| Talk about the bone Tissue. | Specialized skeletal CT, derived from mesenchyme, composed of cells in ECM with crystallized mineral salts making it rigid and impermeable. Hard and brittle, innervated and richly vascularized, dynamic constantly being renewed and throughout the lifetime of individuals. |
| What are the main functions done by the bone tissue? | -major part of skeleton
-supports body and soft tissues
-mechanical: point of attachment of muscles for locomotion
-protects organs including fragile ones
-metabolic: regulates phospho-calcium metabolism
-Hematopoesis: hosts red bone marrow. |
| What are the main cells of the bone tissue? | Resulting from balance of activities between them
-Osteoblastic line (bordering cells, osteoblasts and osteocytes, mesenchymal, elaborate and maintain bone development responsible for osteogenesis
-Osteoclastic line (hematopoietic origin, destroy bone (resorption) |
| Talk about bordering cells. | flat, thin, elongated, cover surface of bone area not subjected to formation or resorption, few organelles and not active, communicate through gap junctions, emit prolongations within bone matrix, some say they are at rest others suggest that if activated, they differentiate into osteoblasts, Roles: protective role against degredation of ECM
regulation of bone nutrition. |
| Where are osteoblasts originated from? | Undifferentiated mesenchymal cell called osteoprogenitor (precursor) |
| How are osteoblasts found ? | arranged in a continuous layer, just like bordering cells, but at surface of developing the bone tissue |
| Describe the osteoblast. | cuboidal or polyhedral, large basal oval nucleus having large nucleoles.
Basophilic cytoplasm rich in organelles, involved in protein synthesis, numerous mitochondria, irregular osteoblast shapes, long cytoplasmic extensions, directed towards developing bone tissues, contact among them and between them and their extensions is by gap junctions.
Young and active cells. |
| What are the roles of the osteoblast? | Praticipate in costruction of the bone by synthesizing and secreting organic component of ECM of new bone (osteoid) which will be added to pre-existing organic matrix, release tricalcium phosphates and alkaline phosphatase to control mineralization of formed bone tissue.
participate in regulation of bone remodeling, secreting proteolytic enzymes or indirectly by acting on osteoclasts. |
| Talk about the fate of the osteoblast. | die by apoptosis
rest in form of bordering cells
those that lock themselves into mineralized matrix produce 10 % make osteocytes. |
| Describe osteocytes. | Differentiated cells that can no longer divde, persistent, star shaped have cellular body having extensions detach and embedded in surrounding matrix, central and ovoid nucleus, no organelles in extensions, reduced RER and golgi, mitochondria and lysosomes are poorly developed, basophilic cytoplasm that is less marked (having organelles) according to activity. |
| How are osteocytes found? | In a lacunae, or osteoplast, which are interconnected by canaliculi containing the cytoplasmic extensions connected via gap junctions, allowing osteocytes to access into different nutrients, between osteocyte and osteoplast, there is a thin non mineralized periosteocytic space containing collagen fibers and high concentration of proteoglycans. |
| What are the roles of osteocytes? | Permenant exchange of minerals between tissue and blood, maintaining phospho- calcium balance.
Ensure maintainance of bone tissue by ensuring renewal of ECM
Regulation of bone remodeling and resorption at lacuna periphery, secreting citric acid, acid phosphate, proteolytic enzymes, and peptidases, wiithout intervention of other matrix components. |
| Talk about the formation of osteoclasts. | Monocytes (WBC) migrate to bone tissue and differentiate into preosteoclasts, which fuse together making multinucleated osteoclast, localized in bone surface spaces left free by bordering cells and osteoblasts. |
| Describe the osteoclasts. | Large, multinucleated, polarized, surface adjacent to bone tissue shows radical striation (brush border differentiation with long microvilli) called ruffled border. rich in vesicles, phagocytic vacuoles and lysosomes grouped under ruffled border. Cytoplasm ranges from basophilic to acidophilic (when resorption activity predominates) marking functional difference between osteoclasts |
| What is the function of osteoclasts? | Bone resorption, mobile and phagocytic, controlled by osteoblasts, through growth factors, coordinating bone development and destruction.
Once activated, microvilli bind to ECM, and provide through pumps acidification of microenvironment located between ruffled border and bone where pH=5, causing dissolution of mineral fraction, lysosomal hydrolase causes degradation of organic matrix, some degraded products are resorbed by osteoclast endocytosis to be fully degraded, which forms a cavity along its pathway called Howship lacuna |
| How is the bone tissue ECM classified? | Two parts related, organic (30%) and mineral (70%) |
| Talk about organic matrix. | acidophilic AKA osteoid, formed of
-collagen fibers type I mainly with presence of type III and V, orientation and disposition determine bone shape.
-Ground substances: poorly hydrated, consists of proteoglycans and sulphated GAG, growth factors, signaling molecules and some lipid (cholesterol and triglycerides) structural glycoproteins are also found. |
| Talk about the mineral matrix. | Complex of ions and mineral salts arranged along and inside collagen fibers, give bone hardness, and rigidity, calcium and phosphorus are most common, in form of hydrated crystals,other calcium salts and magnesium are also found (bicarbonate, cirates, calcium flouride, Ca10PO46OH2 |
| Talk about the periosteum. | Covers outer surface of the bone,, in adults has a thin outer layer of dense CT (tediniform or fibrous layer) and a predominantly cellular and well vascularized inner layer (osteogenic fibro-elastic layer) of loose CT, containing stem cells, there are bundles of non-oriented collagen fibers penetrating deep into bone tissue, Sharpey's fibers that attach periosteum to the bone. |
| Talk about the endosteum. | Thin layer of non-specialized CT lining internal cavities of the bones, related to red bone marrow, same osteogenic potentialities as periosteum, cells can transform into osteoblasts in case of bone fracture. (osteogenic role) |
| What roles do periosteum and endosteum play? | Growth in thickness of bone and bone repair |
| Talk about immature bones. | AKA woven, non-lamellar, or reticular or primary, first to form, elaborated from cartilage or CT, occurs mostly in fetus, very short lifetime, (transient and replaced by mature lamellar secondary bone tissues) mechanically weak and formed of trabeculae. |
| Talk about the composition of primary bone tissues, | Numerous osteocytes, arranged without an order nor orientation, irregular shape and variable size, but larger than those of secondary bones, matrix is poorly mineralized, random arrangement of collagen fibers bundles, rich in proteoglycans. |
| Talk about mature bones. | AKA lamellar, secondary, derives from secondary ossification of primary bones, mechanically strong, adult bones are mostly lamellar, resistant. |
| Talk about mature bone composition. | Superposed concentric lamellae, in each collagen fibers are fine and homogenously oriented, varies between lamellae, osteocytes are regularly distributed within the matrix and elongated parallel to lamellae. |
| What are the classifications of secondary bone tissues? | Based on lamellar arrangement, Haversian compact, non-Haversian compact, and spongy or trabecular. |
| Talk about the Haversian compact lamellar bone tissue. | Forms major part of diaphysis of long bones, consists of cylindrical structures, osteons or Haversian systems/ |
| What is an osteon? | made of 4-20 cylindrical bony lamellae concentrically arranged around Haversian canal containing blood capillaries, amyelinated nerve and bile capillary embedded in loose CT, collagen fibers are arranged parallel to each other within the same lamella, but in varying directions amongst different lamellae. Osteoplasts contain osteocytes. |
| How are osteons arranged in Haversian lamellar bone tissue. | parallel to each other and parallel to major axis of diaphysis. Interconnected through medullary cavity with surface of bone by transverse canals (Volkamann canals) |
| What are incomplete osteons? | Remnants of old, partially resorbed osteons , forming interstitial lamellar bone (intermediate Haversian system) observed between complete ones. |
| Talk about compact non-Haversian bone tissues. | Diaphysis of long bones is bordered by large bony lamellae concentric to medullary cavity separating Haversian tissues from periosteum and endosteum (Internally and externally) |
| Talk about spongy lamellar bone tissues. | Organized in trabeculae separated by large cavities, trabeculae of various thickness, consist of few bone lamellae. Collagen fibers have same orientation in each lamella. there are osteoplasts containing osteocytes. Cavities communicate with each other and contain red bone marrow.
Forms epiphyses and metaphyses of long bones and diploe of flat and short bones. |
| What is the result of primary ossification? | initial formation of bones in fetus, results in formation of non-lamellar primary bone from mesenchyme or cartilage. |
| Talk about endomembranous ossification. | AKA intramembranous, endoconnective, concerns most of bones of face and cranium (flat) embryonic mesenchyme proliferate around blood vessels, and differentiate into osteoblasts secreting osteoid and minerlizing. |
| Talk about endochondral primary ossification. | AKA endocartilagous, most skeletal bones (long short and flat) main consequence of length growth of bone, continues after childhood until adulthood. |
| Talk about ossification of diaphysis of long bones. | from epiphysis to diaphysis :
Hyaline growth cartilage (reserve zone)
serial cartilage (by axial isogenic groups (proliferation zone)
Hypertrophied cartilage (large cells and reduced ground substances Hypertrophic zone)
Calcified cartilage (infilterated ground substance with limestone process of cell degeneration (calcification zone)
Erosine (cartilage becomes destroyed by vasculo-cojunctive buds
Osteogenic zone (bone replaces cartilage. |
| Talk about the ossification of epiphysis. | Late start (at birth) primary ossification is advanced, carried out by endochondral ossification. respects periphery of the epiphysis a layer of cartilage to become articular and epiphysial growth plate (inside) |
| Talk about After birth primary ossification. | Lengthening (endochondral ossification) and widening (diaphysis level, successive peripheral apposition of new layers of bone tissues from periosteum activity; osteoblasts add lamellae to external surface of bone, spongy first but compact during remodeling. |
| Talk about secondary ossification | Maturation till end of puberty, remodeling replacement of bone tissues by new ones, woven replaced by lamellar, fast turnover, lifespan is few months, longer elderly, mineralization is progressive, younger osteons being slightly mineralized. |
