Skeletal Tissue
Chapter 7
Types of Bone Tissue
• Compact bone
– Dense or solid
appearance
• Cancellous or
spongy bone
– Open spaces
filled with
needle-like
bone
structures
Structural Classification of Bones
• Long bones
– typically longer than wide
– Have shaft w/ heads at both
ends
– contains mostly compact
bone
– Ex: femur, humerus, ulna,
radius
• Short bones
– Cube or box-shaped
– Mostly spongy bone
– Ex: carpals & tarsals
• Flat bones
– Thin, flattened
– Usually curved surface
– Thin layer of compact bone
covering spongy bone
– Ex: ribs, skull, sternum,
scapulae
– Bone marrow aspirations
occur here
• Irregular bones
– Various shapes/sizes
– Do not fit into other
categories
– Ex: vertebrae, facial bones
– Sesamoid bones: occur
singularly (ex: patella)
Long Bones – In More Detail
• Diaphysis
– Shaft of the bone
– Hollow, compact bone
• Epiphyses
–
–
–
–
–
Ends of the long bones
Points of muscle attachment
Stability to joints
Spongy bone filled with red marrow
Epiphyseal plate: area between diaphysis and
epihyses (“growth plate”)
Long Bones – In More Detail
• Articular cartilage
– Hyaline cartilage that covers joint surfaces
• Periosteum
– Dense, white fibrous membrane that covers bone
(excepts joint surfaces)
– Tendon fibers interlace with these fibers creating
a firm attachment
• Medullary (marrow) cavity
– Hollow space in diaphysis of long bones
– Filled with yellow marrow (CT rich in fat)
• Endosteum
– Epithelial membrane that lines the medullary cavity
Bone Tissue
• Connective tissue
• Consists of cells, fibers, extracellular
matrix
– Matrix predominates
– Matrix hard and calcified
– High content of collagen fibers
Composition of Bone Matrix
Extracellular bone matrix can be subdivided
into two components:
–
–
Inorganic salts
Organic matrix
–
Hydroxyapatite – specialized chemical
crystals of calcium and phosphate
1. Inorganic salts
•
–
–
Needle-like; found btwn spaces of collagen
fibers; oriented to reduce stress
Deposition of these chemicals = calcification
Mg, Na, sulfate, F are also found in bone
Composition of Bone Matrix
2. Organic matrix
– Collagenous fibers
– Ground substance
• Protein & polysaccharide mixture
• Provides support & adhesion for cellular & fibrous
elements
• Necessary for growth & repair
• Chondroitin sulfate – important component of
ground substance
• Glucosamine and chondroitin sulfate required for
bone & cartilage repair and maintenance
Microscopic Structure of
Compact Bone
• Structural unit of compact bone =
osteon or Haversian system
– Each osteon surrounds a cannal & runs
lengthwise
– Bone cells “cemented” within these units
– Structure permits delivery and removal of
nutrients and wastes
• Structures within each osteon:
– Lamellae, lacunae, canaliculi, Haversian
canal
Osteon structure
• Lamellae: concentric, cylinder-shaped layers
of calcified matrix
• Lacunae (“little lakes”): small spaces filled
with tissue fluid which hold bone cells
• Canaliculi: very small canals connecting lacunae
together
• Haversian canal: extend lengthwise through
the center of an osteon
– contains blood vessels, lymphatic vessels & nerves
• Volkmann’s canal: (not part of osteon)
transverse canals containing nerves and blood
vessels
– Carry blood from exterior surface of bone to
osteons
Microscopic Structure of
Cancellous (spongy) Bone
• No osteons
• Needle-like bony spicules – trabeculae
– Bone cells found within the trabeculae
• Spongy bone usually lies between two layers
of compact bone
– Diploe
– Ex: skull bones
• Bony spicules arranged along lines of stress
– Varies for different types of bones
Types of Bone Cells
1. Osteoblasts – bone-forming cells
– synthesize & secrete a specialized organic matrix =
osteoid; important part of ground substance
– Osteoid serves as the framework for calcium &
phosphate deposits = accumulation of mineralized
bone
2. Osteoclasts – bone-reabsorbing cells
–
–
–
–
Giant multinucleated cells
Large number of mitochondria and lysosomes
Responsible for erosion of bone minerals
Break down bone matrix for remodeling & release
of calcium
3. Osteocytes – mature bone cells
– Mature, nondividing osteoblasts
– Lie within lacunae
Bone Marrow
• Bone marrow = myeloid tissue
– Specialized, soft CT
• Site of blood cell production
• Found within medullary cavities of long
bones & spongy bone
• Red marrow
– In infant and children – red marrow dominates
– RBC production
– In adults - Ribs, bodies of vertebrae, ends of
long bones, pelvis still contain red marrow
– During times of blood loss – yellow  red
Bone Marrow
• During aging red marrow becomes yellow
• Marrow cells become saturated with fat
• Inactive during blood cell production
1.
Functions of Bone
–
Support
Shape, alignment, positioning of body parts
2. Protection
–
Protects organs
–
–
Bones and joints act as levers
Muscles attached to bones produce movement of
joints
3. Movement
4. Mineral storage
–
–
Calcium and phosphorous
Homeostasis of blood calcium levels
–
Blood cell formation
5. Hematopoiesis
Regulation of Blood Calcium Levels
• Bones store approx 98% of body’s
calcium
• Roles of calcium in the body:
– Transmission of nerve signals
– Skeletal & cardiac muscle contractions
• Osteoblasts – remove calcium from
blood
• Osteoclasts – release calcium into blood
Mechanisms of Calcium
Homeostasis
• ***Parathyroid Hormone*** – parathyroid
glands
– Ca levels below homeostatic “set point”:
• Osteoclast activity stimulated
• Calcium absorbed from urine in renal system
• Vitamin D synthesis stimulated  increases absorption of
calcium in intestine
• Calcitonin – thyroid gland
– High blood Ca levels 
• Stimulate osteoblast activity and inhibit osteoclast
activity
– Miacalcin: calcitonin nasal spray; used in
osteoporosis pts
Development of Bone
• Infant – cartilage  replaced by calcified
bone matrix
– Requires osteoblast & osteoclast activity
– Osteogenesis
• Intramembranous ossification: process by
which most flat bones are formed within
fibrous connective tissue membranes
– Ex: skull bones (flat bones) & irregular bones
Endochondral Ossification
(fig 7-8 pg. 198)
•
1.
2.
3.
4.
5.
6.
7.
–
–
Bones formed from cartilage model
Occurs from center to ends
Typical of long bones
Cartilage model
Periosteum  ring or collar of bone
Primary ossification center and entrance of blood
vessels
Medullary cavity; thickening/lengthing of collar
Secondary ossification center in epiphyseal cartilage
Enlargement of secondary centers; bone growth moves
toward diaphysis
Epiphyseal plates close
Bone Growth & Resorption
• Bones grow in diameter
– Osteoclasts enlarge diameter of medullary cavity
– Osteoblasts in the periosteum build new bone from
the outside
– Grow in length (at epiphyseal plates)
• Childhood/adolescence – growth > resorption
• Adulthood – growth = resorption
• > 35-40 yrs – growth < resorption
Bone Remodeling
• Formation of new Haversian systems
(osteons)
– Osteoclasts erode surface of bone 
grooves
– Blood vessels lie in these grooves
– New bone covers these blood vessels
(osteoblast activity)
– Grooves  canals
– New lamallae develops
Bone Fracture Repair
•
•
1.
Fracture = break in the continuity of bone
Vascular damage initiates repair sequence
Vascular damage  hemorrhage  blood
clot (fracture hematoma)
2. Hematoma resorbed  callus
–
Specialized repair tissue that binds the broken
ends of the fracture together
3. Callus replaced by normal bone tissue
–
Proper alignment and immobilization necessary
Questions
1. Name the two types of bone tissue.
2. List the six structural components of a
typical long bone visible to the naked eye.
3. What are the two principal chemical
components of bone matrix?
4. What disease is characterized by loss of
bone mineral density?
5. List and briefly describe the four
structures found within an osteon.
6. Name and briefly describe the three major
bone cell types.
7. What are the 5 functions of bone?
8. Briefly describe the steps in endochondral
ossification.
Clarification
Resorption = destruction
Role of osteoclasts is bone resorption
(destruction); erodes bone tissues
releasing calcium into the blood