Bones
H.Smith
BoneTissue
Question…are bones alive?
Bones are tissues
• Tissues are made up of…
• There are 4 types of bone cells
• Osteo means..
1. Osteoblasts
• Found within bones
• Function: make new bone tissue
2. Osteocytes
• Made by Osteoblasts; mature bone cells
• Surrounded by bone as they are made
• Function: maintain bone as a living tissue
3. Osteoclasts
• Formed in the bone marrow (Related to WBC)
• Function: Dissolve & absorb old bone tissue
4. Hematopoietic
• Found in bone marrow
• Function: produce blood cells
Bone maintenance
• Bone is constantly being broken down &
rebuilt.
• What cells break it down?
• What cells rebuild it?
Bone tissue organization
Compact Bone
• Found on the outside of bones
• Composed of osteons
• Covered by the periosteum: membrane that
acts as attachment points for muscles.
Closer look at Osteons; AKA Haversian
system
• Central tube: nerves & blood supply
• Lamellae: rings made of calcium & collagen
(provide hardness!)
• Lacunae: small spaces between lamellae
– Home of osteocytes
• Canaliculi
– Tiny channels between lacunae, function to allow
nutrients to the osteocytes & wastes to leave
them
Compact bone & osteons
Now You Practice
Lets review:
• 4 types of bone cells:
–
–
–
–
Let’s review
• How is bone maintained?
Let’s review:
• Compact bone is found….
• Compact bone is made up of….
• Compact bone is covered by…
Let’s review:
• 4 parts of an osteon
Inside compact bone is…Spongy bone
Spongy Bone
• Provides strength to weight bearing bones
• Protects the bone marrow (hematopoietic
cells)
Function of Bones
• Support
• Bones provide a hard
framework that
supports the body
• Bones provide support
for internal organs
Function of Bone
• Protection
• Skull protects the brain
• Spinal cord is
surrounded by
vertebrae
• Rib cage protects vital
organs
Function of Bone
• Movement
• Skeletal muscle
attached to bones use
the bones as levers to
move the body
• Arrangement of bones
and joints determine
the movements
possible
Function of Bones
• Mineral Storage
• Bone serves as a
mineral reservoir
• Phosphate and calcium
ions can be released
into the blood steam for
distribution
• Deposition and removal
are ongoing
Function of Bones
• Blood cell formation
• Hematopoiesis occurs
within the marrow
cavities of the long
bones
• The majority of
hematopoiesis occurs in
bones
Ossification
• Cartilage is covered by bone & internal
hyaline cartilage is broken down
Epiphyseal Plates
• Site of bone growth in
length
Bone Growth Through Adolescence
• Controlled by growth hormone, and after
puberty, sex hormones
• Longitudinal growth – occurs at epiphyseal
plates
– Completely ossified by end of adolescence
Bone Remodeling
• Constant osteoblast & osteoclast activity
throughout life
• Causes:
– Ca+2 levels in blood
• If too low, parathyroid hormone activates
osteoclasts
• If higher than needed, calcitonin (a hormone)
activates osteoblasts
– Pull of gravity & muscles
• Activates osteoblasts
• If not active, activates osteoclasts – atrophy
– Partial reason for some bed-ridden individuals
Fractures
• Reduction – realignment of bone ends
– AKA “resetting”
– 4 Stages of healing
Bone Healing
1. Fracture hematoma
– blood from broken
vessels forms a clot.
– 6-8 hours after injury
– swelling and
inflammation
2. Fibrocartilaginous callus
• lasts about 3 weeks
-Chondroblasts create a
cartilage callus around the
fracture
3. Bony callus
• (after 3 weeks and
lasts about 3-4
months)
– osteoblasts replace
cartilage with bone
4. Bone Remodeling
• Osteoclasts
remodel bone
into compact
bone and spongy
bone
– Often no trace
of fracture line on
X-rays.
Cool facts about bone breaks:
• Your body is so good at healing broken bones,
it can be impossible to detect a fracture line
after a full recovery.
• Collarbone is most commonly broken among
children.
• Overall most common break is the wrist
(before 75 years of age) and the hip (after 75
years of age)
Common Types of Fractures
Review
1.
2.
3.
4.
Which cell type forms new bone?
Which cell type destroys bone?
Which cell type is a mature bone cell?
What is the name of the “space” that a mature
bone cell is enclosed within?
5. What kind of tissue are fetal bones made of?
6. What is ossification?
7. What is the site of longitudinal bone growth
called?
8. Which hormones control bone growth through
adolescence?
9. Which hormones control bone remodeling?
What does each one do?
10. If a doctor reduces a fracture, what is she doing?