Human Anatomy & Physiology, Sixth Edition
6Bones and Skeletal Tissues
Skeletal Cartilage
Avascular & without nerves Vascularized perichondrium Three types
Hyaline
Elastic
Fibrocartilage
Growth of Cartilage
2 types of growth Appositional –perichondrium cells secrete matrix Interstitial – chondrocytes within cartilage secrete
matrix Calcification
bone growth geriatric
Classification of Bones by Skeletal Region
Axial skeleton skull, vertebral column, ribs &
sternum Appendicular skeleton
limbs, pectoral girdle, & pelvic girdle
Classification of Bones: By Shape
Long bones
Figure 6.2a
Classification of Bones: By Shape
Figure 6.2b
Long bones Short bones
Cube-shaped carpals, tarsals, & patella
Classification of Bones: By Shape
Long bones Short bones Flat bones
sternum, & most skull bones
Figure 6.2c
Classification of Bones: By Shape
Long bones Short bones Flat bones Irregular
bones Vertebrae
& pelvic bones
Figure 6.2d
Gross Anatomical Bone Features
Bulges, depressions, and holes that serve as: Attachment sites for ligaments & tendons (muscles) Joint surfaces Conduits for blood vessels and nerves
Table 6.1 Know It
Gross Anatomy: Structure of Long Bone
Figure 6.3
Bone Membranes Periosteum –
Outer – dense, regular connective tissue Inner (osteogenic) - osteoblasts and osteoclasts nerves, blood, & lymphatic vessels
enter via nutrient foramina Secured to underlying bone
by Sharpey’s fibers Endosteum
Thin membrane covering internal surfaces of bone
Endosteum
Structure of Short, Irregular, and Flat Bones
Periosteum-covered compact bone on the outside Endosteum-covered spongy bone (diploë) on the
inside no diaphysis or epiphyses Red marrow among
trabeculae of diploë
Bone Marrow
Red Hematopoietic stem cells childhood
medullary cavity & all areas of spongy bone adults
diploë of flat bones, head of the femur & humerus
Yellow Adipose-like tissue Medullary cavity & epiphyseal spongy bone
Microscopic Structure of Bone: Compact Bone
Osteoid
Ossified minerals
Composition of Bone: Components
Osteocytes – mature bone cells Osteoblasts – bone-forming cells Osteoclasts – resorb or break down bone matrix
Osteoid – unmineralized ECM of proteoglycans & collagen
Hydroxyapatite calcium phosphates 65% of bone by mass
Bone Development
Chondrogenesis forms cartilaginous model of skeleton in embryos beginning in 6th week
Osteogenesis begins by 8th week of embryonic development collagen matrix
Ossification Intramembranous
develops within a fibrous membrane Endochondral
replacement of hyaline cartilage model
Intramembranous Ossification
Formation of most of the flat bones of the skull and the clavicles
Fibrous connective tissue membranes are formed by mesenchymal cells
Stages of Intramembranous Ossification
Stages of Intramembranous Ossification
Endochondral Ossification
Formation of the long bones and many irregular bones (vertebrae)
Chondrocytes 1st form cartilaginous model of the bone that is replaced by osteoblasts and then mineralized
1
Hyaline cartilage
Primary ossification center
Bone collar
Stages of Endochondral Ossification
1
2
Hyaline cartilage
Primary ossification center
Bone collar
Deteriorating cartilage matrix
Stages of Endochondral Ossification
1
2
3
Hyaline cartilage
Primary ossification center
Bone collar
Deteriorating cartilage matrix
Spongy bone formation
Blood vessel of periosteal bud
Stages of Endochondral Ossification
1
2
3
4
Hyaline cartilage
Primary ossification center
Bone collar
Deteriorating cartilage matrix
Spongy bone formation
Blood vessel of periosteal bud
Secondary ossification center
Epiphyseal blood vessel
Medullary cavity
Stages of Endochondral Ossification
1
2
3
4
5
Hyaline cartilage
Primary ossification center
Bone collar
Deteriorating cartilage matrix
Spongy bone formation
Blood vessel of periosteal bud
Secondary ossification center
Epiphyseal blood vessel
Medullary cavity
Epiphyseal plate cartilage
Spongy bone
Articular cartilage
Stages of Endochondral Ossification
Figure 6.8
Functional Zones in Long Bone Growth
Long Bone Growth and Remodeling
Figure 6.10
Osteoblasts beneath periosteum secrete bone matrix & form ridges following periosteal blood vessels
1 2 3 4As the ridges meet, they form a tunnel containing the blood vessel
The periosteum lining the tunnel is transformed into an endosteum and the osteoblasts just deep to the tunnel endosteum secrete bone matrix, narrowing the canal.
As 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.
Artery Periosteum Penetrating canal
Central canal of osteonPeriosteal ridge
Appositional Growth of Bone
Figure 6.11
During infancy and childhood, epiphyseal plate activity is stimulated by growth hormone
During puberty, testosterone and estrogens:
Hormonal Regulation of Bone Growth
Bone Remodeling
Osteoblasts and osteoclasts deposit and resorb bone at periosteal and endosteal surfaces
Requires protein, vitamins C, D, A, Ca, P, Mg, & Mn
Resorption Osteoclasts in resorption bays secrete
enzymes that digest matrix acids that dissolve Ca salts
Deposition Osteoblasts
Lay down fresh osteoid matrix and induce mineralization
Control of Remodeling
Hormonal control loops regulate bone remodeling & maintain Ca homeostasis in the blood
Mechanical and gravitational forces
Hormonal Mechanism
Figure 6.12
Importance of Ionic Calcium in the Body
Transmission of nerve impulses Muscle contraction Blood coagulation Secretion by glands and nerve cells Cell division
Response to Mechanical Stress
Wolff’s law – A bone grows and/or remodels in response to
mechanical stresses Bones are thickest where the stresses are maximal
Long bones - midway along the shaft Curved bones where the curvature is greatest
Trabeculae form along lines of stress Large, bony projections occur where heavy, active
muscles attach
Response to Mechanical Stress
Figure 6.13
Bone Fracture Classification
Position of the bone ends nondisplaced v displaced
Completeness of the break Orientation of the break to the long axis
linear v transverse Whether or not the ends penetrate skin
compound v simple
Common Types of Fractures
Common Types of Fractures
Common Types of Fractures
Stages in the Healing of a Bone Fracture
Hematoma formation
Figure 6.14.1
1
Hematoma
Hematoma formation
Stages in the Healing of a Bone Fracture
Fibrocartilaginous callus formation (soft callus) Granulation tissue
(fibrocartilage) grows Capillaries grow and
phagocytic cells clear debris
Figure 6.14.2
2 Fibrocartilaginous callus formation
External callus
New blood vessels
Spongy bone trabeculae
Internal callus (fibrous tissue and cartilage)
Stages in the Healing of a Bone Fracture
Bony callus formation fibrocartilage of
fibrocartilaginous callus converts into spongy bone
Bone callus begins 3-4 weeks after injury, and continues until firm union is formed 2-3 months later
Figure 6.14.3
3 Bony callus formation
Bony callus of spongy bone
Stages in the Healing of a Bone Fracture
Bone remodeling Excess material on
is removed Compact bone is
laid down to reconstruct shaft walls
Figure 6.14.4
4 Bone remodeling
Healing fracture
Homeostatic Imbalances
Ca deficiency conditions Dietary or hormonal (vit D) Inadequate mineralization causing softened,
weakened bones Osteomalacia
elderly Rickets
children
Osteoporosis
Pathology Condition when bone reabsorption outpaces bone deposit Spongy bone is most vulnerable (especially spine) Bones become very fragile Occurs most often in postmenopausal women
Preventive measures Dietary Ca and vitamin D Increased weight-bearing exercise
Treatments Hormone replacement therapy (HRT) – estrogens Statins
Paget’s Disease
Excessive bone remodeling Initially, an excess of spongy to compact bone forms Later, osteoclast activity wanes, but osteoblast
activity continues resulting in filling in spongy bone and loss of marrow
Usually localized in the spine, pelvis, femur, and skull
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)
By age 25, nearly all bones are completely ossified In old age, bone resorption predominates