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