Bone Structure and Tissue Student Version PDF

Bone Structure and Tissue Professor Frazier Community College of Allegheny County Biol 161 Student Learning Outcomes STUDENTS WILL BE ABLE TO: Identify the types and structures of bone Identify and explain the process of bone development Explain how the proces...

Bone Structure and Tissue Professor Frazier Community College of Allegheny County Biol 161 Student Learning Outcomes STUDENTS WILL BE ABLE TO: Identify the types and structures of bone Identify and explain the process of bone development Explain how the process of bone maintenance and remodeling Explain the process of bone repair and the types of breakage Explain the importance of parathyroid hormone, calcitriol, and calcitonin Functions of the Skeletal System Support: Bone is hard and rigid Cartilage is flexible yet strong Ligaments connect bone to bone Protection: Skull protects brain Ribs, sternum, vertebrae protect organs of thoracic cavity and spinal cord Movement: Produced by muscles attached to bones via tendons. Ligaments prevent excessive, beyond normal, movement Storage: Calcium and phosphate stored and released as needed Adipose can be stored in bone cavities Blood cell production: Bones Start as Cartilage… Bone begins as cartilage and is replaced by bone via ossification Hyaline cartilage Fibrocartilage Elastic cartilage Cartilage has an outer double protective layer called the perichondrium Inner: Contains chondroblasts that form matrix Outer: Receives blood vessels and nerves as cartilage is avascular Bones Start as Cartilage… Cartilage grows in two ways: Appositional: New chondrocytes and matrix at are produced at the periphery and get sent inward. Interstitial: Chondrocytes within the matrix divide and add more matrix between the cells. Types of Osseus (Bone) Tissue Axial vs Appendicular Skeleton 206 bones classified by shape, which also determines their function, and are divided into the axial skeleton and the appendicular skeleton: Axial Skeleton: Anything pertaining to the center of the body Skull Vertebrae Ribcage Sternum Appendicular Skeleton: Anything pertaining to the limbs of the body Bones of arms Bones of legs Bone Classification Long Short Femur Wrist and ankle Humerus Tibia Irregular Vertebra Flat Sternum Ribs Scapula Sesamoid Patella Cranial Bones Types Bones types are classified by shape, which also determines their function. Divided into the axial skeleton and the appendicular skeleton: Short: Small, cube-like shaped bones Provide a gliding motion Found in the wrist and ankle Carpals Tarsals Flat: Flat, as the name implies Perfect for protection Cover large areas of the body Bones Types Bones types are classified by shape, which also determines their function. Divided into the axial skeleton and the appendicular skeleton: Long: Provide weight bearing ability Found in the limbs Femur Tibia Fibula Humerus Ulna Radius Have heads, condyles, tubercles, and tuberosities covered by articular cartilage Form connections to other bones and create the joints that we’ve looked at in kinematics Bones Types Bones types are classified by shape, which also determines their function. Divided into the axial skeleton and the appendicular skeleton: Irregular: Have different shapes to fulfill various needs Vertebra Provide path and protection for spinal cord Facial bones House teeth Provide airways in the nose Sesamoid: Bone covered by tendons Perfect for protection Cover large areas of the body Bone Composition Composition of Osseus (Bone) Tissue Bones protect internal aspects of the body and provide the scaffolding for a system of levers that can be moved by forces from attached muscles: Osseus Tissue Components: Minerals that provide stiffness and rigidity (60%-70% inorganic matter) Hydroxyapatite: Calcium phosphates and calcium carbonate Provides a bone with compressive strength The ability to resist the compression or the maximum compression load that a bone can withstand before entering the plastic region of the deformation curve Protein provides flexibility (10% inorganic matter) Collagen Provides a bone with tensile strength The ability to resist pulling and stretching or the maximum tension load that a bone can withstand before entering the plastic region of the deformation curve Types of Osseus (Bone) Tissue Depending on the type of bone and its function, the composition of minerals, collagen, and water, vary to form varied bone densities: Trabecular (Spongy) Bone: Contain small amounts of calcium salts Create mesh of bone called trabecula Space filled with red or yellow bone marrow Contain higher amounts of collagen High porosity (30% + porous bone volume) Found in epiphysis’ of long bones and vertebra Very flexible and can thus withstand strain (bend) Cortical (Compact) Bone: Contain high amounts calcium salts Contain lower amounts of collagen Low porosity (5% - 30% porous bone volume) Found in diaphysis of long bones Surrounds the outside of all bones Very stiff and can thus withstand stress (compression) Structure vs. Strength Bones are anisotropic meaning that they respond to different applied loads differently, and their porosity (cortical vs trabecular) determines how: Compression Force: Easiest force to withstand Best opposed by cortical bone Trabecular bone is less strong Tension Force: Best opposed by trabecular bone Cortical bone is less strong Shear Force: The most difficult force to withstand A good mixture of compression and tensile strength is best to withstand shear force Compact (Lamellar) Bone Compact bone forms as layers of lamellae encase blood vessels to form a central canal. Once ends of lamellae fuse concentric lamellae form: Each subsequent ring of compact bone is separated by osteocytes Haversian and Volkmann canals carry neurons and blood supply to to all areas of the compact bones Volkmann canals carry blood from the periosteum into the haversian canal Empty into canaliculi that feeds nutrients to the osteoblasts on the circumferential lamellae (exterior) and osteocytes that lay in the lacunae of the osteon Interstitial lamellae (degraded) fill the space between active osteons Compact (Lamellar) Bone Spongy Bone Found in cranial bones, ribs, but primarily at the ends of long weight bearing bones: Trabecula form in a sponge like pattern Found in the spaces between trabecula is bone marrow Blood cell formation Fat storage This formation, though not dense, forms along stress lines to resist breakage Unlike compact bone, there are not central canals for blood supply so nutrients come from the endosteum Osseous Tissue Cells Osteoblasts: Cells that perform ossification or bone formation by releasing unmineralized osteoid Made up of collagen from the endoplasmic reticulum Use calcium salts from blood supply to ossify matrix Osteoclasts: Cells that work in opposition to osteoblasts and degrade bone into calcium salts to be brought into the blood stream Release H+ ions that create acids Osteocytes: Cells that maintain bone matrix Respond to presence or lack of stress placed on bones Increased weight causes bone remodeling to increase bone density Zero gravity causes bone remodeling to decrease bone density Osteogenic cells: Bone Development Bone Development Ossification is the development of bone and begins in the first trimester of pregnancy: Complete bone development continues until the end of puberty when epiphyseal plates fuse into epiphyseal lines which ends growth Ossification occurs in two ways: Intramembranous ossification Bone develops from fibrous membrane Endochondral ossification Bone forms by replacing hyaline cartilage Form most of skeleton Both methods create woven bone that is remodeled and are then indistinguishable Intramembranous Ossification Takes place in connective tissue membrane formed from embryonic mesenchymal cells Forms: Frontal Parietal Occipital Temporal Clavicle diaphysis Centers of ossification are located near the middle of each bone and develop outward Areas between developing bones are referred to as fontanels or soft spots and will disappear as bones fully form and fuse Intramembranous Ossification Occurs in four steps: 1. Ossification centers are formed when mesenchymal cells cluster and become osteoblasts 2. Osteoid is secreted and calcified 3. Woven bone is formed when osteoid is laid down around blood vessels, resulting in trabeculae Outer layer of woven bone forms periosteum 4. Lamellar bone replaces woven bone, and red marrow appears Endochondral Ossification Hyaline cartilage forms at week four and begins to ossify around week eight and continues until the end of puberty Forms: All bones below the skull Clavicle epiphysis Begins at the primary ossification center Blood vessels infiltrate perichondrium, converting it to periosteum Endochondral Ossification Occurs in five steps: 1. Perichondrium converts to periosteum and produces a bone collar 2. Central cartilage in diaphysis calcifies, then develops cavities 3. Blood vessels, nerves, red marrow, osteogenic cells, and osteoclasts invades cavities, leading to formation of spongy bone 4. Diaphysis elongates, and medullary cavity forms Secondary ossification centers appear in epiphyses 5. Epiphyses ossify aside from Bone Growth Longitudinal vs Circumferential Growth Bone growth can either be in length or in width. Each changes depending on what stage of life you are in and the conditions the bones are under: Longitudinal (interstitial) growth: Increase in bone length Occurs at the epiphyseal plates Plates contain cartilage New cartilage is made and lengthens bone Old/dead cartilage becomes ossified into bone Plates ossify at the end of puberty Circumferential (appositional) growth: Increase in bone thickness Occurs on surface of bone due to remodeling to accommodate changes in stress Accomplished by osteocyte, osteoblast, and osteoclasts activity Interstitial (Longitudinal) Growth Longitudinal growth is lengthwise growth of bone and requires the division of cartilage to lengthen bone and for conversion to bone cells: Epiphysial Plate: Plate thickness remain constant until fusion Rapidly dividing hyaline cartilage is replaced by bone Cartilage division ends at end of puberty Plate shrinks and remaining cartilage ossifies Epiphysis fuses together with diaphysis to form one solid piece of bone via an epiphysial line Zones of the Epiphysial Plate: 1. Resting zone 2. Proliferation zone 3. Hypertrophic zone 4. Calcification zone 5. Ossification zone Interstitial (Longitudinal) Growth 1. Resting zone Area of cartilage on epiphyseal side of epiphyseal plate that is relatively inactive 2. Proliferation zone Area of cartilage on diaphysis side of epiphyseal plate that rapidly divides New cells formed move upward, pushing epiphysis away from diaphysis, causing lengthening 3. Hypertrophic zone Older chondrocytes closer to diaphysis Cartilage lacunae enlarge and erode, forming interconnecting spaces 4. Calcification zone Surrounding cartilage matrix calcifies; chondrocytes die and deteriorate 5. Ossification zone Chondrocyte deterioration halts cartilage formation Calcified cartilage is degraded by osteoclasts and is replaced with spongy bone Circumferential (Appositional) Growth Appositional growth occurs at the same time as longitudinal growth to accommodate the increase in weight during puberty and throughout life: Circumferential (appositional) growth: Increases to accommodate increased weight Allows for increase in stress resistance Occurs when the periosteum forms concentric layers of bone on top of existing one and around blood supply This done with the use of osseus tissue cells: Osteoblasts: Cells that ossify by depositing calcium salts Osteoclasts: Cells that break down osseus tissue into to Factors Controlling Bone Growth Outside of genetics nutrition and hormones play the largest role: Proteins are the building blocks of muscle and bone Collagen is the most abundant protein in bones and body To synthesize collagen in osteoblasts vitamin C is requires Vitamin C deficiency: Scurvy Calcium is required from our diets to create hydroxyapatite To absorb calcium the aid of vitamin D is required Can be ingested Can be produced when exposed to sun Vitamin D deficiencies: Rickets Osteomalacia Factors Controlling 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 Gigantism and acromegaly Dwarfism Testosterone and estrogen: Promote adolescent growth spurts during puberty End growth by inducing epiphyseal plate closure Excesses or deficits of any hormones cause abnormal skeletal Bone Maintenance Bone Remodeling Constant cycle of calcium deposition and resorption based on need: Increased stress results in an increase in osteoblast activity increasing bone density Reduced stress results in an increase in osteoclast activity decreasing bone density Hormones and calcium salt availability also play a large role in bone remodeling Osteoclasts: Responsible for degradation and calcium reabsorption Activated by parathyroid hormone (PTH) Released in response to decreased levels of calcium in blood (Hypocalcemia) This causes an increase in calcitriol which absorbs more calcium in intestines Osteoblasts: Responsible for calcium salt deposition and bone formation Activated by calcitonin from parafollicular cells of thyroid Released in response to increased levels of calcium in blood (Hypercalcemia) Bone Remodeling Paget’s Disease: Excessive and haphazard bone deposit and resorption cause bone to grow fast and develop poorly Very high ratio of spongy to compact bone and mineralization Occurs in spine, pelvis, femur, and skull Rarely occurs before age 40 Treatment includes calcitonin and bisphosphonates Fracture Types and Repair Fracture Classifications Fractures are breakages in bone caused by trauma: Older individuals are at a greater risk due to lack of balance and fall risks Fracture classifications: Position of bone ends after fracture Nature of the break Nondisplaced: ends retain normal position Linear (stress or hairline) Displaced: ends are out of normal alignment Spiral Completeness of break Depressed Complete: broken all the way through Comminuated Incomplete: not broken all the way through Compression Epiphyseal Whether skin is penetrated Open (compound): skin is penetrated Greenstick (kids) Closed (simple): skin is not penetrated Types of Fractures Under a load that is exceeds the strength of a bone (size and density), the bone will fracture causing a disruption in the continuity of the bone: Fissured (linear): Simple and incomplete break Caused by repetitive loading on bone (running) Also referred to as stress or hairline fractures Spiral: Complete break May be simple or compound Caused by excessive bending loads from opposite directions, and torsional loads Common in sports Greenstick: Simple and incomplete break Caused by bending or torsional loads More common in children as their bones have large amounts of collagen Types of Fractures Under a load that is exceeds the strength of a bone (size and density), the bone will fracture causing a disruption in the continuity of the bone: Comminuated: Complete break that may be simple or compound Bone fragments upon high velocity impact Car accidents, falls from a height, explosions Transverse: Complete break that may be simple or compound Breaks at a right angle to the axis of the bone Caused by large perpendicular force to bone Oblique: Complete break that may be simple or compound Breaks at a none-right angle to the axis of the bone Types of Fractures Under a load that is exceeds the strength of a bone (size and density), the bone will fracture causing a disruption in the continuity of the bone: Impacted: Caused by compression forces from either side of a bone Break comes in the form of crushing Very rare Depression: Bone becomes pressed into the underlying tissue Caused by excessive loads on surface of flat bones Seen in the cranial bones Avulsion: Occurs when a tendon/ligament separates from bone Some bone chips off with the tendon Bone Repair For proper bone repair to take place the bone must be realigned and immobilized so that the bone may heal back to as close to its original shape as possible: Reduction: Realignment of broken bone ends Closed reduction: physician manipulates to correct position Open reduction: surgical pins or wires secure ends Immobilization of bone by cast or traction is needed for healing Time needed for repair depends on break severity, bone broken, and age of patient If fracture is exposed to forces while healing it can turn into a stress fracture Once the bone(s) have been set bone repair proper can take place: 1. Hematoma formation 2. Fibrocartilaginous callus formation 3. Bony callus formation 4. Bone remodeling Bone Repair 1. Hematoma formation Torn blood vessels hemorrhage, forming mass of clotted blood called a hematoma Site is swollen, painful, and inflamed 2. Fibrocartilaginous callus formation Capillaries grow into hematoma Phagocytic cells clear debris Fibroblasts secrete collagen fibers to span break and connect broken ends Fibroblasts, cartilage, and osteogenic cells begin reconstruction of bone 3. Callus ossification New trabeculae appear and callus is converted to bony (hard) callus of spongy bone Bony callus formation continues for about 2 months until firm union forms 4. Bone remodeling Excess material on diaphysis exterior and within medullary cavity is removed Age Related Changes in Bone The older you become the less dense bones are: In children and adolescents, bone formation exceeds resorption Males tend to have greater mass than females In young adults, both are balanced In adults bone resorption exceeds formation Bone matrix decreases leading to more brittle bones Due to lack of collagen and less hydroxyapatite Bone mass, mineralization, and healing ability decrease with age beginning in 40’s Women are more at risk Increased bone fractures Bone loss causes deformity, loss of height, pain, stiffness Stooped posture Loss of teeth Osteoporosis Osteoporosis Osteoporosis is a disorder involving decreased bone mass and strength with age that causes pain and bone fractures when engaging in daily activities: Osteoporosis: Begins as osteopenia Predominance of osteoclast activity and reduction in osteoblast cell (and thus activity) leading to decrease in bone mineral density and possible fractures and deformations Collagen also breaks down as you age leading to brittle bones Types of Osteoporosis: Type I: Considered postmenopausal osteoporosis Affects about 50% of women after the age of 50 Type II: Osteoporosis Isn’t Only in the Elderly Though very uncommon, osteoporosis can be seen in younger individuals as well if they are susceptible to calcium deficiencies or have low body weight: Female Athlete Triad: Some female athletes partake in sports where low body weight is crucial Gymnasts, runners, and swimmers If food intake is not monitored this may lead to the female athlete triad 1. Lack of macromolecules intake leads to low energy availability 2. Lack of micromolecules (calcium specifically) leads to irreversible bone loss Causes high rate of fractures and permanent deformities due to lack of healing 3. Low weight give third part of the triad which is loss of amenorrhea Coaches and medical staff need to monitor to maintain athlete health Eating Disorders and Inactivity: Individuals with eating disorders may also suffer calcium deficiencies Anorexics and bulimics specifically Individuals who are not active do not place strain on bones and have weak bones How is Osteoporosis Treated? The best way to treat osteoporosis is the do the opposite of what causes it to happen in the first place: Exercise: Adding weight-bearing exercises adds stress/strain to them Lift weights, body exercises, cycling, team sports, etc Increases osteoblast activity to withstand added stress Most important during early years to ensure a good base to maintain over lifetime Improve Diet: Treat any eating disorder Ensure proper consumption and absorption of calcium Hormone Therapy: Females may take estrogen treatments to alleviate menopause risk