Bone Tissue and Structure (Bone Histology, Classification, and Ossification) Nestor T. Hilvano, M.D., M.P.H.

Learning Objectives You should be able to: 1. State the primary functions of the skeletal system. 2. Describe the types of bones classified by shape. 3. Describe the general features of a long bone. 4. Describe the cells and ground matrix of bone tissue. 5. Compare the structures and functions of compact bone and spongy bone. 6. Describe intramembranous and endochondral ossifications. 7. Explain how mature bone grow and remodel itself. 8. Discuss the effects of exercise, nutrition, hormones, and aging on bone development. 9. Describe fractures and explain how it heal.

Skeletal System and Functions Skeletal system – bones, cartilages, ligaments, and connective tissues Functions – Support, Protection, Leverage (force of motion), Storage of minerals and lipids, and Blood cell production * Babies are born with 270 bones and many of these will fuse together by the age of 20 into 206 hard, permanent bones.

Bone Shapes a. Flat bones b. Irregular bones c. Long bones d. Short bones e. Sesamoid bones f. Sutural (wormian) bones Classify the following as to shape: ___ carpal (wrist) and tarsal (ankle) bones ___ phalanges (digits of fingers & toes) ___ bones of the arm (humerus), and forearms (radius & ulna), ___ bones of the thigh (femur), and leg (tibia & fibula) ___ clavicle (collarbone), sternum (breast bone), and rib ___ vertebrae ___ patella (knee cap)

Bone Structure I- Long bone, consists of a. Diaphysis (shaft) - outer wall= compact bone - central space= medullary cavity b. Epiphysis (wide part at each end) - spongy (cancellous) bone - articular cartilage (protection) c. Metaphysis - where diaphysis and epiphysis meet II- Flat bone, consists of a. Cortex (plates of cranium) = compact bone b. Diploe (in between the plates) = spongy bone

Bone Matrix Made up of: I. 1/3 Organic matter –Composed primarily of protein fibers, ___. –Resist tension; provide flexibility II. 2/3 Inorganic matter –85% hydroxyapatite crystals of ___. –Resist compression; provide hardness a. calcium phosphate b. collagen c. magnesium d. phospholipid ___ What substance is responsible in building strong bones and are needed for physiological processes such as muscle contraction, nerve impulse conduction, blood clotting, and membrane transport systems? a. potassium b. calcium c. iron d. sodium

Cells of Bone Tissue _____- Mesenchymal stem cells _____- Immature bone cells, responsible for osteogenesis (production of new bone), bone-forming cells _____- Mature bone cells that maintain the bone matrix, lodged in lacunae _____- Giant, multinucleate cells, which dissolve the bony matrix and cause osteolysis, bone-destroying cells a. osteoclast, b. osteoprogenitor, c. osteocyte, d. osteoblast

Compact Bone (dense) Functions - Protect, support, and resist stress Haversian system = also called osteon, basic structural unit Central canal Osteocytes in lacunae Concentric lamellae Canaliculi Volkmann canals –perpendicularly joining central canals Periosteum- outside membrane Endosteum- on the inside Found in cortex (plates) of flat bones, diaphysis of long bones What structure provides nutrients to bone cells? _____. a. lamellae b. central canal c. canaliculi d. volkmann canal

Spongy Bone (cancellous) Functions – storing marrow and support Spongelike appearance formed by plates of bone called trabeculae Osteocytes in lacunae Spaces filled with RBM Found in medullary canal of long bones, diploe of flat bones

Ossification (Bone Formation) Intramembranous ossification- bone is formed from a membrane (mesenchyme); formation of maxillae and mandible, flat bones of skull Endochondral (intracartilagenous) ossification- bone is formed from a fetal, hyaline cartilage; formation of short bones and long bones

Bone Growth and Remodeling Bones increase in length by ______ of epiphyseal plate. Bones increase in width by ______ at the outer surface of bone. Bones remodeled throughout life- greater density and mass of bone in athletes is an adaptation to stress, affected by hormones, nutrition, and aging. a. interstitial growth b. appositional growth

Abnormal Bone Development Increase Growth Hormone - Gigantism – before puberty - Acromegaly – after puberty Dwarfism * Achondroplasia (dominant disorder) –long bones stop growing in childhood; failure of cartilage growth –normal torso, short limbs * Pituitary Dwarf –lack of growth hormone –normal proportions with short stature Vit. D/ Calcium deficiency = abnormal softness in children (rickets) and in adults (osteomalacia). Osteoporosis – reduction in bone mass, effect of aging process. People get shorter with age due to in part to loss of bone density in the vertebrae.

Fractures What is a fracture? Types: 1.Closed or simple fractures 2.Open or compound fractures

Homework (Self- Review) 1. Define the following: bone, periosteum, endosteum, osteocyte, osteoblast, osteoclast, osteon, canaliculi, volkmann canal, osteogenesis, metaphysis, intramembranous ossification, endochondral ossification, diaphysis, epiphysis, fracture, osteoporosis, interstitial growth, appositional growth, haversian canal, osteomalacia, rickets, osteoporosis, acromegaly, achondroplasia. 2. Describe the structures and functions of compact bone and spongy bone. 3. Classify bones as to shape and give example to each. 4. What is pituitary dwarfism?