2Functions of the Skeletal System SupportPermission of movementBlood cell formation (hematopoiesis)ProtectionDetoxification (removal of poisons)Provision for muscle attachmentMineral storage
3Bone Classification Bones are classified according to shape Long bones are long with expanded ends, Ex: forearm and thigh boneShort bones are cube like, Ex: wrist, ankleFlat bones are broad and plate like, Ex: ribs, scapulae, and some skull bonesIrregular bones vary in shape, Ex: vertebraeSesamoid or round bones are small bones embedded in tendons, Ex: kneecap (patella)
9Parts of BoneEpiphysis: end of the bone which articulates (forms a joint) with another bone.The epiphyses are composed of spongy bone and covered with hyaline cartilage called articular cartilage.Figure 7.2
10Parts of BoneDiaphysis: shaft of the bone between the epiphyses, composed of compact bone with a medullary cavity in the center.
11Parts of BonePeriosteum: fibrous tissue covering of the bone.
12Compact BoneOsteocytes and layers of intercellular material lie in concentric rings around an osteonic canal.This unit is called an osteon or Haversian system.Osteonic canals contain blood vessels and nerve fibers and are interconnected by transverse perforating (Volkmann’s) canals.
13Microscopic Structure of Bone: Compact Bone Figure 6.6a, b
18Bone Growth and Development The skeletal system begins to form during the first weeks of prenatal development.Some bones originate within sheets of connective tissue (intramembranous bones).Some bones begin as models of hyaline cartilage that are replaced by bone (endochrondral bones).
19Intramembranous Bones Broad, flat skull bones are intramembranous bones.During osteogenesis layers of primitive, connective tissue supplied with blood vessels appear at the site of future bone.
20Intramembranous Bones Cells differentiate into osteoblasts (bone-building cells) which deposit spongy bone.Osteoblasts become osteocytes when surrounded by bony matrix in lacunae.
21Intramembranous Bones Connective tissue on the surface of the bone forms the periosteum.Osteoblasts on the inside of the periosteum deposit compact bone over spongy bone.This process is called intramembranous ossification.
22Endochondral BonesHyaline cartilage forms a model of the bone during embryonic development.Cartilage degenerates, periosteum forms.Periosteal blood vessels and osteoblasts invade the bone forming a primary ossification center in the diaphysis.Secondary ossification centers develop in the epiphyses.
23Endochondral BonesOsteoblasts form spongy bone in the space occupied by cartilage.Osteoblasts become osteocytes when bony matrix surrounds them.
24Endochondral BonesOsteoblasts beneath the periosteum deposit compact bone around spongy bone.A band of cartilage remains between the diaphysis and epiphyses as the epiphyseal disk.
25Bone GrowthGrowth of long bones occurs along four layers of cartilage in the epiphyseal disk.First Layer: resting cells that do not grow.Second Layer: young mitotic cells.Third Layer: older cells that enlarge.Fourth Layer: dead cells and calcified intercellular substances.
26Formation of the Bony Skeleton Begins at week 8 of embryo developmentIntramembranous ossification – bone develops from a fibrous membraneEndochondral ossification – bone forms by replacing hyaline cartilage
27Intramembranous Ossification Formation of most of the flat bones of the skull and the claviclesFibrous connective tissue membranes are formed by mesenchymal cells
28Stages of Intramembranous Ossification An ossification center appears in the fibrous connective tissue membraneBone matrix is secreted within the fibrous membraneWoven bone and periosteum formBone collar of compact bone forms, and red marrow appears
29Stages of Intramembranous Ossification Figure 6.7.1
30Stages of Intramembranous Ossification Figure 6.7.2
31Stages of Intramembranous Ossification Figure 6.7.3
32Stages of Intramembranous Ossification Figure 6.7.4
33Endochondral Ossification Begins in the second month of developmentUses hyaline cartilage “bones” as models for bone constructionRequires breakdown of hyaline cartilage prior to ossification
34Stages of Endochondral Ossification Formation of bone collarCavitation of the hyaline cartilageInvasion of internal cavities by the periosteal bud, and spongy bone formationFormation of the medullary cavity; appearance of secondary ossification centers in the epiphysesOssification of the epiphyses, with hyaline cartilage remaining only in the epiphyseal plates
35Stages of Endochondral Ossification Secondary ossification centerArticular cartilageEpiphyseal blood vesselSpongy boneDeteriorating cartilage matrixHyaline cartilageEpiphyseal plate cartilageSpongy bone formationPrimary ossification centerMedullary cavityBone collarBlood vessel of periosteal bud1Formation of bone collar around hyaline cartilage model.2Cavitation of the hyaline cartilage within the cartilage model.3Invasion of internal cavities by the periosteal bud and spongy bone formation.4Formation of the medullary cavity as ossification continues; appearance of secondary ossification centers in the epiphyses in preparation for stage 5.5Ossification of the epiphyses; when completed, hyaline cartilage remains only in the epiphyseal plates and articular cartilagesFigure 6.8
36Postnatal Bone Growth Growth in length of long bones Cartilage on the side of the epiphyseal plate closest to the epiphysis is relatively inactiveCartilage abutting the shaft of the bone organizes into a pattern that allows fast, efficient growthCells of the epiphyseal plate proximal to the resting cartilage form three functionally different zones: growth, transformation, and osteogenic
37Functional Zones in Long Bone Growth Growth zone – cartilage cells undergo mitosis, pushing the epiphysis away from the diaphysisTransformation zone – older cells enlarge, the matrix becomes calcified, cartilage cells die, and the matrix begins to deteriorateOsteogenic zone – new bone formation occurs
42Appositional Growth of Bone Central canal of osteonPeriosteal ridgePeriosteumPenetrating canalArtery1Osteoblasts beneath the periosteum secrete bone matrix, forming ridges that follow the course of periosteal blood vessels.2As the bony ridges enlarge and meet, the groove containing the blood vessel becomes a tunnel.3The periosteum lining the tunnel is transformed into an endosteum and the osteoblasts just deep to the tunnel endosteum secrete bone matrix, narrowing the canal.4As the osteoblasts beneath the endosteum form new lamellae, a new osteon is created. Meanwhile new circumferential lamellae are elaborated beneath the periosteum and the process is repeated, continuing to enlarge bone diameter.Figure 6.11
43Bone RemodelingRemodeling units – adjacent osteoblasts and osteoclasts deposit and resorb bone at periosteal and endosteal surfaces
44Bone HomeostasisAfter bone formation, osteoclasts and osteoblasts continue to remodel the bone.Resorption and deposition are regulated to keep bone mass constant.
45Nutrition and Bone Development Vitamin D is necessary to absorb calcium in the small intestine.Vitamin D deficiency leads in rickets in children and osteomalacia in adults.
46Nutrition and Bone Development Vitamin A is necessary for osteoblast and osteoclast activity.Vitamin C is necessary for collagen synthesis.
47Hormones and BoneGrowth Hormone (GH) stimulates epiphyseal cartilage cell division.Deficiency of G H: pituitary dwarfism. Excess GH: pituitary gigantism in children and acromegaly in adults.
48Hormones and BoneThyroid hormone stimulates cartilage replacement in the epiphyseal disks.Sex steroids promote formation of bone tissue close the epiphyseal disk.
49Physical Factors Affecting Bone Physical stress stimulates bone growth.Weight bearing exercise stimulates bone tissue to thicken and strengthen (hypertrophy).Lack of exercise leads to bone wasting (atrophy).
50Bone Function Bones shape, support, and protect body structures. Bones act as levers to create body movement with muscles.Bones house blood cell producing tissue.Bones store inorganic salts.
51Support and Protection Bones give shape to the head, face, chest, and limbs.Bones of the skull protect structures like the eyes, ears, and brain.Bones of the rib cage and shoulder protect the heart and lungs.Bones of the pelvic girdle protect the abdominal and reproductive organs.
52Body MovementWhen body parts move, bones and muscle act as levers.
53Body MovementA lever has four parts: a bar, a fulcrum, an object moved, a force to supply energy.There are three classes of levers.Figure 7.13
58Fracture RepairBlood escapes from damaged blood vessels and forms a hematoma.Spongy bone forms in regions near blood vessels and fibrocartilage forms farther away.A bony callus replaces the fibrocartilage.Osteoclasts remove excess bony tissue, restoring new bone much like the original.
59Blood Cell FormationBlood cell formation (hematologists) occurs in yolk sac in early development.Later it occurs in the liver and spleen.In the adult red and white blood cells are formed in the red bone marrow.
60Blood Cell FormationRed marrow fills the cavity in the diaphesis of the long bones in infants. In adults it is replaced with yellow marrow (fat).Adult red marrow is found in spongy bone of the skull, ribs, sternum, vertebrae, pelvis.
61Inorganic Salt Storage Salts account for 70% of the bone matrix.These salts are mostly calcium phosphate crystals called hydroxyapatite.
62Inorganic Salt Storage Parathyroid hormone stimulates osteoclasts to break down bone when Ca levels are low.Calcitonin stimulates osteoblasts to build bone when Ca levels are high.Bone contains Mg, Na, K, and carbonate ions.
63Axial SkeletonThe skeleton has two divisions: the axial and the appendicular skeleton.The axial skeleton consists bones that support organs of the head, neck, and trunk.Skull :cranium and facial bones.Hyoid bone.Vertebral column.Thoracic cage: ribs and sternum.
64Appendicular Skeleton The appendicular skeleton consists of the bones of the limbs and bones that anchor the limbs to the axial skeleton.Pectoral girdle: scapula, clavicle.Upper limbs: humerus, radium, ulna, carpals, metacarpals, phalanges.Pelvic girdle: coxal bones.Lower limbs: femur, tibia, fibula, patella, tarsals, metatarsals, phalanges.
67Cranium Frontal bone: forehead Parietal bones: top of the skull Occipital bone: back of the skullTemporal bones: side of skull, near earsSphenoid bone:base of the craniumEthmoid bone: roof of the nasal cavity
74Facial Skeleton Maxillary bones: upper jaw, hard palate Palatine bones: hard palate, nasal cavityZygomatic bones: cheek bonesLacrimal bones: orbit of the eyeNasal bones: bridge of the noseVomer bone: nasal septumNasal conchae:walls of the nasal cavityMandible: lower jaw
78Infantile Skull The skull at birth is not fully developed. Fibrous membranes, fontanels, connect the cranial bones.The fontanels allow movement of the bones to enable the skull to pass through the birth canal.The fontanels close as cranial bones grow.
81Vertebral ColumnCervical vertebrae: seven vertebrae of the neck, includes atlas and axisThoracic vertebrae: twelve vertebrae that articulate with the ribsLumbar vertebrae: five vertebrae that make up the small of the back
82Vertebral Column Figure 7.34 Sacrum: five vertebrae that fuse in early adulthood, part of the pelvisCoccyx: four small fused vertebraeFigure 7.34
83Thoracic CageRibs: twelve pair of ribs attached to each thoracic vertebrae.Seven pairs: true ribs and attach to the sternum by costal cartilage.Two pairs: false ribs that attach to cartilage.
84Thoracic CageTwo pairs: floating ribs that do not attach to the sternum or its cartilage.Sternum: the manubrium, the body, and the xyphoid process.
85Pectoral GirdleClavicles: collar bones that attach the sternum to the shoulder anteriorly.Scapulae: shoulder blades with two processes.Acromion process: tip of the shoulder.Coracoid process: attaches to the clavicle and provides attachments for muscles.Glenoid fossa articulates with the humerus.
87Upper limbHumerus: upper arm bone, articulates with the glenoid fossa of the scapula
88Upper limbRadius: thumb side of the forearm, articulates with the capitulum of the humerus and the radial notch of the ulnaUlna: longer bone of the forearm, olecranon and coronoid processes articulate with the humerus
89Hand Carpal bones: eight small bones of the wrist. Metacarpal bones: five bones, the framework of the palm.Phalanges: finger bones, three in each finger (proximal, middle, distal phalanx), two in the thumb.
91Pelvic GirdleCoxal bones: two hips bones composed of three fused bones.Ilium: superior part of the coxal bone.Ischium: lowest portion of the coxal bone.Pubis: anterior part of the coxal bone. The two pubic bones joint at the symphysis pubis.
94Male and Female Pelvis Female iliac bones are more flared. The female pubic arch angle is greater.There is a greater distance between the ischial spines and tuberosities in the female.The sacral curvature is shorter and flatter.The differences create a wider pelvic cavity.
96Lower Limb Femur: thigh bone, longest bone Patella: kneecap, located in a tendon, femur, tibia, and patella form the knee jointTibia: shinbone, lateral malleolus forms the ankleFibula: slender bone lateral to the tibia, not part of the knee joint
98FootTarsal bones: seven small bones in the ankle. The calcaneus (heel bone) is the largest, located below the talus.Metatarsal bones: elongated bones that form the arch of the foot.Phalanges: each toe has three except the great tow which has two.