A Chemical Analysis of Bone
Bones provide:
• Support and movement (limbs, axial
skeleton)
• Protection (skull bones)
• Mineral storage
• Blood cell development (long bone
marrow)
Bone is made up of:
• 35% collagen, ground substance and cells
• 65% calcium
Bone is alive! Bone cell types:
• Osteoblasts: Make and deposit
components of bone extracellular matrix
• Osteoclasts: Degrade and resorb bone for
remodeling
• Osteocytes: “watcher cells” Sit in bone
and monitor its current status
Cartilage and Bone
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Cartilage--function, types, location
Bone Tissue--structure, types
Long Bone Structure and Development
Most common bone problems
– Fractures
– Osteoporosis
What is cartilage?
• Skeletal tissue--maintains certain shape
and form
• Very resilient (bouncy or rubbery), mostly
water
• Grows fast--forms embryonic skeleton
Kinds of cartilage
• Hyaline cartilage--most common in the
body, found in joints
• Elastic cartilage--epiglottis, ear
• Fibrocartilage--intervertebral disk,
menisci of knee
Types of bony tissue
Compact Bone
• Osteon - basic function unit of compact bone
– Central canal - run parallel to surface of bone
• contains blood vessels
– Concentric lamellae - cylinders of bone
– Lacunae - house osteocytes
– Canaliculi - minute passageways that lacunae
• Processes of osteocytes extend into canaliculi
– Perforating or Volkmann’s canal • run perpendicular to long axis.
• contain blood vessels that then branch to enter central canal
STRUCTURE OF COMPACT
BONE
Types of bony tissue
• Compact Bone
– Dense tissue at surface of bones
– Haversian canals
– Osteocytes in lacunae
– Highly vascularized
Types of bony tissue
• Trabecular (“spongy”) bone
– Trabeculae (oriented to give mechanical
strength)
– Interior of long bones, skull bones
– Epiphyses of long bones
– Intramembranous ossification (osteoblasts lay
down bone around blood vessels in
connective tissues of dermis (after 8 weeks of
development)
View of Spongy Bone
Osteoporosis - Affects elderly, especially women
Bone resorption proceeds faster than deposition
Low estrogen levels implicated but estrogen replacement
now considered risky
Flat, Short, Irregular Bones
• Flat Bones
– No diaphyses or
epiphyses
– A sandwich of
cancellous (spongy)
bone between
compact bone
• Cancellous bone
(Spongy bone)
– Composed of bony
plates known as
trabeculae
Bone Shapes
• Long
– Ex. Upper and lower
limbs
• Short
– Ex. Carpals and
tarsals
• Flat
– Ex. Ribs, sternum,
skull, scapulae
• Irregular
– Ex. Vertebrae, facial
Bone Matrix
If mineral removed, bone is too bendable
If collagen removed, bone is too brittle
Bone Fractures
• Treatment is reduction
– Closed--set in place by physical manipulation
from outside body
– Open--surgical placement of pins or screws
• Healing
– Hematoma
– Fibrocartilaginous callus
– Bony calllus
– Remodeling by osteoclasts/osteoblasts
Types of Fractures
Types of Fractures
Comminuted
Compression
Spiral fracture
Epiphyseal fx
Depressed fx
Greenstick fx
Fracture repair in stages
Calcium regulation is negative
feedback mechanism
Calcium Homeostasis
Correction for Hypercalcemia
Factors Affecting Bone Growth
• Size and shape of a bone determined genetically but can be
modified and influenced by nutrition and hormones
• Nutrition
– Lack of calcium, protein and other nutrients during growth and
development can cause bones to be small
– Vitamin D
• Necessary for absorption of calcium from intestines
• Can be eaten or manufactured in the body
• Rickets: lack of vitamin D during childhood
• Osteomalacia: lack of vitamin D during adulthood leading to
softening of bones
– Vitamin C
• Necessary for collagen synthesis by osteoblasts
• Scurvy: due to deficiency of vitamin C
• Lack of vitamin C also causes wounds not to heal, teeth to fall out
Why do bones need to “remodel?”
Bone Growth at an Epiphyseal
Cartilage
Effects of Aging on Skeletal System
• Bone matrix decreases.
– More brittle due to lack of collagen; but also less
hydroxyapetite.
• Bone mass decreases.
– Highest around 30.
– Male bone mass denser due to testosterone and greater
weight.
– African Americans and Hispanics have higher bone
masses than Caucasians and Asians.
– Rate of bone loss increases 10 fold after menopause.
• Cancellous bone lost first, then compact.
• Increased bone fractures
• Bone loss causes deformity, loss of height, pain, stiffness
– Stooped posture
– Loss of teeth