Bio153 Ch6 Bones and Skeletal Tissue PDF

Bio153 Ch6 Bones and Skeletal Tissue Skeletal cartilage Contains no blood vessels or nerves Surrounded by the perichondrium (dense irregular connective tissue) that resists outwards expansion 3 types - Hyaline - Elastic - Fibrocartilage Hyali...

Bio153 Ch6 Bones and Skeletal Tissue Skeletal cartilage Contains no blood vessels or nerves Surrounded by the perichondrium (dense irregular connective tissue) that resists outwards expansion 3 types - Hyaline - Elastic - Fibrocartilage Hyaline cartilage Provides support, flexibility, and resilience Is the most abundant skeletal cartilage Is present in these cartilage - Articular: covers the end if the long bones - Costal: connects the ribs to the sternum - Respiratory: makes up larynx, reinforces air passages - Nasal: supports nose Elastic cartilage Similar to hyaline cartilage bit contains elastic fibers Found in the external ear and the epiglottis Fibrocartilage Highly compressed with great tensile strength Contains collagen fibers Found in menisci of the knee and in intervertebral discs Growth of cartilage Appositional: cells in the perichondrium secrete matrix against the external face existing cartilage Interstitial: lacunae-bound chondrocytes inside the cartilage divide and secrete new matrix, expanding the cartilage from within  Calcification of cartilage occurs - During normal bone growth - During old age Classification of bones Axial skeleton: bones of the skull, vertebral column, and rib cage Appendicular skeleton: bones of the upper and lower limbs, shoulder, and hip Long bones: longer than they are wide (humerus) Short bones - Cube-shaped bones of the wrist and ankle - bones that form within tendons (patella) Flat bones: thin, flattened, and a bit curved (sternum, most skull bones) Irregular bones: with complicated shapes (vertebrae, hip bones) Function of bones Support: form the framework that supports the body and cradles soft organs Protection: provide protective case for the brain, spinal cord, and vital organs Movement: provide levers from muscles Mineral storage: reservoir for minerals, especially calcium and phosphorus Blood cell formation: hematopoiesis occurs within the marrow cavities of bones Bone marking Bulges, depressions, and holes that serve as: - Sites of attachment for muscles, ligaments, and tendons - Joint surfaces - Conduits for blood vessels and nerves Muscle and ligament attachment Tuberosity: rounded projection Crest: narrow, prominent ridge of bone Trochanter: large, blunt, irregular surface Line: narrow ridge of bone Tubercle: small rounded projection Epicondyle: raised area above a condyle  Spine: sharp, slender projection Process: any bony prominence Head: bony expansion carried on a narrow neck Facet: smooth, nearly flat articular surface Condyle: rounded articular projection Ramus: armlike bar of bone Meatus: canal-like passageeay Sinus: cavity within bone Fossa: shallow basing-likr depression Groove: furrow Fissure: narrow, slit-like opening Foramen: round or oval opening through bone Bone texture Compact bone: dense outer layer Spongy bone: honeycomb of trabeculae filled with yellow bone marrow Structure of long bone Long bones consist of a diaphysis and an epiphysis Diaphysis - Tubular shaft that forms the axis of long bones - Composed of compact bone that surrounds the medullary cavity - Yellow bone marrow (fat is contained in the medullary cavity epiphyses - Expanded ends of long bones - Exterior is compact bone, and the interior is spongy bone - Joint surface is covered with articular (hyaline) cartilage - Epiphyseal line separates the diaphysis from the epiphyses Bone membranes Periosteum: double-layered protective membrane - Outer fibrous layer is dense regular connective tissue - Inner osteogenic layer is composed of osteoblasts and osteoclasts - Richly supplied with nerve fibers, blood, and lymphatic vessels, which enter the bone via nutrients foramina - Secured to underlying bone by sharpey’s fibers Endosteum: delicate membrane covering internal surfaces of bone Structure of short, irregular, and flat bones Thin plates of periosteum-covered compact bones on the outside with endosteum-covered spongy bone (diploe) on the inside Have no diaphysis or epiphysis Contain bone marrow between the trabeculae Hematopoietic tissue (red marrow) In infants - Found in the medullary cavity and all areas of spongy bone In adults - Found in the diploe of flat bones, and the head of the femur and humerus Compact bone Haversian system, or osteon: the structural unit of compact bone - Lamella: weight-bearing, column-like matric tubes composed mainly of collageds - Haversian, ot central canal: central channel containing blood vessels and nerves - Volhmann’s canals: CHannels lying at right angles to the central canal, connecting blood and nerve supply of the periosteum to that of the haversian canal Osteocytes: mature bone calls Lacunae: small cavities in bone that contain osteocytes Canaliculi: hairlike canals that connect lacunae to each other and the central canal Chemical composition of bone: organic Osteoblasts: bone-forming cells Osteocytes: mature bone cells  Osteoclasts: larger cells that resorb or break down bone matrix Osteoid: unmineralized bone matrix composed of proteoglycans, glycoproteins and collagen Chemical composition of Bone: inorganic hydroxyapatites , or mineral salts - Sixty-five percent of bone by mass - Mainly calcium phosphates - Responsible for bone hardness and its resistance to compression Bone development Osteogenesis and ossification: the process of bone tissue formation, which leads to: - The formation of the bony skeleton in embryos - Bone growth until early adulthood - Bone thickness, remodeling, and repair Formation of the bony skeleton Begins at week 8 of embryo development Intramembranous ossification: bone develops from a fibrous membrane Endochondral ossification: bone forms by replacing hyaline cartilage Intramembranous ossification Formation of most of the flat bones of the skull and the clavicles Fibrous connective tissue membranes are formed by mesenchymal cells Stages of intramembranous ossification An ossification center appears in the fibrous connective tissue membrane Bone matrix is secreted within fibrous membrane Woven bone and periosteum form Bone collar of compact bone forms and red marrow appears Endochondral ossification Begins in the second month of development Uses hyaline cartilage “bones” as models for bone construction Requires breakdown of hyaline cartilage prior to ossification Stages of endochondral ossification Formation of bone collar Cavitation of the hyaline cartilage Invasion of internal cavities by the periosteal bud, and spongy bone formation Formation of the medullary cavity, appearance of secondary ossification centers in the epiphyses Ossification of the epiphyses, with hyaline cartilage remaining only in the epiphyseal plates Postnatal bone growth Growth in length of long bones - Cartilage on the epiphyseal plate closest to the epiphysis is relatively inactive - Cartilage abutting the shaft of the bone organizes into a pattern that allows fast, efficient growth - Cells of the epiphyseal plate proximal to the resting cartilage form thre functionally different zones: growth, transformation, and osteogenic Functional zones in long bone growth Growth zone: cartilage cells undergo mitosis, pushing the epiphysis away from the diaphysis Transformation zone: older cells enlarge, the matrix becomes calcified, cartilage cells die, and the matrix begins to deteriorate Osteogenic zone: new bone formation occurs Long bone growth and remodeling Growth in length: cdartilage continually grows and is replaced by bone as shown Remodeling: bone is resorbed and added by appositional growth as shown Hormonal regulation of bone growth during youth During infancy and childhood, epiphyseal plate activity is stimulated by growth hormone During puberty, testosterone and estrogens: - Initially promote adolescents growth spurts - Cause masculinization and feminization of specific parts of the skeleton - Later induce epiphyseal plate closure, ending longitudinal bone growth Bone remodeling Remodeling units: adjacent osteoblats and osteoclasts deposit and resorb bone at periosteal and endostral surfaces Bone deposition Occurs where bone is injured or added stregth is neede Requires a diet rich in protein, vitamins C, A & D, and calcium, phosphorus, magnesium, and manganese Alkaline phosphatase is essential for minarlizatikon Sites of new matrix deposition are revealed by the: - Osteoid seam: unmineralized band of bone matrix - Calcification front: abrupt transition zone between the osteoid seam and the older mineralized bone Bone resorption Accomplished by osteoclasts Resorption bays: grooves by osteoclasts as they break down bone matric Resorption involves osteoclast secretion of:  - Lysosomal enzymes that digest organic matric - Acids that convert calcium dslts into soluble forms Dissolved matric is transcytosed acriss the osteoclast’s cell where it is secretedf into the interstitial fluid and then into the blood Importance of ionic calcium in body Calcium is necessary for: - Transmission of nerve impulses - Muscle contraction - Blood coagulation - Secretikon by glands and nerve cells - Cell division Carpopedal spasm Hypocalcemia causing overexcitability of nervous system and muscle spasm of hands and feet Control of remodeling Teo control loops regulate bone remodeling - Hormonal mechanism maintains calcium homeostasis in the blood - Mechanical and gravitational forces acting on the skeleton Hormonal machanism Rising blood Ca2+ levels trigger hte thyroid to release calcitonin Calcitonin stimulates calcium salt deposit in bone Falling bloos Ca2+ levels signal the parathyroid glands to release PTH PTH signals osteoclats to degrade bone matrix and release Ca2+ into the blood Calcitriol synthesis & action Response to mechanical stress Wolff’s law: a bone grows or remodels in response to the forces or demands pplaced upon it Observation supposting wolff’s law include - Long bones are thickest midway along the shaft (where bending stress is greatest) - Curved bones are thickest where they are most likely to buckle Trabeculae form along lines of stress Large, bony projections occur when heavy, active, muscles attach Bone fractures (breakes) Bone are classified by: - The position of hte bone ends after fracture - The completeness of the break - The orientation of the bone to the long axis - Whether or not the bones ends penetrate the skin Types of bone features Nondisplaced: bone ends retain their normal position Displaced: bone ends are out of normal alignment Complete: bone is broken all the way through Incomplete: bone is not broken all the way through Linear: the fracture is parallel to the long axis of the bone (it breaks right down) Transverse: the fracture is perpendicular to the long axis of the bone Compound (open): bone ends penetrate the skin Simple (closed): bone ends do not penetrate the skin Common types of fractures Comminuted: bone fragments into three or more pieces; common in the elderly Spiral: ragged break when bone is excessively twisted; common sports injury Depressed: broken bone portion pressed inward; typical skull facture Compression: bone is crushed; common in porous bones Epiphyseal: epiphysis separates from diaphysis along spiphyseal lines; occurs where cartilage cells are dying Greenstick: incomplete fracture where one side of the bone breaks and the other side bends; coom in children Stages in the healing of a bone fracture Hematoma formation - Torn blood vessels hemorrhage - A mass of clotted blood (hematoma) forms at the fracture site  - Sites becomes swollen, painful, and inflamed - Fibrocartilaginous callus forms - Granulation tissue (soft callus) forms a few days after the fracture - Capillaries grow into the tissue and phagocytic cells begin cleaning debris The fibrocartliaginous callus forms when: - Osteoblasts and fibroblasts migrate to the frature and begin reconstructing the bone - Fibroblasts secrete collagen fibers that connect broken bone ends - Osteoblasts begin forming spongy bone - Osteoblasts furthest from sapillaries secrete an externally bulging cartilaginous matric that later calcifies Bony callus formation - New bone trabeculae appear in the fibrocartilaginoud callus - Fibrocartilagious callus converts into a bony (hard) callus - Bone callus begins 3-4 weeks after injury, and continues until firm union is formed 2-3 months later Bone remodeling - Excess material on the bone shaft exterior and in the medullary canal is removed - Compact bone is laid down to recontust shaft walls Healing of fractures Normally healing takes 8-12 weeks (longer in elderly) Stages of healing - Fracture hematoma (1) ➔ Broken vessels form a blood clot - Granulation tissue (2) ➔ Fibrous tissue formed by fibroblast & infiltrated by capillaries - Callus formation (3) ➔ Soft callus of fibrocartilage replaced by hard callus of bone in 6 weeks - Remodeling (4) ➔ Occurs over nest 6 months as spongy bone is replaced with compact bone Homeostatic imbalances osteomalacia - Bones are inadepquately mineralized causing softened, weakened bones (osteiod w/o minerals) - Main symptoms is pain when weight is put on the affected bone - Caused by insufficient calcium in the diet, or by vitamin D deficiency  Rickets (in Children) - Bones of children are inadequately mineralized causing softene weaken bones - Bowed legs and deformities of the pelvis, skull, and rib cage are common - Caused by insufficient calcium in the diet, or by vitamin D deficiency osteoporosis - Group of diseases inw hich bone reabsorption outpaces bone deposit - Spongy bone of the spine is most vulnerable - Occurs most often in postmenopausal women - Bones become so fragile that sneezing or stepping off a curb can cause fractures ★ Treatment ➔ Calcium and vitamin D supplements ➔ Increased weight-bearing exercise ➔ hormone (estrogen) replacement therapy (HRT) slows bone loss ➔ Natural progesterone cream prompts new bone growth ➔ Statin increase bone mineral density Isolated cases of rickets Rickets have been essentially eliminated in the US Only isolated cases appear Example: infants of breastfeeding mother deficient in vitamin D will also be Vitamin D deficient and develop rickets Paget’s disease Characterized by excessive bone formation and breakdown Pagetic bone with an excessively high ratio of woven (spongy) to compact bone is formed Pagetic bone, along with reduced mineralization, causes spotty weakening of bone Osteoclast activity wanes, but osteoblast activity continues to work (can get irregular bone thickenings) Usually localized in the spine, pelvis, femur, and skull Unknown cause (possiblty viral) Treatment includes the drugs Didronate and Fosamax (also calcitonin by inhalation) Development aspects of bones Mesoderm gives rise to embryonic mesenchymal cells,l which produce membranes and cartilages that form the embryonic skeleton The embryonic skeleton ossifies in a predictable timeable that allows fetal age to be easily determined from songrams  At birth, most long bones are well ossified (except for their eiphnyses) By age 25, nearly all bones are completely offified In old age, bone resoptioion predominates A single gene that codes for vitamin D docking determines both the tendency to accumulate bone mass early in life, and the risk for osteoporosis later in life.