University:
Glendale Community College
Course:
BIO160 | Introduction to Human Anatomy and Physiology
Academic year:

2019
Views:

279

Pages:

19
Author:

Jamison Bradshaw

Bone Tissue • Bone is alive and continuously changing. • Bone tissue (osseous tissue) is a type of connective tissue with cells, vessels, nerves and a matrix hardened by minerals (mostly calcium phosphate) • Bones are units of the skeletal system – individual bones are made up of bone tissue, marrow, cartilage and periosteum • Functions of the skeletal system include – support, protection, movement, blood formation, calcium and phosphate reservoir, pH balance Compact Bone and Spongy Bone Compact Bone does not have any spaces or hollows in the bone matrix that are visible to the eye. Compact bone forms the thick-walled tube of the shaft (or diaphysis) of long bones, which surrounds the marrow cavity (or medullary cavity). A thin layer of compact bone also covers the epiphyses of long bones. Spongy Bone (also called trabecular bone or cancellous bone) consists of a delicate network of trabeculae which branch and intersect to form a sponge-like tissue. The ends of long bones (or epiphyses) contain mainly spongy bone. Compact Bone and Spongy Bone Spongy Bone Compact Bone Features of Long Bones • Diaphysis (shaft) is a cylinder of compact bone containing the marrow cavity (medullary cavity) – Diaphysis covered with periosteum • Marrow Cavity contains hematopoeitic tissue • Epiphyses (enlarged ends) are spongy bone covered with a thin layer of compact bone – enlarged ends strengthen joint and provide attachment of tendons and ligaments • Joint Surface is covered with articular cartilage (smooth, low friction hyaline cartilage and synovial fluid) Features of Long Bones Periosteum and Endosteum Endosteum Perforating Fibers Periosteum is a layer of vascular, innervated, dense connective tissue surrounding the non-articular surfaces of bone. Perforating Fibers (also called Sharpey’s fibers) are collagen fibers that connect the periosteum to the bone matrix. The endosteum is a thin layer of connective tissue that lines the inside of the marrow cavity and any canals passing through the compact bone. Both the periosteum and the endosteum membranes are osteogenic – they contain cells that can produce bone. During growth or following injury, osteogenic cells can differentiate into bone-forming osteoblasts. Structure of a Flat Bone • External and internal surfaces of flat bone are composed of compact bone. • Middle layer is spongy bone and it is also called the diploe. • An impact to the skull may fracture the outer layer and crush the spongy bone, but not harm inner compact bone or the underlying brain. Osteogenic Cells • Osteogenic Cells are found in the endosteum and periosteum. – arise from embryonic mesenchymal cells – multiply continuously and differentiate into osteoblasts in response to stress or fractures • Osteoblasts produce an extracellular matrix of about 35% collagen fibers and 65% mineral (mostly calcium phosphate). • Osteocytes are osteoblasts that have completely surrounded themselves with the extracellular matrix they produce. • Spicules are isolated, newly formed pieces of bone. Osteocytes Osteocytes are completely surrounded by bone matrix. • Lacunae are the pits in the matrix occupied by the cells. • Filopods (also called pseudopods, cytoplasmic extensions, dendritic processes) are long thin extensions of the osteocytes that produce bone matrix around the cell. • Filopods are inside tiny canals in the matrix called canaliculi. Osteocytes Osteocytes are arranged in rings called lamellae that are around a central canal that contains blood vessels and nerves. Tips of filopods absorb nutrients from the central canal. Adjacent osteocytes are inter-connected with gap junctions at the tips of the filopods. Osteocytes transfer nutrients from one cell to another through gap junctions. Osteoclasts Macrophages • Some stem cells in bone marrow develop into macrophages white blood cells called macrophages. Some macrophages leave the blood and move into bone tissue. In the bone, 3-50 of these macrophages can merge into giant, multinucleated cells called osteoclasts. A single cell formed by the fusion of several cells is called a syncitium. • The surface of an osteoclast facing bone is folded into a ruffled border that releases lysosomes that contain enzymes and acids that erode bone matrix and produce pits in the matrix called resorption bays (also called Howship’s lacunae). Osteoclasts Four multinucleated osteoclasts producing resorption bays ( Howship’s lacunae) in the blue-stained bone matrix. The ruffled border of the osteoclasts is facing the the bone matrix. Dissolved components of the bone matrix (calcium and amino acids) accumulate in the interstitial space and are reabsorbed into the blood. Bone Matrix • Bone Matrix is about 35% organic and 65% inorganic • Bone Organic matter consists of: – collagen – glycosaminoglycans (chondroitin sulfate) – proteoglycans – glycoproteins • Bone Inorganic matter consists of: – 85% hydroxyapatite (calcium phosphate crystals) – 10% calcium carbonate – 5% other minerals (fluoride, sulfate, potassium, magnesium) • Combination of organic and inorganic materials makes bones both strong and resilient – minerals resist compression – collagen give some flexibility – Bone matrix is similar to fiberglass that is composed of strong glass fibers embedded in a flexible polymer Bone Matrix Compact Bone • Osteon (Haversian system) is the basic structural unit of bone. – Osteons are cylinders of bone tissue formed from layers (concentric lamellae) of osteocytes and matrix arranged around a central (Haversian) canal. – Central Canal is lined with endosteum and contains a neurovascular bundle. – Neurovascular Bundles contain an artery, vein, nerve and lymphatic vessel – Osteocytes are connected to each other and their blood supply by thin pseudopods within canaliculi. • Perforating Canals (Volkmann’s canals) are perpendicular branches of the central (Haversian) canal • Circumferential lamellae ring the outer circumference and the marrow cavity. • Bony trabeculae branch off the compact bone surrounding the marrow cavity, filling the cavity with spongy bone. Osteon = Haversian System Circumferential lamellae Histology of Compact Bone Osteon = Haversian System Lacunae Canaliculi Haversian (central) Canal Concentric Lamellae Perforating (Volkman’s) Canal Central (Haversian) Canal