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Chapter 5 The Skeletal System
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Skeletal System: Made of Connective Tissue
The skeletal system is made up of three types of connective tissue Bone Ligaments Cartilage
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Bones – Functions Bones: hard elements of the skeleton
Five important functions Support Protection Movement Blood cell formation Mineral storage Calcium Phosphate
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Bone – Structure Bone: hard inorganic matrix of calcium salts & collagen fibers) Compact bone: forms shaft and ends Spongy bone: red marrow is found here Cells: osteoblast (makes new bone matrix), osteocytes (maintains the bone matrix), osteoclasts (breaks down bone matrix) Bone shapes: long, short, flat, irregular Periosteum: connective tissue covering the outside of the bone
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Figure 5.1 Central canal Osteon Osteocytes c) 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 d) 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 Periosteum Central cavity (contains yellow bone marrow) Spongy bone Compact bone Epiphysis Osteoblasts Blood vessels and nerve in central canal a) A partial cut through a long bone. b) A closer view of a section of bone. Compact bone is a nearly solid structure with central canals for the blood vessels and nerves. Figure 5.1
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Spongy bone (spaces contain red bone marrow) Epiphysis Compact bone Yellow bone marrow Blood vessel Diaphysis Periosteum Central cavity (contains yellow bone marrow) Epiphysis a) A partial cut through a long bone. Figure 5.1a
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Osteon Spongy bone Compact bone Osteoblasts Blood vessels and nerve in central canal b) A closer view of a section of bone. Compact bone is a nearly solid structure with central canals for the blood vessels and nerves. Figure 5.1b
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Cartilage and Ligaments
Function: support Types Fibrocartilage (menisci of knee, intervertebral discs) Hyaline (most cartilage is of this type) Elastic cartilage (ears, epiglottis) Ligaments Function: attach bone to bone Dense fibrous connective tissue
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Bone Development Early fetal development: cartilage model
Formed by chondroblasts (cartilage-forming cells) Later fetal development: osteoblasts replace cartilage with bone Childhood: primary and secondary ossification sites formed Adolescence: elongation at growth plates
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Figure 5.2 Adolescence Cartilage growth plate Childhood Fetus: At
2–3 months Fetus: First 2 months Developing periosteum Compact bone containing osteocytes Blood vessel Cartilage growth plate a) Chondroblasts form hyaline cartilage, creating a rudimentary model of future bone. b) The periosteum begins to develop and cartilage starts to dissolve. Newly developing blood vessels transport osteoblasts into the area from the periosteum. c) Osteoblasts secrete osteoid and enzymes, facilitating the deposition of hard hydroxyapatite crystals. d) The growth plates in long bones move farther apart and osteoblast activity continues just below the periosteum. The bone lengthens and widens. Figure 5.2
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Chondroblasts deposit new cartilage at the outer surface
Osteoblasts convert cartilage to bone at the inner surface Chondroblasts deposit new cartilage at the outer surface Joint cartilage Growth plate Figure 5.3
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Bone Growth
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Hormonal Control of Bone Growth
Preadolescence 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
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Cells Involved in the Development and Maintenance of Bone
Chondroblasts: cartilage-forming cells Osteoblasts: young bone-forming cells Osteocytes: mature bone cells Osteoclasts: bone-dissolving cells
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Mature Bone Remodeling and Repair
Changes in shape, size, strength Dependent on diet, exercise, age Bone cells regulated by hormones Parathyroid hormone (PTH): removes calcium from bone Calcitonin: adds calcium to bone Repair: hematoma and callus formation
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Figure 5.4 Compressive force Bone removed here New bone added here
a) 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. (b) Over time, bone is deposited on the inside curvature and removed from the outside curvature. c) The final result is a bone matched to the compressive force to which it is exposed. Figure 5.4
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Bone Repair
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Human Skeleton 206 bones Axial skeleton Appendicular skeleton
Skull, vertebral column, sternum, ribs Appendicular skeleton Pectoral girdle, pelvic girdle, limbs
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Figure 5.5 Axial skeleton Appendicular skeleton Cranium (skull)
Maxilla Mandible Clavicle Scapula Sternum Ribs Humerus Vertebrae Ulna Radius Carpals Metacarpals Sacrum Phalanges Coxal bone Femur Patella Tibia Fibula Tarsals Metatarsals Phalanges Figure 5.5
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Temporal bone Parietal bone Frontal bone Sphenoid bone Ethmoid bone Lacrimal bone Nasal bone Zygomatic bone Maxilla Occipital bone Mandible External auditory meatus Maxilla Zygomatic bone Palatine bone Sphenoid bone Vomer bone Foramen magnum Occipital bone Figure 5.6
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Figure 5.7 1 2 3 Cervical vertebrae (7) 4 5 6 7 1 2 3 4 5 6 Thoracic
(12) 7 8 9 10 11 12 1 2 Lumbar vertebrae (5) 3 4 5 Sacrum (5 fused) Coccyx (4 fused) Figure 5.7
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Axial Skeleton: Vertebral Column (cont.)
Regions: cervical, thoracic, lumbar, sacral, coccygeal Intervertebral disks: cushion vertebrae; assist in movement and flexibility Ribs Twelve pairs Bottom two pair floating Sternum: breastbone Three bones fused together
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Figure 5.8 Spinal cord Articulations with another vertebra
Intervertebral disk Spinal nerve Articulation with ribs Main bodies of vertebrae a) Healthy disks. Herniated area pressing against a nerve b) A herniated disk. Figure 5.8
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Articulation with ribs
Spinal cord Articulations with another vertebra Intervertebral disk Spinal nerve Articulation with ribs Main bodies of vertebrae a) Healthy disks. Figure 5.8a
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Herniated area pressing against a nerve b) A herniated disk.
Figure 5.8b
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C7 T1 1 2 Sternum (breastbone) 3 4 Ribs 5 6 T11 Cartilage 7 T12 8 9
Vertebral column L1 10 12 L2 11 Floating ribs Figure 5.9
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Appendicular Skeleton
Pectoral girdle: shoulder Clavicle and scapulas Pelvic girdles: hip Coxal bones, sacrum, pubic symphysis Limbs Arms: humerus, radius, ulna, wrist and hand bones Legs: femur, tibia, fibula, ankle and foot bones
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Clavicle (collar bone) Pectoral girdle Scapula (shoulder blade) Humerus (upper arm) Ulna Forearm Radius 8 Carpals (wrist) 5 Metacarpals (hand) 14 Phalanges (finger bones) Figure 5.10
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sacrum Coxal bones and sacrum (pelvis) Pubic symphysis
Femur (upper leg) Patella (knee cap) Tibia Lower leg Fibula 7 Tarsals (ankle) 5 Metatarsals (foot) 14 Phalanges (toe bones) Figure 5.11
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Joints (Articulations)
Classified by degree of movement Fibrous joint: immovable (e.g., sutures of the skull) Cartilaginous joint: slightly movable, cartilage connection (e.g., pubic symphysis) Synovial joint: freely movable
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Figure 5.12 Femur Thigh muscles Hyaline cartilage Posterior
cruciate ligament Tendon Ligament Anterior cruciate ligament Patella Meniscus Meniscus Joint capsule Fibula Ligaments Ligaments Tibia Ligament Patella Tendon a) 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. b) 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. Figure 5.12
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Femur Hyaline cartilage Posterior cruciate ligament Ligament Anterior cruciate ligament Meniscus Meniscus Fibula Tibia Ligament Patella Tendon a) 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. Figure 5.12a
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Thigh muscles Tendon Patella Joint capsule Ligaments Ligaments b) 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. Figure 5.12b
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Synovial Joints Joint capsule: synovial membrane
Synovial membrane secretes synovial fluid as a lubricant Hyaline cartilage acts as a cushion Types of synovial joints Hinge joint Ball and socket joint Tendons – join bone to muscle Ligaments-join bones to each other
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Figure 5.13 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 Abduction Adduction Abduction Imaginary cone off movement Adduction Rotation: Movement of a body part around its own axis Abduction Adduction a) Abduction and adduction. b) Rotation and circumduction. Extension Supination: Rotation of the forearm so palm faces anteriorly. Pronation: Rotation of the forearm so palm faces posteriorly Flexion Hyperextension Flexion: Decreases the angle of a joint Humerus Flexion Hyperextension: Extension beyond the anatomical position Ulna Ulna Extension Radius Radius Flexion Hyperextension Extension: Increases the angle of a joint Extension c) Flexion, extension, and hyperextension. d) Supination and pronation. Figure 5.13
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Abduction: Movement of a
limb away from a body’s midline Adduction: Movement of a limb toward the body’s midline Abduction Adduction Abduction Adduction Abduction Adduction a) Abduction and adduction. Figure 5.13a
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Circumduction: Movement of a limb so that it describes a cone Imaginary cone of movement Rotation: Movement of a body part around its own axis b) Rotation and circumduction. Figure 5.13b
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Extension Flexion Hyperextension Flexion: Decreases the angle of a joint Flexion Hyperextension: Extension beyond the anatomical position Extension Flexion Hyperextension Extension Extension: Increases the angle of a joint c) Flexion, extension, and hyperextension. Figure 5.13c
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Supination: Rotation of the forearm so palm faces anteriorly Pronation: Rotation of the forearm so palm faces posteriorly Humerus Ulna Ulna Radius Radius d) Supination and pronation. Figure 5.13d
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Diseases and Disorders of the Skeletal System
Sprains: stretched or torn ligaments Bursitis and tendinitis: inflammations Arthritis: inflammation of joints Osteoarthritis Rheumatoid arthritis Osteoporosis: excessive bone loss
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