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) Not very complex
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
chondroblasts that secrete a cartilage matrix
iv) Osteoblasts begin 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