Skeletal System: Overview, Bone Growth, and Diseases | PDF

Skeletal System Overview, Chapter 6 Robert S. Kellar, Ph.D. 1  What makes up the skeletal system? Bones Cartilage – Embryonic framework for bones Ligaments 2 What do bones do for me? Support...

Skeletal System Overview, Chapter 6 Robert S. Kellar, Ph.D. 1  What makes up the skeletal system? Bones Cartilage – Embryonic framework for bones Ligaments 2 What do bones do for me? Support Protection Movement Electrolyte balance Acid-base balance Blood formation 3  How are bones classified? Long bones Short bones Flat bones Irregular Sesamoid 4 Bone categories by location Axial skeleton Appendicular skeleton 5 What are the types of bone tissue? Compact bone – 1/4 of all bone Spongy bone – medullary cavity Diploe: characteristic of bone organization 6 What are some bone features? Diaphysis Epiphysis Periosteum – Outer fibrous collagen layer – Inner osteogenic layer – Nutrient foramina 7 What are some bone features? Endosteum – Reticular CT – Osteoclasts – Osteoblasts Epiphyseal plate – Point of elongation – Hyaline cartilage→ bone – Transforms to epiphyseal line 8  Skeletal System Bone cells, matrix and marrow 9  Review: what makes up CT? Matrix Cells (blast, cyte) Bone: – Matrix – Cells 10 What are the four types of bone cells? Osteogenic cells – Endosteum – Periosteum Osteoblasts – Non-mitotic – Endosteum – Periosteum – Secrete collagen encrusts w/ hydroxyapatite 11 What are the four types of bone cells? Osteocytes – Trapped in matrix – Canaliculi connect cells 12 What are the four types of bone cells? Osteoclasts – from bone marrow cells – Cellular fusion – Resorption bays – Secrete acid phosphatase (digest collagen) HCl (digest minerals) 13  What’s in the bone matrix? 1/3 Organic, 2/3 inorganic matter – 1/3 organic by weight Organic – collagen, glycoproteins, proteoglycans – Resists tension and bending Inorganic: 85% hydroxyapatite – Resists compression 14 What are the parts of osseous tissue? Lamellae – Connected to other lamellae via canaliculi Haversian canal (AKA “Central Canal”) Osteon Volkmann (perforating) canal 15  What are the parts of spongy (cancellous) bone? Trabeculae – Develop along lines of stress Spaces: filled with bone marrow Advantage of osseous tissue 16  What is bone marrow? Soft tissue – Between trabeculae – Medullary cavities Red bone marrow – Hemopoietic tissue – Children vs. adults 17 What is bone marrow? Yellow bone marrow – Mostly adipocytes – Replaces red bone marrow – Can revert to hemopoietic – Old age → gelatinous bone marrow 18  Application Turn to your class partner and discuss what would happen to a patient whose bone marrow became compromised from disease? Why is the bone marrow so important? 19  Skeletal system Intramembranous ossification 20  How do bones form and develop? Ossification – AKA osteogenesis Two types – Intramembranous ossification – Endochondral ossification 21 What is intramembranous ossification? Formation of flat bones – week 8 of development 1: ossification centers form Mesenchymal cells differentiate into osteoblasts 22 What is intramembranous ossification? 2: osteoblasts create trabeculae Secrete soft matrix Calcium phosphate deposited Forming trabeculae become spongy bone (diploe) Osteoblasts → osteocytes 3: formation of compact bone Outermost trabeculae calcify Compact bone and periosteum form 23 How does the skull change after birth? Flat bones in skull fuse – Via sutures – A fibrous CT joint between skull bones – Fontanels – Why? 24  When do fontanels disappear? Frontal (anterior) fontanel Others close within first year – Sphenoidal (anterior lateral) – Mastoidal (posterior lateral) – Occipital (posterior) 25  Skeletal system Endochondral ossification 26  What is endochondral ossification? Most bones formed this way Overview: – Mesenchyme becomes hyaline cartilage ~ week 6 of development – Hyaline serves as template for ossification 27  What are the steps for endochondral ossification? Step 1: bone collar forms – Trigger is blood vessels invasion of perichondrium and forming a periosteum – Osteoblasts differentiate in periosteum Form bone collar 28  What are the steps for endochondral ossification? Step 2: chondrocytes swell (hypertrophy) – Signals mineralization of matrix – Collar cuts off circulation to chondrocytes = death Matrix deteriorates Serves as splint/support – Primary marrow site forms 29  What are the steps for endochondral ossification? Step 3: periosteal bud forms – Cavity invaded by blood vessels, hematopoietic cells, nerves, osteoblasts, osteoclasts – osteoblasts form primary ossification center Deposit osteoid matrix over calcified cartilage Forms spongy bone: ossification spreads 30 towards epiphysis  What are the steps for endochondral ossification? Step 4: Medullary cavity forms – Osteoclasts – Secondary ossification centers form Step 5: spongy bone develops at heads – Blood vessels invade head – Development similar to process in bone shaft 31  Summary Introduction to skeletal system Types of bones Bone cells Bone marrow Intramembranous ossification Endochondral ossification 32 Skeletal system Lecture 2 Bone growth 33  How do bones grow after birth? Interstitial growth – Cartilage organizes in zones Epiphyseal side: new cartilage added Diaphysis side: osteoblasts invade and produce bone Also some appositional growth 34  How does endochondral ossification happen? Five zones of cartilagenous /osseous cells Zone 1: reserve cartilage zone Zone 2: proliferation zone – Chondrocytes multiply 35  How does endochondral ossification happen? Zone 3: hypertrophy zone Zone 4: calcification zone Zone 5: deposition zone – Osteoblasts invade, secrete osseous matrix 36 After growth finishes… 37 Other locations… 10 year old female. 38  How does appositional growth happen? Balanced events – Helps maintain proper bone shape – Osteoclasts in endosteum dissolve bone Expand medullary cavity – Osteoblasts in periosteum produce new bone 39 Osteon = ~200 um 40 41 42  Moment of Inertia I = mr2 The more the density of mass from the neutral axis the stronger the resistance to bending 43 Skeletal system Bone remodeling 44  Two types of bone growth Person A: Intramembranous ossification Person B: Endochondral ossification With a partner, discuss the differences 45  How do endochondral ossification and intramembranous ossification differ? Does it – or – Is ___ Endo. Intramemb. Make a table of present? similarities and differences: Start w/cartilage? – Answer yes or no for each Bone collar? Hypertrophy? Matrix changes? What would happen to Cell death? the shape and strength of bone if only Periosteal bud? intramembranous ossification growth occurred? Bone formation? Occurs in full-grown adults? 46  This bone-related event does NOT involve activity in/on the medullary cavity. A. Endochondral ossification B. Appositional growth C. Intramembranous ossification D. Two of these do not involve activity in the medullary cavity 47  What controls epiphyseal plate? Hormones in childhood – Growth hormone – Thyroid hormone Sex hormones at puberty – Estrogen/testosterone – make bone formation outpace cartilage growth – Epiphyseal line forms women = 18 men = 21 48  Achondroplasia Autosomal dominant disease Pathology – Failure of epiphyseal cartilage to grow 49  Achondroplasia Characteristics Treatment/prognosis 50  Are bones static in adults? No! Osteocytes respond to stress – Wolf’s Law Osteoclasts and osteoblasts in balance = healthy bone – Out of balance = disease 51  Wolff’s Law Julius Wolff, German anatomist – Julius Wolff (1836 – 1902 in Berlin) was a German surgeon who served as military surgeon during the Franco-Prussian War and some other minor campaigns. – Wolff's law is a theory developed by the German Anatomist/Surgeon Julius Wolff (1836-1902) in the 19th century that states that bone in a healthy person or animal will adapt to the loads it is placed under. Reference: Wolff J. "The Law of Bone Remodeling". Berlin Heidelberg New York: Springer, 1986 (translation of the German 1892 edition) 52  Wolff’s Law Julius Wolff, German anatomist Resorption – Response to decreased stress – Osteoclasts dominate Disuse, immobilization, microgravity Deposition – Response to increased stress – Osteoblasts dominate Weight-bearing exercise 53 How does spine shape change? Newborn: C-shaped Primary curvature Secondary curvature – Cervical – Lumbar 54  Inactivity Bed rest can induce a bone mass loss of 1% per week. Decreased size reduces moment of inertia = weaker strength of bone A 20% decrease in diameter = 60% reduction in strength in torsion 55  Demineralization Loss of calcium – Osteoporosis – Osteomalacia (adults) Vit D deficiency Rickets (children) 56 How is bone homeostasis maintained? 5-7% of bone mass recycled weekly – Head of femur turns over every 5-6 mos. Shaft takes longer – Use determines rate of replacement – At both endosteal and periosteal surfaces 57 What happens during remodeling? Bone dissolved, followed by deposition Osteoclasts secrete? – Excavate a tunnel, releasing calcium Osteoblasts enter tunnel and secrete matrix – Matrix mineralizes 58  What controls remodeling? Calcium levels in blood monitored Thyroid and parathyroid hormones – Thyroid: calcitonin – Parathyroid: PTH 59  What if calcium is out of balance? Hypocalcemia: too little – Excessive excitation of nerves – Tetanus (esp. carpopedal spasm) – Laryngospasm Hypercalcemia: too much (rare) – Less excitable nerves, muscles – Muscle weakness, sluggish reflexes – Cardiac arrest possible 60  Summary Bone growth Bone remodeling Achondroplasia Wolf’s Law Bone homeostasis 61 Skeletal system Lecture 3, Part I Repair 62  Given these zones within the epiphyseal plate: 1. zone of calcification 2. zone of resting cartilage 3. zone of proliferation 4. zone of hypertrophy Arrange them in the correct order, from the diaphysis to the epiphysis. A. 1 2 3 4 B. 1 3 4 2 C. 2 3 4 1 D. 2 3 1 4 E. 1 4 3 2 63  In which direction is the epiphysis moving? A C B D 64  Types of fractures Closed Compound Spiral Greenstick Comminuted 65  How do you treat fractures? Closed reduction – Manipulation – No surgery Open reduction – Surgical exposure – Screws, pins, etc. Immobilize – Cast or traction 66 How does the body repair fractures? Similar to skin repair Fibrous callus forms – Similar to granulation step Bony callus forms Remodeling of spongy bone into original shape 67  Salter-Harris Fracture Epiphysis fractures 5 classifications Stunt growth in the involved limb A portion of the damaged growth plate may remain functional (open) and thus the bone and limb becomes twisted 68 Salter-Harris Fracture 69 Salter-Harris Fracture 70 Torsional Fracture. The radiograph illustrates the typical spiral oblique fractures of the tibia and fibula resulting from a torsional injury such as a skiing accident. 71 An Ilizarov fixator. The Ilizarov construct is applied externally to stabilize fractures and lengthen limbs. (Photo courtesy of James J. McCarthy, MD, Shriners Hospitals for Children, Philadelphia, PA) 72  Moment of Inertia I = mr2 The more the density of mass from the neutral axis the stronger the resistance to bending 73 Note: Polar Moment of Inertia 74 75  Skeletal system Lecture 3, Part II Disease 76  What is osteoporosis? Loss of bone mass – Cancellous tissue – Most common in elderly women – Onset: menopause Prevention Drugs 77 Normal Osteoporotic bone 78  Osteoporosis: bone resorption > bone deposits Osteoporosis is a disease of bone that leads to an increased risk of fracture. In osteoporosis the bone mineral density (BMD) is reduced, bone microarchitecture is disrupted, and the amount and variety of non- collagenous proteins in bone is altered. Osteoporosis is defined by the World Health Organization (WHO) in women as a bone mineral density 2.5 standard deviations below peak bone mass (20- year-old healthy female average) as measured by DXA. Osteoporosis is most common in women after menopause, when it is called postmenopausal osteoporosis, but may also develop in men, and may occur in anyone in the presence of particular hormonal disorders and other chronic diseases or as a result of medications, specifically glucocorticoids, when the disease is called steroid- or glucocorticoid-induced osteoporosis (SIOP or GIOP). 79  Osteoporosis: Facts In the United States, nearly 10 million people already have osteoporosis. Another 18 million people have low bone mass that places them at an increased risk for developing osteoporosis. Eighty percent of those with osteoporosis are women. Of people older than 50 years, 1 in 2 women and 1 in 8 men are predicted to have an osteoporosis-related fracture in their lifetime. 80  Osteoporosis: Medications & Treatments Estrogens – slows or stops bone loss. Can be taken orally or transdermally (skin patch) such as Climara or Estraderm SERMS (selective estrogen receptor modulators) – for patients who cannot take estrogen replacement (breast cancer risk patients). Example: Raloxifine Calcium and Vit D. Bisphosphonates: e.g. Fosamax (Merck), Boniva Calcitonin (Miacalcin)- hormone extracted from salmon that slows bone loss and may increase bone density 81 82 An artificial joint introduces several different materials into a bone. The system can no longer be modeled as a beam of homogeneous bone. The effects of the joint replacement stem and bone cement (if used) must be accounted for. 83  Osteoporosis CLINICAL PRESENTATION: MG is an independent 78 year old woman who fell on the dance floor at her daughter's wedding. She was unable to walk and complained of moderate pain about her left groin and thigh. Examination in the Emergency Department revealed a good range of motion of the left hip, although it was painful. No deformity was noted. 84  Osteoporosis 9 yrs old, total right hip 85 nondisplaced pertrochanteric fracture (arrows) 86 Osteoporosis 87  Osteoporosis Group Discussion: Patient is currently on aspirin and coumadin. Has high blood pressure. What type of gait issues do you expect this patient will experience? What type of dietary suggestions might you suggest? Any exercise(s) for this patient? If so, what type(s)? 88  Bone Regeneration MSC-mediated bone regeneration in preclinical animal models of segmental defect repair. A. defects fitted with cell-free HA/TCP carrier. B. defects fitted with HA/TCP carrier loaded with rat MSCs C. Radiographic appearance of the three different treatment groups. D. Biomechanical torsion testing results after 12 weeks. (Lanza, Langer, Vacanti, 2000). 89  Let’s talk bone health… What disease do people worry about getting with respect to their bones? Interplay of three things: – Excessive bone resorption Cells? – Inadequate new bone formation during remodeling Cells? – Inadequate peak bone mass…  Bone health and calcium Which is the most important age range for taking action to prevent osteoporosis? A. 0-20 years old B. 21-40 years old C. 41-60 years old D. 61-80 years old 91 92  Graph of calcium intake and age Think of your bones like a BANK in which you make deposits for later withdrawal… 93 Image from: http://library.med.utah.edu/WebPath/TUTORIAL/OSTEO/OSTEOPOR.html  What about men? Do they get osteoporosis? 94  What is the average bone mass for men in their 80s? A. About 600 g B. About 800 g C. About 1300 g D. About 1500 g E. Cannot determine from the information given 95 What is the standardized, average hip BMD (bone mineral density) of a black male at age 70? A. 1.0 B. 0.98 C. 1.05 D. 1.1 E. Less than 0.9 Age 96 So do females consume enough calcium? Image from: http://www.surgeongeneral.gov/library/bonehealth/chapter_6.html 97  How much calcium does it take to get the RDA? Teenagers & >50 = 1200 mg Adults 20-49 = 1000 mg Less than 30% of calcium is actually absorbed!!! 98  What’s your favorite soda? A. Coke or Pepsi (or diet Coke/Pepsi, Coke with lime, etc…) B. Root beer (or diet…) C. 7-Up (or Sprite or Fresca or diet, etc…) D. Dr. Pepper (or Mr. Pibb, or diet, etc.) E. Some other dark-colored soda pop F. Some other light-colored soda pop G. I don’t really drink soda pop Hang tight…there IS a connection to the skeletal system! 99  What does this have to do with bone Phosphoric acid health? – Maybe also caffeine? – Women vs. men – Teenagers study 100  What’s the benefit of exercise? Impact or weight- bearing is preferred Window of opportunity for building BMD 101 Image from: http://www.surgeongeneral.gov/library/bonehealth/chapter_6.html  Summary Bone repair Bone disease Osteoporosis / Inactivity / demineralization Wolf’s Law Medical health data 102