.

(Hypomineralized regions appear darker)

DEJ


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ENAMEL SPINDLES, TUFTS & LAMELLAE

all hypomineralized areas of enamel

Dentinwith dentinal

tubules

Enamel

Enamel tuft

rich in enamelproteins

Enamel spindle tip of odontoblastprocess trapped in enamel

Enamellamella

region

containing

trapped

organicmaterial

DEJ


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DENTINForms bulk of tooth, supports the overlying brittle enamelHard, elastic, avascular tissue that encloses the pulp chamberComposed of 65-70% hydroxyapatite crystals, 20-25% organicmaterial (collagen, PGs, glycoproteins) & ~ 10% water

Coronal under crown, radicular under cementumOrganic components synthesized and maintained byodontoblasts at boundary of dental pulp which persist after

eruption

Contains closely packed tubules which house cytoplasmicextensions of odontoblastsTubules extend from the pulp to the dentinoenamel junction(DEJ) or dentinocemental junction (DCJ)

Capable of repair (tertiary or reparative dentin)Sensitive


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DENTINOGENESISPolarized nucleus rER Golgi Junctional complex Peritubular dentin

MineralizationPredentinOdontoblastic layerCell rich

zoneCell-free

zone


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Intertubular dentin

DENTINAL TUBULES

Dentinal tubules canaliculi that traverse dentin, housed odontoblastic

processes. Peritubular dentin collar of highly mineralized dentin

surrounding the tubule. Intertubular dentin located between tubules,

less mineralized than peritubular dentin, 1st secretory product of

odontoblasts, fibrils arranged at right angles to dentinal tubules.

Dentinal tubule

Peritubular dentin(Intratubular dentin)


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GLOBULAR & INTERGLOBULAR DENTIN

Mineralized dentin

Mineralization front

Predentin

Dentin is mineralized after it isformed. This begins in small

spherical areas which become

larger and fuse with one another

to form a mineralization front.

Enamel rods

Interglobular dentin

DEJ

Interglobular dentin refers to areasof hypo- or non- mineralized dentin

where globular zones of minerali-

zation have failed to fuse within

mature dentin. Tubules can pass

through but no peritubular dentin

exists where they do.


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FORMS OF

DENTIN

Mantle dentin part of

primary, laid down first,

mineralizes differently

Tertiary dentin reparative,

may not have tubules

Primary dentin

circumpulpal, laid down first

Secondary dentin laiddown after root formation,

less permeable than primary

dentin

Predentin unmineralized


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SCLEROTIC DENTINIf dentin is damaged the

odontoblastic processes dieleaving empty dentinal

tubules which form areas of

dead tracts (A).

Dead tracts become filled withmineral and are called blind

tracts (B).

The dentin of blind tracts is

known as sclerotic dentin.

ROOT FORMATION


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ROOT FORMATION

Cervical loop reflection of outer to

inner dental epithelium. Grows down

to form Hertwigs epithelial root sheath which outlines future root andsecretes factors which induce root pulp cells to differentiate into

odontoblasts. Sheath then breaks up, leaving isolated epithelial cell

rests of Mallassez that lie between fibers of PDL.

PDL

RootcanalCementum

Attachment organODE

IDE

Cervicalloop

ATTACHMENT ORGAN & JUNCTIONAL


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ATTACHMENT ORGAN & JUNCTIONALEPITHELIUM (JE)

Circular arrangement of epithelialcells at the base of gingival sulcus

(JE) attaches to both the tooth

(enamel) and underlying connective

tissue, forming a protective seal

between the oral cavity & underlying

tissues.JE is formed during tooth eruptionby fusion of reduced enamel

epithelium and overlying oral

epithelium and thus has two basal

laminae; one at each surface.

JE cells constantly renewed underinfluence of factors secreted by

underlying CT cells.

Basal laminae

shown in green

JE

3-4 cells thick

15-30cells thick


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GROUPS OF FIBERS WITHIN GINGIVA

CEMENTUM


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DCJ

Cellular

cementum synthesized

rapidly

around apical

1/3 of roots of

premolars

and molars

after teeth are

in occlusion.

Cells become

trapped in

matrix.

CEMENTUM

Dentin

Acellular

cementum

deposited

around roots

of all teeth.Cells do not

become

trapped but

move further

away from the

DCJ.

Granular Layer of Tomes small

hypomineralized areas reflecting

arrangement of matrix proteins at

the dentino-cemental interface

Cementoblasts differentiate from cells of the dental follicle after

exposure to dentin following the breakdown of Hertwigs epithelialroot sheath


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PERIODONTAL LIGAMENT

Attaches tooth to alveolar bone via collagen fibers anchoredinto cementum or alveolar bone as Sharpeys fibers. PDL fibersdo not become oriented until tooth is in occlusion. Mostly

collagen fibers (types I, III & XII), also oxytalan fibers. PDL

permits tooth to withstand forces of mastication. Also sensory

role. High rate of turnover.

Dentin

Cementum

Bundle bone

PDL(Major fiber bundle)


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GROUPS OF FIBERS WITHIN PDL

Alveolar crest fibers just belowCEJ to rim of alveolus

Horizontal fibers below apicalgroup, run from cementum to bone

just below alveolar crest

Oblique fibers most numerous,

run from cementum into alveolarbone, greatest support againstmasticatory forces, resist movementof tooth in apical direction

Apical fibers radiate from

cementum around the apex of theroot to the bone, resist movement oftooth in an occlusal direction

Interradicular fibers found onlybetween roots of multirooted teeth,run from cementum into bone

2013 histology review-1

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