copyright © 2003 pearson education, inc. publishing as benjamin cummings developmental aspects of...
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Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Developmental Aspects of Tissue
• Primary germ layers: ectoderm, mesoderm, and endoderm
• Three layers of cells formed early in embryonic development
• Specialize to form the four primary tissues
• Nerve tissue arises from ectoderm
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Developmental Aspects of Tissue
• Muscle, connective tissue, endothelium, and mesothelium arise from mesoderm
• Most mucosae arise from endoderm
• Epithelial tissues arise from all three germ layers
Figure 4.13
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Skeletal Cartilage
• Contains no blood vessels or nerves
• Surrounded by the perichondrium (dense irregular CT) that resists outward expansion
• Three types – hyaline, elastic, and fibrocartilage
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BONES and SKELETAL TISSUE
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Bones and Cartilages of the Human Body
Figure 6.1
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Function of Bones
• Support – form the framework that supports the body and cradles soft organs
• Protection – provide a protective case for the brain, spinal cord, and vital organs
• Movement – provide levers for muscles
• Mineral storage – reservoir for minerals, especially calcium and phosphorus
• Blood cell formation – hematopoiesis occurs within the marrow cavities of bones
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Reminder -Structure of Long Bone
Figure 6.3a, c
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Reminder-Structure of Short, Irregular, and Flat Bones
Figure 6.4
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Location of Hematopoietic Tissue (Red Marrow)
• In infants
• Found in the medullary cavity and all areas of spongy bone
• In adults
• Found in the spongy bone of flat bones, and the head of the femur and humerus
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Chemical Composition of Bone: Organic
• Osteoblasts – bone-forming cells
• Osteocytes – mature bone cells
• Osteoclasts – large cells that resorb or break down bone matrix
• Osteoid – unmineralized bone matrix composed of proteoglycans, glycoproteins, and collagen
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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
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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
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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
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Postnatal Bone Growth
• Growth in length of long bones
• Cartilage on the side of 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
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Long Bone Growth and Remodeling
• Growth in length – cartilage continually grows and is replaced by bone as shown
• Remodeling – bone is resorbed and added by appositional growth as shown
Figure 6.10
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• During infancy and childhood, epiphyseal plate activity is stimulated by growth hormone
• During puberty, by testosterone and estrogens
• Initially promote adolescent growth spurts
• Cause masculinization and feminization of specific parts of the skeleton
• Later induce epiphyseal plate closure, ending longitudinal bone growth
Hormonal Regulation of Bone Growth During Youth
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Bone Remodeling
• Remodeling units – adjacent osteoblasts (deposit) and osteoclasts (resorb) bone at periosteal and endosteal surfaces
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Bone Deposition
• Occurs where bone is injured or added strength is needed
• Requires a diet rich in protein, vitamins C, D, and A, calcium, phosphorus, magnesium, and manganese
• Alkaline phosphatase is essential for mineralization of bone
• Sites of new matrix deposition are revealed by:
• Osteoid seam – unmineralized band of bone matrix
• Calcification front – abrupt transition zone between the osteoid seam and the older mineralized bone
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Bone Resorption
• Accomplished by osteoclasts
• Resorption bays – grooves formed by osteoclasts as they break down bone matrix
• Resorption involves osteoclast secretion of:
• Lysosomal enzymes that digest organic matrix
• Acids that convert calcium salts into soluble forms
• Dissolved matrix is transcytosed across the osteoclast’s cell where it is secreted into the interstitial fluid and then into the blood
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Importance of Ionic Calcium in the Body
• Calcium is necessary for:
• Transmission of nerve impulses
• Muscle contraction
• Blood coagulation
• Secretion by glands and nerve cells
• Cell division
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Control of Remodeling
• Two control loops regulate bone remodeling
• Hormonal mechanism that maintains calcium homeostasis in the blood
• Mechanical and gravitational forces acting to the skeleton
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Hormonal Mechanism
• Rising blood Ca2+ levels trigger the thyroid to release calcitonin
• Calcitonin stimulates calcium salt deposit in bone
Figure 6.11
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Hormonal Mechanism
• Falling blood Ca2+ levels signal the parathyroid glands to release PTH
• PTH signals osteoclasts to degrade bone matrix and release Ca2+ into the blood
Figure 6.11
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Response to Mechanical Stress
• Wolff’s law – a bone grows or remodels in response to the forces or demands placed upon it
Figure 6.12
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Response to Mechanical Stress
• Observations supporting 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
Figure 6.12
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Response to Mechanical Stress
• Large, bony projections occur where heavy, active muscles attach
Figure 6.12
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Bone Fractures (Breaks)
• Bone fractures are classified by:
• The position of the bone ends after fracture
• Completeness of the break
• The orientation of the bone to the long axis
• Whether or not the bones ends penetrate the skin
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Types of Bone Fractures
•Learn table with fracture types 6.2?
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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
• Site becomes swollen, painful, and inflamed
Figure 6.13.1
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Stages in the Healing of a Bone Fracture
• 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
Figure 6.13.2
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Stages in the Healing of a Bone Fracture
• Bony callus formation
• New bone trabeculae appear in the fibrocartilaginous callus
• Fibrocartilaginous 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
Figure 6.13.3
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Stages in the Healing of a Bone Fracture
• Bone remodeling
• Excess material on the bone shaft exterior and in the medullary canal is removed
• Compact bone is laid down to reconstruct shaft walls
Figure 6.13.4
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Homeostatic Imbalances
• Osteomalacia
• Bones are inadequately mineralized causing softened, weakened bones
• Main symptom is pain when weight is put on the affected bone
• Caused by insufficient calcium in the diet, or by vitamin D deficiency
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Homeostatic Imbalances
• Rickets
• Bones of children are inadequately mineralized causing softened, weakened 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
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Homeostatic Imbalances
• Osteoporosis
• Group of diseases in which bone reabsorption outpaces bone deposit
• Spongy bone of the spine is most vulnerable
• Occurs most often in postmenopausal women
• Treatment
• Calcium and vitamin D supplements
• Increased weight bearing exercise
• Hormone (estrogen) replacement therapy (HRT)
• Prevented or delayed by sufficient calcium intake and weight-bearing exercise
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Paget’s Disease
• Characterized by excessive bone formation and breakdown
• Pagetic bone with an excessively high ratio of woven 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
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Developmental Aspects of Bones
• Mesoderm gives rise to embryonic mesenchymal cells, which produce membranes and cartilages that form the embryonic skeleton
• The embryonic skeleton ossifies in a predictable timetable that allows fetal age to be easily determined from sonograms
• At birth, most long bones are well ossified (except for their epiphyses)
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Developmental Aspects of Bones
• By age 25, nearly all bones are completely ossified
• In old age, bone resorption 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
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Joints (Articulations)
• Weakest parts of the skeleton
• Articulation – site where two or more bones meet
• Functions
• Give the skeleton mobility
• Hold the skeleton together
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Classification of Joints: Structural
• Structural classification focuses on the material binding bones together and whether or not a joint cavity is present
• The three structural classifications are:
• Fibrous
• Cartilaginous
• Synovial
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Classification of Joints: Functional
• Functional classification is based on the amount of movement allowed by the joint
• The three functional class of joints are:
• Synarthroses – immovable
• Amphiarthroses – slightly movable
• Diarthroses – freely movable
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Figure 8.11c
Example - Synovial Joints: Major Ligaments and Tendons (Anterior View)
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Inflammatory and Degenerative Conditions
• Bursitis
• An inflammation of a bursa, usually caused by a blow or friction
• Symptoms are pain and swelling
• Treated with anti-inflammatory drugs; excessive fluid may be aspirated
• Tendonitis
• Inflammation of tendon sheaths typically caused by overuse
• Symptoms and treatment are similar to bursitis
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Arthritis
• More than 100 different types of inflammatory or degenerative diseases that damage the joints
• Most widespread crippling disease in the U.S.
• Symptoms – pain, stiffness, and swelling of a joint
• Acute forms are caused by bacteria and are treated with antibiotics
• Chronic forms include osteoarthritis, rheumatoid arthritis, and gouty arthritis
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Osteoarthritis (OA)
• Most common chronic arthritis; often called “wear-and-tear” arthritis
• Affects women more than men
• 85% of all Americans develop OA
• More prevalent in the aged, and is probably related to the normal aging process
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Osteoarthritis: Treatments
• OA is slow and irreversible
• Treatments include:
• Mild pain relievers, along with moderate activity
• Magnetic therapy
• Glucosamine sulfate decreases pain and inflammation
• SAM-e (s-adenosylmethionine) builds up cartilage matrix and regenerates tissue
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Rheumatoid Arthritis (RA)
• Chronic, inflammatory, autoimmune disease of unknown cause, with an insidious onset
• Usually arises between the ages of 40 to 50, but may occur at any age
• Signs and symptoms include joint tenderness, anemia, osteoporosis, muscle atrophy, and cardiovascular problems
• The course of RA is marked with exacerbations and remissions
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Rheumatoid Arthritis: Course
• RA begins with synovitis of the affected joint
• Inflammatory blood cells migrate to the joint, causing swelling
• Inflamed synovial membrane thickens into a pannus
• Pannus erodes cartilage, scar tissue forms, articulating bone ends connect
• The end result, ankylosis, produces bent, deformed fingers
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Rheumatoid Arthritis: Treatment
• Conservative therapy – aspirin, long-term use of antibiotics, and physical therapy
• Progressive treatment – anti-inflammatory drugs or immunosuppressants
• The drug Embrel, a biological response modifier, removes cells that promote inflammation
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Gouty Arthritis
• Deposition of uric acid crystals in joints and soft tissues, followed by an inflammation response
• Typically, gouty arthritis affects the joint at the base of the great toe
• In untreated gouty arthritis, the bone ends fuse and immobilize the joint
• Treatment – colchicine, nonsteroidal anti-inflammatory drugs, and glucocorticoids
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Developmental Aspects of Joints
• By embryonic week 8, synovial joints resemble adult joints
• Few problems occur until late middle age
• Advancing years take their toll on joints including:
• Ligaments and tendons shorten and weaken
• Intervertebral discs become more likely to herniate
• OA is inevitable, and all people of 70 have some degree of OA
• Prudent exercise (especially swimming) that coaxes joints through their full range of motion is key to postponing joint problems
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Sprains
• The ligaments (bone to bone) reinforcing a joint are stretched or torn
• Partially torn ligaments slowly repair themselves
• Completely torn ligaments require prompt surgical repair
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Cartilage Injuries
• The snap and pop of overstressed cartilage
• Common aerobics injury
• Repaired with arthroscopic surgery
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Dislocations
• Occur when bones are forced out of alignment
• Usually accompanied by sprains, inflammation, and joint immobilization
• Caused by serious falls and are common sports injuries
• Subluxation – partial dislocation of a joint