PERIODONTIUM 1

Overview of the cells 2nd October 20149.00 10.00 pm

Lecture ContentsStructures of the cell (general)Types of cellsFibroblastOdontoblast The bone cellsTypes of tissuesEpithelial tissueEpithelial cellHistology of epithelial tissueType of epithelial tissueFunction of epithelial tissueConnective tissueComponents of connective tissueTypes of connective tissueFunction of connective tissueMuscle tissueNervous tissue

Learning ObjectivesList and describe the cell structuresList and describe the types of cellDescribe the types of tissues and functionsIntroductionCELL- the smallest and functional unit of all living organisms:

Histology study of the microscopic structures & functions of cells

2 types of cells :-

i. Eukaryote - nucleus surrounded by a nuclear membraneii. Prokaryote nucleus without nuclear membrane, mainly bacteria

Human cells vary in size, shape and functionIntroductionINTERACTION OF THE CELLS

1 ) Exocytosis Active transport of material from a vesicle within the cell out into the extracellular environment

2) Endocytosis Uptake of materials from the extracellular environment into the cell

3) Phagocytosis Engulf & digest of solid waste through enzymatic breakdown CELL STRUCTURESCELL STRUCTURES

Reference: Mary Bath-Balogh & Margaret J. Fehrenbach. Dental Embryology, Histology, and Anatomy

Reference: Mary Bath-Balogh & Margaret J. Fehrenbach. Dental Embryology, Histology, and AnatomySTRUCTURES OF THE CELL

1) CELL MEMBRANE

A bilayer membrane surround the cell, composed of phospholipids & proteinPhospholipid as a diffusion regulatorProtein serve as structural reinforcement and also as a receptor for:-i. Specific hormonesii. Neurotransmittersiii. Immunoglobulins (antibodies)Cytoplasm: semifluid portion within the cell membrane as skeletal system of support (cytoskeleton)

2) MAJOR ORGANELLES

Nucleus Membrane - bounded compartment containing the largest variety of protein to form chromosomes, nucleolus and the molecular machinery - to maintain the integrity of genes & to control the cell activity by regulating gene expression

Mitochondria - As a powerhouses of cell on the cristae (the folds of the inner membrane) cellular respiration occurs and- site of oxidative phosphorylation (the process that leads to the production of adenosine triphosphate (ATP))

Figure: ELECTRON MICROGRAPH OF A THIN SECTION OF A NUCLEUS.(Courtesy of Don Fawcett, Harvard Medical School, Boston, Massachusetts.)Reference : Pollard. Cell Biology 2nd ed. Saunders, 2007 Ribosomes - Composed of ribosomal RNA and proteins : as a primary site of protein synthesis (translation)

Endoplasmic reticulum (ER) Composed of i. Rough present of ribosomesii. Smooth - absence of ribosomes - Site for modification, storage, segregation & transport of proteins from ribosome to other sections of the cell/ outside

v. Golgi Complex second largest organelle after nucleus : site for modification of protein molecules from ER

vi. Lysosomes - Small bodies in the cytoplasm contain powerful digestive enzymes to enhance the breakdown of celullar components

vii. Centrosome Oval-shaped organelle & located near the nucleus- Contains a pair of cylindrical structures (centrioles)- plays a significant role in forming the mitotic spindle apparatus during cell division

Figure: Figure 1-11ELECTRON MICROGRAPH OF A THIN SECTION OF A LIVER CELL SHOWING ORGANELLES. (Courtesy of Don Fawcett, Harvard Medical School, Boston, Massachusetts.)Reference : Pollard. Cell Biology 2nd ed. Saunders, 2007 FIBROBLASTOriginate from mesenchymal cellsPredominant cells of connective tissueFunctions:-i. formation and maintenance of the fibrous components & the ground substance of connective tissueii. to form and maintain the pulp matrixiii. also responsible and play an important role in wound healing mechanisms in the pulp

iv. synthesis and secrete collagen and other extracellular collagenous matrix components of the pulp, including fibronectin, proteoglycans and glycosaminoglycans

Also can be found in the cell-rich zone in the pulp

Reference: Ten Cates Oral Histology Development, Structure and FunctionTypes of fibroblastThe histology of the fibroblast cells is dependent on their functional state

1)The resting fibroblast elongated cell, little cytoplasm & flattened nucleus

2) Active fibroblast oval cell, greater amount of cytoplasm, abundant rough endoplasmic reticulum and pale staining nucleus

AResting fibroblast (A) cells, flat and spindle-shaped (x100).Secretory products of fibroblastSynthesize and secrete an extracellular molecules, included:-Fibrous element of the extracellular matrixAmorphous ground substanceProteinaseCytokineGrowth factors ODONTOBLASTCan be seen around the periphery of the dental pulpResponsible to form dentineArise from undifferentiated mesenchymal cells of the pulpConnected to each other with interodontoblastic collagen (von Korff fibers)

The morphology of odontoblasts reflects their functional activity

Individual odontoblasts communicate with each other via junctions

The numbers of odontoblasts corresponds to the number of dentinal tubules present at the pulp-dentin interface

ABCDFigure : Photomicrograph of haematoxylin and eosin stained sections showing cellular detail of area used for cell counts at the crown and root (A. Pre-dentine, B. Odontoblasts, C. Subodontoblasts, D. Fibroblasts, x 40) Secretory product of odontoblastsecrete and synthesis protein especially type 1 collagenalso secretes and synthesis non-collagenous component of the extracellular dentine matrix:-Proteoglycansglycosaminoglycans Phosphoprotein play a central role in the transportation of calcium to the dentine (Magloire et al. 2003)Types of odontoblast cellMorphology of the odontoblasts reflects their functional activity and they can vary from being active, transitional and restingSecretory odontoblast (active)- columnar in shape, highly polarized and contain numerous organelles- Most of organelles are located mainly in the large supranuclear region with the nucleus at the base of the cell- secrete the first layers of mantle dentine

ASecretory odontoblasts (A), elongated and columnar shapedii) Transitional odontoblasts- ovoid in shape- The cells are narrower with reduced number of organelles- less polarized and the amount of rough endoplasmic reticulum is reduced than in the secretory phase- The nucleus is displaced from the basal extremity and exhibit chromatin condensation

ATranstional odontoblasts (A), changes shape from columnar to ovoid and shorter in length iii) Aging odontoblast (resting)- quiescent in shape- The cells are shorter and more crowded and giving a pseudostratified appearance at the odontoblast layer - have reduced number of the organelles and they are mainly located in the infranuclear region - even though the ultra structures are different between active, transitional and resting the function of odontoblast remain the same:-continuously producing pre-dentineretain the ability to up-regulate protein synthesis activity response to trauma throughout the life of the tooth but at a slower rate

AResting odontoblasts (A) cells changes shape from columnar to ovoid, becomes shorter and more crowded and giving pseudo-stratified appearance at the odontoblast layer THE BONE CELLSThe cells are associated with the bone arei. Preosteoblastii. Osteoblastiii. Osteocyteiv. OsteoclastPreosteoblast synthesis osteonectin & proteoglycansOsteoblast responsible for secretion of bone matrix Osteocyte - responsible for bone formation and maintenanceOsteoclast - responsible for the removal of one crystals & matrix in bone resorption

Reference: Ten Cates Oral Histology Development, Structure and FunctionOsteoblastA plump cells with extensive rough endoplasmic reticulum & Golgi apparatus

Functions:-Responsible to secrete bone matrix (osteoid) and calcify it to form bone

Synthesis :-osteonectin, proteoglycans, bone sialoprotein, osteopontin osteocalcin

To form a layer of cells at the bone surface to protect osteoid and bone from resorption by osteoclasts

OsteocytesOsteoblasts that trapped within the lacunae in the boneNo alkaline phosphatase activityFunction:-Responsible for the maintenance of the bone around them

OsteoclastLarge cells with many nucleiArise from monocytesContain of lysosomes and also secrete organic acidsThese acids can dissolve the apatite crystals and metalloproteinases which can digest the collagen fibres of the boneOsteoclast can also phagocytes the matrix proteins

Reference: David B. Ferguson. Oral Bioscience

AAABBBCA Osteoblasts line forming the bone surfaceB Osteocytes entrapped in the boneC Osteoclasts, the numerous of them indicate that the bone are being formed & turned over rapidlyReference: Ten Cates Oral Histology Development, Structure and FunctionTypes of tissuesCells with similar functions and characteristic are grouped to form tissueFour types of tissues:-EpithelialConnectiveMuscleNerve

Epithelial tissueEpithelial tissues line and cover all body surfaces except the articular cartilage, the enamel of the tooth, and the anterior surface of the irisEpithelial tissues lining the skin and oral regions are from ectodermThose lining the respiratory & digestive tract are from endodermThose lining the urinary tract are from mesoderm

Epithelial cellsContains all the components normally present in the cellsAlso contains the 4 major junctions:-Tight junction closest contact between the adjacent cells at the apical regionSeparate the apical and the basal region based on their polarizationIntermediate filaments (fibrous protein), aggregate to form tonofibrils

Desmosomes (intercellular bridges) Cohesion between cellsAdhesion between the epithelium & connective tissue by hemidesmosomes

Gap junction - intercellular channels in the plasma membrane of adjacent cells & small molecules can diffuse across the channel and into the cytoplasm of the other cell

Image from: http://scienceblogs.comTypes of Epithelial CellsSquamous cells flattened cellsCuboidal cells cube shaped cells Columnar cells rectangular or tall cells

Squamous cells flattened and the height lower then the width

Cuboidal cells cube shaped and the height & width are equalColumnar cells rectangular and the height higher then the widthReference: Mary Bath-Balogh & Margaret J. Fehrenbach. Dental Embryology, Histology, and AnatomyHistology of epithelial tissueAvascular tissueNo blood supply of its ownNutrition comes from adjoining connective tissue (diffusion)

Types of Epithelial tissuesSimple epithelium consists of a single layer of epithelial cellsi. Simple squamous epithelium lining blood & lymphatic vessel, heart & serous cavities (endothelium)ii. Simple cuboidal epithelium lining the various ducts of the glands, ex: salivary gland ductsiii. Simple columnar epithelium2) Pseudostratified epithelium falsely appears as multiple cell layers under a low-power magnification - Reality, the cell nuclei appear at different levels- Simple epithelium- Lining the upper respiratory tract include nasal cavity and paranasal sinuses

Reference: Mary Bath-Balogh & Margaret J. Fehrenbach. Dental Embryology, Histology, and Anatomy3) Transitional epitheliumConsist of two or more layers of cellsCombination of cells

4) Stratified epitheliumConsist of two or more layers of cellsi. Cuboidal cells Stratified cuboidal epithelium ii. Columnar cells Stratified columnar epitheliumiii. Squamous cells Stratified squamous epithelium

Functions of epithelial tissues

i) Protection (skin) ii) Absorption (small and large intestine) iii) Transport of material at the surface (mediated by cilia) iv) Secretion (glands) v) Excretion (tubules of the kidneys) vi) Gas exchange (lung alveolus) vii) Gliding between surfaces (mesothelium)

CONNECTIVE TISSUEConnective tissue serves a connecting functionSupport & bind other tissuesComposed of cells and large amount of intercellular substance & fibers between the cellsThe cells are capable of mitosis and produce their own matrix renewable tissueVascularised (except cartilage) and having their own blood suppliesComponents of connective tissueCells Fibroblast synthesis intercellular substance & protein fibersMonocytes (leukocytes)NeutrophilsBasophils (mast cells)-produce histamin & heparinLymphocytes (plasma cell)

2) Collagen fiber (extracellular fiber) in all connective tissues (except blood) 3) Ground substance

Types of connective tissueLoose Connective TissueFunctions:-i. Holds organ in placeii. Attaches epithelial tissue to other underlying tissues

Composed of three main types of fibers:-i. Collagenous Fibers made of collagen and consist of bundles of fibrilsii. Elastic fibers made of elastin and stretchableiii. Reticular fibers join connective tissues to other tissues

2)Fibrous connective tissue - Composed of large amounts of closely packed collagenous fibers in tendon & ligaments

3)Specialized connective tissuei. Adipose stores fatii. Cartilage composed of closely packed collagenous fibers in chondrin and provides flexible supportiii. Bone mineralized connective tissue contains of collagen and calcium phosphateiv. Blood different function in comparison with other connective tissues and no extracellular matrix. The matrix is erythrocytes, leukocytes & platelets are suspended in plasma

Functions of connective tissueConnective tissues are involved in:-SupportAttachment PackingInsulationStorageTransportRepairDefense MUSCLE TISSUESMuscle cells are specialized to generate the mechanical& for contractingTo generate force and movementThey attached to:- bones and produce movements of the limbs or trunkskin, as for example, the muscles producing facial expressionenclose hollow cavities so that their contraction expels the contents of the cavity, as in the pumping of the heartalso surround many of the tubes in the body exp blood vessels & and their contraction changes the diameter of these tubes.3 types of muscle tissues:-i. Skeletal muscle - Skeletal muscle fibers occur in muscles which are attached to the skeletonstriated in appearance under voluntary control

MUSCLE TISSUESii. Cardiac muscle Cardiac muscle cells are located in the walls of the heart - Pump blood out of the heart- Striated in appearance Under involuntary control

iii. Smooth muscle Smooth muscle fibers are located in walls of hollow visceral organsControl movement of contents through hollow tubes and organsSpindle-shaped in appearanceUnder involuntary control

NERVOUS TISSUESConsists of cells specialized for initiating & transmitting electric impulseA signal may initiate new electric signals in other nerve cells, or it may stimulate secretion by a gland cell or contraction of a muscle cellFound in the brain, spinal cord, nerves & special sense organs

provide a major means of controlling the activities of other cellsThe incredible complexity of nerve-cell connections and activity underlie such phenomena as consciousness and perception.

NERVOUS TISSUESReferencesDavid B. Ferguson. Oral bioscience. Churchill Livingstone, 1999Mary Bath Balogh & Margaret J. Fehrenbach. Dental Embryology, Histology and Anatomy. Elsevier and Saunders, 2006Antonio Nanci. Ten Cates Oral Histology Development, Structure and Function. Mosby Elsevier, 2008Thomas D. Pollard & William C. Earnshaw. Cell Biology 2nd Edition. Saunders, 2007Human Physiology, from cells to systems. 7th edition. Lauralee Sherwood, 2010Vander. Human Physiology The Mechanism of Body functions. 8th Edition, McGraw- Hill, 2001