Chapter 6: Bones And The Skeletal System PDF

Chapter 6: Bones and the Skeletal System  Adult cartilage  No blood vessels or nerves  High water content  Surrounded by perichondrium  Dense irregular connective tissue, blood supply Three types  Hyaline (articular, costal, respiratory, nasal)  Elastic (external ear, epigl...

Chapter 6: Bones and the Skeletal System  Adult cartilage  No blood vessels or nerves  High water content  Surrounded by perichondrium  Dense irregular connective tissue, blood supply Three types  Hyaline (articular, costal, respiratory, nasal)  Elastic (external ear, epiglottis)  Fibrocartilage (knee, intervertebral discs) Functions of Bone (organ) Support: framework that supports the body Protection : protective case for the brain, spinal cord, and vital organs Movement: anchors/levers for muscles Mineral storage: reservoir for minerals, especially calcium and phosphate, and growth factors Blood cell formation: hematopoiesis Triglyceride storage: fat Hormone production: osteocalcin, energy cycle Classification of Bones: Location Axial skeleton  Skull  Vertebrae  Rib cage Appendicular skeleton  Upper and lower limbs  Shoulders  Hips  Classification of Bones: Shape Long bones  Longer than they are wide Flat bones  Thin, flattened, curved  Includes sternum, scapula, skull and ribs Classification of Bones: shape Short bones  Cube-shaped, wrist/ankle  Sesamoid, inside tendons Irregular bones  Odd shapes (ex. Vertebrae) Bone markings: for muscle/ligament/tendon attachment, joint surfaces, or conduits for blood vessels/nerves Condyle –round prominence at the end of a bone, often at a joint articulation Epicondyle –a prominence on the distal part of a long bone, attachment point for muscles and ligaments Trochanter –protruberances by which muscles attach or bones connect to each other Tubercle –a round nodule, small emience Tuberosity –a rounded, long/oblong prominence Trochlea –a grooved structure like a pulley’s wheel Fossa –a depression or hollow Foramen –an opening Meatus –external opening of a canal/passage leading into the body Gross Anatomy of Bones Compact bone – dense outer layer, smooth surface Gross Anatomy of Bones Spongy bone – inner honeycomb layer= trabeculae filled with red/yellow marrow Structure of flat, irregular, short bones Sandwich-like Thin plates of spongy bone, diploë , covered in compact bone No defined marrow cavity No diaphysis or epiphyses Covered by connective tissue layers Structure of Long Bone I. Diaphysis Tubular shaft Exterior: compact bone collar, thin layer of spongy bone Interior: medullary cavity with yellow marrow (fatty marrow) Structure of Long Bone II.. Epiphyses Expanded ends of long bones Exterior is compact bone Interior is spongy bone Epiphyseal line/plate separates the diaphysis from the epiphyses Which of the following is not a type of cartilage? a) Hyaline b) Elastic c) Fibrocartilage d) Dense regular What type of cartilage is found at the joint surface between two bones? A.Fibrocartilage B. Hyaline C. Elastic Structure of Long Bone Bone Membranes Periosteum (two layers) Outer fibrous layer is dense irregular connective tissue Inner osteogenic layer contains osteogenic stem cells Richly supplied with nerve fibers, blood, and lymphatic vessels Anchoring point, collagen Bone Membranes Endosteum – delicate layer covering internal bone surfaces Covers trabeculae of spongy bone Lines the canals of compact bone Contains osteogenic stem cells Which membrane would you find on the outer surface of this skull bone? A. Periosteum B. Endosteum Which membrane would you around the trabeculae of this skull bone? A. Periosteum B. Endosteum Hematopoietic Tissue (Red Marrow) Infants  Found in the medullary cavity (long bones) and all areas of spongy bone Adults  Found in the diploë of flat bones (hip, sternum, etc.), and the head of the femur and humerus Homeostatic help: yellow marrow can convert to red marrow under conditions of extreme anemia If you were treating a person with leukemia, where would you try to get healthy bone marrow from a donor? A. Hip B. Humerus C. Skull D. Vertebrae Types of Bone cells Osteogenic cell  Bone stem cell (actively dividing cells)  Gives rise to osteoblasts and more progenitors. Osteoblasts  Bone-building cells Types of Bone cells Osteocytes (mature bone cells)  Monitor and maintain bone matrix  In lacunae or lining bone surfaces Osteoclasts  Bone-digesting cells (resorption) Microscopic Structure: Compact Bone Haversian system/Osteon: structural unit, pillar Lamella : weight-bearing columns, collagen in adjacent lamella alternate to resist twisting Haversian/ Central canal: contains blood vessels and nerves Volkmann’s canals: horizontal channels connecting the medullary cavity to the Haversian canal and Periosteum Microscopic Bone Structure Microscopic Structure: Compact Bone Haversian system/Osteon: structural unit, pillar Osteocytes: mature bone cells Lacunae: small cavities in bone containing osteocytes at lamella junctions Canaliculi: hair-like canals that connect lacunae to each other and the central canal Microscopic Bone Structure Microscopic Structure: Spongy bone Trabeculae align along lines of stress Irregularly arranged lamella with osteocytes and canaliculi  Chemical Composition of Bone Organic Components –resist tension  Bone cells  Osteoid : unmineralized bone matrix  Osteoblasts secrete: proteoglycans, glycoproteins, and collagen ▪ Allows bone to resist stretching and twisting ▪ About 1/3 of the bone matrix ▪ “Sacrificial bonds” between collagen break and reform to prevent large-scale fractures Chemical Composition of Bone Inorganic components– resist compression  Mineral salts  65% of bone by mass  Mainly calcium phosphate crystals tightly packed around the collagen fibers  Responsible for bone hardness and resistance to compression Bone Development Osteogenesis (ossification) includes: The formation of the bony skeleton in embryos Bone growth until early adulthood Bone thickness, remodeling, and repair in adults  Embryonic development Most of the human skeleton is first formed of cartilage or fibrous membranes Cartilage cells are able to divide and multiply quickly. Thus, the cartilage can grow as rapidly as the fetus does http://schoolbag.info/biology/humans/6.html Embryonic development Beginning in the third month and continuing through prenatal development, the cartilage is gradually replaced by bone Formation of the Bony Skeleton Begins at week 8 of embryonic development A.) Intramembranous ossification Bone develops from a fibrous membrane Forms flat, cranial bones of skull B.) Endochondral ossification Bone forms by replacing hyaline cartilage Forms all other bones of the body Stages of Intramembranous Ossification 1. Mesenchymal cells produce fibrous membrane 2. Ossification center appears with osteoblasts Stages of Intramembranous Ossification 3. Bone matrix is woven in-between blood vessels 4. Spongy bone and outer periosteum form Stages of Intramembranous Ossification 5. Compact (lamellar) bone forms 6. Red marrow appears in spongy bone Endochondral Ossification Uses hyaline cartilage “bones” as models for bone construction Requires breakdown of hyaline cartilage prior to ossification Stages of Endochondral Ossification 1. Blood vessels infiltrate the perichrondrium converting it to periosteum = primary ossification center 2. Mesenchymal cells become osteoblasts Stages of Endochondral Ossification 3. Formation of bone collar around the diaphysis 4. Hyaline cartilage calcifies, matrix deteriorates, creates cavities as chondrocytes die Stages of Endochondral Ossification 5. Invasion of internal cavities by the periosteal bud, spongy bone formation by osteoclasts and osteoblasts 6. Formation of the medullary cavity, elsewhere cartilage continues expanding Stages of Endochondral Ossification 7. @birth, secondary ossification centers form in the epiphyses 8. Spongy bone replaces cartilage of the epiphyses Hyaline cartilage remains only in the epiphyseal plates, articular cartilage Growth of Bone/Cartilage Appositional (outside-in)  Cells secrete matrix against the external face of existing cartilage Growth of Bone/Cartilage Interstitial (inside-out)  Lacunae-bound cells divide and secrete new matrix, expanding the tissue from within Growth of Bone/Cartilage Long bones lengthen by interstitial growth Bones get thicker by appositional growth Timing  Most bone/cartilage development is complete by adolescence Calcification (hardening) of cartilage occurs  During normal bone growth  During old age Postnatal Bone Growth: Long bones Cartilage closest to the epiphysis is quiescent (resting) Cartilage next to the diaphysis is organized into stacks that allow fast, efficient growth Four distinct zones form Proliferative/Growth Hypertrophic Calcification O. ssification Functional Zones: Long Bone Growth Growth zone Chondrocytes divide, pushing the epiphysis away from the diaphysis Functional Zones: Long Bone Growth Transformation zones Older chondrocytes hypertrophy (enlarge) Matrix calcification; chondrocytes die Functional Zones: Long Bone Growth Ossification zone New bone formation by osteoblasts and osteoclasts Long Bone Growth+Remodeling Epiphyseal ends are remodeled to maintain the correct proportion diaphysis:epiphyses Bone Growth+Remodeling Appositional growth for width Osteoblasts Add bone appositionally (outside in) from periosteum Osteoclasts Resorb bone near surface of endosteum Overall effect Bone increases in width Bone doesn’t get too heavy Epiphyseal plate closure Chondroblasts divide less often Plate becomes thinner, replaced with bone tissue ~18 females ~21 males Hormonal Regulation of Bone Growth Infancy and childhood Growth hormone and thyroid hormone Deficiencies or excesses  homeostatic imbalances Hormonal Regulation of Bone Growth Puberty Primarily testosterone and. estrogens Initially promotes adolescent growth spurts Causes masculinization and feminization of the skeleton Later induces epiphyseal plate closure (You’re done growing up!) Bone homeostasis: remodeling 5-10% of our bone is recycled every year WHY? calcium storage/release Spongy bone: replaced every 3-4 years Compact bone: replaced every 10 years Prevents bones from becoming brittle High-stress areas remodeled more frequently (femur) Bone Deposition Occurs where bone is injured or added strength is needed by osteoblasts Diet: Requires protein, vitamins C, D, and A, calcium, phosphorus, magnesium, and manganese Enzyme: Requires alkaline phosphatase for mineralization of bone High alkaline phosphatase levels in blood may indicate: A. Osteoporosis B. Bone Cancer C. Bed-ridden patient with a lack of physical activity Bone Resorption Osteoclasts secrete: Lysosomal enzymes digest organic matrix Hydrochloric acid that converts calcium salts into soluble forms Phagocytosis matrix/osteocytes Result: stored calcium is released into blood supply  Physiological Roles for Calcium  Transmission of nerve impulses  Muscle contraction  Blood coagulation  Cell division  Secretion by glands and nerve cells  Bone structure  Intestine absorbs using Vitamin D  Control of Remodeling 1.) Hormonal mechanisms maintain calcium homeostasis in the blood -Conversation between intestine, brain, and bones -Decides whether and when remodeling occurs 2.) Mechanical forces act on the skeleton -Decides where remodeling occurs Control of Remodeling 1.) Hormonal mechanisms maintain calcium homeostasis in the blood Falling blood Ca2+ levels signal the parathyroid glands to release PTH= parathyroid hormone PTH signals osteoclasts to degrade bone matrix and release Ca2+ into the blood  Hormonal Mechanism 1) Hormonal: Rising blood Ca2+ levels trigger the thyroid to release calcitonin Calcitonin stimulates calcium deposit and storage in bone NOTE: Calcitonin’s effects are more pronounced in childhood than adulthood  Response to Mechanical Stress 2.) Mechanical forces act on the skeleton Wolff’s law: Bones grow in response to the forces placed upon them Curved bones are thickest where they are most likely to buckle Bones atrophy when not stressed/used Bony projections =muscle attachments Deforming a bone makes an electrical current ->osteocytes  How is this person handed? A. Left handed B. Right handed http://biomedicalcomputationreview.org/4/1/posters/taylor_Tennis_poster.pdf In a patient whose parathyroid glands have been removed, you would expect that person’s blood calcium levels to _______. a) decrease b) increase c) stay the same d) increase twofold Bone Fractures (Breaks) Bone fractures are classified by: POSITION: Displaced v. Non-displaced DEGREE OF BREAK: Complete v. Incomplete ORIENTATION: Linear v. transverse SKIN DAMAGE: Compound (open/breaks skin) v. Simple (closed/no break in skin) Common Types of Fractures Comminuted Bone breaks into three or more pieces Common in the elderly Spiral Ragged break when bone is severely twisted Common sports injury Depressed Bone is pressed inward Typical of skull fractures Common Types of Fractures Spiral Ragged break when bone is severely twisted Common sports injury Common Types of Fractures Depressed Bone is pressed inward Typical of skull fractures Common Types of Fractures. Compression Bone is crushed Typical of osteoporosis (crushed vertebrae) Common Types of Fractures Epiphyseal Epiphysis separates from diaphysis Common Types of Fractures Greenstick Incomplete fracture (one side of the bone breaks and the other side bends) Common in children with growing, flexible bones Treatment Reduction – realignment of broken bone ends Immobilization –by cast or traction Stages of Bone Healing Hematoma formation Torn blood vessels hemorrhage, mass of clotted blood Cells without blood supply die off Pain and inflammation  Stages of Bone Healing Fibrocartilaginous callus forms “splint” across fracture New blood vessels form Phagocytic cells begin cleaning debris Fibroblasts secrete collagen across the break Chondroblasts secrete cartilage Stages of Bone Healing Bony callus formation Osteoblasts form spongy bone Fibrocartilaginous callus converts into a bony (hard) callus Process continues for 2-3 months similar to endochondral ossification Stages of Bone Healing Bone remodeling Excess material is removed New compact bone rebuilds shaft walls Takes several months to complete Total 6-8 weeks for young adults, longer for elderly New treatments for damaged bones Electrical stimulation: speeds healing after large fractures Ultrasound: reduces time to heal broken arms and shins Fibular graft: improved way to graft bone in areas with severe damage  New treatments for damaged bones VEGF: growth factor that increases blood supply Bone substitutes (implanted at damaged sites) Includes natural (coral) and synthetic materials Sometimes coated with BMP (bone morphogenic protein) 3-D printed bones Perfectly designed to match a patient Made out of titanium powder - heated and fused together by a laser, one layer at a time Includes passages for nerves and blood vessels Which treatment would you choose for a severe break? A. 3-D printed bone B. Fibular graft C. Coral/synthetic bone Homeostatic Imbalances Osteomalacia Bones are inadequately mineralized causing softened, weakened bones Main symptom is pain when weight is put on the affected bone Caused by insufficient calcium or vitamin D  Homeostatic Imbalances.Rickets Bones of children are inadequately mineralized causing softened, weakened bones Bowed legs and deformities of the pelvis, skull, and rib cage are common Caused by insufficient calcium or vitamin D What treatments would you recommend for someone with Osteomalacia or Rickets? A. Calcium rich foods B. Sunlight C. A and B D. None of the above What type of bone disorder is shown here (b)? A. Osteomalacia B. Greenstick fracture C. Osteoporosis Homeostatic Imbalances Osteoporosis Group of diseases in which bone reabsorption outpaces bone deposit Bones are porous and light Spongy bone of the spine, femur neck are vulnerable Occurs most often in postmenopausal women Severe cases: Even sneezing or stepping off a curb can cause fractures (pathologic fractures)  Osteporosis prevention Good diet EARLY in life (calcium and Vitamin D) Weight-bearing exercise Don’t smoke (reduces estrogen levels) Drink fewer carbonated beverages/alcohol Fluoride (already in water supply) NOTE: Genetic change in Vitamin D receptor increases risk of osteoporosis Osteoporosis Treatments Calcium, Vitamin D supplements Weight-bearing exercise Drugs that stimulate osteoblasts, inhibit osteoclasts Hormone replacement therapy (only slows bone loss) Other risks Paget’s Disease Characterized by excessive bone formation and breakdown RESULT: spotty weaknesses in bone Overabundance of spongy bone relative to compact bone Generally affects adults over age 40 Usually localized to spine, femur, pelvis and skull Other bone disorders ACHONDROPLASIA Form of genetic dwarfism (FGFR-3 gene) Reduced cartilage formation reduces endochondral bone formation Other bone disorders OSTEOGENESIS IMPERFECTA Insufficient collagen deposition Bones become brittle and shatter easily Other bone disorders OSTEOSARCOMA Bone cancer Most common between ages of 10 and 25 Why?????