Skeletal 2_student.pptx

Skeletal II Bone Development Ossification or osteogenesis—the formation of bone Two methods – Intramembranous ossification – Endochondral ossification Intramembranous Ossification Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Mesenchymal cell Osteocyte...

Skeletal II Bone Development Ossification or osteogenesis—the formation of bone Two methods – Intramembranous ossification – Endochondral ossification Intramembranous Ossification Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Mesenchymal cell Osteocyte Osteoblasts Trabecula Sheet of condensing mesenchyme Blood capillary Calcified bone Osteoid tissue Fibrous periosteum 2 Deposition of osteoid tissue by osteoblasts on mesenchymal surface; entrapment of first osteocytes; formation of periosteum 1 Condensation of mesenchyme into soft sheet permeated with blood capillaries Osteoblasts T rabeculae Osteocytes Fibrous periosteum Osteoblasts Spongy bone Marrow cavity Compact bone 3 Honeycomb of bony trabeculae formed by continued mineral deposition; creation of spongy bone 4 Surface bone filled in by bone deposition, converting spongy bone to compact bone. Persistence of spongy bone in the middle layer. Produces flat bones of skull and clavicle Intramembranous Ossification Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Periosteum: Fibrous layer Osteogenic layer Osteoid tissue Osseous tissue (bone) Osteoblasts Osteocytes © Ken Saladin Note the periosteum and osteoblasts Endochondral Ossification Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Articular cartilage Spongy bone Epiphyseal line Perichondrium Secondary marrow cavity Hyaline cartilage 1Early cartilage model Epiphysis Secondary ossification center Enlarging chondrocytes Bony collar Primary ossification center Blood vessel Periosteum Epiphyseal plate Nutrient foramen Marrow cavity Metaphysis Compact bone Diaphysis Primary marrow cavity Periosteum 2 Formation of 3 Vascular invasion, formation of primary primary marrow cavity, and ossification center, bony collar, and appearance of periosteum secondary ossification center Secondary ossification center Metaphysis Cartilage 4 Bone at birth, with 5 Bone of child, with enlarged primary epiphyseal plate at marrow cavity and distal end appearance of secondary marrow cavity in one epiphysis 6 Adult bone with a single marrow cavity and closed epiphyseal plate Endochondral Ossification During infancy and childhood, the epiphyses fill with spongy bone Cartilage limited to the articular cartilage covering each joint surface, and to the epiphyseal plate (growth plate) – Epiphyseal plate (Growth plate) Thin layer of cartilage separating the primary and secondary marrow cavities in childhood and adolescence Growth for bone elongation The Fetal Skeleton at 12 Weeks Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Cranial bones Mandible Vertebrae Humerus Radius Ulna Scapula Ribs Femur Pelvis © Biophoto Associates/Photo Researchers, Inc. Bone Growth and Remodeling Ossification continues throughout life with the growth and remodeling of bones Bones grow in two directions – Length – Width Bone Elongation Growth plate – Interstitial growth – Consists of typical hyaline cartilage in the middle with a transition zone (Metaphysis) on each side – Growth plate closure–By late teens to early 20s Bone can no longer grow in length Zones of the Metaphysis Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Zone1 Zone5 1 Zone of reserve cartilage 2 Zone of cell proliferation Enlarging chondrocytes 3 Zone of cell hypertrophy Breakdown of lacunae 4 Zone of calcification 5 Zone of bone deposition Multiplying chondrocytes Calcifying cartilage Bone marrow Osteoblasts Osteocytes Trabeculae of spongy bone 7-10 X-Ray of Child’s Hand Epiphyseal Plates Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Diaphysis Epiphysis Epiphyseal (growth) plate Metacarpal bone Epiphyseal (growth) plates Courtesy of Utah Valley Regional Medical Center, Department of Radiology Bone Widening and Thickening Appositional growth—bones increase in width throughout life – Deposition of new bone at the surface – Osteoblasts lay down matrix in layers parallel to surface Forms circumferential lamellae over surface – Osteoclasts of endosteum enlarge marrow cavity Bone Remodeling Bone remodeling occurs throughout life— 10% per year – Repairs microfractures, releases minerals into blood, reshapes bones in response to use and disuse – Wolff’s law: bone density determined by mechanical stresses placed on it and bones adapt to withstand those stresses Adaptation to stress=Remodeling – action of osteoblasts and osteoclasts Bony processes grow larger in response to mechanical stress Mineral Deposition and Resorption Mineral deposition (mineralization or calcification) – Crystallization process – Osteoblasts produce collagen  Fibers become encrusted with minerals – Osteoblasts neutralize calcification inhibitors in bone matrix – First few crystals (seed crystals) attract more calcium and phosphate from solution Mineral Deposition and Resorption Abnormal calcification (ectopic ossification) – May occur in lungs, brain, eyes, muscles, tendons, or arteries (arteriosclerosis) – Calculus: calcified mass in an otherwise soft organ such as the lung http://www.rad.washington.edu/academics/academic-sections/msk/teaching-materials/online-musculoskeletalradiology-book/soft-tissue-calcifications Mineral Deposition and Resorption Mineral resorption—the process of dissolving bone and releasing minerals into the blood – Performed by osteoclasts at the ruffled border – Hydrogen pumps secrete hydrogen into space between the osteoclast and bone surface Chloride ions follow by electrical attraction Hydrochloric acid (pH 4) dissolves bone minerals – Acid phosphatase enzyme digests the collagen Calcium Homeostasis Calcium and phosphate are used for much more than bone structure Phosphate is a component of DNA, RNA, ATP, phospholipids, and pH buffers Calcium needed in neuron communication, muscle contraction, blood clotting, and exocytosis Minerals are stored in the skeleton and withdrawn when they are needed for other purposes Calcium Homeostasis About 1,100 g calcium in adult body – 99% in the skeleton As easily exchangeable calcium ions and more stable hydroxyapatite reserve Normal calcium concentration in blood plasma is 9.2 to 10.4 mg/dL – 45% as Ca2+ can diffuse across capillary walls and affect other tissues; rest in reserve, bound to plasma proteins Calcium Homeostasis Calcium homeostasis depends on a balance between dietary intake, urinary and fecal losses, and exchanges between osseous tissue Calcium homeostasis is regulated by three hormones: – Calcitriol, calcitonin, and parathyroid hormone Calcitriol Synthesis and Action Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Calcium Homeostasis Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Blood Ca2+ deficiency Blood Ca2+ returns to normal Parathyroid hormone secretion Increased osteoclast activity More bone resorption Reduced osteoblast activity Less bone deposition More urinary phosphate excretion Prevention of hydroxyapatite formation Less urinary calcium excretion Conservation of calcium (b) Correction for hypocalcemia Calcium Homeostasis Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Blood Ca2+ excess Blood Ca2+ returns to normal Calcitonin secretion Reduced osteoclast activity Less bone resorption Increased osteoblast activity More bone deposition (a) Correction for hypercalcemia Calcium Homeostasis Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Calcitriol, calcitonin, and PTH maintain normal blood calcium concentration Calcium Homeostasis Hypocalcemia has a wide variety of causes – – – – – Vitamin D deficiency Diarrhea Underactive parathyroids Pregnancy and lactation Accidental removal of parathyroid glands during thyroid surgery Hypercalcemia-rare – Vit. D toxicosis Phosphate Homeostasis Average adult has 500 to 800 g phosphorus 85% to 90% of phosphate is in the bones Normal plasma concentration is 3.5 to 4.0 mg/dL Occurs in two principal forms – HPO42− and H2PO4− (monohydrogen and dihydrogen phosphate ions) Phosphate Homeostasis Phosphate levels are not regulated as tightly as calcium levels – No functional disorders Calcitriol promotes its absorption by small intestine PTH lowers blood phosphate level by promoting its urinary excretion Other Factors Affecting Bone Bone growth rapid in puberty and adolescence – Surges of growth hormone, estrogen, and testosterone occur and promote ossification – These hormones stimulate multiplication of osteogenic cells, matrix deposition by osteoblasts, and chondrocyte multiplication and hypertrophy in metaphyses – Girls grow faster than boys and reach full height earlier Estrogen stronger effect than testosterone on bone growth – Males grow for a longer time and taller Bone Disorders Orthopedics—originated as the name implies, as the treatment of skeletal deformities in children Deals with the prevention and correction of injuries and disorders of bones, joints, and muscles Includes the design of artificial joints and limbs and the treatment of athletic injuries Disorders cont. – Dwarfism Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Achondroplastic dwarfism – Long bones stop growing in childhood Normal torso, short limbs – Failure of cartilage growth in metaphysis – Spontaneous mutation produces mutant dominant allele Pituitary dwarfism – Lack of growth hormone – Normal proportions with short stature © The McGraw-Hill Companies, Inc./Joe DeGrandis, photographer Disorders Rickets—soft bones due to deficiency of calcium salts Osteogenesis imperfecta – excessively brittle bones due to lack of protein, collagen Disorders cont. – Fractures and Repair Stress fracture—break caused by abnormal trauma to a bone – Falls, athletics, and military combat Pathological fracture—break in a bone weakened by some other disease – Bone cancer or osteoporosis – Would not break a healthy bone Fractures classified by structural characteristics – Direction of fracture line – Break in the skin – Multiple pieces Types of Bone Fractures a: Custom Medical Stock Photo, Inc.; c: © Lester V. Bergman/Corbis; d: Custom Medical Stock Photo, Inc. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Healing of Fractures The Treatment of Fractures Closed reduction—procedure in which the bone fragments are manipulated into their normal positions without surgery Open reduction—involves surgical exposure of the bone and the use of plates, screws, or pins to realign the fragments Cast—normally used to stabilize and immobilize healing bone Salter-Harris Fractures http://orthoinfo.aaos.org/figures/A00040F02.jpg Disorders cont. Osteoporosis—the most common bone disease – Severe loss of bone density – Bone break down greater than absorption by age 40 – Estrogen increases osteoblast activity – Risk factors: women, Caucasian or Asian, thin, family history, early menopause, smoking, diet low in calcium, excessive caffeine or alcohol consumption, sedentary lifestyle – Can lead to fractures and other complications Spinal Osteoporosis Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. (a) (b) a: © Michael Klein/Peter Arnold, Inc.; b: © Dr. P. Marzzi/Photo Researchers, Inc. Osteoporosis Cont. Treatments – Estrogen replacement therapy (ERT) slows bone resorption, but increases risk of breast cancer, stroke, and heart disease – Drugs: Fosamax, Actonel destroy osteoclasts – PTH slows bone loss if given as daily injection Forteo (PTH derivative) increases density by 10% in 1 year – May promote bone cancer so use is limited to 2 years – Best treatment is prevention: exercise and a good bone-building diet between ages 25 and 40