The Skeletal System. Yong Jeong, MD, PhD Department of Bio and Brain Engineering

Transcription

1 5 The Skeletal System Yong Jeong, MD, PhD Department of Bio and Brain Engineering The Skeletal System Parts of the skeletal system Bones (skeleton) Joints Cartilages Ligaments Two subdivisions of the skeleton Axial skeleton Appendicular skeleton 1

2 Functions of Bones Support the body Protect soft organs Skull and vertebrae for brain and spinal cord Rib cage for thoracic cavity organs Allow movement due to attached skeletal muscles Store minerals and fats Calcium and phosphorus Fat in the internal marrow cavity Blood cell formation (hematopoiesis) Bones of the Human Body The adult skeleton has 206 bones Two basic types of bone tissue Compact bone Homogeneous Spongy bone Small needle-like pieces of bone Many open spaces 2

3 Spongy bone Compact bone Figure 5.1 Classification of Bones on the Basis of Shape Bones are classified as: Long Short Flat Irregular 3

4 Classification of Bones Long bones Typically longer than they are wide Shaft with heads situated at both ends Contain mostly compact bone All of the bones of the limbs (except wrist, ankle, and kneecap bones) Example: Femur Humerus Figure 5.2a 4

5 Classification of Bones Short bones Generally cube-shaped Contain mostly spongy bone Includes bones of the wrist and ankle Sesamoid bones are a type of short bone which form within tendons (patella) Example: Carpals Tarsals Figure 5.2d 5

6 Classification of Bones Flat bones Thin, flattened, and usually curved Two thin layers of compact bone surround a layer of spongy bone Example: Skull Ribs Sternum 6

7 Classification of Bones Irregular bones Irregular shape Do not fit into other bone classification categories Example: Vertebrae Hip bones Figure 5.2b 7

8 Anatomy of a Long Bone Diaphysis Shaft Composed of compact bone Epiphysis Ends of the bone Composed mostly of spongy bone Articular cartilage Proximal epiphysis Diaphysis Spongy bone Epiphyseal line Periosteum Compact bone Medullary cavity (lined by endosteum) Distal epiphysis (a) Figure 5.3a 8

9 Anatomy of a Long Bone Periosteum Outside covering of the diaphysis Fibrous connective tissue membrane Perforating (Sharpey s) fibers Secure periosteum to underlying bone Arteries Supply bone cells with nutrients Endosteum Yellow bone marrow Compact bone Periosteum Perforating (Sharpey s) fibers Nutrient arteries (c) Figure 5.3c 9

10 Anatomy of a Long Bone Articular cartilage Covers the external surface of the epiphyses Made of hyaline cartilage Decreases friction at joint surfaces Articular cartilage Compact bone Spongy bone (b) Figure 5.3b 10

11 Anatomy of a Long Bone Epiphyseal plate Flat plate of hyaline cartilage seen in young, growing bone Epiphyseal line Remnant of the epiphyseal plate Seen in adult bones Articular cartilage Proximal epiphysis Diaphysis Spongy bone Epiphyseal line Periosteum Compact bone Medullary cavity (lined by endosteum) Distal epiphysis (a) Figure 5.3a 11

12 Anatomy of a Long Bone Marrow (medullary) cavity Cavity inside of the shaft Contains yellow marrow (mostly fat) in adults Contains red marrow for blood cell formation in infants In adults, red marrow is situated in cavities of spongy bone and epiphyses of some long bones Bone Markings Surface features of bones Sites of attachments for muscles, tendons, and ligaments Passages for nerves and blood vessels Categories of bone markings Projections or processes grow out from the bone surface Terms often begin with T Depressions or cavities indentations Terms often begin with F 12

13 Microscopic Anatomy of Compact Bone Osteon (Haversian system) A unit of bone containing central canal and matrix rings Central (Haversian) canal Opening in the center of an osteon Carries blood vessels and nerves Perforating (Volkmann s) canal Canal perpendicular to the central canal Carries blood vessels and nerves Osteon (Haversian system) Lamellae Perforating fibers Compact bone Periosteal blood vessel Periosteum (a) Central (Haversian) canal Perforating (Volkmann s) canal Blood vessel Blood vessel continues into medullary cavity containing marrow Spongy bone Figure 5.4a 13

14 Microscopic Anatomy of Bone Lacunae Cavities containing bone cells (osteocytes) Arranged in concentric rings called lamellae Lamellae Rings around the central canal Sites of lacunae Osteon Lamella Osteocyte Lacuna (b) Canaliculus Lacuna Central (Haversian) canal (c) Central canal Interstitial lamellae Figure 5.4b 14

15 Microscopic Anatomy of Bone Canaliculi Tiny canals Radiate from the central canal to lacunae Form a transport system connecting all bone cells to a nutrient supply Lamella Osteocyte (b) Canaliculus Lacuna Central (Haversian) canal Figure 5.4b 15

16 Formation of the Human Skeleton In embryos, the skeleton is primarily hyaline cartilage During development, much of this cartilage is replaced by bone Cartilage remains in isolated areas Bridge of the nose Parts of ribs Joints Bone Growth (Ossification) Epiphyseal plates allow for lengthwise growth of long bones during childhood New cartilage is continuously formed Older cartilage becomes ossified Cartilage is broken down Enclosed cartilage is digested away, opening up a medullary cavity Bone replaces cartilage through the action of osteoblasts 16

17 Bone Growth (Ossification) Bones are remodeled and lengthened until growth stops Bones are remodeled in response to two factors Blood calcium levels Pull of gravity and muscles on the skeleton Bones grow in width (called appositional growth) In an embryo New center of bone growth Medullary cavity Bone starting to replace cartilage Bone collar Hyaline cartilage model Hyaline cartilage In a fetus Growth in bone length Articular cartilage Spongy bone Epiphyseal plate cartilage Invading blood vessels New bone forming Epiphyseal plate cartilage In a child New bone forming Growth in bone width Figure

18 Bone growth Bone grows in length because: 1 Cartilage grows here. 2 Cartilage is replaced by bone here. 3 Cartilage grows here. 4 Cartilage is replaced by bone here. Bone remodeling Growing shaft is remodeled as: Articular cartilage Epiphyseal plate 1 Bone is resorbed here. 2 Bone is added by appositional growth here. 3 Bone is resorbed here. Figure 5.6 Types of Bone Cells Osteocytes mature bone cells Osteoblasts bone-forming cells Osteoclasts giant bone-destroying cells Break down bone matrix for remodeling and release of calcium in response to parathyroid hormone Bone remodeling is performed by both osteoblasts and osteoclasts 18

19 Bone Fractures Fracture break in a bone Types of bone fractures Closed (simple) fracture break that does not penetrate the skin Open (compound) fracture broken bone penetrates through the skin Bone fractures are treated by reduction and immobilization Common Types of Fractures Table

20 Repair of Bone Fractures Hematoma (blood-filled swelling) is formed Break is splinted by fibrocartilage to form a callus Fibrocartilage callus is replaced by a bony callus Bony callus is remodeled to form a permanent patch Hematoma Internal callus (fibrous tissue and cartilage) External callus New blood vessels Spongy bone trabecula Bony callus of spongy bone Healed fracture 1 Hematoma 2 Fibrocartilage 3 Bony callus 4 Bone remodeling forms. callus forms. forms. occurs. Figure 5.7, step 4 20

21 The Axial Skeleton Forms the longitudinal axis of the body Divided into three parts Skull Vertebral column Bony thorax Skull Facial bones Cranium Clavicle Thoracic cage (ribs and sternum) Vertebral column Sacrum Scapula Sternum Rib Humerus Vertebra Radius Ulna Carpals Phalanges Metacarpals Femur Patella Tibia Fibula Tarsals Metatarsals Phalanges (a) Anterior view Figure 5.8a 21

22 Cranium Clavicle Scapula Rib Humerus Vertebra Radius Ulna Carpals Bones of pelvic girdle Bones of pectoral girdle Upper limb Phalanges Metacarpals Femur Tibia Lower limb Fibula (b) Posterior view Figure 5.8b The Skull Two sets of bones Cranium Facial bones Bones are joined by sutures Only the mandible is attached by a freely movable joint 22

23 Coronal suture Parietal bone Temporal bone Lambdoid suture Squamous suture Occipital bone Zygomatic process External acoustic meatus Mastoid process Styloid process Mandibular ramus Frontal bone Sphenoid bone Ethmoid bone Lacrimal bone Nasal bone Zygomatic bone Maxilla Alveolar processes Mandible (body) Mental foramen Figure 5.9 Frontal bone Sphenoid bone Cribriform plate Crista galli Optic canal Ethmoid bone Temporal bone Sella turcica Foramen ovale Jugular foramen Internal acoustic meatus Parietal bone Occipital bone Foramen magnum Figure

24 Hard palate Maxilla (palatine process) Palatine bone Maxilla Zygomatic bone Temporal bone (zygomatic process) Vomer Mandibular fossa Styloid process Mastoid process Sphenoid bone (greater wing) Foramen ovale Carotid canal Jugular foramen Temporal bone Occipital condyle Parietal bone Occipital bone Foramen magnum Figure 5.11 Coronal suture Parietal bone Frontal bone Nasal bone Superior orbital fissure Sphenoid bone Ethmoid bone Lacrimal bone Zygomatic bone Maxilla Mandible Optic canal Temporal bone Middle nasal concha of ethmoid bone Inferior nasal concha Vomer Alveolar processes Figure

25 Paranasal Sinuses Hollow portions of bones surrounding the nasal cavity Functions of paranasal sinuses Lighten the skull Give resonance and amplification to voice Frontal sinus Ethmoid sinus Sphenoidal sinus Maxillary sinus (a) Anterior view Figure 5.13a 25

26 Frontal sinus Ethmoid sinus Sphenoidal sinus Maxillary sinus (b) Medial view Figure 5.13b The Hyoid Bone The only bone that does not articulate with another bone Serves as a moveable base for the tongue Aids in swallowing and speech 26

27 Greater horn Lesser horn Body Figure 5.14 The Fetal Skull The fetal skull is large compared to the infant s total body length Fetal skull is 1/4 body length compared to adult skull which is 1/8 body length Fontanels fibrous membranes connecting the cranial bones Allow skull compression during birth Allow the brain to grow during later pregnancy and infancy Convert to bone within 24 months after birth 27

28 Frontal bone Anterior fontanel Parietal bone Posterior fontanel (a) Occipital bone Figure 5.15a Parietal bone Posterior fontanel Anterior fontanel Sphenoidal fontanel Frontal bone Occipital bone Mastoid fontanel (b) Temporal bone Figure 5.15b 28

29 The Vertebral Column Each vertebrae is given a name according to its location There are 24 single vertebral bones separated by intervertebral discs Seven cervical vertebrae are in the neck Twelve thoracic vertebrae are in the chest region Five lumbar vertebrae are associated with the lower back The Vertebral Column Nine vertebrae fuse to form two composite bones Sacrum Coccyx 29

30 Anterior 1st cervical vertebra (atlas) 2nd cervical vertebra (axis) 1st thoracic vertebra Transverse process Spinous process Intervertebral disc Intervertebral foramen 1st lumbar vertebra Posterior Cervical curvature (concave) 7 vertebrae, C 1 C 7 Thoracic curvature (convex) 12 vertebrae, T 1 T 12 Lumbar curvature (concave) 5 vertebrae, L 1 L 5 Sacral curvature (convex) 5 fused vertebrae Coccyx 4 fused vertebrae Figure 5.16 The Vertebral Column Primary curvatures are the spinal curvatures of the thoracic and sacral regions Present from birth Form a C-shaped curvature as in newborns Secondary curvatures are the spinal curvatures of the cervical and lumbar regions Develop after birth Form an S-shaped curvature as in adults 30

31 Figure 5.18 A Typical Vertebrae Body Vertebral arch Pedicle Lamina Vertebral foramen Transverse processes Spinous process Superior and inferior articular processes 31

32 Transverse process Lamina Posterior Spinous process Vertebral arch Superior articular process and facet Pedicle Vertebral foramen Body Anterior Figure 5.19 (a) ATLAS AND AXIS Transverse process Posterior arch Anterior arch Superior view of atlas (C 1 ) Transverse process Dens Body Superior view of axis (C 2 ) Spinous process Facet on superior articular process Figure 5.20a 32

33 (b) TYPICAL CERVICAL VERTEBRAE Facet on superior articular process Superior articular process Spinous process Superior view Body Spinous process Vertebral foramen Transverse process Transverse process Facet on inferior articular process Right lateral view Figure 5.20b (c) THORACIC VERTEBRAE Transverse process Spinous process Vertebral foramen Facet for rib Facet on superior articular process Facet on transverse process Superior view Spinous process Body Facet on superior articular process Body Costal facet for rib Right lateral view Figure 5.20c 33

34 (d) LUMBAR VERTEBRAE Spinous process Transverse process Body Superior articular process Superior view Vertebral foramen Facet on superior articular process Body Spinous Facet on inferior process articular process Right lateral view Figure 5.20d Sacrum and Coccyx Sacrum Formed by the fusion of five vertebrae Coccyx Formed from the fusion of three to five vertebrae Tailbone, or remnant of a tail that other vertebrates have 34

35 Ala Sacral canal Superior articular process Auricular surface Body Sacrum Median sacral crest Coccyx Posterior sacral foramina Sacral hiatus Figure 5.21 The Bony Thorax Forms a cage to protect major organs Consists of three parts Sternum Ribs True ribs (pairs 1 7) False ribs (pairs 8 12) Floating ribs (pairs 11 12) Thoracic vertebrae 35

36 Clavicular notch T 1 vertebra Jugular notch True ribs (1 7) Manubrium Sternal angle Body Xiphisternal joint Xiphoid process Sternum False ribs (8 12) Intercostal spaces L 1 Vertebra Floating Costal cartilage ribs (11, 12) (a) Figure 5.22a T 3 T 4 T 2 Jugular notch Sternal angle Heart T 9 Xiphisternal joint (b) Figure 5.22b 36

37 The Appendicular Skeleton Composed of 126 bones Limbs (appendages) Pectoral girdle Pelvic girdle Skull Facial bones Cranium Clavicle Thoracic cage (ribs and sternum) Vertebral column Sacrum Scapula Sternum Rib Humerus Vertebra Radius Ulna Carpals Phalanges Metacarpals Femur Patella Tibia Fibula Tarsals Metatarsals Phalanges (a) Anterior view Figure 5.8a 37

38 Cranium Clavicle Scapula Rib Humerus Vertebra Radius Ulna Carpals Bones of pelvic girdle Bones of pectoral girdle Upper limb Phalanges Metacarpals Femur Tibia Lower limb Fibula (b) Posterior view Figure 5.8b The Pectoral (Shoulder) Girdle Composed of two bones Clavicle collarbone Articulates with the sternum medially and with the scapula laterally Scapula shoulder blade Articulates with the clavicle at the acromioclavicular joint Articulates with the arm bone at the glenoid cavity These bones allow the upper limb to have exceptionally free movement 38

39 Acromioclavicular joint Clavicle Scapula (a) Articulated right shoulder (pectoral) girdle showing the relationship to bones of the thorax and sternum Figure 5.23a Posterior Sternal (medial) end Acromial (lateral) end Superior view Acromial end Anterior Anterior Sternal end Posterior Inferior view (b) Right clavicle, superior and inferior views Figure 5.23b 39

40 Suprascapular notch Coracoid process Superior angle Acromion Spine Glenoid cavity at lateral angle Medial border Lateral border (c) Right scapula, posterior aspect Figure 5.23c Coracoid process Acromion Suprascapular notch Superior border Superior angle Glenoid cavity Lateral (axillary) border Medial (vertebral) border Inferior angle (d) Right scapula, anterior aspect Figure 5.23d 40

41 Bones of the Upper Limbs Humerus Forms the arm Single bone Proximal end articulation Head articulates with the glenoid cavity of the scapula Distal end articulation Trochlea and capitulum articulate with the bones of the forearm Greater tubercle Head of humerus Head of humerus Lesser tubercle Anatomical neck Intertubercular sulcus Anatomical neck Surgical neck Deltoid tuberosity Radial groove Deltoid tuberosity Radial fossa Medial epicondyle Medial epicondyle Olecranon fossa Coronoid fossa Lateral Capitulum Trochlea Trochlea epicondyle (a) (b) Figure 5.24a 41

42 Bones of the Upper Limbs The forearm has two bones Ulna medial bone in anatomical position Proximal end articulation Coronoid process and olecranon articulate with the humerus Radius lateral bone in anatomical position Proximal end articulation Head articulates with the capitulum of the humerus Head Neck Radial tuberosity Radius Trochlear notch Olecranon Coronoid process Proximal radioulnar joint Ulna Interosseous membrane Radial styloid process Ulnar styloid process Distal radioulnar joint (c) Figure 5.24c 42

43 Bones of the Upper Limbs Hand Carpals wrist Eight bones arranged in two rows of four bones in each hand Metacarpals palm Five per hand Phalanges fingers and thumb Fourteen phalanges in each hand In each finger, there are three bones In the thumb, there are only two bones Phalanges (fingers) Distal Middle Proximal Metacarpals (palm) Carpals (wrist) Hamate Pisiform Triquetrum Lunate Trapezium Trapezoid Scaphoid Capitate Ulna Radius Figure

44 Bones of the Pelvic Girdle Formed by two coxal (ossa coxae) bones Composed of three pairs of fused bones Ilium Ischium Pubis Pelvic girdle = 2 coxal bones, sacrum Bony pelvis = 2 coxal bones, sacrum, coccyx Bones of the Pelvic Girdle The total weight of the upper body rests on the pelvis It protects several organs Reproductive organs Urinary bladder Part of the large intestine 44

45 lliac crest Sacroiliac joint Coxal bone (or hip bone) llium Sacrum Pelvic brim Pubis Coccyx Ischial spine Acetabulum Ischium Pubic symphysis Pubic arch (a) Figure 5.26a Posterior superior iliac spine Posterior inferior iliac spine Greater sciatic notch Ischial body Ala IIium IIiac crest Anterior superior iliac spine Anterior inferior iliac spine Acetabulum Body of pubis Ischial spine Pubis Ischial tuberosity Inferior pubic ramus Ischium Obturator Ischial ramus foramen (b) Figure 5.26b 45

46 Gender Differences of the Pelvis The female inlet is larger and more circular The female pelvis as a whole is shallower, and the bones are lighter and thinner The female ilia flare more laterally The female sacrum is shorter and less curved The female ischial spines are shorter and farther apart; thus the outlet is larger The female pubic arch is more rounded because the angle of the pubic arch is greater False pelvis Inlet of true pelvis Pelvic brim False pelvis Pubic arch (less than 90 ) Inlet of true pelvis Pelvic brim Pubic arch (more than 90 ) (c) Figure 5.26c 46

47 Bones of the Lower Limbs Femur thigh bone The heaviest, strongest bone in the body Proximal end articulation Head articulates with the acetabulum of the coxal (hip) bone Distal end articulation Lateral and medial condyles articulate with the tibia in the lower leg Neck Intertrochanteric line Head Head Lesser trochanter Lesser trochanter Gluteal tuberosity Greater trochanter Intertrochanteric crest Lateral condyle Intercondylar fossa Medial condyle Lateral condyle Patellar surface (a) (b) Figure 5.27a 47

48 Bones of the Lower Limbs The lower leg has two bones Tibia Shinbone; larger and medially oriented Proximal end articulation Medial and lateral condyles articulate with the femur to form the knee joint Fibula Thin and sticklike; lateral to the tibia Has no role in forming the knee joint Intercondylar eminence Lateral condyle Head Proximal tibiofibular joint Fibula Medial condyle Tibial tuberosity Interosseous membrane Anterior border Tibia Distal tibiofibular joint Medial Lateral malleolus malleolus (c) Figure 5.27c 48

49 Bones of the Lower Limbs The foot Tarsals seven bones Two largest tarsals Calcaneus (heel bone) Talus Metatarsals five bones form the sole of the foot Phalanges fourteen bones form the toes Phalanges: Distal Middle Proximal Tarsals: Medial cuneiform Intermediate cuneiform Navicular Metatarsals Tarsals: Lateral cuneiform Cuboid Talus Calcaneus Figure

50 Arches of the Foot Bones of the foot are arranged to form three strong arches Two longitudinal One transverse Medial longitudinal arch Transverse arch Lateral longitudinal arch Figure

51 Joints Articulations of bones Functions of joints Hold bones together Allow for mobility Two ways joints are classified Functionally Structurally Functional Classification of Joints Synarthroses Immovable joints Amphiarthroses Slightly moveable joints Diarthroses Freely moveable joints 51

52 Structural Classification of Joints Fibrous joints Generally immovable Cartilaginous joints Immovable or slightly moveable Synovial joints Freely moveable Fibrous Joints Bones united by collagenic fibers Types Sutures Immobile Syndesmoses Allows more movement than sutures but still immobile Example: Distal end of tibia and fibula Gomphosis Immobile 52

53 Fibrous joints Fibrous joints Fibrous connective tissue (a) Suture (b) Syndesmosis Figure 5.30a Tibia Fibula Fibrous connective tissue Cartilaginous Joints Bones connected by cartilage Types Synchrondrosis Immobile Symphysis Slightly movable Example: Pubic symphysis, intervertebral joints 53

54 Cartilaginous joints First rib Hyaline cartilage (c) Synchondrosis Sternum Figure 5.30c Cartilaginous joints Vertebrae Fibrocartilage (d) Symphysis Figure 5.30d 54

55 Cartilaginous joints Pubis Fibrocartilage (e) Symphysis Figure 5.30e Synovial Joints Articulating bones are separated by a joint cavity Synovial fluid is found in the joint cavity 55

56 Synovial joints Scapula Articular capsule Articular (hyaline) cartilage Humerus (f) Multiaxial joint (shoulder joint) Figure 5.30f Synovial joints Humerus (g) Uniaxial joint (elbow joint) Articular (hyaline) cartilage Articular capsule Radius Ulna Figure 5.30g 56

57 Synovial joints Carpals Ulna Radius Articular capsule (h) Biaxial joint (intercarpal joints of hand) Figure 5.30h Features of Synovial Joints Articular cartilage (hyaline cartilage) covers the ends of bones Articular capsule encloses joint surfaces and lined with synovial membrane Joint cavity is filled with synovial fluid Reinforcing ligaments 57

58 Structures Associated with the Synovial Joint Bursae flattened fibrous sacs Lined with synovial membranes Filled with synovial fluid Not actually part of the joint Tendon sheath Elongated bursa that wraps around a tendon Acromion of scapula Ligament Bursa Ligament Tendon sheath Tendon of biceps muscle Joint cavity containing synovial fluid Articular (hyaline) cartilage Synovial membrane Fibrous layer of the articular capsule Humerus Figure

59 Nonaxial Uniaxial Biaxial Multiaxial (a) Plane joint (a) Figure 5.32a Nonaxial Uniaxial Biaxial Multiaxial (b) Humerus Ulna (b) Hinge joint Figure 5.32b 59

60 Nonaxial Uniaxial Biaxial Multiaxial (c) Ulna Radius (c) Pivot joint Figure 5.32c Nonaxial Uniaxial Biaxial Multiaxial (d) Metacarpal Phalanx (d) Condylar joint Figure 5.32d 60

61 Nonaxial Uniaxial Biaxial Multiaxial Carpal Metacarpal #1 (e) (e) Saddle joint Figure 5.32e (f) Nonaxial Uniaxial Biaxial Multiaxial Head of humerus Scapula (f) Ball-and-socket joint Figure 5.32f 61

62 Inflammatory Conditions Associated with Joints Bursitis inflammation of a bursa usually caused by a blow or friction Tendonitis inflammation of tendon sheaths Arthritis inflammatory or degenerative diseases of joints Over 100 different types The most widespread crippling disease in the United States Initial symptoms: pain, stiffness, swelling of the joint Clinical Forms of Arthritis Osteoarthritis Most common chronic arthritis Probably related to normal aging processes Rheumatoid arthritis An autoimmune disease the immune system attacks the joints Symptoms begin with bilateral inflammation of certain joints Often leads to deformities 62

63 Clinical Forms of Arthritis Gouty arthritis Inflammation of joints is caused by a deposition of uric acid crystals from the blood Can usually be controlled with diet More common in men Developmental Aspects of the Skeletal System At birth, the skull bones are incomplete Bones are joined by fibrous membranes called fontanels Fontanels are completely replaced with bone within two years after birth 63

64 Frontal bone of skull Mandible Parietal bone Occipital bone Clavicle Scapula Radius Ulna Humerus Femur Tibia Ribs Vertebra Hip bone Figure 5.34 Skeletal Changes Throughout Life Fetus Long bones are formed of hyaline cartilage Flat bones begin as fibrous membranes Flat and long bone models are converted to bone Birth Fontanels remain until around age 2 64

65 Skeletal Changes Throughout Life Adolescence Epiphyseal plates become ossified and long bone growth ends Size of cranium in relationship to body 2 years old skull is larger in proportion to the body compared to that of an adult 8 or 9 years old skull is near adult size and proportion Between ages 6 and 11, the face grows out from the skull Figure 5.35a 65

66 Figure 5.35b Skeletal Changes Throughout Life Curvatures of the spine Primary curvatures are present at birth and are convex posteriorly Secondary curvatures are associated with a child s later development and are convex anteriorly Abnormal spinal curvatures (scoliosis and lordosis) are often congenital 66

67 Figure 5.18 Skeletal Changes Throughout Life Osteoporosis Bone-thinning disease afflicting 50 percent of women over age percent of men over age 70 Disease makes bones fragile and bones can easily fracture Vertebral collapse results in kyphosis (also known as dowager s hump) Estrogen aids in health and normal density of a female skeleton 67

68 Figure 5.36 Figure