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Overview of Skeletal Tissue
The skeletal system consists of connective tissue: bone, cartilage and connective tissue proper (ligaments) Bone development begins in the embryo in a hyaline cartilage model Mature bone undergoes remodeling and repair Skeleton protects, supports, and permits movement Joints form connections between bones Ligaments hold bones together at joints, stabilizing them diseases and disorders of the skeletal system
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Connective Tissue Three types of connective tissue: 1. Bone
Hard elements of the skeleton 2. Ligaments: Dense fibrous connective tissue Attach bones to other bones 3. Cartilage: Specialized connective tissue, elastic and collagen fibers in a gel-like ground substance
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Which Problems does the Skeletal System Solve?
1. Support for the organs 2. Protection of organs and brain 3. Movement to hunt and gather Provide levers for muscles 4. Blood cell formation in the medullary cavity 5. Mineral storage which is useful is overall calcium homeostasis Calcium Phosphate
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Fetal Bone Early fetal development: cartilage model forms
Formed by chondroblasts (cartilage-forming cells) The skull is composed of fibrous connective tissue and undergoes intramembranous ossification. Later fetal development: osteoblasts replace cartilage with bone Childhood: primary and secondary ossification sites formed Adolescence: elongation at growth plates
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Maturing Bone Preadolescence Early Adolescence Late Adolescence
Growth hormone stimulates bone lengthening Early Adolescence Estrogen and testosterone stimulate bone lengthening Late Adolescence Estrogen and testosterone cause replacement of cartilage growth plates with bone • Intramembranous ossification – bone develops from a fibrous membrane in the skull • Endochondral ossification – bone forms by replacing hyaline cartilage in long and irregular bones at the epiphyseal plates
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ENDOCHONDRAL OSSIFICATION
Figure 5.2 ENDOCHONDRAL OSSIFICATION Adolescence Cartilage growth plate Childhood Fetus: At 2–3 months Fetus: First 2 months Developing periosteum Compact bone containing osteocytes Blood vessel Chondroblasts form hyaline cartilage, creating a rudimentary model of future bone. The periosteum begins to develop and cartilage starts to dissolve. Newly developing blood vessels transport osteoblasts into the area from the periosteum. Osteoblasts secrete osteoid and enzymes, facilitating the deposition of hard hydroxyapatite crystals. Figure 5.2 How bone develops. Cartilage growth plate The growth plates in long bones move farther apart and osteoblast activity continues just below the periosteum. The bone lengthens and widens. 6
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Endochondral Ossification
Figure 5.3 Endochondral Ossification Osteoblasts convert cartilage to bone at the inner surface Chondroblasts deposit new cartilage at the outer surface Joint cartilage Figure 5.3 How long bones increase in length. Growth plate Epiphyseal plate 7
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Intramembranous Ossification
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Compact and Spongy Bone
Figure 5.1 Central canal Compact and Spongy Bone Osteon Osteocytes A photograph of an osteon of compact bone showing osteocytes embeded within the solid structure. Osteocyte Lacuna Osteon Spongy bone (spaces contain red bone marrow) Epiphysis Canalicula A single osteocyte in a lacuna. Osteocytes remain in contact with each other by cytoplasmic extensions into the canaliculi between cells. Compact bone Yellow bone marrow Blood vessel Diaphysis Figure 5.1 Structure of bone. Periosteum Volkman’s Canals Central cavity (contains yellow bone marrow) Spongy bone Compact bone Haversian Canals Epiphysis Blood vessels and nerve in central canal Osteoblasts A closer view of a section of bone. Compact bone is a nearly solid structure with central canals for the blood vessels and nerves. A partial cut through a long bone. 9
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Chemical Composition and cells 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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Homeostasis Parathyroid hormone (PTH): Calcitonin:
PTH secretion increases when blood levels of Ca fall Stimulates osteoclasts to secrete more bone-dissolving enzymes Calcitonin: Calcitonin secretion increases when blood levels of Ca are high Stimulates osteoblasts to add calcium and phosphate to bone
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Remodeling Remodeling: changes in shape, size, strength
Dependent on diet, exercise, age Weight-bearing exercise increases overall bone mass and strength Bone homeostasis depends upon balance of osteoblast and osteoclast activity Bone Remodeling Remodeling units – adjacent osteoblasts and osteoclasts deposit and resorb bone at periosteal and endosteal surfaces Osteoporosis: loss of bone mass due to prolonged imbalance of osteoblast and osteoclast activity
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The application of force to a slightly bent bone produces
Figure 5.4 Compressive force Bone removed here New bone added here Figure 5.4 Bone remodeling. The application of force to a slightly bent bone produces a greater compressive force on the inside curvature. Compressive force produces weak electrical currents, which stimulate osteoblasts. Over time, bone is deposited on the inside curvature and removed from the outside curvature. The final result is a bone matched to the compressive force to which it is exposed. 14
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Structure of Long Bones
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Cartilages Function: support under pressure Types Fibrocartilage
Intervertebral disks between vertebrae Menisci in knee joints Hyaline Forms embryonic structure which later form bone Covers and protects ends of long bones in joints, providing protection, reducing friction Elastic cartilage Flexible, outer ear, epiglottis
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Ligaments Function: attach bone to bone
Made of dense fibrous connective tissue Provide strength in joints yet enable movement
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Bone Shapes 206 bones Four types of bones
Long (bones of limbs and fingers) Short (wrist bones) Flat (cranial bones, sternum, ribs) Irregular (coxal bone, verterbrae)
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Shapes of Bones
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Appendicular skeleton
Figure 5.5 Axial skeleton Appendicular skeleton Cranium (skull) Maxilla Mandible Clavicle Scapula Sternum Ribs Humerus Vertebrae Ulna Radius Carpals Metacarpals Sacrum Phalanges Figure 5.5 The human skeleton. Coxal bone Femur Patella Tibia Fibula Tarsals Metatarsals Phalanges 21
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2- inferior nasal conchae 2- zygomatic 2- lacrimal 1-vomer 1- mandible
Figure 5.6 Temporal bone Parietal bone Frontal bone Facial bones-14 bones 2-maxilla 2-palatine 2-nasal 2- inferior nasal conchae 2- zygomatic 2- lacrimal 1-vomer 1- mandible Sphenoid bone Ethmoid bone Lacrimal bone Nasal bone Zygomatic bone Maxilla Occipital bone Mandible External auditory meatus Cranium- 8 bones 1-frontal 2-temporal 1-occipital 2-paroetal 1-sphenoid 1-ethmoid Maxilla Zygomatic bone Figure 5.6 The human skull. Palatine bone Sphenoid bone Vomer bone Foramen magnum Occipital bone 22
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Figure 5.7 Larynx Figure 5.7 The hyoid bone. Hyoid bone 23
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Cervical vertebrae (7) Thoracic vertebrae (12) Lumbar vertebrae (5)
Figure 5.8 1 2 3 Cervical vertebrae (7) 4 5 6 7 1 2 3 4 5 6 Thoracic vertebrae (12) 7 8 9 10 11 12 1 2 Figure 5.8 The vertebral column. Lumbar vertebrae (5) 3 4 5 Sacrum (5 fused) Coccyx (4 fused) 24
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Healthy disks. A herniated disk. Spinal cord Articulations
Figure 5.9 Spinal cord Articulations with another vertebra Intervertebral disk Spinal nerve Articulation with ribs Main bodies of vertebrae Healthy disks. Herniated area pressing against a nerve Figure 5.9 Vertebrae. A herniated disk. 25
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C7 T1 Sternum (breastbone) Ribs T11 Cartilage T12 Vertebral column L1
Figure 5.10 C7 T1 1 2 Sternum (breastbone) 3 4 Figure 5.10 Ribs. Ribs 5 6 T11 Cartilage 7 T12 8 9 Vertebral column L1 12 10 L2 11 Floating ribs 26
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14 Phalanges (finger bones)
Figure 5.11 Clavicle (collar bone) Pectoral girdle Scapula (shoulder blade) Humerus (upper arm) Ulna Forearm Figure 5.11 Bones of the right side of the pectoral girdle and the right arm and hand. Radius 8 Carpals (wrist) 5 Metacarpals (hand) 14 Phalanges (finger bones) 27
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Coxal bones and sacrum (pelvis) Pubic symphysis Femur (upper leg)
Figure 5.12 Coxal bones and sacrum (pelvis) Pubic symphysis Femur (upper leg) Patella (knee cap) Tibia Figure 5.12 Bones of the pelvic girdle and the left leg and foot. Lower leg Fibula 7 Tarsals (ankle) 5 Metatarsals (foot) 14 Phalanges (toe bones) 28
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Figure 5.13 Figure 5.13 The pelvis. Male Female 29
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A cutaway anterior view of the right
Figure 5.14 Femur Thigh muscles Hyaline cartilage Tendon Posterior cruciate ligament Ligament Anterior cruciate ligament Patella Meniscus Joint capsule Meniscus Fibula Ligaments Tibia Ligament Ligaments Figure 5.14 The knee joint is a hinged synovial joint. Patella Tendon A cutaway anterior view of the right knee with muscles, tendons, and the joint capsule removed and the bones pulled slightly apart so that the two menisci are visible. A view of the knee with muscles, tendons, and ligaments in their normal position surrounding the intact joint capsule. The combination of ligaments, tendons, and muscles holds the knee tightly together. 30
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Figure 5.15 Types of movements made possible by synovial joints.
Abduction: Movement of a limb away from a body’s midline Adduction: Movement of a limb toward the body’s midline Circumduction: Movement of a limb so that it describes a cone Supination: Rotation of the forearm so palm faces anteriorly Pronation: Rotation of the forearm so palm faces posteriorly Extension Flexion Abduction Flexion Ulna Flexion: Decreases the angle of a joint Adduction Radius Extension Abduction Imaginary cone of movement Rotation: Movement of a body part around its own axis Flexion Adduction Extension: Increases the angle of a joint Abduction Figure 5.15 Types of movements made possible by synovial joints. Adduction Extension Abduction and adduction. Rotation and circumduction. Flexion and extension Supination and pronation. 31
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