Ch 2 Hist, Embry.pptx

HISTOLOGY AND EMBRYOLOGY Ch 2 Tissue Histology  Basic Tissues  Tissues are categorized according to four basic histological types:  Epithelial  Connective  Muscle  Nerve  Epithelial tissue  Epithelium is the tissue type that covers...

HISTOLOGY AND EMBRYOLOGY Ch 2 Tissue Histology  Basic Tissues  Tissues are categorized according to four basic histological types:  Epithelial  Connective  Muscle  Nerve  Epithelial tissue  Epithelium is the tissue type that covers and lines the external and internal body surfaces, including vessels and small cavities.  Epithelial tissue consists of closely grouped polyhedral cells surrounded by very little or no intercellular substance  Its cells are tightly-joined to each other by desmosomes and to nearby non-cellular surfaces by hemidesmosomes  It is avascular  Cellular nutrition is obtained by diffusion from the adjoining connective tissue  Rapid cellular turnover  Classification of Epithelial Tissues*  Epithelial tissues are classified based on the layering arrangement and shape of their cells:  Simple epithelium consists of a single layer  Stratified epithelium consists of 2 or more layers, with only the lower layer contacting the basement membrane  Most of the epithelial tissues in the body are stratified squamous epithelium  Rete Ridges Has rete ridges-or rete pegs, are extensions of the epithelium into the connective tissue  Basement membrane  A thin, acellular structure located between epithelium and connective tissue  Consists of 2 layers:  The superficial portion is the basal lamina.  It consists of 2 layers:  the lamina lucida nearer the epithelium  the lamina densa nearer the connective tissue  The deeper portion is the reticular lamina  serves to anchor the basal lamina to underlying connective tissue  Connective tissue  Compared with epithelium, connective tissue is usually composed of fewer cells, spaced farther apart, and containing larger amounts of intercellular substance and fibers.  Most connective tissue is vascularized  It functions as support, attachment, packing, insulation, storage, transport, repair and defense  Fibroblast is the most common cell in all types of connective tissue  Turnover of the connective tissue is slower than epithelial tissues  Connective tissue cont’d  The connective tissue proper is both loose and dense connective tissue layers.  Is deep to the epithelium and basement membrane.  It is called the dermis in skin and is found deep to the epidermis*  It is called the lamina propria in the oral cavity and is found deep to the epithelium*  Papillary Layer: Loose Connective Tissue  AKA the papillary layer.  The papillary layer has connective tissue papillae, which are extensions of loose connective tissue into the epithelium.  These papillae are opposite the rete ridges (interdigitations from the epithelial layer)  Reticular Layer: Dense Connective Tissue  AKA the reticular layer.  Deep to the loose connective tissue  It is tightly packed and consists mainly of protein fibers, which give this tissue its strength  Connective Tissue: Cartilage  A firm, non-calcified connective tissue that serves as a skeletal tissue in the body  Forms much of the temporary skeleton of the embryo and serves as structural support for certain soft tissues after birth  Is also present at articular surfaces of most freely movable joints (TMJ)  Is avascular  It depends on its surrounding connective tissue for its cellular nutrition, usually the perichondrium  Has no nerve supply  Histology of Cartilage  2 types of cells:  Chondroblasts, which lie internal to the perichondrium and produce cartilage matrix  Chondrocytes, which are mature chondroblasts that maintain the cartilage matrix  Histology of Cartilage  There are 3 types of cartilage:  Hyaline- most common; contains only collagen fibers as part of its matrix  Elastic-similar, but has numerous elastic fibers in its matrix in addition to its numerous collagen fibers  Fibrocartilage- is never found alone; merges with its neighboring hyaline cartilage  Cartilage growth  Cartilage develops 2 different ways:  Interstitial growth is growth from deep within the tissue.  Appositional growth by the addition of layers from the outside of the tissue mass.  Connective Tissue: Bone  Is a rigid connective tissue that constitutes most of the mature skeleton  Periosteum: outer covering of bone; a double layered, dense connective tissue sheath  Outer layer: blood vessels and nerves  Inner layer: single layer of cells that give rise to osteoblasts  Osteoblasts-cuboidal bone-forming cells that arise from fibroblasts.  Bone  Compact bone (or cortical bone)  Heavy, few tissue spaces  Cancellous bone (or spongy, trabecular bone)  Light,many tissue spaces  Endosteum: lining inside of bones; same composition as periosteum, but thinner  Histology of Bone  Bone matrix is initially formed as osteoid  Osteoid is produced by osteoblasts  Osteocytes are mature osteoblasts trapped in the lacuna (in bone matrix.)  Osteoclast-cell that causes resorption of bone tissue  Connective Tissue: Blood  Is the fluid connective tissue that serves as a transport medium for cellular nutrients  It is carried in endothelium lined blood vessels and its medium consists of plasma and cells  Plasma is the fluid substance in the blood vessels that carries the plasma proteins, blood cells, and metabolites  Serum is a fluid substance (derived from plasma) that remains after the removal of clotting proteins  Most blood cells come from a common stem cell in the bone marrow.  The formed elements of the blood include:  red blood cells  white blood cells  platelets Red Blood Cells (RBCs)  Also known as erythrocytes  Most common cell in the blood  Bi-concave disc with no nucleus; contains hemoglobin  It binds and then transports the oxygen and carbon dioxide  Derived from stem cells in bone marrow-NO mitosis  Platelets  Also known as thrombocytes  Smaller than RBC  Disc-shaped with NO nucleus; cell fragments  Is a clotting mechanism  Considered fragments of bone marrow cells White Blood Cell (WBCs)  Also known as Ieukocyte  Rounded cell with nucleus  Defense of body; inflammatory response and immune response  Derived from bone marrow stem cells  Muscle tissue  The muscle in the body is part of the muscular system.  Each muscle shortens under neural control, causing soft tissue and bony structures of the body to move.  Three types of muscle tissue:  Smooth muscles  Involuntary  Located in organs, glands, and the linings of blood vessels  Cardiac muscle  Involuntary  In the wall of the heart  Skeletal muscles  Voluntary  Usually attached to bones; Includes muscles of facial expression, tongue, mastication, pharynx and upper esophagus Histology of Skeletal Muscle  Striated muscles  Each myofibril is  Composed of composed of even numerous muscle smaller fascicles (bundles) myofilaments. which then are composed of myofibers (muscle cells).  Each myofiber is composed of smaller myofibrils  Nerve Tissue  A nerve is a bundle of neural processes outside the CNS and in the PNS  Nerves function to carry messages or impulses based on electrical potentials.  Nerve tissue in the body:  Causes muscles to contract  Stimulates glands to secrete  Regulates many other systems of the body, such as cardiovascular system  Allows for the perception of sensations such as pain, touch, taste and smell. Histology of Nerve tissue  Neuron is the functional cellular component of the nervous system  It is composed of 3 parts:  One neural cell body  2 types of neural cytoplasmic processes  Axon  Dendrite  A synapse is the junction between two neurons or between a neuron and an effector organ where neural impulses are transmitted.  Histology of Nerve tissue  The two functional types of nerves*:  An afferent nerve, or sensory nerve, carries information or relays impulses from the periphery of the body to the brain (or spinal cord).  An efferent nerve, or motor nerve, carries information away from the brain to the periphery of the body. Embryology Developmental Processes  Mitosis VS Meiosis  Meiosis is the  Mitosis is the process of cell division of the division that parent cell into two reduces the “daughter” cells, number of genetically chromosomes in identical to each reproductive cells other and to their from diploid (46) to parent cell. haploid (23).  Takes place during  Takes place during reproduction growth and repair  Prenatal Development  Begins at the start of pregnancy and continues until the birth of the child.  Consists of three distinct periods: the preimplantation period, the embryonic period, and the fetal period.  The preimplantation and embryonic periods make up the first trimester and the fetal period comprises the last two trimesters.  Preimplantation Period  Takes place in the first week before attachment.  Female germ cell (ovum) + male germ cell (sperm)= fertilization-> creating a zygote  After fertilization, the zygote undergoes mitosis (cell division or cleavage).  Preimplantation Period  As mitosis continues, the zygote becomes a vesicle known as a blastocyst.  The rest of the first week is characterized by continuous mitotic cleavage, resulting in numerous cells.  Implantation in the uterine lining signals the end of this period.  Embryonic Period  Implantation signals the beginning of this period  2nd-8th week  Blastocyst consists of:  outer trophoblast layer that gives rise to prenatal support tissue such as placenta  an inner embryoblast layer that gives rise to the embryo  Increased cellular proliferation, differentiation and morphogenesis results in the development of the bilaminar disc (from the blastocyst). 2 layers result:  Epiblast layer (faces amniotic cavity)  Hypoblast layer (faces yolk cavity)  Embryonic Period  Primitive streak (beginning of 3rd week)  Cells from the epiblast layer proliferate and migrate and form mesenchyme  Mesenchyme (connective tissue) forms mesoderm.  The creation of mesoderm adds a third layer ->creating trilaminar disc (so all the names change!)  Ectoderm (from epiblast)  Mesoderm  Endoderm (from hypoblast)  In the latter part of the 3rd week, the CNS development begins.  Cells from ectoderm differentiate into neuroectoderm. These cells form the neural plate->neural groove->neural fold- >neural tube  Neural tube: Forms the future spinal cord and other neural tissues.  Embryonic Period  Neural crest cells develop from the neuroectoderm and are considered the 4th embryonic layer  Involved in the development of the many face and neck structures.  Embryonic Period  In the 4th week, the disc undergoes embryonic folding into an embryo  establishing the human axis  placing tissues in proper positions for further development.  After embryonic folding, the endoderm lies inside the ectoderm with the mesoderm filling in the area between the two layers.  Fetal Period  Encompasses the beginning of the 9th week through the ninth month.  This is a period of time of maturation of existing structure as the embryo enlarges to become the fetus.  Facial and Palatal Fusion  Facial fusion involves elimination  Palatal Fusion involves 2 of a groove between 2 swellings separate structures from two on the same surface. different surfaces.  Facial Development  Facial development starts in the 4th week and is completed in the 12th week.  4th week-> branchial arches appear on embryo Facial Development Key terms/features:  Frontonasal process, maxillary processes, mandibular processes  Medial and lateral nasal processes  Stomodeum  Placodes  oropharyngeal membrane  oronasal membrane  intermaxillary segment  labial commissures  Facial Development  Stomodeum, or  The FIRST event of primitive mouth, facial development: initially appears as a  In the 4th week, shallow depression at with the the cephalic end disintegration of before the 4th week. the oropharyngeal  oropharyngeal membrane, the membrane stomodeum separates the increases in depth stomodeum from the allowing access to primitive pharynx. the primitive pharynx. Lower Face Formation  After formation of the stomodeum, two bulges appear inferior to the primitive mouth, these are the mandibular  The paired mandibular processes fuse at the midline Mand. Process to form the mandibular arch (also known as the 1st branchial arch).  The point of fusion of the two mandibular processes appears as a faint ridge called the mandibular symphysis.  Lower Face Formation  The mandibular arch gives rise to:  mandible, mandibular teeth and associated tissues, the tongue and the lower lip.  The mesoderm of the mandibular arch gives rise to:  muscles of mastication, some palatal muscles and suprahyoid muscles.  Cartilage that forms within the mandibular arch is known as Meckel’s cartilage  which will help form middle ear bone.  Upper Face Formation  The frontonasal  The frontonasal process forms process and gives rise to:  forehead, primary palate,  Is a bulge of tissue in nasal septum, the nasal the upper facial area, placodes, nasal pits, medial at the most cephalic and lateral nasal processes, end of the embryo and intermaxillary segment.  Is the cranial boundary  Placodes:  rounded areas of of the stomodeum. specialized, thickened ectoderm found at the location of developing special sense organs.  Lens, otic, and nasal placodes  Nose Formation Medial nasal processes: Lateral nasal the middle portion of the processes: tissue growing around The outer portion of the nasal placodes the tissue growing These fuse together around the nasal externally to form: placodes the middle portion of These will give rise to the nose from the root the ala (sides of the to the apex, the center nose) portion of the upper lip, and the philtrum region These fuse internally forming the intermaxillary segment.*  Midface Formation  Maxillary processes  The upper lip is formed  Adjacent swelling that when: forms from the increased  Each maxillary process growth of the mandibular fuses with each medial arch nasal process  Maxillary processes give rise to the:  The two medial nasal  Midface including: sides processes contribute to: of upper lip, cheeks,  the middle of the secondary palate, and upper lip. the posterior portion of  The maxillary processes the maxilla (and canines) contribute to: and its associates tissues.  the sides of the upper  The zygomatic bones and lip portions of the temporal bones. Brachial Apparatus  Branchial arches  Branchial grooves  Pharyngeal pouches  Brachial Apparatus  Branchial arches  Stacked swellings that appear in 4th week  Inferior to the stomodeum  Mandibular arch (1st branchial arch->Meckel's cartilage)  Hyoid arch (2nd branchial arch->Riechert’s cartilage)  Formation of middle ear bone, a process of the temporal bone and portions of the hyoid bone and a portion of tongue formation  3rd branchial arch  formation of portions of the hyoid bone and a pharyngeal muscle.  4-6* branchial arch  formation of most of the laryngeal cartilages and the muscles of the larynx and the pharynx.  Brachial Apparatus  Between the neighboring branchial arches, external grooves are noted on each side of the embryo. These are the branchial grooves.  Only the first brachial groove, located between the first and second branchial arches, gives rise to a definitive mature structure of the head and neck: the external auditory meatus.  By the end of the seventh week, all other grooves are obliterated giving the mature neck a smooth contour.  Four well-defined pairs of pharyngeal pouches (balloon-like structures) develop from the lateral walls lining the pharynx.  1st: auditory tubes  2nd: palatine tonsils  3rd and 4th: parathyroid and thymus glands  Palatal Development  The palate begins  Intermaxillary segment formation in the 5th week gives rise to the primary and is completed in the palate. 12th.  Primary palate will  The palate is formed two contain the maxillary separate embryonic incisors. structures: the primary  Primary palate partially palate and the secondary separates the nasal and palate. oral cavities in the 5th week. Palatal Development  During the 6th week, the bilateral maxillary processes give rise to two palatal shelves.  These shelves will elongate and move medially toward each other, fusing to form the secondary palate.  The secondary palate will give rise to:  the posterior two-thirds of the hard palate and will contain the maxillary canines and posterior teeth.  the soft palate and uvula.  The formation of the secondary palate completes the second stage of palate development.  Palatal Development  To complete the palate, the posterior part of the primary palate meets the secondary palate, and all 3 gradually fuses together in an anterior to posterior direction.  Nasal Cavity and Septum Development  The nasal cavity forms at the same time as the palate-5th to 12th week  The vertical nasal septum fuses with the horizontally oriented final palate after it forms.  Fusion begins in the 9th week and is completed by the 12th week.  With the formation of the nasal septum and the final palate, the nasal and oral cavities become completely separated.  Tongue Development  Tongue develops during the 4th week to 8th weeks.  Tuberculum impar  Lateral lingual swellings*  Copula  Epiglottic swelling  By the end of the 8th week, the tongue has completed fusions of the swellings.  The entire tongue moves out of the pharynx and into the oral cavity proper, where it is located at birth.  Tooth Development  Begins in the 7th week with the inception of 20 primary teeth and continues into late teens resulting in 32 permanent teeth  Stages:  *initiation stage is often excluded  Bud stage  Cap stage  Bell stage  Apposition stage  Maturation stage Dental Lamina Enamel organ Dental papilla Dental sac Cellular layers (next slide) Ameloblasts, odontoblasts, cementoblasts  Bell Stage The inner enamel epithelium (IEE) tall columnar cells of the enamel organ. will differentiate into ameloblasts that will form the enamel matrix.  The stratum intermedium a compressed layer of flat to cuboidal cells The dental papilla now consists Support the production of of two types of tissues and enamel matrix. layers:  The stellate reticulum  The outer cells of the star-shaped cells forming a dental papilla-which will network within the enamel give rise to dentin-secreting organ. cells (odontoblasts) supports the production of  the central cells of the enamel matrix. The outer enamel epithelium dental papilla-which will give rise to the primordium  Apposition Stage  IEE cells differentiate into preameloblast s.  During this differentiation, the nucleus of each cell moves away to the position farthest away from the basement membrane.  This movement occurs during cellular repolarization.  Odontoblasts  After the IEE differentiates into preameloblasts:  the outer cells of the dental papilla are induced by the preameloblasts to differentiate into odontoblasts.  These cells also undergo repolarization  The odontoblasts now begin dentinogenesis  the apposition of dentin matrix (predentin) on their side of the basement membrane  So even though the preameloblast forms first, the odontoblasts start their secretions first.  Odontoblasts Odontoblastic process-attached cellular extensions in the length of the predentin. It is contained in a mineralized cylinder called the dentinal tubule. The enamel matrix is secreted from Tomes’ process  Ameloblasts  After the differentiation of odontoblasts and the formation of predentin:  the basement membrane between the preameloblasts and odontoblasts begins to disintegrate  allowing the preameloblasts to come in contact with the newly formed predentin  inducing the preameloblasts to differentiate into ameloblasts and begin Amelogenesis  apposition of enamel matrix  Root Development  Takes place after the crown is completely shaped and the tooth is starting to erupt into the oral cavity.  The structure responsible for the root development is the cervical loop.  The cervical loop is the most cervical portion of the enamel organ  a bilayer rim that consists of only OEE and IEE.  The cervical loop begins to grow deeper into the surrounding ectomesenchyme of the dental sac:  elongating and moving away from the newly completed crown area  to form Hertwig’s epithelial root sheath (HERS)  The function of HERS is to shape the root and induce dentin formation in the root area so that it is continuous with coronal dentin.  HERS continues only the IEE and the OEE, it does not have the Stratum intermedium or the stellate reticulum. WHY? Root Development  Root Dentin Formation  Root dentin occurs when the outer cells of the dental papilla are induced to undergo differentiation and become odontoblasts.  After the differentiation of odontoblasts in the root area, the cells undergo dentinogenesis and begin to secrete predentin.  Root Dentin Formation  As in the crown area, the basement membrane is located between the IEE of the sheath and the odontoblasts in the root area.  When root dentin formation is completed, this portion of the basement membrane disintegrates as does the entire HERS.  Cementum Formation  The disintegration of the HERS allows the undifferentiated cells of the dental sac to come into contact with the newly formed surface of root dentin.  This contact induces these cells to become immature cementoblasts. The cementoblasts move to cover the root dentin and undergo cementogenesis.  The apposition of cementoid (cementum matrix)  Questions  Can your body continue to produce cementum?  Dentin?  Bone?  What about enamel?  Why?  Answer  Cementum-yes  Dentin-yes  Bone-yes  Enamel-no  REE-reduced enamel epithelium  Oral Mucosa  Mucous membrane lining the oral cavity  Composed of stratified squamous epithelium overlying a lamina propria  It is perforated in several regions by the ducts of salivary glands  3 main classifications of oral mucosa: lining, masticatory and specialized mucosa  Lining mucosa  Type of mucosa known for its softer texture, moist surface, and ability to stretch and be compressed, acting as a cushion for underlying structures  Includes the mucosa of the buccal, labial, alveolar, floor of the mouth, ventral surface of the tongue and soft palate  Histologically associated with non-keratinized stratified squamous epithelium  Has fewer and less pronounced rete ridges and connective tissue papillae with a submucosa present to allow for a movable base  Fordyce’s spots are small, yellowish elevations on the surface of the mucosa resulting from deeper deposits of sebum from trapped sebaceous glands  Masticatory mucosa  Noted for its rubbery surface texture and resiliency  Includes attached gingiva, the hard palate, and the dorsal surface of the tongue  Histologically it is associated with keratinized stratified squamous epithelium  It has numerous and more pronounced rete ridges and connective tissue papillae with little to no submucosa, giving it a firm base  Specialized mucosa  Found on the dorsal and lateral surface of the tongue in the form of lingual papillae, discrete structure composed of epithelium and lamina propria Epithelium of oral mucosa  3 types of stratified squamous epithelium are found within the oral cavity:  non-keratinized  ortho-keratinized  para-keratinized  All forms act as a protective barrier  Non-keratinized stratified squamous epithelium  The most common form of epithelium in the oral cavity  Basal layer, or stratum basale, is the deepest of three layers; single cuboidal layer.  Intermediate layer, or stratum intermedium, is composed of larger stacked polyhedral shaped cells; bulk.  Superficial layer, or stratum superficiale, is the most superficial layer. It is similarly stacked polyhedral epithelial cells with the outer cells flattening into squames  Ortho-keratinized stratified squamous epithelium  Demonstrates keratinization  It is the least common form of epithelium in oral cavity  Basal layer (stratum basale)- deepest layer  Prickle layer (stratum spinosum) is superficial to the basal layer. It makes up the bulk of the ortho- keratinized epithelium  Granular layer (stratum granulosum) are flat and stacked in layer of 3 to 5 cells thick  Keratin layer (stratum corneum) is the most superficial layer. They are flat with no nuclei  Para-keratinized stratified squamous epithelium  Associated with masticatory mucosa of attached gingiva in higher levels than ortho- keratinization, and also the tongues dorsal surface, and specialized mucosa of the lingual papillae on the dorsal surface of the tongue  Has all the same layers as ortho-keratinized epithelium, but the cells in the flat keratin layer have nuclei  Connective Tissue of Oral Mucosa: Lamina Propria  All forms have a lamina propria deep to the basement membrane-mechanical support system that carries nerves and blood vessels  It has 2 layers:  The papillary layer, is the more superficial layer, consisting of loose connective tissue within the connective tissue papillae, along with blood vessels and nerve tissue.  The reticular layer is the deeper portion of the lamina propria. It consists of dense connective tissue with large amounts of fibers.  Epithelium-Connective Tissue Interface  Rete ridges, rete pegs,  Connective tissue papillae  Corrugated arrangement  Increased surface areas  Increases strength of junction  Decreases distance to blood supply  Basement Membrane  A thin, acellular structure located between epithelium and connective tissue  Consists of 2 layers:  The superficial portion is the basal lamina.  It consists of 2 layers:  the lamina lucida nearer the epithelium  the lamina densa nearer the connective tissue  The deeper portion is the reticular lamina  serves to anchor the basal lamina to underlying connective tissue  Specialized Mucosa of the Tongue  Covered with Lingual Papillae  Epithelial layer- stratified squamous epithelium that varies in degree of keratinization  Taste buds are barrel-shaped organs of taste associated with certain lingual papillae on the tongue: fungiform, foliate, and  Filiform Lingual Papillae  The most common lingual papillae located on the body of the dorsal surface of the tongue  Shaped like fine-pointed cones of 2 to 3 mm, with tips naturally turned toward the pharynx  Give the dorsal surface of the tongue its velvety texture  No taste buds are present  An increased amount of keratin causes the whiter color of this lingual papillae. Fungiform Lingual Papillae  Found in lesser numbers than filiform.  Appear as reddish dots that are about 1 mm in diameter, are slightly raised and mushroom shaped  A variable number of taste buds are located in the most superficial (top) portion  Function is taste sensation Filiform and Fungiform  Foliate Lingual Papillae  Appear as 4 to 11 vertical ridges parallel to one another on the lateral surface of the posterior portion of the tongue  Are leaf-shaped structure with a layer of ortho- keratinized or para- keratinized epithelium overlying a core of lamina propria  Taste buds are located on the lateral portions of this leaf-shaped structure  Function is taste sensation  Circumvallate Lingual Papillae*  When the tongue is arched and extended, the circumvallate lingual papillae appear as 7 to 15 large, raised, mushroom- shaped structures just anterior to the sulcus terminalis  They measure 3 to 5mm in diameter  Hundreds of taste buds are located on the sides epithelium surrounding the entire base of each circumvallate  Function is taste sensation  Tooth and Support Tissues (Ch 12-14) Know the specific Know the specific characteristics of the characteristics of the tissues of the tooth: periodontium tissues:  Enamel  Cementum  Dentin  Alveolar bone  Pulp tissue  PDL  Cementum  Enamel  Ameloblasts->amelogenesis  It is avascular, no nerves within it  It is a non-vital, non-renewable  Key terms/features:  Lines of retzius  Enamel lamellae  Enamel tufts  Enamel spindles  Enamel  Ameloblasts->amelogenesis  It is avascular, no nerves within it  It is a non-vital, non-renewable  Key terms/features:  Lines of retzius  Enamel lamellae  Enamel tufts  Enamel spindles  DEJ  REE  Microscopic Features of Mature Enamel  Enamel rods are the crystalline structural unit of enamel.  Most enamel rods extend the width of the enamel from the DEJ to the outer enamel surface.  Enamel rods are oriented perpendicular to the DEJ and outer enamel surface.  Each enamel rod varies in length based on the varying width of enamel in different locations of the crown. A: block of enamel; B: cross section of rod; C: side cut section; D: top cut section  Dentin  Odontoblasts->Dentinogenesis  Pulp  Connective tissue in Cells of the pulp: the innermost tissue of  Fibroblasts are the the tooth. largest group of cells  Formed from the in the pulp. central cells of the  Odontoblasts are the dental papilla 2nd largest group of  Functions: cells  Nutritive-blood supply  Also, histiocytes, red  Formative-odontoblasts and white blood cells,  Sensory-pain sensation and undifferentiated  Protective-tertiary (reactive) dentin mesenchymal cells.  4 Pulp Zones: viewed microscopically 1. Odontoblastic layer 3. Cell Rich Zone  Zone closest to dentin  Next to cell free zone  Lines outer pulpal wall  Increased density of cells  Consists of layer of cell compared to cell free bodies of odontoblasts zone  More extensive vascular 2. Cell Free Zone system than cell free  Appears cell free on low 4. Pulpal Core microscopic power, but is  Located in center of pulp NOT chamber  Next to odontoblastic  Numerous cells and layer extensive vascular supply  Has nerve and capillary  Similar to cell rich, except plexus location  Cementum  No innervation,  Key terms/features: Avascular-receives  Cementoid nutrients from the  Cementocytes surrounding PDL  Acellular  Renewable cementum  Cementoblasts->  Cellular cementum cementogenesis  CEJ  Attaches tooth via sharpeys fibers to PDL  Alveolar Bone  Bony part of maxilla  Alveolar bone and mandible that process-> lamina have teeth dura  Cells: osteoblasts,  Alveolar crest osteocytes,  Interdental septum osteoclasts  Interradicular septum  Terms to know:  Attaches tooth via  Cribriform plate sharpeys fibers to  Compact/Cortical bone PDL  Trabecular/cancellous bone Dental and Bone Composition calcium hydroxyapatite: Ca5(PO4)3(OH)  PDL  Developed from the dental sac and provides for the attachment of the teeth  Consists of groups of fiber bundles: gingival fibers and principle fibers  Principle fiber group: alveolodental ligament  PDL Gingival fiber group  Dento-gingival  Dento-periosteal  Alveolo-gingival  Circular Interdental ligament (also called trans-septal ligament)  This fiber group inserts mesiodistally or interdentally into the cervical cementum of neighboring teeth over the alveolar crest of the alveolar bone proper.  Cells of the PDL  The fibroblast is the most common cell in the PDL (as with all connective tissues)  It also has a line of cementoblasts that line its cemental surface and osteoblasts that line its alveolar bone surface  The PDL also has osteoclasts, odontoclasts and undifferentiated mesenchymal cells