CHAPTER 6
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Babies have ~ 300 bones
Adults have ~ 206 bones
Humans and Giraffes have the same # of
bones in the neck
Longest bone = femur
Smallest bone = inner ear
1.
2.
3.
4.
5.
Support – structural framework
Protection of internal organs
Blood Cell Production (hematopoiesis)
Movement – skeletal muscle attaches to bone
Mineral Homeostasis (calcium and phosphorous)
2 main divisions of the skeletal system
1. Axial skeleton (head, neck, trunk) – 80 bones
2. Appendicular skeleton (limbs) – 126 bones
USE TEXTBOOK TO
LABEL SKELETONS
IN PACKET
1.
2.
3.
4.
Long bones (bones of arms and legs)
Short bones (bones of wrist and ankle)
Flat bones (skull, ribs, shoulder blades)
Irregular bones (vertebrae)
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Diaphysis: central shaft
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Epiphysis: forms joint with
another bone
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Articular Cartilage (Hyaline)
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Medullary cavity: Hollow
chamber filled with bone marrow
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Periosteum: Covers outside of
bone
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Endosteum: Lines medullary
cavity
Bone Tissue types
1. Compact Bone
▪ Solid
▪ Forms the diaphysis of long bones
▪ Contains yellow marrow
2. Spongy Bone (Cancellous bone)
▪ Resembles a network of bony rods separated by spaces
▪ Fills the epiphysis of long bones
▪ Contains red marrow
▪ Reduces the weight of the skeleton
Coverings
1. Periosteum
▪ Outer surface of bone
▪ Tendons and ligaments fuse to connect muscles and bones
▪ Isolates bone from other bone
▪ Provides route for vessels and nerves
▪ Participates in growth and repair
2. Endostium
▪ Lines marrow cavity
▪ Active only during growth and repair
Cells
1. Osteocytes
▪ mature bone cells
▪ Exchange nutrients and wastes with blood
2. Osteoclasts – (clast = break)
▪ Release enzymes to dissolve bone matrix
3. Osteoblasts (blast = precursor)
▪ Produce new bone
Bone Matrix (secreted by osteocytes)
1. Organic Components (33.3%)
▪ Collagen fibers provide resilience against stretching and
twisting
2. Inorganic components (66.7%)
▪ Mg, F, Na, Ca, P
▪ Hydroxyapatite (calcium phosphate and calcium hydroxide)
▪ Provide hardness and resist compression
Other Features
1. Lacunae
▪ Small pockets which house osteocytes
2. Lamellae = “thin plates”
▪ Sheets of calcified matrix
3. Canaliculi = “small channels”
▪ Connect lacunae with blood vessels
Features specific to compact bone
1. Osteon (Haversion System)
▪ Basic functional unit of compact bone
▪ Osteocytes arranged in concentric layers
2. Central canal
▪ Houses blood vessels
3. Perforating Channels (Volkmann’s Canals)
▪ Link blood vessels of the central canal with the periosteum
and marrow cavity
Organization of OSTEON
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Central (haversion) canals run the length of the
bone
Adjacent Haversion canals are connected via
Volkmann’s canals
Around the central canals are concentric lamellae
Between the lamellae are spaces called lacunae
Lacunae contain osteocytes
Lacunae are connected in all directions via
canaliculi
Features specific to spongy bone
1. trabeculae
▪ Support and protect the cells of red bone marrow, important
for blood formation
COMPACT
BONE
COMPACT
BONE
COMPACT
BONE
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SPONGY BONE
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Ossification = the process of replacing other
tissues with bone
 Skeleton begins as cartilage
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Calcification = the deposition of calcium salts
 Occurs during ossification but can also occur in
other tissues besides bone
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Bone Formation occurs in 3 situations
1. Growth during development
2. Remodeling of bones
3. Repair of fractures
1. Intramembranous ossification – continues to age 2
▪ Flat bones of the skull. Lower jaw and collar bones
▪ Bone develops from fibrous connective tissue
▪ Ossification center = where bone growth begins
▪ Growth is outward from the center
Intramembranous ossification
2. Endochondral ossification – continues to age 25
▪ “inside” “cartilage”
▪ Most bones of the body grow this way
▪ Bone develops from hyaline cartilage
1.
2.
3.
4.
Chondrocytes enlarge, calcify and differentiate into osteoblasts
Osteoblasts form spongy bone at the diaphysis (primary ossification
center)
Growth continues outward in both directions
Secondary ossification center at epiphysis
Endochondral
ossification
Growth During puberty:
 Sex hormones speed up osteoblast activity = rapid
growth
 Epihyseal cartilage completely replaced with bone
 Epiphyseal line = former location of epiphyseal
cartilage; still evident by X-Ray through adulthood
 Appositional Growth continues (increase in diameter)
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Ongoing replacement of old bone with new bone
 Due to the action of osteoclasts (breakdown of bone)
and osteoblasts (building of bone)
1.
Fracture hematoma – blood leaks from broken
blood vessels in bone
2.
Callus Formation – fibroblasts invade the tissue and
produce collagen fibers
3.
Bony Callus Formation – osteoblasts begin to build
spongy bone
4.
Bone remodeling – compact bone replaces spongy
bone
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Calcium = most abundant mineral in the body
Stored in skeleton (bone matrix)
Necessary for muscle and nerve
Tightly regulated
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When blood calcium is low
Parathyroid hormone (PTH)
 increases activity of osteoclasts (bone breakers)
 decreases activity of osteoblasts (bone builders)
 stimulates calcitrol, a hormone that promotes
absorption of calcium from food
 Elevates blood Ca2+
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When blood calcium is high
Calcitonin (CT)
 stimulates osteoblasts (bone builders)
 inhibits osteoclasts (bone breakers)
 promotes bone formation
 decreases blood Ca2+
 Decreases blood Ca2+
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Calcium Regulation
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Minerals, especially calcium and phosphate
Vitamin D3 stimulates absorption of calcium
 Rickets – vitamin D3 deficiency – causes bone to soften
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Vitamin A stimulates osteoblasts
Vitamin C for synthesis of collagen
 Scurvy – vitamin - C deficiency
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Process = bony projection or bump
Ramus = curved portion of a bone (ram’s horn)
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Trochanter = large rough projection
Tuberosity = small rough projection
Tubercle = small rounded projection
Crest = prominent ridge
Line = low ridge
Spine = pointed process
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Head = epiphysis
Neck = connection between epiphysis and
diaphysis
Condyle = smooth, rounded bump that forms
joint with another bone
Trochlea = small, grooved pulley shaped
process
Facet = small flat articular
surface
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Fossa = shallow groove or depression
Sulcus = narrow grove
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Foramen = rounded passageway for blood
vessels and nerves
Canal or Meatus = passageway through bone
Fissure = elongated cleft
Sinus = chamber within
bone usually filled with
air