Bone Tissue- Chapter 5 5-1 Bone Functions • • • • • • Support Protection Assistance in movement Mineral storage and release Blood cell production Triglyceride storage 5-2 Bone Chemistry • Water (25%) • Organic Constituent (~25%) – Collagen. • A fibrous protein that provide flexibility. • Inorganic Constituent (~50%) – Calcium phosphate and calcium carbonate. • Mineral salts that provide hardness. 5-3 Bone Cell Types • • • • Osteogenic cells- stem cells. Osteoblasts- bone building cells, secrete matrix & collagen fibers. Osteocytes- mature bone cells that no longer secrete matrix. Osteoclasts- bone digestion. 5-4 80% 20% Compact and Spongy Bone 5-5 Compact Bone- the osteon is the basic unit of structure. 5-6 Histology of Compact Bone • Concentric Lamellae- calcified matrix surrounding a vertically oriented blood vessel. • Lacuna- a small hollow space, contains osteocytes. • Canaliculus- a small channel filled with extracellular fluid that connects lacunae to each other, and to the central canal. • Central Canal- a circular channel that contains blood and lymphatic vessels, and nerves. 5-7 Lacunae, Lamellae, Canaliculi, Haversian Canals 5-8 Spongy Bone • Trabeculae- latticework of thin plates of bone. • Spaces in between the lattice are filled with red marrow, which is where blood cells and platelets develop. • Location- found near ends of long bones and inside flat bones. i.e. hipbones, sternum, sides of skull, and ribs. Histology- no true osteons. 5-9 Anatomy of a Long Bone 5-10 Bone Growth in Length • Epiphyseal plate – Cartilage cells in this plate divide rapidly. – Zone of proliferating cartilage. • Between ages 18-25, the epiphyseal plates close. – Cartilage cells in the plate stop dividing and bone replaces the cartilage. • Growth in length stops at age 25. 5-11 Bone Growth in Width 5-12 Factors Affecting Bone Growth 1 • Nutrition – Adequate levels of vitamins and minerals. • Calcium and phosphorus for bone growth. • Vitamin C for collagen formation. • Vitamins K and B12 for protein synthesis. 5-13 Factors Affecting Bone Growth 2 • Hormones – During childhood growth factors stimulate cell division. • Human growth hormone (hGH) • Thyroid hormones • Insulin – Sex steroids at puberty initiate male and female characteristics. 5-14 Hormonal Abnormalities • Oversecretion of hGH during childhood produces giantism. • Undersecretion of hGH or the thyroid hormones during childhood produces dwarfism. – The epiphyseal plate closes before normal height is reached. • Estrogen is responsible for closing the growth plate. – Both men and women that lack estrogen receptors on cells grow taller than normal. 5-15 Bone Remodeling • Bone Remodeling- the ongoing replacement of old bone tissue by new bone tissue. • Resorption and Deposition – Osteoclasts- removal of minerals and collagen. • 4% per year in compact bone. • 20% per year in spongy bone. – Osteoblasts- deposition of minerals and collagen. 5-16 Aging and Bone Tissue • Demineralization- loss of minerals. – Very rapid in women 40-45 as estrogen levels decrease. – In males, begins after age 60, but is gradual. • Decrease in protein synthesis – Decrease in growth hormone. – Decrease in collagen production, which gives bone its tensile strength, this causes bone to become brittle and susceptible to fracture. 5-17 • Cold spots indicate – Decreased metabolism of decalcified bone. – Fracture. – Infection. 5-18 Osteoporosis • Decreased bone mass resulting in porous bones. • Those at risk – White, thin, menopausal, smoking, drinking females with a family history. – Athletes who are not menstruating due to reduced body fat and decreased estrogen levels. – People allergic to milk or with eating disorders whose intake of calcium is low. • Prevention or decrease in severity of osteoporosis. – Adequate diet, weight-bearing exercise, and estrogen replacement therapy (for menopausal women). – Behavior when young may be most important factor. 5-19 Exercise and Bone Tissue • Mechanical Stress- the pull on bone by skeletal muscle and gravity. • Mechanical stress increases deposition of mineral salts and collagen production. 5-20 Lack of Mechanical Stress Results in Bone Loss. 5-21 5-22 Fracture- any break in a bone. • Named for shape or position of fracture line. • Common fracture types: – Open fracture- skin broken. – Comminuted- broken ends of bones are fragmented. – Greenstick- partial fracture. – Impacted- one side of fracture driven into the interior of other side. – Pott’s- distal fibular fracture. – Colles’- distal radial fracture. – Stress fracture- microscopic fissures from repeated strenuous activities. 5-23 Developmental Anatomy Bone- derived from the Mesoderm germ layer. 5th Week= limb bud appears as mesoderm covered with ectoderm. 6th Week= constriction produces hand or foot plate, skeleton now totally cartilaginous. 7th Week= endochondral ossification begins. 8th Week= upper & lower limbs visible. 5-24 Joints • Joint- a point of contact between – Two bones – Bone and cartilage – Bone and teeth • Joint= articulation=arthrosis. • Arthrology- the scientific study of joints. • Synovial Cavity- the space between articulating bones. 5-25 Classification of Joints • Structural classification based upon: – 1) Type of connective tissue holding bones together. – 2) Presence or absence of space between bones. • Fibrous joint- collagen fibers, no space. • Cartilaginous joint- cartilage, no space. • Synovial joint- dense irregular connective tissue, space. • Functional classification based upon movement: – Synarthrosis- immovable. – Amphiarthrosis- slightly movable. – Diarthrosis- freely movable. 5-26 Synovial Joints • Synovial cavity separates articulating bones. • Freely movable (diarthroses). • Articular cartilage – Reduces friction. – Absorbs shock. • Articular capsule – Surrounds joint. – Thickenings in fibrous capsule called ligaments. • Synovial membrane – Inner lining of capsule. – Secretes synovial fluid containing hyaluronic acid (slippery). 5-27 Hinge Joint • Convex surface of one bone fits into concave surface of 2nd bone. • Monoaxial movement, like a door hinge. • Movements– Flexion- decreasing the joint angle. – Extension- increasing the angle. – Hyperextension- opening the joint beyond the anatomical position. • Examples – Knee, elbow, ankle, interphalangeal joints. 5-28 Elbow Joint- hinge type. 5-29 5-30 Ball and Socket Joint • Ball fitting into a cuplike depression. • Multiaxial movement. • Movement- occurs around all axes. • Examples – Shoulder joint – Hip joint 5-31