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Chapter 7 Bone Tissue

Chapter 7 Bone Tissue. Dynamic tissue that continually remodels itself Bone connective tissue with a matrix hardened by minerals bones make up the skeletal system Functions of the skeletal system support, protection, movement, blood formation, mineral reservoir. Shapes of Bones.

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Chapter 7 Bone Tissue

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  1. Chapter 7Bone Tissue • Dynamic tissue that continually remodels itself • Bone • connective tissue with a matrix hardened by minerals • bones make up the skeletal system • Functions of the skeletal system • support, protection, movement, blood formation, mineral reservoir

  2. Shapes of Bones

  3. Structure of a Long Bone • Parts of a long bone are the: • Epiphysis (ends) • Diaphysis (shaft) • Medullary (marrow) cavity • Endosteum - contains osteoprogenitor cells • Periosteum - membrane around the bone • fibrous layer • osteogenic layer • Articular cartilage - hyaline cartilage covers the surface of joints

  4. HISTOLOGY OF BONE • Bone consists of widely separated cells surrounded by large amounts of matrix • Four principal types of cells: • 1. osteoprogenitor cells - unspecialized can divide • 2. osteoblasts - form bone, secrete collagen • 3. osteocytes – former osteoblasts, strain sensors that detect stress in the bone and talk to osteoblasts on the bone surface • 4. osteoclasts - reabsorb bone

  5. BONE HISTOLOGY (cont.) • Matrix contains some calcium carbonate, calcium phosphate but mostly hydroxyapatite, which is the PRIMARY salt that makes bone hard. • Matrix is deposited in a framework of collagen fibers, - calcification or mineralization • salts confer hardness on bone • collagen fibers give tensile strength • Matrix (Bone) composition = 25% water, 25% protein fibers and 50% minerals

  6. Compact Bone • Bone may be categorized as compact or spongy • Dense bone tissue consists of osteons (Haversian systems) = basic structural unit • cylinders of tissue formed from layers (lamellae) • central canal holding a blood vessel • osteocytes connected to each other and by tiny canals called canaliculi

  7. Histology of Compact Bone

  8. Blood Vessels of Compact Bone

  9. Spongy Bone • Spongelike appearance called trabeculae • spaces filled with red bone marrow • Provides strength with little weight • trabeculae develop along bone’s lines of stress • Spongy bone have few osteons, why?

  10. Spongy Bone Structure and Stress

  11. Primary Ossification Center & Marrow Space • A process called ossification (osteogenesis) forms skeleton of embryo • cells differentiate into osteoblasts and osteoclasts • Begins during the 6 or 7 th week of embryonic life and continues throughout adulthood

  12. Metaphysis & Secondary Ossification Center • Metaphysis is cartilagenous material that remains as growth plate between medullary cavity & secondary ossification centers in the epiphyses.

  13. The Fetal Skeleton at 12 Weeks

  14. Epiphyseal PlatesFuse in Adults

  15. Bone Growth and Remodeling • Grow and remodel themselves throughout life • athletes or history of manual labor have greater density & mass of bone • Most bone is formed by Endochondral ossification (IN- outward) • Step 1 = Cartilage forms • Step 2 = Cartilage grows • Step 3 = Bone replaces the cartilage from the inside center outward.

  16. Hormonal Bone Growth • Hormonal Regulation of Bone Growth • Human Growth Hormone (GH) stimulate bone deposition, in addition to thyroid hormone, parathyroid hormone, and calcitonin • variation of these hormones can lead to either gigantism or dwarfism • At puberty the sex hormones stimulate sudden growth and modify the skeleton • thyroid hormone - promotes growth and maturity • calcitonin - thyroid gland - promotes bone formation, inhibits osteoclast activity • parathyroid hormone - promotes bone resorption, increase activity of osteoclasts

  17. Mineral Resorption • Bone is the major reservoir for calcium (Ca++) • Blood level of calcium ions is very important in cardiac, nerve, enzyme, blood • If blood levels get to low, the body will pull from the bones

  18. BONE HOMEOSTASIS • Remodeling • Replacement of old bone tissue with new bone tissue • Destroyed by osteoclasts (clubbed) and is constructed by osteoblasts (built) • Increased _____ activity/ decreased _____ activity causes bone loss • Increased _____ activity/ decreased _____ activity causes bone creation

  19. Example of Bone Remodeling • Dental braces reposition teeth, creating greater pressure on the bone on one side of the tooth and less on the other side • increased pressure stimulates osteoclasts; decreased pressure stimulates osteoblasts to remodel jaw bone

  20. Fractures • Stress fracture is a break caused by abnormal trauma to a bone • car accident, fall, athletics, etc • Pathological fracture is a break in a bone weakened by some other disease • bone cancer or osteoporosis

  21. Types of Bone Fractures (Table 7.3)

  22. Healing of Fractures • Normally healing takes 8 - 12 weeks (longer in elderly) • Stages of healing • fracture hematoma (1) • granulation tissue (2) • callus formation (3) • remodeling (4) occurs over next 6 months • Electrical stimulation is used on fractures that take longer than 2 months to heal • Silica- Horsetail herb, repairs fractures

  23. Healing of Fractures 1 2 3 4

  24. Fracture and Repair I

  25. Fracture and Repair II

  26. Bone Diseases • Abnormal softness of the bones is called rickets in children and osteomalacia in adults • Paget's disease = massive osteoclastic resorption and extensive bone formation • Osteoporosis: most common bone disease • Bones lose mass & become brittle • risk of fracture of hip, wrist & vertebral column • lead to fatal complications such as pneumonia, why? • widow’s (dowager’s) hump is deformed spine • Best treatment is prevention -- exercise & calcium intake (1,500 mg/day) while young & old

  27. Effects of OsteoporosisLumbar Normal Abnormal

  28. Nutrition for good bones • Vitamins • A - controls activity of osteoblasts and osteoclasts, rarely toxic in high dosage • D - promotes removal of Calcium from the bone (1,500 mg maximum) • C - maintains the matrix • AVOID SODA DRINKS • Minerals • calcium and phosphorus - make matrix hard • magnesium - deficiency inhibits osteoblast • manganese - inhibit formation of new bone, supports ligaments (Boneless chickens)

  29. EXERCISE AND BONE • Response to mechanical stress increases deposition of mineral salts and production of collagen fibers (aids osteoporosis) • Removal of mechanical stress weakens bone through demineralization • Weight-bearing activities help build and retain bone mass

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