bones and skeletal tissues
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Bones and Skeletal TissuesChapter 6
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Skeletal Cartilages
• Contain no blood vessels or nerves• Perichondrium (dense irregular connective
tissue girdle) contains blood vessels for nutrient delivery to cartilage
• Types– Hyaline– Elastic– Fibrocartilage
Figure 6.1
Axial skeleton
Appendicular skeleton
Hyaline cartilages
Elastic cartilages
Fibrocartilages
Cartilages
Bones of skeleton
EpiglottisLarynx
TracheaCricoidcartilage Lung
Respiratory tube cartilagesin neck and thorax
ThyroidcartilageCartilage in
external earCartilages innose
ArticularCartilageof a jointCostalcartilage
Cartilage inIntervertebraldisc
Pubicsymphysis
Articular cartilageof a joint
Meniscus (padlikecartilage inknee joint)
Growth of Cartilage
• Appositional– Cells secrete matrix against the
external face of existing cartilage• Interstitial– Chondrocytes divide and secrete
new matrix, expanding cartilage from within
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Figure 6.1
Cartilage inexternal ear
Cartilages innose
ArticularCartilageof a jointCostalcartilage
Cartilage inIntervertebraldisc
Pubicsymphysis
Articular cartilageof a joint
Meniscus (padlikecartilage inknee joint)
Bones of the Skeleton
Classification of Bones by Shape
• Long bones
• Short bones
• Flat bones
• Irregular bones
Functions of Bones
• Support• Protection• Movement• Mineral & Growth Factor
Storage• Blood cell formation • Triglyceride storage• Hormone Production
Bone Structure• Bones are organs!–Multiple tissue types• Bone (osseous) tissue, nervous tissue, cartilage,
fibrous connective tissue, muscle and epithelial cells (in its blood vessels)
Bone Texture• Compact– Dense outer layer; smooth
and solid• Spongy (trabecular)– Honeycomb of flat pieces of
bone (trabeculae) deep to compact
– Space b/w trabeculae filled with red or yellow bone marrow
Structure of Short, Irregular, and Flat Bones
• Periosteum covered compact bone on the outside
• Endosteum covered spongy bone within – diploë
• Bone marrow b/w the trabeculae
• Hyaline cartilage on articular surfaces
Structure of Typical Long Bone
• Diaphysis– Tubular shaft forms long axis– Compact bone surrounds medullary cavity
• Epiphyses (bone ends)– Compact bone outside; spongy bone inside– Articular cartilage covers articular surfaces
• Epiphyseal line– b/w diaphysis and epiphysis– Remnant of epiphyseal plate
Membranes of Bone
• Periosteum–Outer fibrous layer– Inner osteogenic layer–Contains nerve fibers, nutrient blood
vessels, and lymphatic vessels that enter the bone via nutrient foramina– Secured to underlying bone by Sharpey’s
fibers
Membranes of Bone
• Endosteum– Delicate membrane on
internal surfaces of bone
– Contains osteogenic cells
Hematopoietic Tissue (Red Marrow)
• Infants (long bones)– Medullary cavities and
spongy bone• Adults (long bones)– Little red marrow
• Red marrow in flat and some irregular bones is most active
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Bone Markings
• Projections, depressions, and holes– Sites of attachment for muscles, ligaments, and
tendons– Joint surfaces– Passageways for blood vessels and nerves
Bone Markings: Projections• Sites of muscle and
ligament attachment– Tuberosity– Crest– Trochanter– Line– Tubercle– Epicondyle– Spine– Process
• Projections that help to form joints– Head– Facet– Condyle– Ramus
Bone Markings: Depressions and Openings
• Passages for blood vessels and nerves– Meatus– Sinus– Fossa– Groove– Fissure– Foramen
Microscopic Anatomy of Bone
Microscopic Anatomy of Bone: Compact Bone
• Haversian system (or osteon)– Lamellae– Central
(Haversian) canal
• Perforating (Volkmann’s) canals• Lacunae• Canaliculi
Microscopic Anatomy of Bone: Compact Bone
Microscopic Anatomy of Bone: Spongy Bone
• Trabeculae– Align along lines of stress– No osteons– Irregularly arranged lamellae, osteocytes, and
canaliculi– Capillaries in endosteum supply nutrients
Chemical Composition of Bone• Organic– Bone cells– Osteoid—organic bone matrix secreted by
osteoblasts• Ground substance, collagen fibers
• Inorganic– Hydroxyapatites (mineral salts)• 65% of bone by mass• Mainly calcium phosphate crystals
Bone Development
• Ossification (osteogenesis): process of bone tissue formation– Formation of bony skeleton• Begins in 2nd month of development
– Postnatal bone growth• Until early adulthood
– Bone remodeling and repair• Lifelong
Types of Ossification
• Endochondral ossification– Bone forms by replacing hyaline cartilage– Majority of skeleton
• Intramembranous ossification– Bone develops from fibrous membrane– Bones called membrane bones– Forms flat bones, e.g. clavicles and cranial bones
Endochondral Ossification
• Forms most all bones inferior to base of skull (except clavicles)
• Begins late in 2nd month of development• Uses hyaline cartilage models • Hyaline cartilage must be broken down before
ossification
Figure 6.9
Hyalinecartilage
Area ofdeterioratingcartilage matrix
Epiphysealblood vessel
Spongyboneformation
Epiphysealplatecartilage
Secondaryossificationcenter
Bloodvessel ofperiostealbud
Medullarycavity
Articularcartilage
Childhood toadolescence
BirthWeek 9 Month 3
Spongybone
BonecollarPrimaryossificationcenter
1 2 3 4 5
Intramembranous Ossification
• Forms cranial bones of the skull and clavicles• Begins within fibrous connective tissue membranes
formed by mesenchymal cells• Ossification centers appear• Osteoid is secreted• Woven bone and periosteum form• Lamellar bone replaces woven bone & red marrow
appears
Figure 6.9 Intramembranous ossification.
Fibrous periosteum
Osteoblast
Plate ofcompact bone
Diploë (spongy bone)cavities contain redmarrow
4 Lamellar bone replaces woven bone, just deep to the periosteum. Red marrow appears.
Mesenchymalcell
Collagen fibril
Ossification center
Osteoid
Osteoblast
1 Ossification centers appear in the fibrous connective tissue membrane.
Osteoblast
Osteoid
Osteocyte
Newly calcifiedbone matrix
2 Osteoid is secreted within the fibrous membrane and calcifies.
Mesenchymecondensingto form the periosteum
Trabeculae ofwoven bone
Blood vessel
3 Woven bone and periosteum form.
Postnatal Bone Growth
• Interstitial growth: – length of long bones
• Appositional growth: – thickness and remodeling of all bones by
osteoblasts and osteoclasts on bone surfaces
Interstitial (Longitudinal) Growth
• Epiphyseal plate cartilage organizes into 5 important functional zones: – Resting (quiescent) zone– Proliferation (growth)– Hypertrophic– Calcification– Ossification (osteogenic)
Figure 6.10
Calcified cartilagespicule
Osseous tissue(bone) coveringcartilage spicules
Resting zone
Osteoblast depositingbone matrix
Proliferation zoneCartilage cells undergo mitosis.
Hypertrophic zoneOlder cartilage cells enlarge.
Ossification zoneNew bone formation is occurring.
Calcification zoneMatrix becomes calcified; cartilage cells die; matrix begins deteriorating.
1
2
3
4
Appositional Growth
• Growth in Width– Osteoblasts active in periosteum– Osteoclasts active in the endosteum– Building > Breaking down = thicker stronger bone
Figure 6.11
Bone growth Bone remodeling
Articular cartilage
Epiphyseal plate
Cartilagegrows here.
Cartilageis replacedby bone here.Cartilagegrows here.
Bone isresorbed here.
Bone isresorbed here.
Bone is addedby appositionalgrowth here. Cartilage
is replacedby bone here.
Hormonal Regulation of Bone Growth
• Growth hormone • Thyroid hormone • Testosterone and
Estrogen
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Bone Remodeling
• Bone is constantly being “recycled” • Occurs @ surface of periosteum and
endosteum• Deposit– Injury or needed strength, requires good diet– Osteoid seam and Calcification front
• Resorption– Osteoclasts secrete: lysosomal enzymes, acids– Dissolved matrix is transcytosed
Control of Remodeling
• What controls continual remodeling of bone?– Hormonal mechanisms
that maintain calcium homeostasis in the blood
– Mechanical and gravitational forces
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Hormonal Control of Blood Ca2+
• Most calcium in the body is in the bones• Less that 1.5g in blood – tightly regulated
narrow range• Calcium is necessary for– Transmission of nerve impulses– Muscle contraction– Blood coagulation– Secretion by glands and nerve cells– Cell division
Figure 6.12
Osteoclastsdegrade bonematrix and release Ca2+
into blood.
Parathyroidglands
Thyroidgland
Parathyroidglands releaseparathyroidhormone (PTH).
StimulusFalling bloodCa2+ levels
PTH
Calcium homeostasis of blood: 9–11 mg/100 mlBALANCEBALANCE
Hormonal Control of Blood Ca2+
• May be affected to a lesser extent by calcitonin
Blood Ca2+ levels
Parafollicular cells of thyroid release calcitonin
Osteoblasts deposit calcium salts
Blood Ca2+ levels
Response to Mechanical Stress
• Wolff’s law: A bone grows or remodels in response to forces or demands placed upon it
Hormones and Mechanical Stress
• Hormones – – when remodeling occurs– As a response to what???
• Mechanical Stress– Where the remodeling occurs
Classification of Bone Fractures • Bone fractures may be classified by four
“either/or” classifications
1. Position of bone ends after fracture:• Nondisplaced or Displaced
2. Completeness of the break• Complete or Incomplete
3. Orientation of the break to the long axis of the bone:• Linear or transverse
4. Whether or not the bone ends penetrate the skin• Compound (open) or Simple (closed)
Common Types of Fractures
• In addition to the previous classification, all fractures can be described in terms of– Location– External appearance– Nature of the break
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Table 6.2
Table 6.2
Table 6.2
Fracture Healing
1. Hematoma forms2. Fibrocartilaginous
callus forms
Fracture Healing
3. Bony callus formation4. Bone remodeling
Homeostatic Imbalances
• Osteomalacia and Rickets– Calcium salts not deposited– Rickets (childhood disease)
causes bowed legs and other bone deformities
– Cause: vitamin D deficiency or insufficient dietary calcium
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Homeostatic Imbalances
• Osteoporosis– Loss of bone mass– Spongy bone of spine
and neck of femur become most susceptible to fracture
– Risk factors• Lack of estrogen, calcium
or vitamin D; petite body form; immobility; low levels of TSH; diabetes mellitus; smoking
Developmental Aspects of Bones
• Embryonic skeleton ossifies predictably so fetal age easily determined from X rays or sonograms
• At birth, most long bones are well ossified (except epiphyses)
Developmental Aspects of Bones
• Nearly all bones completely ossified by age 25• Bone mass decreases with age beginning in
4th decade• Rate of loss determined by genetics and
environmental factors • In old age, bone resorption predominates
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