Bone Tissue- Chapter 5

Bone Functions Support Protection Assistance in movement Mineral storage and release Blood cell production Triglyceride storage

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.

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.

Compact and Spongy Bone 80% 20% Compact and Spongy Bone

Compact Bone- the osteon is the basic unit of structure.

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.

Lacunae, Lamellae, Canaliculi, Haversian Canals

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.

Anatomy of a Long Bone

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.

Bone Growth in Width

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.

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.

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.

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.

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.

Cold spots indicate Decreased metabolism of decalcified bone. Fracture. Infection.

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.

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.

Lack of Mechanical Stress Results in Bone Loss.

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.

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.

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.

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.

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).

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.

Elbow Joint- hinge type.

Ball and Socket Joint Ball fitting into a cuplike depression. Multiaxial movement. Movement- occurs around all axes. Examples Shoulder joint Hip joint