Chapter 6 week 6 Kin 290
Chapter 6 week 6 Kin 290 Kin 290
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This 14 page Class Notes was uploaded by Leonard Carey on Monday April 11, 2016. The Class Notes belongs to Kin 290 at 1 MDSS-SGSLM-Langley AFB Advanced Education in General Dentistry 12 Months taught by Dr. Satern in Spring 2016. Since its upload, it has received 10 views. For similar materials see Anatomy & Physiology in Kinesiology at 1 MDSS-SGSLM-Langley AFB Advanced Education in General Dentistry 12 Months.
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Date Created: 04/11/16
Chapter 6 Chapter 6 Bones and Skeletal Tissue Why This Matters • Understanding bone anatomy and the process of bone remodeling allows you to work effectively with patients with bone diseases such as osteoporosis 6.1 Skeletal Cartilages • The human skeleton initially consists of just cartilage, which is replaced by bone, except in areas requiring flexibility Basic Structure, Types, and Locations • Skeletal cartilage: made of highly resilient, molded cartilage tissue that consists primarily of water • Contains no blood vessels or nerves • Perichondrium: layer of dense connective tissue surrounding cartilage like a girdle • Helps cartilage resist outward expansion • Contains blood vessels for nutrient delivery to cartilage • Cartilage is made up of chondrocytes, cells encased in small cavities (lacunae) within jellylike extracellular matrix Basic Structure, Types, and Locations (cont.) (Figure 6.1 – p. 174) Three types of cartilage: • Hyaline cartilage • Provides support, flexibility, and resilience • Most abundant type; contains collagen fibers only • Articular (joints), costal (ribs), respiratory (larynx), nasal cartilage (nose tip) • Elastic cartilage • Similar to hyaline cartilage, but contains elastic fibers • External ear and epiglottis • Fibrocartilage • Thick collagen fibers – has great tensile strength • Menisci of knee; vertebral discs Growth of Cartilage Cartilage grows in two ways: • Appositional growth • Cartilageforming cells in perichondrium secrete matrix against external face of existing cartilage • New matrix laid down on surface of cartilage • Interstitial growth • Chondrocytes within lacunae divide and secrete new matrix, expanding © 2016 Pearson Education, Inc. 1 Chapter 6 cartilage from within • New matrix made within cartilage Growth of Cartilage (cont.) Calcification of cartilage occurs during normal bone growth in youth, but can also occur in old age • Hardened cartilage is not the same as bone 6.2 Functions of Bones There are seven important functions of bones: 1. Support • For body and soft organs 2. Protection • Protect brain, spinal cord, and vital organs 3. Movement • Levers for muscle action 4. Mineral and growth factor storage • Calcium and phosphorus, and growth factors reservoir Functions of Bones (cont.) 5. Blood cell formation • Hematopoiesis occurs in red marrow cavities of certain bones 6. Triglyceride (fat) storage • Fat, used for an energy source, is stored in bone cavities 7. Hormone production • Osteocalcin secreted by bones helps to regulate insulin secretion, glucose levels, and metabolism 6.3 Classification of Bones (Figure 6.1 – p. 174) 206 named bones in human skeleton Divided into two groups based on location • Axial skeleton • Long axis of body • Skull, vertebral column, rib cage • Appendicular skeleton • Bones of upper and lower limbs • Girdles attaching limbs to axial skeleton Classification of Bones (cont.) (Figure 6.2 – p. 176) Bones are also classified according to one of four shapes: 1. Long bones • Longer than they are wide © 2016 Pearson Education, Inc. 2 Chapter 6 • Limb bones 2. Short bones • Cubeshaped bones (in wrist and ankle) • Sesamoid bones form within tendons (example: patella) • Vary in size and number in different individuals Classification of Bones (cont.) 3. Flat bones • Thin, flat, slightly curved • Sternum, scapulae, ribs, most skull bones 4. Irregular bones • Complicated shapes • Vertebrae and hip bones 6.4 Bone Structure Bones are organs because they contain different types of tissues • Bone (osseous) tissue predominates, but a bone also has nervous tissue, cartilage, fibrous connective tissue, muscle cells, and epithelial cells in its blood vessels Three levels of structure • Gross • Microscopic • Chemical Gross Anatomy Compact and spongy bone • Compact bone: dense outer layer on every bone that appears smooth and solid • Spongy bone: made up of a honeycomb of small, needlelike or flat pieces of bone called trabeculae • Open spaces between trabeculae are filled with red or yellow bone marrow Gross Anatomy (cont.) (Figure 6.3 – p. 177) Structure of short, irregular, and flat bones • Consist of thin plates of spongy bone (diploe) covered by compact bone • Compact bone sandwiched between connective tissue membranes • Periosteum covers outside of compact bone, • endosteum covers inside portion of compact bone • Bone marrow is scattered throughout spongy bone; no defined marrow cavity • Hyaline cartilage covers area of bone that is part of a movable joint Gross Anatomy (cont.) (Figure 6.4 – p. 178) Structure of typical long bone © 2016 Pearson Education, Inc. 3 Chapter 6 • All long bones have a shaft (diaphysis), bone ends (epiphyses), and membranes • Diaphysis: tubular shaft that forms long axis of bone • Consists of compact bone surrounding central medullary cavity that is filled with yellow marrow in adults • Epiphyses: ends of long bones that consist of compact bone externally and spongy bone internally • Articular cartilage covers articular (joint) surfaces • Between diaphysis and epiphysis is epiphyseal line • Remnant of childhood epiphyseal plate where bone growth occurs Gross Anatomy (cont.) • Membranes: two types (periosteum and endosteum) • Periosteum: white, doublelayered membrane that covers external surfaces except joints • Fibrous layer: outer layer consisting of dense irregular connective tissue consisting of Sharpey’s fibers that secure to bone matrix • Osteogenic layer: inner layer abutting bone and contains primitive osteogenic stem cells that gives rise to most all bone cells • Contains many nerve fibers and blood vessels that continue on to the shaft through nutrient foramen openings • Anchoring points for tendons and ligaments Gross Anatomy (cont.) • Membranes (cont.) • Endosteum • Delicate connective tissue membrane covering internal bone surface • Covers trabeculae of spongy bone • Lines canals that pass through compact bone • Like periosteum, contains osteogenic cells that can differentiate into other bone cells Gross Anatomy (cont.) Hematopoietic tissue in bones • Red marrow is found within trabecular cavities of spongy bone and diploë of flat bones, such as sternum • In newborns, medullary cavities and all spongy bone contain red marrow • In adults, red marrow is located in heads of femur and humerus, but most active areas of hematopoiesis are flat bone diploë and some irregular bones (such as the hip bone) • Yellow marrow can convert to red, if person becomes anemic Gross Anatomy (cont.) © 2016 Pearson Education, Inc. 4 Chapter 6 Bone markings • Sites of muscle, ligament, and tendon attachment on external surfaces • Areas involved in joint formation or conduits for blood vessels and nerves Microscopic Anatomy of Bone Cells of bone tissue • Five major cell types, each of which is a specialized form of the same basic cell type 1. Osteogenic cells 2. Osteoblasts 3. Osteocytes 4. Bonelining cells 5. Osteoclasts Microscopic Anatomy of Bone (cont.) 1. Osteogenic cells (Figure 6.5a – p. 179) • Also called osteoprogenitor cells • Mitotically active stem cells in periosteum and endosteum • When stimulated, they differentiate into osteoblasts or bonelining cells • Some remain as osteogenic stem cells Microscopic Anatomy of Bone (cont.) 2. Osteoblasts (Figure 6.5b – p. 179) • Boneforming cells that secrete unmineralized bone matrix called osteoid • Osteoid is made up of collagen and calciumbinding proteins • Collagen makes up 90% of bone protein • Osteoblasts are actively mitotic (divide and subdivide to make new bone) Microscopic Anatomy of Bone (cont.) 3. Osteocytes (Figure 6.5c – p. 179) • Mature bone cells in lacunae that no longer divide • Maintain bone matrix and act as stress or strain sensors • Respond to mechanical stimuli such as increased force on bone or weightlessness • Communicate information to osteoblasts and osteoclasts (cells that destroy bone) so bone remodeling can occur Microscopic Anatomy of Bone (cont.) 4. Bonelining cells Microscopic Anatomy of Bone (cont.) 5. Osteoclasts (Figure 6.5d – p. 179) © 2016 Pearson Education, Inc. 5 Chapter 6 • Derived from same hematopoietic stem cells that become macrophages • Giant, multinucleate cells function in bone resorption (breakdown of bone) • When active, cells are located in depressions called resorption bays • Cells have ruffled borders that serve to increase surface area for enzyme degradation of bone • Also helps seal off area from surrounding matrix Microscopic Anatomy of Bone (cont.) Compact bone • Also called lamellar bone • Consists of: • Osteon (Haversian system) • Canals and canaliculi • Interstitial and circumferential lamellae Microscopic Anatomy of Bone (cont.) (Figure 6.6 – p. 180) Osteon (Haversian system) • An osteon is the structural unit of compact bone • Consists of an elongated cylinder that runs parallel to long axis of bone • Acts as tiny weightbearing pillars • An osteon cylinder consists of several rings of bone matrix called lamellae • Lamellae contain collagen fibers that run in different directions in adjacent rings • Withstands stress and resist twisting • Bone salts are found between collagen fibers Microscopic Anatomy of Bone (cont.) (Figure 6.7 – p. 181) Canals and canaliculi • Central (Haversian) canal runs through core of osteon • Contains blood vessels and nerve fibers • Perforating (Volkmann’s) canals: canals lined with endosteum that occur at right angles to central canal • Connect blood vessels and nerves of periosteum, medullary cavity, and central canal Microscopic Anatomy of Bone (cont.) Canals and canaliculi (cont.) • Lacunae: small cavities that contain osteocytes • Canaliculi: hairlike canals that connect lacunae to each other and to central canal • Osteoblasts that secrete bone matrix maintain contact with each other and osteocytes via cell projections with gap junctions © 2016 Pearson Education, Inc. 6 Chapter 6 • When matrix hardens and cells are trapped the canaliculi form • Allow communication between all osteocytes of osteon and permit nutrients and wastes to be relayed from one cell to another Microscopic Anatomy of Bone (cont.) Spongy bone (Figure 6.3 – p. 177) • Appears poorly organized but is actually organized along lines of stress to help bone resist any stress • Trabeculae, like cables on a suspension bridge, confer strength to bone • No osteons are present, but trabeculae do contain irregularly arranged lamellae and osteocytes interconnected by canaliculi • Capillaries in endosteum supply nutrients Chemical Composition of Bone Bone is made up of both organic and inorganic components • Organic components • Includes osteogenic cells, osteoblasts, osteocytes, bonelining cells, osteoclasts, and osteoid • Osteoid, which makes up onethird of organic bone matrix, is secreted by osteoblasts • Consists of ground substance and collagen fibers, which contribute to high tensile strength and flexibility of bone Chemical Composition of Bone (cont.) Organic components (cont.) • Resilience of bone is due to sacrificial bonds in or between collagen molecules that stretch and break to dissipate energy and prevent fractures • If no additional trauma, bonds reform Inorganic components • Hydroxyapatites (mineral salts) • Makeup 65% of bone by mass • Consist mainly of tiny calcium phosphate crystals in and around collagen fibers • Responsible for hardness and resistance to compression Chemical Composition of Bone (cont.) Inorganic components (cont.) • Bone is half as strong as steel in resisting compression and as strong as steel in resisting tension • Lasts long after death because of mineral composition • Can reveal information about ancient people 6.5 Bone Development © 2016 Pearson Education, Inc. 7 Chapter 6 Ossification (osteogenesis) is the process of bone tissue formation – Formation of bony skeleton begins in month 2 of development – Postnatal bone growth occurs until early adulthood – Bone remodeling and repair are lifelong Formation of the Bony Skeleton Up to about week 8, fibrous membranes and hyaline cartilage of fetal skeleton are replaced with bone tissue Endochondral ossification – Bone forms by replacing hyaline cartilage – Bones are called cartilage (endochondral) bones – Form most of skeleton Intramembranous ossification – Bone develops from fibrous membrane – Bones are called membrane bones Formation of the Bony Skeleton (cont.) Endochondral ossification – Forms essentially all bones inferior to base of skull, except clavicles – Begins late in month 2 of development – Uses previously formed hyaline cartilage models – Requires breakdown of hyaline cartilage prior to ossification – Begins at primary ossification center in center of shaft Blood vessels infiltrate perichondrium, converting it to periosteum Mesenchymal cells specialize into osteoblasts Formation of the Bony Skeleton (cont.) (Figure 6.8 – p. 184) Five main steps in the process of ossification: 1. Bone collar forms around diaphysis of cartilage model 2. Central cartilage in diaphysis calcifies, then develops cavities 3. Periosteal bud invades cavities, leading to formation of spongy bone Bud is made up of blood vessels, nerves, red marrow, osteogenic cells, and osteoclasts Formation of the Bony Skeleton (cont.) Five main steps in the process of ossification: 4. Diaphysis elongates, and medullary cavity forms Secondary ossification centers appear in epiphyses 5. Epiphyses ossify Hyaline cartilage remains only in epiphyseal plates and articular cartilages Postnatal Bone Growth © 2016 Pearson Education, Inc. 8 Chapter 6 Long bones grow lengthwise by interstitial (longitudinal) growth of epiphyseal plate Bones increase thickness through appositional growth Bones stop growing during adolescence – Some facial bones continue to grow slowly through life Growth in Length of Long Bones (Figure 6.10 – p. 186) Interstitial growth requires presence of epiphyseal cartilage in the epiphyseal plate Epiphyseal plate maintains constant thickness – Rate of cartilage growth on one side balanced by bone replacement on other Epiphyseal plate consists of five zones: 1. Resting (quiescent) zone (bone replacement) 2. Proliferation (growth) zone 3. Hypertrophic zone 4. Calcification zone 5. Ossification (osteogenic) zone (growth is beginning) Growth in Length of Long Bones (cont.) 1. Resting (quiescent) zone – Area of cartilage on epiphyseal side of epiphyseal plate that is relatively inactive 2. Proliferation (growth) zone – Area of cartilage on diaphysis side of epiphyseal plate that is rapidly dividing – New cells formed move upward, pushing epiphysis away from diaphysis, causing lengthening Growth in Length of Long Bones (cont.) 3. Hypertrophic zone – Area with older chondrocytes closer to diaphysis – Cartilage lacunae enlarge and erode, forming interconnecting spaces 4. Calcification zone – Surrounding cartilage matrix calcifies; chondrocytes die and deteriorate Growth in Length of Long Bones (cont.) 5. Ossification zone – Chondrocyte deterioration leaves long spicules of calcified cartilage at epiphysis diaphysis junction – Spicules are then eroded by osteoclasts and are covered with new bone by osteoblasts – Ultimately replaced with spongy bone – Medullary cavity enlarges as spicules are eroded Growth in Length of Long Bones (cont.) Near end of adolescence, chondroblasts divide less often Epiphyseal plate thins, then is replaced by bone © 2016 Pearson Education, Inc. 9 Chapter 6 Epiphyseal plate closure occurs when epiphysis and diaphysis fuse Bone lengthening ceases – Females: occurs around 18 years of age – Males: occurs around 21 years of age Growth in Width (Thickness) Appositional Growth (Figure 6.11 – p. 186) Growing bones widen as they lengthen through appositional growth – Can occur throughout life Bones thicken in response to increased stress from muscle activity or added weight Osteoblasts beneath periosteum secrete bone matrix on external bone Osteoclasts remove bone on endosteal surface Usually more building up than breaking down which leads to thicker, stronger bone that is not too heavy Hormonal Regulation of Bone Growth Growth hormone: most important hormone in stimulating epiphyseal plate activity in infancy and childhood Thyroid hormone: modulates activity of growth hormone, ensuring proper proportions Testosterone (males) and estrogens (females) at puberty: promote adolescent growth spurts – End growth by inducing epiphyseal plate closure Excesses or deficits of any hormones cause abnormal skeletal growth 6.6 Bone Remodeling About 5–7% of bone mass is recycled each week – Spongy bone replaced ~ every 34 years – Compact bone replaced ~ every 10 years Bone remodeling consists of both bone deposit and bone resorption – Occurs at surfaces of both periosteum and endosteum – Remodeling units: packets of adjacent osteoblasts and osteoclasts coordinate remodeling process Bone Deposit New bone matrix is deposited by osteoblasts Osteoid seam: band of unmineralized bone matrix that marks area of new matrix Calcification front: abrupt transition zone between osteoid seam and older mineralized bone Bone Deposit (cont.) Trigger for deposit not confirmed but may include: © 2016 Pearson Education, Inc. 10 Chapter 6 – Mechanical signals – Increased concentrations of calcium and phosphate ions for hydroxyapatite formation – Matrix proteins that bind and concentrate calcium – Appropriate amount of enzyme alkaline phosphatase for mineralization Bone Resorption Resorption is function of osteoclasts – Dig depressions or grooves as they break down +atrix – Secrete lysosomal enzymes and protons (H ) that digest matrix – Acidity converts calcium salts to soluble forms Bone Resorption (cont.) Osteoclasts also phagocytize demineralized matrix and dead osteocytes – Digested products are transcytosed across cell and released into interstitial fluid and then into blood – Once resorption is complete, osteoclasts undergo apoptosis Osteoclast activation involves PTH (parathyroid hormone) and immune T cell proteins Control of Remodeling Remodeling occurs continuously but is regulated by genetic factors and two control loops 1. Hormonal controls Negative feedback loop that controls blood Ca levels Calcium functions in many processes, such as nerve transmission, muscle contraction, blood coagulation, gland and nerve secretions, as well as cell division 99% of 1200–1400 gms of calcium are found in bone Intestinal absorption of Ca requires vitamin D 2. Response to mechanical stress Control of Remodeling (cont.) (Figure 6.13 – p. 189) 2. Response to mechanical stress – Bones reflect stresses they encounter Bones are stressed when weight bears on them or muscles pull on them – Wolf’s law states that bones grow or remodel in response to demands placed on them Stress is usually off center, so bones tend to bend Bending compresses one side, stretches other side – Diaphysis is thickest where bending stresses are greatest © 2016 Pearson Education, Inc. 11 Chapter 6 – Bone can be hollow because compression and tension cancel each other out in center of bone Control of Remodeling (cont.) – Wolf’s law also explains: Handedness (right or lefthanded) results in thicker and stronger bone of the corresponding upper limb Curved bones are thickest where most likely to buckle Trabeculae form trusses along lines of stress Large, bony projections occur where heavy, active muscles attach – Weight lifters have enormous thickenings at muscle attachment sites of most used muscles Bones of fetus and bedridden people are featureless because of lack of stress on bones Control of Remodeling (cont.) Mechanical stress causes remodeling by producing electrical signals when bone is deformed – VeCompressed and stretched regions are oppositely charged – Compression/tension changes fluid flows within canaliculi, which may also stimulate remodeling Hormonal controls determine whether and when remodeling occurs in response to changing blood calcium levels, but mechanical stress determines where it occurs 6.7 Bone Repair Fractures are breaks – During youth, most fractures result from trauma – In old age, most result from weakness of bone due to bone thinning 6.8 Bone Disorders Imbalances between bone deposit and bone resorption underlie nearly every disease that affects the human skeleton. Three major bone diseases: – Osteomalacia and rickets – Osteoporosis – Paget’s disease Osteoporosis (Figure 6.15 – p. 192) Osteoporosis is a group of diseases in which bone resorption exceeds deposit Matrix remains normal, but bone mass declines – Spongy bone of spine and neck of femur most susceptible Vertebral and hip fractures common © 2016 Pearson Education, Inc. 12 Chapter 6 Osteoporosis (cont.) Risk factors for osteoporosis – Most often aged, postmenopausal women Affects 30% of women aged 60–70 years and 70% by age 80 30% of Caucasian women will fracture bone because of osteoporosis Estrogen plays a role in bone density, so when levels drop at menopause, women run higher risk – Men are less prone due to protection by the effects of testosterone Osteoporosis (cont.) Additional risk factors for osteoporosis: – Petite body form – Insufficient exercise to stress bones – Diet poor in calcium and protein – Smoking – Hormonerelated conditions Hyperthyroidism Low blood levels of thyroidstimulating hormone Diabetes mellitus – Immobility – Males with prostate cancer taking androgensuppressing drugs Osteoporosis (cont.) Treating osteoporosis – Traditional treatments Calcium Vitamin D supplements Weightbearing exercise Hormone replacement therapy – Slows bone loss but does not reverse it – Controversial because of increased risk of heart attack, stroke, and breast cancer Osteoporosis (cont.) Preventing osteoporosis – Plenty of calcium in diet in early adulthood – Reduce consumption of carbonated beverages and alcohol Leach minerals from bone, so decrease bone density – Plenty of weightbearing exercise Increases bone mass above normal for buffer against agerelated bone loss © 2016 Pearson Education, Inc. 13 Chapter 6 © 2016 Pearson Education, Inc. 14
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