Cartilage and bone
Perichondrium
Cellular dense connective tissue layer at surface which gives rise to new chondrocytes. Articular surface of joint cartilages lacks perichondrial layer (partly why poor repair after injury)
Growth of epiphyseal plate
Chondrocytes in deeper layers of epiphyseal cartilage can proliferate to produce elongation. As new cells are produced programmed to be replaced by bone. Series of zones. Growth controlled by genetics, hormones, growth factors.
Primary lamellae
Lamellae of complete osteons
Territorial matrix
Layer which surrounds chondrocytes in cartilage. Basophilic due to proteoglycans.
Osteons
Laying bone down within previous sites of erosion so that lamellae laid down from the outside in. Newest are immediately surrounding the Haversion canal and oldest at the perimeter.
Periosteum
Lines the outside of the long bone. Contains osteogenic layer.
Hyaline cartilage structure
Protein core with chondroitin sulfate GAGs and keratin sulfate GAGs which make an aggrecan monomer. Pale, hydrated homogeneous matrix with anionic (acidic) GAGs predominate and impart light basophilia. Collagen type II fibrils form network which is not visible with standard staining. Shock absorber due to hydration of GAGs.
Thyroid hormone in cartilage
Regulates cartilage hypertrophy and cell death
Osteocytes
Resident cells of bone. Reside in lacunae surrounded by bone matrix they produce. Send spider-like cytoplasmic processes into tiny canaliculi in matrix. Communicate in a network with other osteocytes via gap junctions. Function in turnover and maintenance of matrix by sensing mechanical stress on bone. Have ability to deposit or remove calcium from bone (for homeostasis).
Chondrocytes
Resident cells of cartilage
Secondary lamellae
Residual lamellae between fully formed primary osteons
Osteoporosis
Resorption exceeds new bone formation, bone develops resorption cavities, and loses structural integrity. Less bone density, loss of strength and fractures. Note: Exacerbated by exogenous steroids
Organic bone matrix
Rich in type I collagen and accounts for eosinophilia of demineralized preparations
How cessation of bone growth occurs
Secondary centers of ossification are a prelude to the cessation of growth when the entire growth plate is replaced by bone.
Diaphysis
Shaft of the long bone, connected to the epiphysis by the metaphysis region.
Endosteum
Single layer of osteogenic cells lining the marrow cavity
Resorption cavities
Sites of bone removal that create larger spaces intersecting the boundaries of osteons. Often cross sections of tunnels called cutting cones in which osteoclasts remove bone at the tip of the cone.
Lacunae
Spaces where chondrocytes and osteocytes are found
Trabecular bone
Thin anastamosing (branches that come together again) trabeculae which contain entrapped osteocytes. Layer of osteoblasts cover surface producing osteoids on the surface of mineralized trabeculae. Osteogenic cells resemble low cuboidal epithelium (but they aren't). Osteocytes nourished by diffusion from surface through canalicular channels b/c trabeculae thin and surrounded by sinusoidal capillaries of marrow cavity.
3 causes of osteoporosis
1. Decreased estrogen and bone formation 2. Decreased vitamin D and calcium absorption in alcoholic cirrhosis 3. Decreased vitamin D, hypercalcemia , secondary hyperparathyroidism in renal disease
2 forms of cartilage growth
1. Interstitial 2. Appositional
Process of long bone formation (3)
1. Long bones first formed from cartilage models in fetus 2. Epiphyseal cartilages permit joints to function while bones grow 3. Intramembranous bone formation in the shaft lends support during growth
5 zones of the epiphyseal plate
1. Reserve cartilage 2. Proliferation 3. Hypertrophy 4. Calcified cartilage 5. Vascular invasion, bone deposition, and resorption (osteoblasts in the marrow cavity lay down bone on the residual calcified cartilage)
Osteophytes
AKA bone spurs. Bony projections that form along joint margins in deteriorating bones (arthritis).
Osteoarthritis
Very common (85% by age 75). Chondrocyte death and loss of joint cartilage, inflammation of synovial membranes, narrowing of joint space, thickened subchondral bone, development of osteophytes. Painful, nonfunctioning joint.
Osteoblasts
Bone cells active in proliferating/producing new organic bone matrix (osteoid). Found on bone surfaces where they lay down new matrix during appositional growth.
Intramembranous bone formation/ossification
Bone formation in dense connective tissue membranes. Occurs from mesenchymal stem cells which differentiate into osteoprogenitor cells and begin to mineralize their surrounding bone matrix to form bone.
Development of fetal bones/growing epiphyses of long bones
Bone replaces cartilage in a process called endochondral ossification. Cartilage model provides flexible structure for growth (interstitial and appositional) and remodeling of immature skeleton.
Haversion canal
Contains neurovascular bundle of vein, artery, and nerve
Cutting cones
Cross sections of tunnels (resorption cavities) in which osteoclasts spearhead bone removal
Inorganic bone matrix
Crystalline matrix produced by mineralization composed of hydroxyapatite rich in Ca(PO4)
Haversion systems (osteons)
Cylindrical units of compact bone with concentric lamellae organized axis of Haversion canal
Fibrocartilage
Dense network of collagen type I fibers that stain with eosin. Looks like dense connective tissue with differences in lacunar arrangements and fiber arrays which are sometimes pinnate instead of linear.
Compact bone
Dense outer shell with subunits with calcified layers arranged in concentric layers or lamellae around a core of vessels and nerves. May lack regular Haversian systems (woven bone).
Osteoclasts
Develop from monocytes stimulated by cytokines (M-CSF and RANKL) and direct interaction with osteoblasts. Attach to bony surface, remove inorganic matrix, and digest organic matrix. Stimulated by parathyroid hormone through osteoblasts. Inhibited through binding by calcitonin. Create acidic microenvironment for demineralization and lysosomal digestion of organic matrx.
Yellow marrow
Fatty bone marrow (increases with age)
Fracture repair
Fibrin in blood clot at fracture site produces scaffold for organization of fibroblasts (like a scar) which generate cartilaginous callus or union. Soft callous undergoes transformation into vascularized bony callus. Remodeling can make fracture site indistinguishable.
Cartilage
Forms a flexible skeletal support which can grow and provide substrate for bone formation during development. Avascular-lacking capillary network and nourished by diffusion through cartilage matrix. 3 types: Hyaline, elastic, and fibrocartilage.
Hyaline cartilage
Forms the bulk of embryonic skeleton. Supporting role in adults in some locations. Resists compressive forces and provides smooth surfaces for articulation at diarthrodial joints.
IFG-1 and somatomedin
From excess growth and causes acromegaly
Paget's disease
Generalized skeletal disorder associated with thickening and weakening of bones related to disregulation of osteoclastic and osteoblastic activity
Osteomalacia
Group of disorders characterized by failure to form normal mineralized matrix. Unmineralized matrix forms soft bone. In growing skeleton called Rickets.
Isogenous groups
Groups of 2-8 cells within one lacunae suggesting that a cell divided but daughter cells have not yet produced enough matrix to be separated
Bone morphogenetic proteins, IGF-1, Wnt proteins
Growth factors and hormones which regulate the process of osteogenitor differentiation to osteoblasts and osteoblast secretion of inorganic matrix (osteoid)
Epiphyseal plate
Growth plate in the intermediate region of the long bone.
Epiphysis
Head of long bone, usually with expanded surface on which the articular cartilage is attached
Red marrow
Hematopoetic bone marrow
Spongy bone
Interconnected network of trabeculae or bone spicules which provide supporting framework beneath compact bone. Can remodel in response to stress. Marrow permeates between bony spicules.
Osteogenic layer
Inner cellular layer of periosteum which can give rise to new bone on the outside (single layer called endosteum)
Volkmann's canals
Interconnect Haversion canals and appear to be perpendicular to the longitudinal axis of osteons.
Elastic cartilage
Looks similar to hyaline but contains bundles of elastic fibers which need special stains to be visualized. Deformability and resilience.
What is the origin of cartilage and bone tissue?
Mesenchymal
Osteoclast structure
Multinucleated (3-8) giant cells. Found in erosion pits (Howship's lacunae) that they have created on bony trabecular surface of spongy bone or may be active in resorption cavitiies within compact bone.
Appositional growth in cartilage
Occurs from perichondrium where cells on inner surface give rise to new chondrocytes
Interstitial growth in cartilage
Occurs from within by division of chondrocytes and expansion of flexible matrix
Appositional growth in bone
Only form of growth in bone since matrix cannot expand from within. Addition of bone occurs on surfaces (e.g. trabeculae of spongy bone) or on walls of resorption cavities created by osteoclasts within compact bone.
Bone
Support, protection, and attachments for tendons and ligaments. Mineral storage depot, remodels in response to damage/stress, blood cell production. Highly vascular.
Metaphysis region
Where the epiphysis (head) and diaphysis (shaft) of the long bone connect