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UWL BIO 312 - Skeletal System

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Lecture 5 Outline of Current Lecture I Growth hormonea. Parathyroid GlandII Bone diseasesa. OsteoporosisIII Bone Fracturesa. Classificationb. treatmentCurrent LectureGrowth Hormone: - Estrogen and testosterone (anabolic)o Stimulate the synthesis of macromolecules (amino acids into proteins, muscle growth)- Insulin: stimulates protein synthesis- Thyroid Hormone: enhances effect of GH (increases number of receptors)o Needed for nervous system to developo Deficiency in infancy could cause cretinism (cretin dwarf)Bone Plays Essential Role in Regulating Blood Ca 2+ levels- Plasma [Ca 2+] is precisely regulatedo [Ca 2+] influences vital functions in body such as Blood clotting Exocytosis (hormone and neurotransmitter release) “excitation-contraction coupling” in cardiac and smooth muscle Excitability of neurons controlling skeletal muscle (hypocalcemic tetany)- Can cause spasm of skeletal muscle or even paralyze the diaphragmo About 99% of Ca 2+ in our body is contained in bone as hydroxyapatites (bone matrix)o Bone can release Ca2+ (and phosphate) into ECF when blood levels of Ca 2+ fall too lowo Role of bone in ECF Ca2+ homeostasis is regulated by parathyroid hormone and calcitonin come from parathyroid gland which are embedded in thyroid glad located directly below larynxo Roles of PTH during hypocalcemia  Activates osteoclasts causing calcium and phosphate ions released into blood Increases calcium absorption from food Promotes activation of vitamin D in kidney to better absorb calcium During hypercalcemia, PTH levels drop and calcitonin levels rise which generally has opposite effects on [Ca] as PTHBio 312Suppose a patient has tumor in parathyroid gland and excess PTH released. What are the consequences to skeleton?- Increased osteoclasts activity would reduce bone mass as well as strength of bone- Higher incidence of fractures- Elevated levels of calcium and phosphate ions- Increased incidence of kidney stonesNutritional Influences on Bone Health, Remodeling and Repair:- Bone growth and remodeling depends ono Synthesis and secretion of matrix by chondroblasts and osteoblastso Deposition of calcium salts (calcium phosphate)- Scurvy: results from Vit. C deficiency over long period of timeo Vit. C required for synthesis of collagen fiberso Production of matrix is impairedo In children epiphyseal plates are weaker and growth is impairedo Slow healing woundso Weak blood vesselso Loosening of teeth- Rickets: caused by insufficient calcium in diet or Vit D deficiencyo Vitamin d needed to absorb ingested calciumo Osteoid produced but it does not become calcifiedo Results in soft, deformed bones (bow legs)- Osteomalacia: means soft bones, adult form of ricketso Caused by insufficient VIt D and/or calciumo Osteoid produced in a normal manner through remodeling but the matrix does not become properly calcifiedo Bones soften and weaken, may become deformed, higher incidence of fractures- Osteoporosis: group of diseases in which rate of bone resorption exceeds bone formationo Loss of bone mass, affects entire skeletono Chemical composition (proportion of each chemical) unaffectedo Effects both compact and spongy boneo Osteoporotic bone is porous and susceptible to fracture (pathological fracture)o neck of femur and spongy bone of vertebral body especially vulnerableo accounts for high incidence of hip fractures and compression fractures of vertebrae in elderlyo high incidence of fractures in ribs, radius and ulna alsoo Risk factors for osteoporosis: Age, gender (menopause), body build, race (whites and asians), lack of exercise, smoking, hyperthyroidism, excess glucocorticoids, calcium deficiency, vit D deficiency, pregnancy/nursingo Treatment: calcium and vit d supplements, weight bearing exercise, estrogen replacement therapy, drugs to suppress osteoclast activity, statins (increase mineral density)Classification of Bone Fractures:- Complete vs incomplete (partial)- Open (compound) vs. closed (simple)- Orientation of break: transverse vs linear vs oblique- Pathological fracture: fracture that would not have occurred if bone were healthy- Comminuted fracture: bone fractures into three or more pieces- Compression fractures: bone is crushed, common in porous bone subjected to trauma- Greenstick fracture: incomplete fracture where one side breaks but the other bends (kids)- Epiphyseal fracture: epiphysis separates from the diaphysis along the epiphyseal plate- Spiral fracture: uneven break, occurs when excessive rotational forces applied to boneTreatment of Fractures:- Reduction: realignment of broken bone pieces (open vs closed reduction)- Fixation: procedure to keep pieces in proper alignment until healing occurs (cast, splint, pins, screws)- Fracture Remodeling:o Hematoma forms from broken blood vessels in boneo Cells from damaged periosteum, endosteum and marrow differentiate into fibroblasts, chondroblasts, osteoblasts and osteoclastso Differentiated chondro and osteoblasts form a bridge of tissue (fibrocartilage)o Spongy bone replaces fibrocartilageo Compact bone replaces spongy bone- Timeframe of healing:o Ageo Which boneo Fracture typeo Nutritional statuso Health


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UWL BIO 312 - Skeletal System

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