Skeletal TissueA. Tissues

1. CartilageA) 3 types

1) Hyaline cartilagea) Articular cartilage – covers ends of bones

Skeletal Tissueb) Costal cartilage – connects the ribs to

the sternumc) Laryngeal cartilage – forms skeleton of

the larynxd) Tracheal & bronchial cartilage –

reinforces passageways of respiratory system

e) Nasal cartilage – supports the external nose

Skeletal Tissue2) Elastic cartilage

a) External earb) Epiglottis

3) Fibrocartilagea) Intervertebral discs b) Menisci of the kneec) Pubic symphysis

Skeletal TissueB) Cartilage Growth

1) Appositional growtha) New matrix is secreted by chondroblasts onto the edges of the already existing piece

2) Interstitial growtha) Chondroblasts within the lacunae secrete new matrix within the already existing piece

Skeletal Tissue2. Osseous Tissue (Bone)

A) 2 main types1) Compact – small amount of space between its hard components

Skeletal Tissue2) Spongy – large

spaces between its hard components; known as trabeculae

Skeletal TissueB) Histology of Bone

1) Compact bone a) Osteon

(Haversian system)i) Concentric lamella – circular layers of compact bone

Skeletal Tissue

ii) Haversian canaliii) Volkmann’s canals

– connect adjacent Haversian canals

iv) Lacunae – small gaps at lamellar junctions

v) Osteocytes

Skeletal Tissuevi) Canaliculi –

connect the lacunae

b) Interstitial lamella – between osteons

c) Circumferential lamella – around entire outside of bone just under periosteum

Skeletal Tissue2) Spongy bone

a) Not very complexi) composed of

several layers of lamella & osteocytes

ii) no osteons or blood vessels

Skeletal TissueC) Bone Development

1) ossification – process of bone tissue formationa) intramembranous ossification – bone develops from a CT membranei) responsible for most skull bones and the clavicle

ii) begins at 8th week of development

Skeletal Tissueb) endochondral ossification – bone

develops from a hyaline cartilage modeli) all other bonesii) begins by the end of the 3rd month

Skeletal Tissue2) bone growth in

lengtha) occurs at

epiphyseal plates (growth plates)i) chondrocytes

in this area are stacked upon one another

Skeletal Tissueii) cells at

epiphyseal end divide rapidly

iii) cells at diaphyseal end enlarge, calcify, and ultimately die

iv) osteoid replaces calcified cells

Skeletal Tissueb) slows with age until epiphysis and

diaphysis fusei) about 18 for females and 21 for males

3) bone growth in widtha) appositional growth

i) osteoblasts beneath periosteum (outer surface) lay down new bone tissue

ii) osteoclasts beneath the endosteum (inner surface) break down old bone tissue, but usually at a slower rate

Skeletal Tissue4) hormonal control of bone growth

a) human growth hormone (hGH) – from pituitary glandi) controls growth at growth plate

b) thyroid hormones (T3 & T4)i) regulate the function of hGH

Skeletal Tissuec) testosterone & estrogen (sex

hormones)i) released at pubertyii) cause growth spurt and skeletal

changes associated with pubertyiii) also induce epiphyseal plate

closure; now known as epiphyseal line

Skeletal TissueD) Bone homeostasis

1) Remodelinga) the ongoing replacement of old/worn

bone tissue with new bone tissueb) areas of increased stress can be

replaced a couple times a year while some bones never have their tissue completely replaced

c) also replaces injured bone

Skeletal Tissued) cells involved

i) osteoclasts – responsible for the breakdown of bone tissue

ii) osteoblasts – responsible for production of new bone tissue

iii) osteocytes – mature bone cells

Skeletal Tissuef) process – similar to appositional

growthi) osteoclasts digest bone tissue by

releasing enzymes & acidsii) osteoblasts produce new bone

tissue around themselves until surrounded

iii) once osteoblast is surrounded it becomes an osteocyte

Skeletal Tissueg) unlike growth in length & width this

process occurs in specific areas and is coordinated so as not to alter bone shape

2) Calcium homeostasisa) bone contains almost 99% of the body’s

Ca++ storesb) blood levels are very closely regulated

i) if they rise too high = cardiac arrestii) if they drop too low = respiratory arrest

Skeletal Tissuec) nerve action, muscle contraction,

enzymes, and clotting all require specific Ca++ amounts to function properly

d) bone acts to buffer blood Ca++ levelsi) if levels are too high, Ca++ is taken

up (new bone tissue is generated)ii) if levels are too low, Ca++ is

released (current bone tissue is broken down)

Skeletal Tissuee) regulated by hormones

i) parathyroid hormone – from parathyroid gland(a) increases osteoclast activity

ii) calcitonin – from thyroid gland(a) increases osteoblast activity

Skeletal TissueE) Bone repair (of fractures or breaks)

1) Fractures are treated by reduction – realignment of broken bone endsa) Closed reduction – bone ends coaxed back into place by the physician’s hands

b) Open reduction – involves surgery; bone ends are secured together with pins or wires

Skeletal Tissue2) Process of bone repair

a) Hematoma formationi) Blood vessels in bone tear and hemorrhage occurs resulting in a mass of clotted blood

b) Fibrocartilage callus formationi) Capillaries grow into the hematoma and phagocytic cells invade the area

Skeletal Tissueii) Fibroblasts, chondroblasts, and

osteoblasts migrate to the fractureiii) Fibroblasts secrete collagen fibers

and chondroblasts that secrete a cartilage matrix

iv) Osteoblasts begin forming spongy bone

v) The mass of tissue is referred to as a fibrocartilage callus

Skeletal Tissuec) Bony callus formation

i) Osteoblasts and osteoclasts continue to migrate inward and continue to replace connective tissue with bone tissue

ii) The tissue is now called the bony callus

d) Bone remodeling

Skeletal Tissue3) Fracture types:

a) Simple (closed) – bone breaks cleanly, but does not penetrate the skin

b) Compound (open) – broken ends of bone protrude through the tissue and skin

c) Comminuted – bone breaks into many pieces

d) Compression – bone is crushed (due to porous bone)

Skeletal Tissuee) Depressed – broken bone is pressed

inward (skull)f) Colle’s – distal part of the radius breaksg) Transverse – break occurs across the long

axis of a boneh) Impacted – broken bone ends are forced

into each otheri) Spiral – ragged break as a result of

excessive twisting of the bone

Skeletal Tissuej) Epiphyseal – break occurring along the

epiphyseal platek) Greenstick – bone breaks incompletelyl) Pott’s – malleolus of tibia and/or fibula

break

Skeletal TissueF) Bone Disorders

1) Metastatic calcification – deposition of calcium in tissues that normally don’t store calcium

2) Osteomyelitis – infection of periosteum, medullary cavity and bone

3) Osteoporosis – bone breakdown outpaces bone production

Skeletal Tissue4) Spina bifida – portions of vertebrae of

spinal column fail to form a complete bony arch around the spinal cord

5) Achondroplasia – defective cartilage growth and deficient ability of endochondral bone formation (dwarfism)

6) Acromegaly – delaying of ossification of epiphyseal cartilage (gigantism)

7) Osteotitis – inflammation of bony tissue

Skeletal Tissue8) Osteomalacia – inadequate

mineralization of bone due to insufficient calcium as a result of a vitamin D deficiency (Ricketts)

9) Osteoma – tumor composed of bone tissue

10) Osteotomy – cutting of bone11) Ostectomy – surgical removal of

bone12) Ostalgia – pain in bone