HistoReview_1stShift.pdf

UST FACULTY OF MEDICINE AND SURGERY Class of 2016

Histology First Shifting Reviewer

Cytoplasm 

CELL STRUCTURE AND FUNCTION    

Histology: study of normal structure Cell: functional unit of all living organisms Eukaryote: have defined nucleus enclosed by a membrane Prokaryote: lacks membrane-bound organelles

Nucleus   

Membrane Structure   

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Plasmalemma: outer limiting membrane Davson and Danieli: Classical Model o Trilaminar appearance of 2 protein layers sandwiching a lipid layer Singer and Nicholson: Fluid Mosaic Model o Phospholipid amphipathic bilayer, with a hydrophilic head and a non-polar hydrophobic tail o Polar head: glycerol conjugated to a nitrogenous compound o Non-polar tail: two long-chain fatty acids (one unsaturated, one saturated) o Fluidity and flexibility is due to presence of unsaturated fatty acids and cholesterol Integral proteins o Incorporated within the membrane o Transmembrane if it spans the entire thickness of the membrane Peripheral proteins o Held to inner and outer surfaces by weak electrostatic forces Glycocalyx o Glycoproteins and glycolipids projecting from the surface of the bilayer forming an outer coating involved in protection, cell recognition, formation of intercellular adhesions, and adsorption of molecules o Role in histocompatibility Functions o Filtration barrier o Ion permeability o Receptor sites o Cell recognition o Pinocytosis/ phagocytosis/ exocytosis

Ground substance subdivided into: o Endoplasm: manifest active streaming with cell components carried along o Exoplasm: gel-like

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Largest organelle; found in all cells except RBC Control center of the cell Types: o Pyknotic Nucleus: small, condensed o Chromatic Nucleus: blotchy o Vesicular Nucleus: cleared out appearance Contents: o Chromatin  Contains DNA and proteins  Heterochromatin: tightly coiled inactive chromatin found in irregular clumps (in females, Barr Body exist as inactivated X chromosomes)  Euchromatin: electronluscent, active in RNA synthesis o Nucleoprotein  Synthesis in the cytoplasm and imported to the nucleus  Histone proteins: LMW, positively charged, bind tightly to DNA and control coiling and expression of genes  Non-Histone: enzymes for the synthesis of DNA and RNA o RNA  mRNA, tRNA, rRNA

Nucleolus and Protein Synthesis 

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Nucleoli are sites of RNA synthesis and ribosome assembly o Filamentous components: sites of ribosomal RNA synthesis o Granular components: sites of ribosome assembly Intensely basophilic o Pars Amorpha/ Pars Fibrosa  Closely packed filaments on interior o Nucleolonema/ Pars Granulosa  Surrounds pars amorpha, reticulum of anastomosing strands

By: Sachi Estreller |Section B

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UST FACULTY OF MEDICINE AND SURGERY Class of 2016 

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Protein Synthesis o Transcription: DNA template copied to form a complementary mRNA o Introns (non-coding sequences) are spliced out of the mRNA before passing through the nuclear pore complex o Translation: mRNA binds to ribosomes that read the sequence and make a chain of AAs for a particular protein Ribosomes o Composed of a strand of RNA with associated ribosomal proteins o Aligns mRNA so that tRNA will be brought into position and AAs are added sequentially to form protein o Polyribosomes: ribosomes attached to mRNA o Ribosomes in RER  Proteins are folded to form tertiary structure, intrachain disulphide bonds are formed and first steps of glycosylation take place  Lysosomal proteins, proteins for export, and integral membrane proteins are made o Free Ribosomes  Proteins destined for the cytoplasm, nucleus, and mitochondria are produced

Nuclear Envelope     

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Thicker than cell membrane Consist of 2 membranes enclosing a narrow perinuclear space that communicates with cisternae of RER Inner and outer layers have phospholipid bilayer with different integral proteins Outer lipid bilayer o Continuous with RER Inner lipid bilayer o Contains the nuclear lamina, a layer of intermediate filaments that consist of lamins that link inner membrane proteins and heterochromatin Nuclear pore o Contains a nuclear pore complex, cylindrical structure consisting of 50 proteins forming a central pore o Permit the exchange of metabolites, macromolecules and ribosomal subunits o Hold together the two lipid bilayers

Endoplasmic Reticulum  

Most abundant organelle May have flattened and tubular cisterns

Rough Endoplasmic Reticulum  With ribosomes  Active in protein synthesis Smooth Endoplasmic Reticulum  Without ribosomes  Active in lipid synthesis and membrane synthesis and repair  Synthesize cholesterol and phospholipids (FAs, and triglycerides are synthesized in cytoplasm)  Found in the liver o Rich in cytochrome P450 and plays a role in the metabolism of glycogen and detoxification of metabolic byproducts  Found in muscle o Called sarcoplasmic reticulum o Involved in storage and release of calcium

Golgi Apparatus    

Stacked, saucer-shaped, membrane-bound cisternae Cis: convex, forming face Trans: concave, maturing face Process: o Proteins synthesized in RER transported to cis Golgi face in coated vesicles (coat protein is called COP II) o Coat proteins disengage and fuse with the cis face o Proteins are passed from cistern to cistern by COP I coat proteins o Glycosylation of proteins is completed by sequential addition of sugar residues and the proteins are packaged for transport to their final destination o At the trans face, proteins are sorted into secretory vesicles destined for extracellular space, plasma membrane, or other organelles o Secretory granules are liberated by exocytosis

By: Sachi Estreller |Section B

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UST FACULTY OF MEDICINE AND SURGERY Class of 2016 o

Cell Transport Passive Diffusion  Dependent on presence of concentration gradient  Lipids and lipid-soluble molecules  In general, plasma membrane is impermeable to hydrophilic molecules; however, water, urea, and bicarbonate are able to pass through passive diffusion Facilitated Diffusion  Concentration-dependent, requires presence of protein carriers  Example: Aquaporins o Allow water molecules to pass through similar to passive diffusion Active Transport  Operates against concentration gradient  ATP is required Bulk Transport  Mediated by subcellular, transient structures known as coated vesicles  Transport proteins embedded in the membrane of a vesicle or soluble cargo within the lumen of the vesicle  Dependent on the fluidity and deformability of lipid membranes and mobility of intrinsic membrane proteins  Formation of a coat vesicle: o Coat proteins bind to membrane and induce it to form a bud that is pinched off o Formed vesicle sheds coat proteins and is moved by cytoskeleton to target site  Exocytosis o Secretory granules dock with plasma membrane at the cell apex forming a transient opening called a porosome o Secretory product exits through the porosome o Secretory vesicle is recycled o Regulated secretion  Dependent on signal o Constitutive secretion  Continuous exocytosis  Receptor-mediated Endocytosis o Important in uptake of ligands that bind to surface receptors o Receptors: intrinsic membrane proteins with extracellular and cytoplasmic domains

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Process:  Cytoplasmic tail of receptor binds to clathrin coat protein in a coated pit  Receptors with ligands are concentrated in the coated pit  The pit buds off and forms coated vesicle  Vesicles lose clathrin coat and fuse with sorting endosomes  Sorting endosomes dissociate receptor and ligand (d/t acid PH)  Membrane and receptors are shuttled to recycling endosomes  Sorting endosome containing the ligand converts into a late endosome called a multivesicular body  Multivesicular body moved to golgi to fuse with lysosomes Phagocytosis o Cells of the defense system ingest and kill pathogenic organisms o Process:  Bacterium binds to cell receptors  Formation of pseudopodia that extend around bacterium  Enveloping pseudopodia form a phagosome  Phagosome fuses with lysosome  phagolysosome  Bacterium is broken down by lysosome enzymes  Dead bacteria may be released and maintained in cytoplasm as residual body, or expelled from cell

Transmembrane Signalling  Signalling molecules bind and activate membrane receptors (usually enzymes)

By: Sachi Estreller |Section B

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UST FACULTY OF MEDICINE AND SURGERY Class of 2016 Mitochondria and Energy Production Mitochondria  Elongated, cigar-shaped organelles  Very mobile, moves through microtubules  Localize at sites of maximum energy requirement  Contains DNA and ribosomes resembling chromosomes and ribosomes of bacteria  Undergo self-replication and synthesize some of their own constituent proteins  Aerobic respiration takes place in the matrix and inner membrane  Marker: succinate dehydrogenase  Four compartments: o Outer membrane  Contains porin which allows passage of small molecules  Contains enzymes that convert lipid substrates into forms that can be metabolized within mitochondrion o Inner membrane  Forms the cristae o Mitochondrial Matrix  Contains dense matrix granules that are binding sites for calcium  Site of Kreb’s Cycle, protein and lipid synthesis o Intramembranous Space  Contains a variety of enzymes Energy Production and Storage  Cellular respiration: supplies energy stored in the form of ATP  Main substrates are simple sugars and lipids  Glycolysis o Begins in the cytosol where it is degraded to form pyruvic acid o Pyruvic acid diffuses into mitochondria where it is degraded to CO2 and H2O  Fatty Acid o Pass directly to mitochondria

Lysosomes   

Membrane-bound organelles containing amorphous granular material Lysosomal enzymes: proteases, lipases, nucleases, collectively known as acid hydrolases that are optimally active at PH 5 Involved in degradation of bacteria (heterophagy) and cellular organelles (autophagy)

Peroxisomes/ Microbodies    

Small, spherical, similar to lysosomes but contain different material Contain oxidases involved catabolic pathways which result in formation of hydrogen peroxide Contain catalase that regulates hydrogen peroxide concentration Nucleoid: central crystalloid structure that contains urate oxidase (not present in humans)

Annulate Lamellae    

Visible in Electron Microscopy Parallel arrays of cisternae with small pores at regular intervals along length Presence of diaphragms closing the pores Functional significance not known

Cytoplasmic Inclusions Pigments  Lipofuscin o Represents an insoluble degradation product of organelle turnover o “Wear and Tear” or “age” pigment o Residual bodies (remnants of undigested molecules) may appear as brown lipofuscin granules  Melanin o Responsible for skin color Lipids   

Precursor molecules: FAs, triglycerides, and cholesterol Lipid droplets in the cell do not have limiting membranes Functions: o Maintain constant turn-over of cell membranes o Store excess energy

Glycogen  Present in large amounts in liver cells  Glycogen granules are either: o Beta Particles: irregular single granules o Alpha Particles: glycogen rosettes Others   

Crystals Secretory granules Vacuoles

By: Sachi Estreller |Section B

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UST FACULTY OF MEDICINE AND SURGERY Class of 2016 Cytoskeleton 

Functions: o Maintains the shape and polarity of the cell o Movement o Contractility o Reorganization of constituents in cell division Microfilaments  Extremely fine strands of actin cytoplasmic filaments and granules  Lack of glycogen granules o Mast cell degranulation results in the release of histamine and other vasoactive mediators which induce immediate hypersensitivity and anaphylactic shock

Macrophages o Active cells exhibit irregular cytoplasmic projections or pseudopodia which are involved in amoeboid movement and phagocytosis o Functions:  Tissue scavengers  Antigen presenting cells during opsonisation  Cytokine secretion that enhances immune response  Lymphokines: increase the metabolic and phagocytic activity of macrophages

Connective Tissue Fibers Collagen Fibers  Most abundant protein in the body  Most notable function is tensile strength  Secreted in the form of tropocollagen that polymerize in the ECM to form collagen  Types: o Type I: in fibrous supporting tissue, dermis of the skin, tendons, ligaments, and bone o Type II: hyaline cartilage o Type III: reticulin, found in highly cellular tisues  also called argyrophillic fibers because it is stained through silver impregnation o Type IV: basement membrane o Type VII: anchoring fibrils for basement membrane Elastin Fibers  Has stretch and elasticity  Secreted in the form of tropoelastin  Deposition of elastin as fibers requires that presence of fibrillin (structural glycoprotein)  Found in lungs, skin, urinary bladder, and blood vessels

Ground Substance     

Consist of GAGs or mucopolysacharrides GAG: double sugar units usually uronic acid and amino acid sugar (N-acetylglucosamin and Nacetylgalactosamine) Hyaluronic Acid: predominant GAG, without sulphate side groups Other GAGs: chondroitin-4 and 6- sulphate, dermatan sulphate, heparin and heparin sulphate, and keratin sulphate GAGs are hydrophilic  ECF confers turgor

By: Sachi Estreller |Section B

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UST FACULTY OF MEDICINE AND SURGERY Class of 2016 Structural Glycoproteins    Fibrillin 

Loose Areolar Connective Tissue  Few collagen fibers present  Found in lamina propria, superficial and deep fascia

Enhance adhesion between other extracellular constituents and deposition of fibers in elastin

Dense Regular Connective Tissue  Compact collagen fibers oriented unidirectionally  Found in tendons, ligaments, and aponeurosis

Fibronectin  Control deposition and orientation of collagen in ECM  Enhance binding of cell to extracellular material Laminin  Form links between cell membranes and basement membrane Entactin  Bind laminin to Type IV collagen in basement membrane Tenascin  Binds to integrins and play a role in embryonic nerve cell growth

Basement Membrane   

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Adult Connective Tissue

Fibrillary: fibrillin, fibronectin Non-Fibrillary: laminin, entactin, tenascin Function as links between cells and ECM

Sheet-like arrangements of ECM that act as interface between support tissues and parenchymal cells Main constituents: heparin sulphate, collagen type IV, fibronectin, laminin, and entactin Functions: o Metabolic support o Control of epithelial growth and differentiation o Regulation of permeability Layers: o Lamina Lucida  Electron lucent  Mainly type IV collagen bound to basal plasma membrane by laminin  Entactin mediates binding of laminin to collagen o Lamina Densa  Electron dense, intermediate layer o Lamina Fibroreticularis  Merges with underlying supporting tissue  Mainly type III collagen bound to integrin of parenchymal basal membrane by fibronectin

Dense Irregular Connective Tissue  Compact collagen fibers oriented multidirectionally  Found in GIT, dermis, periosteum, perichondrium Elastic Connective Tissue  Contain elastin fibers, slender and refractile  Found in wall of hollow organs, blood vessels, trachea, bronchi, yellow ligaments, suspensory ligaments Reticular Connective Tissue  Contains reticulin fibers  Supporting framework of hematopoietic and lymphoid organs Adipose Connective Tissue  Adipocytes o Adapted for storage of fat in lipid droplets o Derived from mesenchymal cells that develop as lipoblasts o Signet-ring appearance with the nucleus at the periphery o Secrete adipocytokines that modulate energy metabolism o Generally has a rich blood supply o Have receptors for insulin, glucocorticoids, growth hormone and noradrenaline  Stored fat from: o Triglycerides from liver o Circulating dietary fat o Triglycerides from glucose within adipocytes  Types: o White Adipose Tissue  Unilocular  Energy store, thermal insulator, and cushion o Brown Adipose Tissue  Multilocular  Found in newborns and hibernating mammals

By: Sachi Estreller |Section B

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UST FACULTY OF MEDICINE AND SURGERY Class of 2016 

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Function in body temperature regulation: nonshivering thermogenesis induced by cold stress Contains thermogenin which uncouples mitochondrial metabolism from production of ATP to produce heat Cytochrome accounts for the brown color of adipocytes

Embryonic Connective Tissue Mesencymal Connective Tissue  With capacity for differentiation Mucuous Connective Tissue  Formed by primitive fibroblasts (spindleshaped/stellate)  Wharton’s jelly of umbilical cord

Specialized Connective Tissue 

Cartilage, bone, and blood to be discussed in a later section

By: Sachi Estreller |Section B

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UST FACULTY OF MEDICINE AND SURGERY Class of 2016 SKELETAL TISSUES     

Mesodermal in origin Rigid form of connective tissue due to calcification of ground substance Inorganic elements: Mg, Ca, Na Organic elements: calcified matrix Functions: o Internal support o Attachment of muscles and tendons o Contains bone marrow o Protect vital organs o Calcium storage

Cartilage   

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provides smooth articular surface and structural support; also important in bone formation made up to extracellular matrix: ground substance + fibers Ground Substance o Made up of proteoglycans o Accound for solid and flexible properties of cartilage o Sulphated GAGs predominate such as chondrotin and keratin sulfate Most are avascular thus exchange of metabolites between chondrocytes and surrounding tissue depends on diffusion through water solvation of ground substance

Cartilage Formation  Primitive mesenchymal cells differentiate to chondroblasts which synthesize ground substance and fiber  Chondroblasts o Separated by cartilaginous matrix and undergo mitotic division in separate areas, maturing into chondrocytes  Chondrocytes o Maintain the integrity of the cartilage matrix o Arranged in clusters of 2-4 enclosed by amorphous cartilage matrix o Involved in synthesis of ground substance and fibers of the ECM o Have prominent RER and Golgi Apparatus  Appositional Growth o Through the perichondrium, a layer surrounding mature cartilage composed of fibers and spindle-shaped cells o Cells transform into chondroblasts and produce new cartilage

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Interstitiial Growth o Occurs through further division of chondrocytes trapped within mature cartilage o Mature cartilage has little capacity to repair and regenerate due to poor vascular supply

Hyaline Cartilage  Most common type  Found in nasal septum, larynx, tracheal rings, articular surfaces  Precursor in the developing bone  Consists of collagen type II (except articular cartilage) Elastic Cartilage  Found in external ear, epiglottis, laryngeal cartilage, and walls of Eustachian tube  Elasticity is derived from elastic fibers in the cartilage matrix Fibrocartilage  Found in intervertebral discs, articular cartilage, and pubic symphysis, joint capsules, ligaments, and tendons  Chondrocytes typically arranged in rows between dense collagen layers

Bone   

Provides a rigid protective and supporting framework Also serves as a calcium reservoir Composed of cells and type I collagen called osteoid, mineralized by deposition of calcium hydroxypatite

Cells of the Bone  Osteoprogenitor o Primitive mesenchymal cell line where osteoblasts and osteoclasts originate  Osteoblasts o Synthesize osteoid and mediate its mineralization; lined up in bone surfaces o Inactive: spindle shaped; active: cuboidal  Osteocytes o Inactive osteoblasts embedded in formed bone; assist in nutrition  Osteoclast o Phagocytic, multi-nucleated cells that erode bone for turnover and refashioning; come from monocytemacrophage cell line

By: Sachi Estreller |Section B

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UST FACULTY OF MEDICINE AND SURGERY Class of 2016 o o

Found in Howship’s lacunae, depressions of resorbed bone With a ruffled border formed by microvilli that secrete organic acids and proteolytic enzymes

Types of Bone According to Collagen Organization  Woven Bone o Collagen fibers arranged randomly and irregularly o Fabricated during periods of rapid bone growth: embryogenesis, reactive, neoplastic o Hypercellular with large osteocytes and lacunae distributed in haphazard fashion o Prone to greenstick fracture o Pleomorphic osteocytes  Lamellar Bone o Collagen fibers arranged in parallel o Synthesized more slowly; stronger o Less cellular, small osteocytes and lacunae o Uniform osteocyte morphology o May be compact or spongy Compact Bone (Substantia Compacta)  Parallel columns made up of concentric bone layers surrounding the haversian canal  Haversian System o Haversian channel  Contains lymphatics, blood vessels, nerves o Volkmann’s Canal  Connect neurovascular bundles in haversian canals with andosteum and periosteum o Lacunae  Containing ostecytes and are seen in between lamella o Canaliculi  Minute interconnecting canals in between lacunae containing cytoplasmic extensions of osteocytes  Provide passage for circulation of ECF and diffusion of metabolites between lacunae and vessels of haversian canals

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Concentric Lamella  Internal/Endosteal Lamella  External/Periosteal Lamella  Interstitial Lamella: remnants of resorbed lamellae no longer surrounding haversian canals Periosteum  Bound to underlying bone by Sharpey’s Fibers  Layer of condensed fibrous tissue containing osteogenic cells

Spongy Bone (Substantia Spongiosa)  Irregular branching bony spicules forming a network of interconnecting spaces  With thin trabeculae made up of irregular lamellae  Trabeculae is lined by thin endosteum containing flat inactive osteoblasts  Number, thickness, and orientation are dependent on the stresses to which the bone is exposed  Contains red (hematopoietic) and yellow (adipose) marrow  No haversian system Types of Bone According to Structure  Long Bone o Diaphysis  Mostly compact bone o Epiphysis  Mostly spongy bone o Epiphyseal Plate  In between epiphysis and diaphysis o Metaphysis  Transition connecting epiphyseal plate and diaphysis o Periosteum and Endosteum  Lining of outside and inside of bone  Flat Bone o Made up of 2 layers of compact bone (inner and outer tables) surrounding spongy bone layer (diploe)

By: Sachi Estreller |Section B

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UST FACULTY OF MEDICINE AND SURGERY Class of 2016 Joints Synovial Joint  Allows extensive movement  Also known as diarthroses  Articular cartilage o Hyaline cartilage that covers articular surfaces o Infers resistance to compressive forces  Synovium o Secretory cell layer that secretes synovial fluid in the cavity to facilitate smooth articulation o May be fibrous (dense), areolar (loose), or adipose (fat) synovium o Synovial fluid contains:  Hyaluronic acid and associated glycoproteins from Type B Synoviocytes  Transudate from capillaries  Leucocytes and monocytes o Type A Synoviocytes  With extensive golgi complex and lysosomes o Type B Synoviocytes  With extensive endoplasmic reticulum  Cruciate ligaments o Internal ligaments that limit joint movement together with fibrous joint capsule and external fibro-elastic ligaments Non-Synovial Joints  Have limited movement  No free articular surface, instead joined by dense collagenous tissue  Types: o Dense fibrous Tissue  Called syndesmoses that transform to synostoses when replaced by bone  Found in sutures of the skull o Hyaline Cartilage  Called synchondrosis  Found in union of first rib with sternum o Fibrocartilage  Called symphyses  Found in pubic symphysis and intervertebral discs

Tendon     

Tough flexible straps that connect muscles to bone Composed of compact linear collagen fibers with nuclei of inactive fibroblasts Poorly vascularised and heals slowly Anchor to muscle through myotendinous junctions Anchor to bone through the periosteum or Sharpey’s Fibers

Bone Development and Growth Bone Matrix and Mineralization  70% inorganic salts o Mainly calcium and phosphate in the form of hydroxypatite crystals o Magnesium carbonate o Sodium o Potassium  30% organic o Type I collagen creates hole zones, the initial site for mineralization o Ground substance proteoglycans consist of hyaluronic acid and chondroitin sulphate o Osteocalcin: involved in binding calcium during mineralization o Osteonectin: bridging function between collagen and mineral component o Sialoprotein  Process o Collagen and other organic components synthesized from RER of osteoblasts  Golgi Apparatus  secreted as osteoids o After maturation phase, calcium phosphate salts precipitate in the hole zones o Pyrophosphate: inhibitor that controls bone mineralization o Alkaline Phosphatase: neutralize effect of pyrophosphate Intramembranous Ossification  Skull vault, maxilla, mandible  Occurs within membranes of condensed, primitive mesenchymal tissue  Process: o Mesenchymal cells differentiate into osteoblasts that begin synthesis of osteoid at “centers of ossification” o Mineralization of osteoid o Osteoblasts trapped in lacunae evolve into osteocytes and cytoplasmic extensions shrink and form canaliculi

By: Sachi Estreller |Section B

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UST FACULTY OF MEDICINE AND SURGERY Class of 2016 o o o

Osteoprogenitor cells continue to form osteoblasts Fusion of adjacent ossification centers occurs Woven bone is remodelled by osteoclastic activity and subsequent osteoblastic deposition of mature compact bone

Endochondral Ossification  Long bones, vertebrae, pelvis, skull base  Permits functional stress to be sustained during skeletal growth  Process of Primary Ossification o Zone of Reserve Cartilage  Cartilage model is first formed in hyaline cartilage o Zone of Proliferation  Appositional growth occurs to form the different parts of bone o Zone of Maturation  Chondrocytes within the model enlarge and resorb the cartilage so as to leave perforated trabeculae of cartilage matrix o Zone of Hypertrophy and Calcification  Cartilage matrix is ossified o Zone of Cartilage Degeneration  Chondrocytes degenerate, primitive mesenchymal cells and blood vessels invade the spaces occupied by chondrocytes and differentiate into osteoblasts and hematopoietic cells o Osteogenic Zone  Osteoblasts begin to form woven bone o Perichondrium develops osteogenic potential and assumes the role of periosteum o Periosteum lays down a thin layer of bone on the surface o Results in bony diaphysial shaft with cartilaginous epiphyses at each end  Process of Secondary Ossification o Conversion of central epiphyseal cartilage into bone

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