Bone and Joint Histology

* It is a specialised connective tissue.* Osteogenic cells osteoblast (makes intercellular substance, officious when young, and after fracture) osteocyte osteoclast (functions in resorption, partition of organise matrix) (makes cavities) (from ocellus monocyte) cram Functions* Framework for support of the skeleton* security brain, spinal cord, lungs and heart* Levers for muscles attached to them via tendons* Reservoir for minerals e.g. calcium, magnesium, phosphates etc. fancy up hyaloplasm* Components* Extracellular matrix (ground mental object and fibres) consists of inorganic material (65%) e.g. calcium phosphate, calcium carbonate, magnesium, sodium, potassium, bicarbonate, fluoride, citrate, sulfate, and hydroxide.* Minerals give osmium hardness and rigidity* Organic component (35%) generally type I collagen (95%)- gives work up slight flexibility and ground substance e.g. GAGs with proteoglycans, which contain chondroitin and keratin sulfates which give oculus sin ister resilience* Development1. tog up starts as osteoid, which is collagen and GAGs with no minerals2. fancy up becomes mineralised (immature, primary, or twist bone). It is the first bone to appear in development and in revivify after fractures3. Bone starts to remodel as the adult form (mature, secondary, lamellar)Bone Cells1. Osteoprogenitor (osteogenic) cells from embryonic mesenchyme, which differentiate into osteoblasts. Found in inside(a) cellular stage of the periosteum, lining Haversian canals, in the endosteum (lining medullary cavity)2. Osteoblasts derived from osteoprogenitor cells, form and grow new bone by synthesis of organic components of bone matrix. Found on the surfaces of animated bone tissue where they deposit new bone matrix (osteoid) which contains no minerals. Later mineralization occurs, tissue is new bone. Osteoblasts extend swear outes with neighbouring osteoblasts for molecular transport. Sit on the edge of bone.3. Osteocytes flat cells with smal l cytoplasmic processes. Aid in the sustenance of bone tissue and storage of minerals. from each one osteoblast becomes surrounded 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- equivalent spaces (canaliculi) which menage the cytoplasmic processes of the osteocytes. The canaliculi allow transfer of nutrients, wastes between the osteocytes and filiation. They argon very dynamical cells. Communicate via cytoplasmic processes in the canaliculi, metabolic communication.4. Osteoclasts large motile, multinucleated cells (150 um diameter) which contain up to 50 nuclei. These cells break up and resorb bone. Osteoclasts occupy shallow depressions (Howships lacunae). The ruffled border (infolded plasma membrane) is that part of the cell that is directly have-to doe with in the resorption of bone. It removes bone enzymatically, mineral deficiencie s thusly the osteoclasts become active to release the minerals that have been stored in bone, hence the person becomes fracture prone. The multinuclear spirit of the osteoclasts is a good identifying factorPeriosteum and Endosteum* Vascular, fibrous layer surrounds bone leave out oer articular surfaces.* 2 layers* Outer layer is collagen with some rubbery fibres. This layer distributes vascular and nerve supply to bone.* Inner layer is cellular (osteogenic layer, osteoprogenitor cells), gives rise to new bone.* Central cavity of bone is lined with endosteum- ignore CT composed of osteoprogenitor cells and osteoblasts.* From the outer layer of periosteum, fine bundles of collagenous fibres (Sharpeys) tick the underlying bone at intervals to attach the periosteum, especially at the sites of fixing of tendons and ligaments.* The periosteum contains blood vessels, nerve endings, and ligament and tendon attachments.Mature bone Organisation* laboured (compact) at the edge* This typ e has Haversian systems (osteons) which is a complex of 4- 20 concentric, weedy circular lamellae surrounding a central (Haversian) canal (20- 100 m diameter)* The canal contains blood vessels, lymphatics, with a few unmyelinated nerve fibres, unclouded CT and flattened osteogenic cells and osteoblast cells that line the lumen of the canal* Osteocytes atomic number 18 in lacunae (in the concentric lamellae) located wi cut down or between the lamellae* A second arrangement of lamellae is found between the osteons (interstitial lamellae- form by the soften of old Haversian systems). These argon remnants of older, partially resorbed Haversian systems.* A third arrangement (circumferential lamellae) argon rings of bone around the entire bone, beneath the periosteum* Radiating from the lacunae are tiny channels (canaliculi). Processes of the osteocytes enter these canals and communicate with adjacent osteocytes where an exchange of gases occurs, nutrients are supplied to the cells an d metabolic wastes are eliminated.* The Haversian canals communicate with the marrow cavity, the periosteum and with each other via the crosswise Volkmanns canals, which run at right angles to the long axis of the bone. Each osteon has a cement line of calcified ground substance with some collagen fibres.* spongelike (Cancelllous Bone)* This type is not organised into Haversian systems but is a meshwork of thin bars (lamellae) or trabeculae of bone lining the marrow cavity* The spaces at heart this latticework are filled with bone marrow. The trabeculae house osteocytes in lacunae that are fed by diffusion from the marrow cavity.Blood and Nerve render* Bones have periosteal vessels, which penetrate the bone of the diaphysis of long mug up and divide into branches that enter the Haversian systems. These vessels supply the osteocytes embedded in the calcified matrix.* Larger vessels hurl the epiphysis to supply the spongy bone and the midshaft to supply the medullary cavity.* thin myelinated and unmyelinated nerves go into the Haversian canals.* The periosteum contains many pain fibres which makes it sensible to injury e.g. blow to the tibiaBone Development and GrowthHistogenesis (differentiation)* Bone development is mesodermal in origin and if the tissue is membrane like (a sheet of mesenchyme or loose CT), it is intramembranous bone governing body* If bone replaces gristle that is largely resorbed before bone is formed, this is endochondral (intracartilaginous) bone development.Intramembranous Bone formation* The process involves mesenchyme to bone directly (osteoblast laying bone)* Locations flat bones, e.g. the skull, mandible, clavicleEndochondral bone formation* The process in this type of bone formation occurs in 2 steps1. A miniature hyaline cartilage model is formed in the region where the bone is to grow within the embryo2. 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)* Locations long, short bones, pelvis and vertebrae developing bone region at epiphyseal plate* Area between shaft and epiphysis is the epiphyseal plate.* Proliferation occurs at the epiphyseal aspect and reclamation by bone takes place at the diaphyseal side of the plate* Growth at both(prenominal) ends of the bone is hormone regulated* on that point are a series of 5 zones beginning at the affection of the disc and go towards the diaphysis1. Zone of reserve cartilage (resting zone) chondrocytes through the matrix are mitotically active producing hyaline cartilage2. Zone of proliferation chondrocytes grow and form stacks of cells that parallel the direction of bone growth. (Cartilage spends- lose blood cells- hence the bone invades the space)3. Zone of maturation and hypertrophy (Expanding) chondrocytes mature, hypertrophy and wrap up glycogen in their cytoplasm. No mitosis occurs4. Zone of ca lcification and cell death Chondrocytes die and the cartilage matrix becomes calcified impregnated with calcium and phosphorus5. Zone of ossification blood vessels invade spaces left 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. Coalescence of trabeculae creates spongy bone. Resorption of spongy bone by osteoclasts in the centre of the diaphysis enlarges the medullary cavity.Summary of histochemical processes for both models of bone formation* Osteoblasts secrete osteoid with no minerals* Formation of primary bone whereby osteoid is mineralized* Formation of secondary bone as compact or spongy boneGrowth in length of long bone* due to interstitial growth of epiphyseal cartilage* Growth continues until around 20 when the epiphyseal pl ate closes (cartilage is replaced by bone) and growth in length moolahGrowth in width of long bone* As a result of appositional growth from the surface and resorption by osteoclasts of the inner shaft so that the marrow space can be blown-upBone Remodelling* Continual remodelling occurs in response to forces (e.g. teeth growing jawbones). Bone is deposited due to traction and resorbed due to pressure.* In young, bone deposition exceeds bone resorption. In the adult bone deposition is balanced with resorption.Joints* Joints are categorise according to the degree of movement between the bones of the joint* Synarthroses teentsy or no movement. There are 3 types based on the tissue making up the union* Syndesmosis is the union of bones by dense CT e.g tibiofibular and radioulnar joints* Synchondrosis is a junction by cartilage e.g. IVDs and symphysis pubic bone* Synostosis is a joint united by bone e.g. skull sutures (Starts off as fontanelles)* Diarthroidal (synovial) e.g. knee, h ip, shoulder have great freedom of movement and have a CT capsule around a joint cavity held by ligaments.* 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 viscosity of the fluid varies with temperature.*Fibrous- collagen- little to no movement- interosseous ligament*Gomphosis- tooth joined by cartilage