Chapter 6: SKELETAL SYSTEM I. FUNCTIONS A. Support B. Protection C. Movement D. Mineral storage E. Lipid storage (Fig. 6.8b) F. Blood cell production (Fig. 6.4) II. COMPONENTS A. Cartilage 1. Hyaline 2. Fibrous B. Growth of cartilage (Fig. 6.1) 1. Interstitial growth a. Chondrocytes in lacunae undergo mitosis and lay new, pushing each other apart as they do so b. When? 2. Appositional growth a. Fibroblasts in perichondrium convert to chrondroblasts which lay new Where? b. When? 28
29 C. Osseous tissue 1. Cells a. Osteoblasts b. Osteocytes c. Osteoclasts 2. Fibers: Collagen (30%) a. Source: Secreted by b. Function: 3. Ground substance: Hyaluronic acid a. Source: Secreted by b. Function: 4. Bone salts: Hydroxyapatite a. Calcium phosphate + calcium carbonate b. Calcium to Phosphorus = 3 to 2 ratio c. Source: d. Function: D. Summary of structure: "Steel reinforced concrete" (Fig. 6.2)
30 III. HISTOLOGY OF OSSEOUS TISSUE A. Cancellous (spongy) bone: Trabeculae (Fig.6.4) B. Compact bone (Fig. 6.6): Osteon 1. Central canal (Haversian canal) contains 2. Concentric lamellae 3. Osteocytes within 4. Canaliculi IV. PRENATAL BONE DEVELOPMENT A. Intramembranous bone formation (Fig.6.10, 6.11) 1. Location: 2. Time frame: 3. Process: Bone tissue forms directly in dense irregular c.t. B. Endochondral bone formation (Fig.6.12) 1. Location: 2. Time frame: 3. Process: a. Hyaline cartilage template (model ) forms. b. Bone collar forms; cartilage within template calcifies and dies. c. Blood vessels and osteoblasts enter dying cartilage at diaphysis. d. Secondary ossification centers form at epiphysis. e. Original cancellous bone is remodeled to compact bone.
31 V. BONE GROWTH IN CHILDHOOD A. Growth in length (Fig. 6.19 [6.17]) 1. The epiphyseal plate (Fig.6.13, 6.14) a. Def.: b. Process (Fig. 6.14) (1) Chondrocytes mitose and lay cartilage. (2) Cartilage calcifies and chondrocytes die. (3) Blood vessels and osteoblasts enter. (4) Osteoblasts lay collagen. (5) Calcification occurs. (6) Result: Cancellous bone c. Fusion of the epiphyseal plate results in an epiphyseal line (Fig.6.19 [6.17]) Effect: B. Growth in diameter (Fig.6.19 [6.17]) 1. Role of osteoblasts: 2. Role of osteoclasts:
32 VI. NUTRITION AND BONE HOMEOSTASIS A. Calcium 1. Source: 2. Absorption: Requires vitamin and magnesium 3. Other functions of calcium: a. Nervous system b. Muscular system c. Vascular system B. Phosphate C. Magnesium D. Vitamin D: Essential to absorb E. Vitamin C: Needed for F. Protein: Needed for
33 VII. HORMONES AND BONE HOMEOSTASIS (Fig. 1.3, Endocrine System) A. Parathyroid Hormone (PTH) (Fig. 6.21 [6.19]) 1. Source: 2. Function: 3. Control: Decreased blood Ca ++ Parathyroid gland Blood Ca ++ PTH Osteoclastic activity Ca ++ absorption from intestines ++ Ca reabsorption from kidneys into blood Vitamin D formation B. Calcitonin 1. Source: 2. Function: 3. Control: ++ High blood Ca Thyroid gland Blood Ca ++ Osteoclastic activity Calcitonin
34 C. Growth hormone (Fig. 6.17, 6.18 [Fig. A]) 1. Source: 2. Function: a. Bone: osteoblastic activity b. Cartilage: chondroblastic activity c. Overall effect: Growth is. 3. Hyposecretion of GH (childhood) (See Clinical Impact, p. 614) a. Dwarfism b. calcification of epiphyseal plates 4. Hypersecretion of GH a. Childhood: Giantism b. Adulthood: Thickened bones D. Thyroid hormone (Fig. 1.3, Endocrine System) 1. Source: 2. Effect of deficiency on skeleton (childhood):
35 E. Reproductive hormones (Fig. 1.3, Endocrine System) 1. Estrogen a. Source: b. Effect on bone: osteoblastic activity calcification of epiphyseal plates c. Result: d. Menopause 2. Progesterone a. Source: b. Effect on bone: c. Menopause 3. Testosterone a. Source: b. Effect on bone: osteoblastic activity calcification of epiphyseal plate c. Result:
36 V. BONE REMODELING A. Functions 1. Convert spongy bone to compact bone 2. Replace worn collagen and hydroxyapatite 3. Increase or decrease mass as needed 4. Reshape bone B. Rate 1. Age-dependent 2. Varies bone to bone 3. Increased by exercise 4. Affected by hormones C. Role of bone cells 1. Osteoblasts: 2. Osteoclasts: a. Secrete acid b. Secrete proteolytic enzymes c. Capable of phagocytosis D. Scheme (Fig. 6.16 [6.17])
37 E. Role of stress (Fig. 6.5) 1. Def.: Compressive force a. Increased stress ---> osteoblastic activity b. Decreased stress ---> osteoblastic activity c. Osteoclastic activity is affected by hormones 2. Examples: a. Weight-lifting b. Tuberosities of female versus male bones c. Left versus right deltoid tuberosity d. Weightlessness in space travel e. Bedridden patients f. Osteoporosis g. Orthodontics h. Walking casts IX. BONE REPAIR AFTER FRACTURE (Fig. 6.20 [6.18]) A. Hematoma forms B. Internal and external cartilaginous calluses form C. Cancellous bone is laid D. Remodeling occurs