Bone Flashcards
What are the 3 primary functions of the skeletal system?
(1) Mechanical support for sites of muscle attachment (2) Protection of vital organs (3) Ion reserve of Ca and PO for metabolic functions
What is bone?
Connective tissue (made of cells and matrix) in which the matrix has been hardened to accommodate a supporting function
Bone Cells & Matrix - Name the 3 key cells of bone tissue, give their unique functions, and state the cell lines from which these cells originate.
(1) Osteoblasts - synthesize bone matrix, responsible for mineralization, derived from osteoprogenitor cells (mesenchymal stem cell line); (2) Osteocytes - Inactive osteoblasts trapped within bone that they formed; (3) Osteoclasts - break down bone matrix through phagocytosis, derived from monocyte (macrophage) cell line
Bone Cells & Matrix - What are Howship’s lacunae?
Pits in bone surface = space between osteoclast and bone, aka resorption bays
Bone Cells & Matrix - What is bone matrix composed of?
(1) Osteoid (unmineralized matrix composed of type I collagen & glycosaminoglycans (GAGs)) (2) Calcium hydroxyapatite (calcium salt crystal gives bone its strength & rigidity)
Bone Cells & Matrix - What is the significance of the balance between osteoblast and osteoclast activity?
Governs bone turnover and ensures that bone is neither overproduced nor over degraded
Bone Cells & Matrix - What are the two types of bone within bones? How do they differ structurally and functionally? Where are they contained in the body?
(1) COMPACT (or Cortical) BONE: thick, dense, area of bone to which ligaments and tendons attach, mechanical function (2) TRABECULAR (or Cancellous/Spongy) BONE: between layers of compact bone, thin, porous, contains bone marrow, metabolic function; Most bones of the body consist of both types of tissue
Macroscopic Bone Structure - Name and describe the 4 main areas of long bones.
(1) Epiphyses - ends, participate in joint surfaces (2) Diaphysis - shaft, walls of compact bone & underlying network of trabecular bone (3) Epiphyseal growth plate - interface between shaft & epiphysis, region in which cartilage proliferates to cause elongation of bone (4) Metaphysis - where shaft joins epiphyseal growth plate
Macroscopic Bone Structure - Name and describe the 3 different tissues that cover bone.
(1) ARTICULAR CARTILAGE - specialized form of hyaline cartilage, protect against friction in joints, line epiphysis; (2) PERIOSTEUM - fibrous external layer onto which muscles, ligaments, & ligaments attach, line outside of diaphysis; (3) ENDOSTEUM - inside diaphysis at border between cortical and cancellous bone, lining trabeculae
Microscopic Bone Structure - Describe the Haversian system of bone. How does this relate to Volkmann’s canals?
Compact bone is organized as parallel columns (aka Haversian systems), which run lengthwise down the axis of long bones; These columns are composed of lamellae = concentric rings of bone surrounding a central channel, or Haverisan canal, containing nerves, blood vessels, & lymphatic system of bone; Parallel Haversian canals are connected to one aother by perpendicular Volkmann’s canals
Microscopic Bone Structure - How are osteoblasts and osteoclasts involved in Haversian systems?
OSTEOBLASTS form lamellae, secrete matrix, become trapped in spaces called lacunae & become known as osteocytes; OSTEOCYTES communicate with Haversian canal through cytoplasmic extensions that run through canaliculi (small interconnecting channels)
Microscopic Bone Structure - What are the layers of long bone (beginning at the external surface)?
Periosteal surface of compact bone, Outer circumferential lamellae, Compact bone (Haversian systems), Inner circumferential lamellae, Endosteal surface of compact bone, Trabecular bone
Bone Development - How does bone development begin? What are the steps that follow?
Replacement of collagenous mesenchymal tissue by bone –> resulting in formation of women bone (primitive form of bone with randomly organized collagen fibers) –> further remodeled into mature lamellar bone (regular parallel rings of collagen) –> Lamellar bone constantly remodeled by osteoclasts & osteoblasts
Bone Development - Name and describe the 2 different methods by which bone is produced from mesenchymal tissue. Give examples of where each method occurs.
ENDOCHONDRAL OSSIFICATION: cartilage progressively replaced by bone at epiphyseal growth plate, occurs in long bones, vertebrae, & pelvis; INTRAMEMBRANOUS OSSIFICATION: mesenchymal tissue directly replaced by bone without an intermediate cartilage step, occurs most notably in skull
Bone Remodeling - Name and briefly describe the key steps in the sequence of bone remodeling.
(1) ACTIVATION: Osteoblasts induce osteoblasts to break down bone matrix (2) RESORPTION: Ruffled border of osteoclasts form sealed zone for isolated bone erosion (3) REVERSAL: Over time, osteoblasts begin to replace osteoclasts at site of bone turnover (4) FORMATION: Osteoblasts begin to lay down new lamellar bone on top of old bone, creating cement lines between old & new bone matrix
