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Skeletal Tissue
A. Tissues
1. Cartilage
A) 3 types
1) Hyaline cartilage
a) Articular cartilage – covers ends of bones
b) Costal cartilage – connects the ribs to the sternum
c) Laryngeal cartilage – forms skeleton of the larynx
d) Tracheal & bronchial cartilage – reinforces passageways of respiratory
system
e) Nasal cartilage – supports the external nose
2) Elastic cartilage
a) External ear
b) Epiglottis
3) Fibrocartilage
a) Intervertebral discs
b) Menisci of the knee
c) Pubic symphysis
B) Cartilage Growth
1) Appositional growth
a) New matrix is secreted by chondroblasts onto the edges of the already
existing piece
2) Interstitial growth
a) Chondroblasts within the lacunae secrete new matrix within the already
existing piece
2. Osseous Tissue (Bone)
A) 2 main types
1) Compact – small amount of space between its hard components
2) Spongy – large spaces between its hard components; known as trabeculae
B) Histology of Bone
1) Compact bone
a) Osteon (Haversian system)
i) Concentric lamella – circular layers of compact bone
ii) Haversian canal
iii) Volkmann’s canals – connect adjacent Haversian canals
iv) Lacunae – small gaps at lamellar junctions
v) Osteocytes
vi) Canaliculi – connect the lacunae
b) Interstitial lamella – between osteons
c) Circumferential lamella – around entire outside of bone just under periosteum
2) Spongy bone
a) Less complex than compact bone
i) composed of several layers of lamella & osteocytes
ii) no osteons or blood vessels
C) Bone Development
1) ossification – process of bone tissue formation
a) intramembranous ossification – bone develops from a CT membrane
i) responsible for most skull bones and the clavicle
ii) begins at 8th week of development
b) endochondral ossification – bone develops from a hyaline cartilage model
i) all other bones
ii) begins by the end of the 3rd month
2) bone growth in length
a) occurs at epiphyseal plates (growth plates)
i) chondrocytes in this area are stacked upon one another
ii) cells at epiphyseal end divide rapidly
iii) cells at diaphyseal end enlarge, calcify, and ultimately die
iv) osteoid replaces calcified cells
b) slows with age until epiphysis and diaphysis fuse
i) about 18 for females and 21 for males
3) bone growth in width
a) 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
4) hormonal control of bone growth
a) human growth hormone (hGH) – from pituitary gland
i) controls growth at growth plate
b) thyroid hormones (T3 & T4)
i) regulate the function of hGH
c) testosterone & estrogen (sex hormones)
i) released at puberty
ii) cause growth spurt and skeletal changes associated with puberty
iii) also induce epiphyseal plate closure; now known as epiphyseal line
D) Bone homeostasis
1) Remodeling
a) the ongoing replacement of old/worn bone tissue with new bone tissue
b) 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
d) 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
f) process – similar to appositional growth
i) osteoclasts digest bone tissue by releasing enzymes & acids
ii) osteoblasts produce new bone tissue around themselves until surrounded
iii) once osteoblast is surrounded it becomes an osteocyte
g) unlike growth in length & width this process occurs in specific areas and is
coordinated so as not to alter bone shape
2) Calcium homeostasis
a) bone contains almost 99% of the body’s Ca++ stores
b) blood levels are very closely regulated
i) if they rise too high = cardiac arrest
ii) if they drop too low = respiratory arrest
c) nerve action, muscle contraction, enzymes, and clotting all require specific
Ca++ amounts to function properly
d) bone acts to buffer blood Ca++ levels
i) 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)
e) regulated by hormones
i) parathyroid hormone – from parathyroid gland
(a) increases osteoclast activity
ii) calcitonin – from thyroid gland
(a) increases osteoblast activity
E) Bone repair (of fractures or breaks)
1) Fractures are treated by reduction – realignment of broken bone ends
a) 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
2) Process of bone repair
a) Hematoma formation
i) Blood vessels in bone tear and hemorrhage occurs resulting in a mass of
clotted blood
b) Fibrocartilage callus formation
i) Capillaries grow into the hematoma and phagocytic cells invade the area
ii) Fibroblasts, chondroblasts, and osteoblasts migrate to the fracture
iii) Fibroblasts secrete collagen fibers and/or differentiate into chondroblasts
that secrete a cartilage matrix
iv) Osteoblasts start forming spongy bone
v) The mass of tissue is referred to as a fibrocartilage callus
c) 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
3) 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)
e) Depressed – broken bone is pressed inward (skull)
f) Colle’s – distal part of the radius breaks
g) Transverse – break occurs across the long axis of a bone
h) Impacted – broken bone ends are forced into each other
i) Spiral – ragged break as a result of excessive twisting of the bone
j) Epiphyseal – break occurring along the epiphyseal plate
k) Greenstick – bone breaks incompletely
l) Pott’s – malleolus of tibia and/or fibula break
F) 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
4) 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
8) 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 bone
11) Ostectomy – surgical removal of bone
12) Ostalgia – pain in bone