'Bone and Joint Histology\r'

'* It is a specialised connective create from raw material.\r\n* Osteogenic cells ⇠tog disclose-forming cell (makes hyaloplasm, prompt when young, and after fracture) ⇠osteocyte ⇠osteoclast (functions in reabsorption, breakdown of os matrix) (makes cavities) (from race monocyte)\r\n fig out Functions\r\n* Framework for support of the bod\r\n* Protection: brain, spinal cord, lungs and heart\r\n* Levers for muscles attached to them via tendons\r\n* root for minerals e.g. calcium, magnesium, phosphates etc.\r\nBone Matrix\r\n* Components\r\n* Extracellular matrix (ground substance and fibres) consists of inorganic material (65%) e.g. calcium phosphate, calcium carbonate, magnesium, sodium, potassium, bicarbonate, fluoride, citrate, sulfate, and hydroxide.\r\n* Minerals give organise hardness and rigidity\r\n* essential component (35%) mostly type I collagen (95%)- gives lift slight flexibility; and ground substance e.g. GAGs with proteogly empennages, which watch chondroitin and keratin sulfates which give osseous tissue resilience\r\n* maturation\r\n1. Bone starts as osteoid, which is collagen and GAG’s with no minerals\r\n2. Bone becomes mineralised (immature, primary, or woven ivory). It is the first trick up to appear in development and in kettle of fish after fractures\r\n3. Bone starts to remodel as the giving form (mature, utility(prenominal), lamellar)\r\nBone Cells\r\n1. Osteoprogenitor (osteogenic) cells: from embryonic mesenchyme, which differentiate into chock up-forming cells. make up in sexual cellular layer of the periosteum, cladding Haversian canals, in the endosteum (lining medullary cavity)\r\n2. Osteoblasts: derived from osteoprogenitor cells, form and grow sweet-fashioned jampack by synthesis of organic components of tog up matrix. Found on the surfaces of existing elevate tissue where they deposit new bone matrix (osteoid) which contains no minerals. Later mineralization occurs, tissue is new bone. Osteoblasts extend processes with neighbouring osteoblasts for molecular(a) transport. Sit on the edge of bone.\r\n3. Osteocytes: flat cells with miniscule cytoplasmic processes. Aid in the maintenance of bone tissue and storage of minerals. Each osteoblast becomes adjoin by secreted matrix, once this occurs, the cell is known as an osteocyte (mature bone cell), and the space it occupies is a lacuna. Radiating out in all directions from the lacuna ar tunnel- c ar spaces (canaliculi) which abode the cytoplasmic processes of the osteocytes. The canaliculi allow transfer of nutrients, wastes among the osteocytes and blood. They argon very active cells. Communicate via cytoplasmic processes in the canaliculi, metabolic communication.\r\n4. Osteoclasts: large motile, multinucleated cells (150 um diameter) which contain up to 50 nuclei. These cells break up and resorb bone. Osteoclasts occupy alter depressions (Howship’s lacunae). The ruffled border (infolded pl asma membrane) is that disperse of the cell that is directly involved in the resorption of bone. It removes bone enzymatically, mineral deficiencies then the osteoclasts become active to release the minerals that watch been stored in bone, hence the mostbody becomes fracture prone. The multinuclear nature of the osteoclasts is a good identifying factor out\r\nPeriosteum and Endosteum\r\n* Vascular, fibrous layer surrounds bone except oer articulary surfaces.\r\n* 2 layers\r\n* Outer layer is collagen with near elastic fibres. This layer distributes vascular and nerve cede to bone.\r\n* Inner layer is cellular (osteogenic layer, osteoprogenitor cells), gives rise to new bone.\r\n* Central cavity of bone is lined with endosteum- trend CT composed of osteoprogenitor cells and osteoblasts.\r\n* From the outer layer of periosteum, okay bundles of collagenous fibres (Sharpey’s) penetrate the underlying bone at intervals to attach the periosteum, especially at the sites of a ttachment of tendons and ligaments.\r\n* The periosteum contains blood vessels, nerve endings, and ligament and tendon attachments.\r\nMature bone composition\r\n* Dense (compact) at the edge\r\n* This type has Haversian systems (osteons) which is a complex of 4- 20 concentric, bony circular lamellae environ a central (Haversian) canal (20- 100 μm diameter)\r\n* The canal contains blood vessels, lymphatics, with a few un myelinated nerve fibres, soft CT and flattened osteogenic cells and osteoblast cells that line the lumen of the canal\r\n* Osteocytes are in lacunae (in the concentric lamellae) located inside or between the lamellae\r\n* A second arrangement of lamellae is found between the osteons (interstitial lamellae- organize by the collapse of old Haversian systems). These are remnants of older, partially resorbed Haversian systems.\r\n* A third arrangement (circumferential lamellae) are rings of bone around the entire bone, at a lower place the periosteum\r\n* Radiat ing from the lacunae are tiny channels (canaliculi). Processes of the osteocytes acquaint these canals and communicate with adjacent osteocytes where an exchange of gases occurs, nutrients are supplied to the cells and metabolic wastes are eliminated.\r\n* The Haversian canals communicate with the nerve cavity, the periosteum and with each other via the transverse Volkmann’s canals, which run at sound angles to the retentive axis of the bone. Each osteon has a cementum line of calcified ground substance with some collagen fibres.\r\n* squishy (Cancelllous Bone):\r\n* This type is not organised into Haversian systems but is a meshwork of thin bars (lamellae) or trabeculae of bone lining the marrow cavity\r\n* The spaces within this wicket are filled with bone marrow. The trabeculae house osteocytes in lacunae that are fed by diffusion from the marrow cavity.\r\nBlood and Nerve Supply\r\n* Bones stupefy periosteal vessels, which penetrate the bone of the diaphysis of d esire bone and divide into branches that enter the Haversian systems. These vessels supply the osteocytes embedded in the calcified matrix.\r\n* Larger vessels pierce the epiphysis cerebri to supply the pulpy bone and the midshaft to supply the medullary cavity.\r\n* Small myelinated and unmyelinated nerves go into the Haversian canals.\r\n* The periosteum contains many hurting fibres which makes it sensitive to injury e.g. blow to the tibia\r\nBone Development and Growth\r\nHistogenesis (differentiation)\r\n* Bone development is mesoblastic in origin and if the tissue is membrane like (a sheet of mesenchyme or loose CT), it is intramembranous bone establishment\r\n* If bone replaces cartilage that is largely resorbed before bone is formed, this is endochondral (intracartilaginous) bone development.\r\nIntramembranous Bone formation\r\n* The process involves mesenchyme to bone directly (osteoblast laying bone)\r\n* Locations: flat bones, e.g. the skull, mandible, clavicle\r\ nEndochondral bone formation\r\n* The process in this type of bone formation occurs in 2 steps:\r\n1. A miniature hyaline cartilage model is formed in the region where the bone is to grow within the embryo\r\n2. The cartilage model grows appositionally and interstitially and serves as a structural scaffold for bone development. It is then resorbed and replaced by bone (all the cartilage is replaced by bone)\r\n* Locations: long, short bones, rose hip and vertebrae\r\nDeveloping bone region at epiphysial plate\r\n* Area between shaft and epiphysis is the epiphyseal plate.\r\n* Proliferation occurs at the epiphyseal aspect and renewal by bone takes place at the diaphyseal side of the plate\r\n* Growth at both ends of the bone is hormone regulated\r\n* There are a series of 5 zones beginning at the centre of the disc and go towards the diaphysis:\r\n1. regularize of reserve cartilage (resting zone) : chondrocytes through the matrix are mitotically active producing hyaline cartila ge\r\n2. geographical zone of proliferation: chondrocytes grow and form stacks of cells that parallel the direction of bone growth. (Cartilage dies- lose blood cells- hence the bone invades the space)\r\n3. Zone of maturation and hypertrophy (Expanding): chondrocytes mature, hypertrophy and accumulate glycogen in their cytoplasm. No mitosis occurs\r\n4. Zone of calcification and cell closing: Chondrocytes die and the cartilage matrix becomes calcified impregnated with calcium and the Tempter\r\n5. Zone of ossification: blood vessels invade spaces odd by the dying chondrocytes carrying osteoprogenitor cells from the periosteum and differentiate into osteoblasts which elaborate matrix that becomes calcified on the surface of calcified cartilage. As the matrix calcifies, some osteoblasts are entrapped as osteocytes and bone trabeculae are formed. compression of trabeculae creates waterlogged bone. Resorption of spongy bone by osteoclasts in the centre of the diaphysis enlarges th e medullary cavity.\r\n abridgment of histochemical processes for both models of bone formation\r\n* Osteoblasts secrete osteoid with no minerals\r\n* Formation of primary bone whereby osteoid is mineralized\r\n* Formation of secondary bone as compact or spongy bone\r\nGrowth in length of long bone\r\n* Due to interstitial growth of epiphyseal cartilage\r\n* Growth continues until around 20 when the epiphyseal plate closes (cartilage is replaced by bone) and growth in length stops\r\nGrowth in width of long bone\r\n* As a result of appositional growth from the surface and resorption by osteoclasts of the inner shaft so that the marrow space can be enlarged\r\nBone Remodelling\r\n* Continual remodelling occurs in response to forces (e.g. teeth growing jawbones). Bone is deposited delinquent to traction and resorbed due to pressure.\r\n* In young, bone depository exceeds bone resorption. In the adult bone bank deposit is balanced with resorption.\r\nJoints\r\n* Joints are classifie d according to the peak of movement between the bones of the vocalize:\r\n* Synarthroses: pocketable or no movement. There are 3 types based on the tissue making up the union:\r\n* Syndesmosis is the union of bones by ponderous CT e.g tibiofibular and radioulnar joints\r\n* Synchondrosis is a junction by cartilage e.g. IVDs and symphysis pubis\r\n* Synostosis is a joint united by bone e.g. skull sutures (Starts off as fontanelles)\r\n* Diarthroidal (synovial) e.g. knee, hip, shoulder have great freedom of movement and have a CT capsule around a joint cavity held by ligaments.\r\n* The joint has an articular cartilage (hyaline) with no perichondrium. The capsule is lined (except over the articular surfaces) with a cellular, vascular, folded synovial membrane made of loose CT which secretes a viscous lubricating, synovial fluid. The viscousness of the fluid varies with temperature.\r\n*Fibrous- collagen- little to no movement- interosseous ligament\r\n*Gomphosis- tooth joined by cartilage\r\n'