Osseous Tissue and Bone Structure

Chapter 6: Osseous Tissue and Bone Structure The Skeletal System • Skeletal system includes: – bones of the skeleton – cartilages, ligaments, and connective tissues Functions of the Skeletal System 1. 2. 3. 4. 5. 6. Support Storage of minerals (calcium) Storage of lipids (yellow marrow) Blood cell production (red marrow) Protection Leverage (force of motion) • Bone are identified by: – shape – internal tissues – bone markings Classification of Bones 1. 2. 3. 4. 5. 6. Long bones Flat bones Sutural bones Irregular bones Short bones Sesamoid bones Bone Shapes Long Bones • Are long and thin • Are found in arms, legs, hands, feet, fingers, and toes Flat Bones • Are thin with parallel surfaces • Are found in the skull, sternum, ribs, and scapula Figure 6–1a Sutural Bones • Are small, irregular bones • Are found between the flat bones of the skull Irregular Bones • Have complex shapes • Examples: – spinal vertebrae – pelvic bones Figure 6–1c Short Bones – ankle – wrist bones • Are small and thick • Examples: Sesamoid Bones • Are small and flat • Develop inside tendons near joints of knees, hands, and feet Figure 6–1e Bone Markings • Depressions or grooves along bone surface • Projections where tendons and ligaments attach and at articulations with other bones • Tunnels where blood and nerves enter bone Long Bones – Femur (ex) • Diaphysis - the shaft – A heavy wall of compact bone, or dense bone – A central space called marrow cavity • Epiphysis-wide part at each end & articulation with other bones – Mostly spongy (cancellous) bone – Covered with compact bone (cortex) • Metaphysis: – where diaphysis and epiphysis meet Figure 6–2a Flat Bones • The parietal bone of the skull • Resembles a sandwich of spongy bone • Between 2 layers of compact bone Figure 6–2b Types And Functions of Bone Cells • • • • Dense, supportive connective tissue Contains specialized cells Produces solid matrix of calcium salt deposits Around collagen fibers Bone (Osseous) Tissue Characteristics of Bone Tissue •Dense matrix, containing deposits of calcium salts and bone cells within lacunae organized around blood vessels Matrix Minerals • 2/3 of bone matrix is calcium phosphate, Ca3(PO4)2: – reacts with calcium hydroxide, Ca(OH)2 – to form crystals of hydroxyapatite, Ca10(PO4)6(OH)2 – which incorporates other calcium salts and ions • 1/3 of bone matrix is protein fibers (collagen) 1. Osteocytes Canaliculi form pathw ays for blood vesse ls excha nge nutrie nts and waste s Bone Cells - 4 • Mature bone cells that maintain the bone matrix • Live in lacunae • Are between layers (lamellae) of matrix • Connect by cytoplasmic extensions through canaliculi in lamellae • Do not divide • Maintains protein and mineral content of matrix • Helps repair damaged bone Figure 6–3 (1 of 4) 2. Osteoblasts • Immature bone cells that secrete matrix compounds (osteogenesis) • Osteoid - Matrix produced by osteoblasts, but not yet calcified to form bone • Osteoblasts surrounded by bone become osteocytes Figure 6–3 (2 of 4) 3. Osteoprogenitor Cells • Mesenchymal stem cells that divide to produce osteoblasts • Are located in inner, cellular layer of periosteum (endosteum) • Assist in fracture repair 4. Osteoclasts • Secrete acids and protein-digesting enzymes • Giant, mutlinucleate cells • Dissolve bone matrix and release stored minerals (osteolysis) • Are derived from stem cells that produce macrophages Figure 6–3 (4 of 4) Bone Tissues - 2 1. Compact Bone Osteon • The basic unit of mature compact bone • Osteocytes are arranged in concentric lamellae • Around a central canal containing blood vessels Figure 6–5 Perforating Canals • Perpendicular to the central canal • Carry blood vessels into bone and marrow Circumferential Lamellae • Lamellae wrapped around the long bone • Binds osteons together • Compact bone is covered with membrane: – periosteum - outside & endosteum - inside • Covers all bones except parts enclosed in joint capsules • It is made up of an outer, fibrous layer and an inner, cellular layer Periosteum Functions of Periosteum 1. Isolate bone from surrounding tissues 2. Provide a route for circulatory and nervous supply 3. Participate in bone growth and repair Endosteum • An incomplete cellular layer: – lines the marrow cavity – covers trabeculae of spongy bone – lines central canals • Contains osteoblasts, osteoprogenitor cells, and osteoclasts • Is active in bone growth and repair Figure 6–8b 2. Spongy Bone • Does not have osteons • The matrix forms an open network of trabeculae • Trabeculae have no blood vessels Figure 6–6 • The space between trabeculae is filled with red bone marrow: – which has blood vessels – forms red blood cells – and supplies nutrients to osteocytes • In some bones, spongy bone holds yellow bone marrow: – is yellow because it stores fat Bone Development • Human bones grow until about age 25 • Osteogenesis: – bone formation • Ossification: – the process of replacing other tissues with bone – Calcification is the process of depositing calcium salts and occurs here – The 2 main forms of ossification are: • intramembranous ossification aka - dermal ossification: – occurs in the dermis – produces dermal bones such as mandible and clavicle • endochondral ossification Intramembranous Ossification – 3 steps 1. Mesenchymal cells aggregate differentiate into osteoblasts, begin ossification at ossification center, develop spicules 2. Blood vessels grow into the area to supply the osteoblasts and spicules connect trapping blood vessels inside bone 3. Spongy bone develops and is remodeled into osteons of compact bone Endochondral Ossification – 6 steps • Ossifies bones that originate as hyaline cartilage (most bones originate as hyaline cartilage). • Long bones 1. Chondrocytes in the center of hyaline cartilage: – Enlarge, form struts and calcify, and die, leaving cavities in cartilage 2. Blood vessels grow around the edges of the cartilage and cells in the perichondrium change to osteoblasts: – Produces layer of superficial bone around shaft which continues to grow & become compact bone 3. Blood vessels enter the cartilage bringing fibroblasts that become osteoblasts and spongy bone develops at the primary ossification center 4. Remodeling creates a marrow cavity: – bone replaces cartilage at the metaphyses 5. Capillaries and osteoblasts enter the epiphyses creating secondary ossification centers 6. Epiphyses fill with spongy bone: – cartilage within the joint cavity is articulation cartilage – cartilage at the metaphysis is epiphyseal cartilage • As long bone matures: Mature Bones – osteoclasts enlarge marrow cavity – osteons form around blood vessels in compact bone • Epiphyseal Lines – When long bone stops growing, after puberty epiphyseal cartilage disappears and are visible on X-rays as an epiphyseal line Blood Supply of Mature Bones – 3 sets 1. Nutrient artery & vein: – a single pair of large blood vessels – enter the diaphysis through the nutrient foramen – femur has more than 1 pair 2. Metaphyseal vessels: – supply the epiphyseal cartilage – where bone growth occurs 3. Periosteal vessels provide: – blood to superficial osteons – secondary ossification centers Figure 6–12 Remodeling of Bone • The adult skeleton maintains itself and replaces mineral reserves by remodeling – Remodeling - recycles and renews bone matrix • involves osteocytes, osteoblasts, and osteoclasts • Heavily stressed bones become thicker and stronger – Mineral recycling allows bones to adapt to stress Effects of Exercise on Bone • Bone degenerates quickly - Up to 1/3 of bone mass can be lost in a few weeks of inactivity Bone Degeneration Effects of Hormones & Nutrition on Bone • Normal bone growth and maintenance requires nutritional and hormonal factors • Minerals - A dietary source of calcium and phosphate salts: – plus small amounts of magnesium, fluoride, iron, and manganese • Vitamins – Vitamin C is required for collagen synthesis, and stimulates osteoblast differentiation – Vitamin A stimulates osteoblast activity – Vitamins K and B12 help synthesize bone proteins • Hormones – Calcitriol • made in kidneys & helps absorb calcium & phosphorus from digestive tract • synthesis requires vitamin D3 (cholecalciferol) – Growth hormone & thyroxine stimulate bone growth – Estrogens & androgens stimulate osteoblasts – Calcitonin & parathyroid hormone regulate calcium & phosphate levels Chemical Composition of Bone • Bones store calcium and other minerals • Calcium - most abundant mineral in the body • Calcium ions are vital to: – Membranes, neurons, muscle cells – esp heart cells – & are closely regulated by homeostasis • is maintained by calcitonin & parathyroid hormone which control storage, absorption, and excretion Parathyroid Hormone (PTH) • Produced by parathyroid glands in neck • Increases calcium ion levels by: – stimulating osteoclasts – increasing intestinal absorption of calcium – decreases calcium excretion at kidneys Calcitonin • Secreted by C cells (parafollicular cells) in thyroid • Decreases calcium ion levels by: – inhibiting osteoclast activity – increasing calcium excretion at kidneys • Fractures cracks or breaks in bones caused by physical stress & repaired in 4 steps 1. a. Bleeding: – produces a clot (fracture hematoma) and establishes a fibrous network b. Bone cells in the area die 2. a. Cells of the endosteum & periosteum: – Divide & migrate into fracture zone b. Calluses stabilize the break: – external callus of cartilage and bone surrounds break – internal callus develops in marrow cavity Fractures 3. Osteoblasts: – replace central cartilage of external callus – with spongy bone 4. Osteoblasts and osteocytes remodel the fracture for up to a year: – reducing bone calluses The Major Types of Fractures • Pott’s fracture • Comminuted fractures • Transverse fractures • Spiral fractures • Displaced • Colles’ • Greenstick • Epiphyseal • Compression Figure 6–16 (4 of 9) • Bones become thinner and weaker with age • Osteopenia begins between ages 30 and 40 • Women lose 8% of bone mass per decade, men 3% Age and Bones • Osteoporosis – The epiphyses, vertebrae, & jaws are most affected resulting in fragile limbs, reduction in height, & tooth loss – Severe bone loss – Affects normal function – Over age 45, occurs in 29% of women & 18% of men • Estrogens & androgens help maintain bone mass •Bone loss in women accelerates after menopause