6-1 Chapter 6 Skeletal System: Bones and Bone Tissue

6-2 Skeletal System Consists of bones, cartilage, tendons, ligaments Functions: –Support –Protection –Movement –Storage –Blood cell production

6-3 Hyaline Cartilage Chondroblasts produce matrix; become chondrocytes Matrix contains collagen fibers (strength) and proteoglycans (trap water) Contains no blood vessels or nerves Perichondrium –Dense connective tissue membrane that surrounds cartilage Cartilage most intimately associated with bone Most bones develop from it

6-4 Hyaline Cartilage (cont’d ) Articular Cartilage: thin layer of hyaline cartilage covering ends of bones at moveable joints Has no perichondrium, no blood vessels, no nerves Growth: Appositional: chondroblasts in perichondrium secrete new matrix; add new chondrocytes to outside of tissue Interstitial: chondrocytes within cartilage divide; add more matrix from inside existing cartilage

6-5 Bone Shapes Long –Upper and lower limbs Short –Carpals and tarsals Flat –Ribs, sternum, skull, scapulae Irregular –Vertebrae, facial, hip

6-6 Long Bone Structure Diaphysis –Shaft –Compact bone Epiphysis –End of the bone –Cancellous bone Epiphyseal plate –Hyaline cartilage –Bone growth in length Epiphyseal line –When bone stops growing in length, becomes ossified

6-7 Long Bone Structure Medullary cavity –Red marrow: site of blood cell formation –Yellow marrow: adipose tissue Periosteum –Glistening, white outer surface of bone –Bone growth in diameter Endosteum –Lines bone cavities

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6-10 Flat, Short, Irregular Bones Flat Bones –No diaphyses, epiphyses –Outer covering of compact bone that surrounds cancellous bone Short and Irregular Bone –Compact bone that surrounds cancellous bone center –No diaphyses and not elongated

6-11 Bone Histology Bone matrix –Organic: Collagen (flexibility) and proteoglycans (traps water) –Inorganic: Hydroxapatite: calcium phosphate (compression) Bone cells –Osteoblasts-produce collagen and proteoglycans in matrix »Bone-forming cells (ossification or osteogenesis) –Osteocytes- mature cells »Produce substances needed to maintain bone matrix –Osteoclasts-responsible for resorption (breakdown) of bone –Stem cells or osteochondral progenitor cells: become osteoblasts or chondroblasts Woven bone: Collagen fibers randomly oriented Lamellar bone: Mature bone in thin layers, called lamellae Cancellous(spongy) bone: Trabeculae Compact bone: Denser: fewer spaces than cancellous bone

6-12 Bone Matrix Collagen gives flexible strength Mineral gives weight-bearing strength

6-13 Bone Cells Osteoblasts –Formation of bone through ossification or osteogenesis Osteocytes –Mature bone cells –Lacunae: Spaces –Canaliculi: Cell processes Osteoclasts –Responsible for bone resorption (breakdown)

6-14 Woven and Lamellar Bone Woven bone –Collagen fibers randomly oriented in many direction –Formed: During fetal development During fracture repair Remodeling –Removing old bone (osteoclasts) and adding new (osteoblasts) Lamellar bone –Mature bone in sheets called lamellae

6-15 Cancellous Bone Consists of trabeculae: interconnecting rods or plates of bone; spaces filled with bone marrow, blood vessels Oriented along lines of stress; provide structural strength

6-16 Compact Bone Central or haversian canals: Parallel to long axis Lamellae: Concentric, circumferential, interstitial Osteon or haversian system: Central canal, contents, associated concentric lamellae and osteocytes Perforating or Volkmann’s canal: Perpendicular to long axis Blood vessels enter bone itself Lamellae oriented around blood vessels

6-17 Bone Development Intramembranous ossification –Takes place in connective tissue membrane –Some skull bones, part of mandible, diaphysis of clavicles –Begins at 8 weeks, ends at 2 years Endochondral ossification –Takes place in cartilage –Most bones develop from cartilage –Begins at 8 weeks; some begins at years Both methods of ossification –Produce woven bone that is remodeled –After remodeling, formation cannot be distinguished as one or other

6-18 Intramembranous Ossification

6-19 Endochondral Ossification

6-20 Endochondral Ossification

6-21 Endochondral Ossification

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6-23 Growth in Bone Length Appositional growth –New bone on old bone or cartilage surface Epiphyseal plate zones –Resting cartilage –Proliferation –Hypertrophy –Calcification

6-24 Growth in Bone Length Epiphyseal plate closure occurs between 12 and 25 years of age

6-25 Growth in Bone Width

6-26 Factors Affecting Bone Growth Nutrition –Vitamin D Necessary for absorption of calcium from intestines Insufficient causes rickets and osteomalacia –Vitamin C Necessary for collagen synthesis by osteoblasts Deficiency results in scurvy Hormones –Growth hormone from anterior pituitary –Thyroid hormone required for growth of all tissues –Sex hormones as estrogen and testosterone Females stop growing earlier than males: estrogen causes quicker closure of epiphyseal plate than testosterone

6-27 Bone Remodeling Converts woven bone into lamellar bone Old bone constantly removed by osteoclasts and new bone formed by osteoblasts Involved in bone growth, changes in bone shape, adjustment of bone to stress, bone repair, calcium regulation

6-28 Bone Repair 4 Steps :

6-29 Calcium Homeostasis Bone is the major storage site for calcium in the body –Calcium moves into bone as osteoblasts build new bone –Calcium moves out of bone as osteoclasts break down bone Osteoclast activity increases when blood calcium levels are too low; decreases when blood calcium too high –When osteoclast and osteoblast activity is balanced, the movement of calcium in and out is equal

6-30 Calcium Homeostasis Cont’d Parathyroid hormone (PTH) from parathyroid glands is the major regulator of blood calcium levels PTH increases blood calcium levels by: –Increasing bone breakdown (increased numbers of osteoclasts) –Increasing calcium absorption from small intestine (by promoting formation of Vitamin D) –Reabsorption of calcium from urine Tumors that secrete large amounts of PTH cause so much bone breakdown that bones become weak and fracture easily Calcitonin from thyroid gland decreases blood calcium by decreasing bone breakdown (decreasing osteoclast activity)

6-31 Calcium Homeostasis

6-32 Effects of Aging on Skeletal System Bone Matrix decreases ( less collagen; matrix formation by osteoblasts slower than matrix breakdown by osteoclasts) and becomes more brittle Bone Mass decreases ( after age 35) Increased bone fractures Bone loss causes deformity, loss of height, pain, stiffness –Stooped posture –Loss of teeth

6-33 Bone Fractures