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Review of Skeletal System 1 Skeletal System • Function: – Protection – Hematopoiesis – Mineral homeostasis • Calcium • Phosphorus • Carbonate • Magnesium 2 Structure • Bone is a connective tissue: – Matrix • Collagen fibers for flexibility and tensile strength • Calcium for rigidity • Hydroxyapatite Ca5(PO4)3OH 3 • Cells: – Osteoblast • Form organic components of matrix – Osteocyte – Osteoblasts • • • • • From monocytes Secrete citric and lactic acids Collagenases and other enzymes Stimulated by PTH Inhibited by Calcitonin 4 5 6 Types of Bone • Dense or Compact (85%) – Osteon (Haversian System) – Central (Haversian) canal – Lamellae – Lacunae with osteocytes – Canaliculi • Spongy (cancellous) bone (15%) – trabeculae 7 8 9 10 Periosteum • Outer layer is dense, irregular CT with nerves and blood vessels • Inner layer – Osteoblasts – Anchored to bone by collagen fibers that penetrate into bone 11 Joints • Degree of movement – Synarthrosis – immovable joint – Amphiarthrosis – slightly movable joint – Diarthrosis – freely movable joint 12 • Synovial joints – Joint capsule • Fibrous CT • Tendons and ligaments • Nerves, blood and lymph vessels – Synovial membrane • Loose fibrous CT • Many blood vessels – good repair – Joint (synovial) Cavity 13 14 • Synovial fluid – Plasma filtrate – Synovial cells and leukocytes phagocytize debris and microbes • Articular cartilage – Reduce friction – Distribute force 15 Bone Pathophysiology • Inherited conditions: – Osteogenesis imperfecta • Inherited defect in collagen synthesis • Osteopenia and brittle bones • Often- defective tooth formation, blue sclera, faulty hearing, other defects • Inheritance can be dominant, recessive or by new mutation • Several degrees of severity ( I,II,III,IV) • Biphosphate treatment can improve bone mass in all types of the disorder 16 • Achondroplasia – Involves a defect in normal cartilage development – Epiphyseal plates close early in long bones; individual has short arms and legs, but normal spine and skull – Dominant inheritance, but frequent new mutations – Other organs develop normally – Individuals live a normal lifespan 17 Acquired disorders • Osteoporosis – “porous bone” – Most common metabolic bone disease in North America – Can be attributed to genetics, diet or hormones – Most osteoporosis is idiopathic osteoporosis – Bone loss due to an identifiable cause is secondary osteoporosis – Bone tissue is mineralized normally, but over time the structural integrity of bone is lost and it becomes thinner and weaker, and more prone to fractures. 18 • Key features: bone fracture and the associated pain. • WHO defines osteoporosis by bone density: – Normal bone > 833 mg/cm2 – Osteopenia 833 to 648 mg/cm2 – Osteoporosis < 648 mg/cm2 • Can be generalized, involving major portions of the axial skeleton • Can be regional, involving one segment of the appendicular skeleton 19 20 • Remodeling is constant – Teen years more bone is laid down than reabsorbed – Peak bone mass or maximum density reached at around 30 years of age – After age 30, bone is reabsorbed faster than it is laid down (loss of about 0.7% /year) – In women, bone loss is most rapid in the first years after menopause, but continues throughout postmenopausal years – Est. 55% of people over 50 have osteoporosis or low bone mass. 21 • Men also lose bone density, but start out with more bone mass so takes longer. • By age 90 about 17% of males have had a hip fracture, vs. 32 % of females • Vertebral fractures also occur → kyphosis • Most common in whites, but affects all races. • African Americans have about half the fracture rates of whites (higher peak bone mass) 22 23 24 25 Risk factors • • • • • • • • • Family history White race Increased age Female sex Small stature Fair or pale skin Thin build Early menopause (natural or surgical) Late menarche 26 Risk factors cont. • • • • • • • • • • Nulliparity Obesity Weight below a healthy range Acidosis Low dietary calcium and vitamin D High caffeine intake Sedentary life style Smoker Excessive alcohol consumption Liver, kidney disease, rheumatoid arthritis, etc. 27 • Often progresses silently for decades until fracture occurs • Bones can fracture spontaneously • Most severe in spine, wrist and hips • Estrogens and androgens may be factors in both sexes – Testosterone is converted into estrogen in peripheral tissues and decreases bone loss • Rapid bone loss is osteoclast mediated • Slow bone loss is osteoblast mediated 28 Clinical manifestations • • • • Pain and bone deformity Kyphosis caused by vertebral collapse Fractures of long bones Fatal complications include fat or pulmonary embolism, pneumonia, hemorrhage and shock • 20 % die as a result of surgical complications 29 Treatment • No known cure • Slow bone loss and promote bone deposition • Calcium and vitamin D supplements • Nasal or subcutaneous calcitonin • Hormone replacement therapy • Biophosphates – inhibit osteoclasts • Dual x-ray absorptiometry for diagnosis • PREVENTION 30 Prevention • Intake of calcium, vitamin D, magnesium and possibly boron • Regular, weight-bearing exercise • Avoid tobacco and glucocorticoids • No alcoholism • Hormone replacement? • Parathyroid hormone? • Testosterone for men and possibly women 31 Rickets and Osteomalacia • Inadequate mineral deposition in essentially normal organic matrix • Softened bone: – Subject to malformation and distortion –pain 32 Rickets • Dietary vitamin D deficiency causes inadequate mineralization of the developing skeleton in infants and children • Rarely seen in Western nations – Poverty – Ignorance • Bones are soft and easily deformed • Tendency to fractures • Therapy: supply vitamin D and calcium 33 www.dinf.ne.jp/.../david/dwe002/dwe00215.htm 34 www.talkorigins.org/faqs/homs/rickets.html 35 Osteomalacia • Rarely due to vitamin D deficiency • Usually GI malabsorption, renal defect or chronic kidney or liver diseases. • Elderly often affected due to inadequate diet or lack of outdoor activity • May accompany and complicate osteoporosis. 36 Joint Disorders • Osteoarthritis – Most common joint disease in North America – Minimal inflammatory component – Differentiated from inflammatory disease by: • Absence of synovial membrane inflammation • Lack of systemic signs and symptoms • Normal synovial fluid – Much of the pain and loss of mobility associated with aging. 37 Osteoarthritis • Incidence increases with age: 85% of people age 65 have some joint degeneration • Incidence similar, but women more severely affected • Exceptional stress on joints: gymnasts, etc. • Biochemical defect in cartilage • Malformed joint, obesity and postural defects • Genetic component • Torn ACL or meniscectomy 38 Osteoarthritis • When associated with known risk factors it is secondary OA • No risk factors – idiopathic OA • Pathological characteristics: – Erosion of the articular cartilage – Sclerosis of subchondral bone – Formation of bone spurs or osteophytes 39 Osteoarthritis • Begins in articular cartilage – Yellow-grey or brownish gray – Thin, irregular, frayed – Cracks or fissures develop (fibrillation) – Fluid filled cysts may form – Microfractures of subchondral bone – Formation of fibrocartilage repair plugs – Bone surface exposed – Bone responds by becoming dense and hard 40 Osteoarthritis • Synovial membrane is indirectly affected – Fragments of fibrocartilage cause inflammation –pain – Fibrous repair of joint capsule restricts motion – Osteophytes form – pain and loss of motion • Joint mice 41 Osteoarthritis • Affects one or more weight-bearing joints – Hand, wrist, lower cervical spine, lumbar spine and sacroiliac, hip, knees, ankles, feet • Aches and stiffness – Symptoms increase with activity; diminish with rest • Usually no swelling or redness of adjacent tissues • Sometimes nocturnal pain – may be referred 42 Osteoarthritis Primary signs and symptoms of joint disease are: pain, stiffness, enlargement or swelling, tenderness, limited range of motion, muscle wasting, partial dislocation, and deformity, crepitus 43 Osteoarthritis • Evaluation made through clinical assessment and radiologic studies, CT scan, arthroscopy and MRI • Treatment: • Glucosamine may decrease pain and slow or stop progression – 1500 mg/day • Chondroitin sulfate – questionable absorption 44 Osteoarthritis • Analgesics and antiinflammatory drugs (NSAIDs) • Injections of corticosteroids or sodium hyaluronate (to improve lubrication) • Range of motion exercises • Reduce aggravating factors – Weight loss – Use of cane, crutches or walker • Surgical removal of bone spurs, and other • Replacement of joint 45 Rheumatoid Arthritis • Systemic disease with prominent involvement of the joints • Inflammatory joint disease characterized by: – Inflammatory damage in the synovial membrane or articular cartilage – Systemic signs of inflammation: fever, leukocytosis, malaise, anorexia, hyperfibrinogenemia) 46 Rheumatoid Arthritis • Systemic autoimmune disease that causes chronic inflammation of connective tissue • Initially affects synovial membrane • Later articular cartilage, joint capsule, ligaments and tendons, and bone • Affects joints of hands, wrists, ankles, and feet, but shoulders, hips and cervical spine may also be involved • Systemic effects on heart, kidney, lungs, skin and other organs 47 Rheumatoid Arthritis • • • • • • • • • Mild to severe Destroys and distorts joints Reduces life expectancy Remission and exacerbation 1 – 2% of adult population Women : men = 3:1 Onset usually in 20’s or 30’s Symptoms lessen during pregnancy Seasonal variation 48 Rheumatoid Arthritis • Idiopathic disease • Immune-mediated destruction of joints • Rheumatoid factors (IgM and IgG) target blood cells and synovial membranes forming antigen-antibody complexes • Genetic predisposition • Possibly bacterial or viral infection (Epstein-Barr) 49 Rheumatoid Arthritis • Chronic inflammation of synovial membrane • Cellular proliferation and damage to the microcirculation • Synovial membrane becomes irregular • Swelling, stiffness and pain • Cartilage and bone destruction • Ankylosis or fusing of joint • Ligaments and tendons also affected 50 Rheumatoid Arthritis • Systemic effects: – Generalized weakness and malaise – Up to 35% develop granulomas called rheumatoid nodules – Systemic inflammation of blood vessels – rheumatoid vasculitis – Serous membranes may be affected 51 Rheumatoid Arthritis • Evaluation : – history – Physical examination – X-ray – Serologic tests for rheumatoid factor and circulating antigen-antibody complexes, esp. antibodies against cyclic citrullinated peptide (CCP) • No cure 52 Rheumatoid Arthritis • Therapy: • Physical and emotional rest • Relieve pain and swelling and retain as much joint function as possible • Resting the joint, or binding or splinting • Use of hot and cold packs • Diet high in calories and vitamins • Strengthening of associated muscles 53 Rheumatoid Arthritis • Drug therapy: – NSAIDS – Methotrexate – Antimalarial drugs and immunosuppression • Surgical – Synovectomy – Correction of deformities – Joint replacement – Joint fusion 54 Review of Muscular System 55 Muscle • Skeletal muscle – > 600 muscles in body • Cardiac muscle • Smooth muscle 56 Muscle cell structure • Sarcolemma motor end plate transverse ( t- ) tubules • Sarcoplasm • Sarcoplasmic Reticulum – Stores Ca++ 57 58 59 • Proteins: – Thick filaments – myosin – Thin filaments – actin • Troponin • Tropomyosin – Sliding Filament Model 60 61 62 63 64 Muscular Dystrophy • Group of rare diseases characterized by a genetic etiology and progressive degeneration of skeletal muscle. • X-linked recessive defect • Most common of the muscular dystrophies • 1 in 3,500 live male births • Affects males • Gene located on the short arm of the X chromosome. 65 • 30% of cases arise as a new mutation • Can be diagnosed immediately after birth by high serum creatine kinase • Muscle weakness and delayed motor skills can be detected early – obvious by age 5 • Age 10 – require leg bracing • Age 12 – wheelchair • Age 15 completely bedridden • Death by 20 – 30 of cardiac arrest or respiratory failure. 66 • Fibrosis → contracture distorts skeletal development – Lordosis – Scoliosis – Compromised respiration • Respiratory insufficiency – Respiratory infection • Cardiac muscle – Dysrythmias – Congestive heart failure • Mental sluggishness 67 • Dystrophin is lacking – Membrane damage – Replaced by fibrous connective tissue and fatty deposits • Therapy – Passive stretching, splints to prevent deformities – Sustain mobility – Sustain respiratory function – Possibly gene therapy 68 Myesthenia gravis • Autoimmune disease in which antibodies (IgG) bind with acetylcholine receptors on muscle cells. (T-lyphmocyte abnormalities) • Reduces the number of acetylcholine receptors at the neuromuscular junction • Characterized by muscle weakness and fatigability • Also associated with other autoimmune disorders, such as SLE, rheumatoid arthritis, and thyrotoxicosis 69 • In 10-25% of people with MG thymic tumors are found – More common in males than females • 70 – 80 % have pathologic changes in the thymus 70 Classification of myasthenia • Neonatal myasthenia – Transitory condition in which 10-15 % of infants born to mothers with MG show symptoms of the disease • Congenital myasthenia • Juvenile myasthenia – onset us.about 10 years • Ocular myasthenia – More common in males – Weakness of eye muscles and eyelids, may also include swallowing difficulties and slurred speech 71 • Generalized autoimmune myasthenia – Involves proximal musculature throughout the body, and has several courses: • A course with periodic remissions • Slowly progressive course • Rapidly progressive course • Fulminating course 72 Pathophysiology • Defect in the nerve impulse transmission at the NMJ • Postsynaptic acetylcholine receptors are no longer recognized as “self” and antibodies are produced against them. • IgG blocks the binding of ACh • Eventually destroys the receptor • Causes diminished transmission of nerve impulse across the NMJ and lack of muscle depolarization 73 • Cause is unknown. Clinical manifestations • Onset typically insidious • May first appear during pregnancy, postpartum or with the administration of certain anesthetic agents • Complaints are fatigue and progressive muscle weakness – Fatigue after exercise – Recent history of recurrent upper respiratory infections 74 Clinical manifestations • Muscles of the eyes, face, mouth, throat and neck are usually affected first – Levator and extraocular muscles affected most Diplopia, ptosis, and ocular palsies – Muscles of facial expression, mastication, swallowing and speech are the next most involved • Facial droop, expressionless face; difficulties in chewing and swallowing, drooling, episodes of choking and aspiration • Nasal, low volume, high-pitched monotonous speech pattern 75 • Less frequently involved are the muscles of the neck, shoulder girdle and hip flexors – Fatigue requires periods of rest – Weakness of arms and legs – Difficulty maintaining head position – Respiratory muscles of chest wall and diaphragm become weak • In advanced stage all muscles are weak 76 Myasthenic crisis • Severe weakness causes quadriparesis or quadriplegia, respiratory insufficiency and extreme difficulty in swallowing 77 Cholinergic crisis • • • • • • • Anticholinesterase drug toxicity Intestinal motility increases Fasciculation Bradycardia Pupillary constriction Increased salivation Increased sweating 78 Evaluation • Improvement with edrophonium chloride (Telison) for several minutes • EMG – amplitude of action potentials declines • Antiacetylcholine receptor antibody titers • Antistriated muscle antibody titers • MRI to rule out thymoma 79 Progression • Varies • Appears first as a mild case that spontaneously remits with a series of relapses and symptom free intervals • Over time can progress leading to death • Ocular myasthenia has a good prognosis 80 Treatment • • • • • • Anticholinesterase drugs Steroids Immunosuppressant drugs Cyclophosphamide Plasmapheresis during myasthenic crisis Thymectomy is treatment of choice for individuals with thymoma 81