1. Bone Structure

2. Functions of the Skeletal System
Support
Protection of delicate structures and organs (brain, heart, lungs & spinal cord)
Lever to which muscles attach
Bones move the body
Stores minerals in the form of salts (Calcium & potassium)
Stores fat
Makes blood cells in process of hemopoiesis

3. Cellular and Tissue Structure of Bone
Skeletal system is made of 2 kinds of connective tissue:
Bone
Cartilage

4. Respiratory tube cartilages in neck and thorax
Epiglottis
Larynx
Thyroid
cartilage
Cartilage in
external ear
Cartilages in
nose
Trachea
Cricoid
cartilage
Lung
Articular
Cartilage
of a joint
Cartilage in
Intervertebral disc
Costal
cartilage
Respiratory tube cartilages
in neck and thorax
Pubic
symphysis
Bones of skeleton
Axial skeleton
Meniscus (padlike
cartilage in
knee joint)
Appendicular skeleton
Cartilages
Articular cartilage
of a joint
Hyaline cartilages
Elastic cartilages
Fibrocartilages
Figure 6.1

5. Bone consists of both living tissue and non-living minerals
Osteocytes: mature bone cells that make up 35% of bone
There are two kinds of osteocytes
Osteoblasts: cells that form new bone tissue
Osteoclasts: cells that break down existing bone tissue
Hydroxyapatites: mineral compounds that makeup the other 65% of bone
Ca3(PO4)2 Calcium phosphate
CaCO3 Calcium carbonate

6. Bone Formation
Ossification: process of forming bone in which cartilage is replaced with bone tissue
The embryonic skeleton is composed of hyaline cartilage and is converted to bone after birth
Ossification begins at week 6 or 7 and continues until adulthood 
There are 2 types of ossification:
1. Intramembranous ossification: simpler and more direct type of bone formation
Osteoblasts form on the surface of fibrous connective tissue (like cartilage)
Usually occurs during childhood
Bone tissue forms from the edges of a bone inward
Occurs mostly in bones of axial skeleton

7. 2. Endochondral ossification: type of ossification seen in bones of the appendicular skeleton. How most bones in the body form.
Cartilage cells are replaced by osteoblasts
Process begins in the diaphysis (shaft) of the bone)
Cartilage in the center of the bone breaks down and forms the hollow medullary cavity
Ossification moves from the center outward to the ends of the bones
In both types of ossification spongy bone forms first and compact bone forms from spongy bone

8. Articular cartilage Compact bone Proximal epiphysis Spongy bone
Epiphyseal
line
Periosteum
Compact bone
Medullary
cavity (lined
by endosteum)
(b)
Diaphysis
Distal
epiphysis
(a)
Figure 6.3a-b

9. Normal bone growth depends on the following:
Calcium
Phosphorous
Vitamin A
Vitamin C
Vitamin D
Growth Hormone (controls all bone growth)

10. Two types of bone tissue:
Compact bone: dense, brittle bone tissue that makes up the outer surface of axial bones and the diaphysis of appendicular bones.
Structure of compact bone:
Made of both minerals and living cells arranged in concentric rings.
The following are the parts of compact bone:
A. Volkmann’s canals: channels through the compact bone. Contain blood vessels and nerve endings that extend from the periosteum to the endosteum. Oriented horizontally.
B. Haversian canals: Arranged longitudinally. They contain blood vessels and nerves that run the length of the bone. The parts of the Haversian canal are:
C. lamellae: concentric rings of hard minerals (hydroxyapatites)

11. D. lacunae: spaces between the lamellae that contain the osteocytes (bone cells) E. osteocytes: mature osteoblasts that have lost their ability to divide and form new cells F. canaliculi: minute canals that radiate in all directions from the lacunae. They carry nutrients to and wastes from the osteocytes -Groups of Haversian canals are arranged into Haversian systems. In a Haversian system, the individual Haversian canals are separated by interstitial lamellae.

12. Artery with capillaries Structures in the Vein central canal
Nerve fiber
Lamellae
Collagen
fibers
run in
different
directions
Twisting
force
Figure 6.6

13. Compact
bone
Spongy bone
Central
(Haversian) canal
Perforating
(Volkmann’s) canal
Endosteum lining bony canals
and covering trabeculae
Osteon
(Haversian system)
Circumferential
lamellae
(a)
Perforating (Sharpey’s) fibers
Lamellae
Periosteal blood vessel
Periosteum
Nerve
Vein
Artery
Lamellae
Central
canal
Canaliculi
Lacuna (with
osteocyte)
Osteocyte
in a lacuna
Lacunae
Interstitial lamellae
(b)
(c)
Figure 6.7a-c

14. II. Cancellous (spongy bone)
found in the center of bones of the axial skeleton and at the ends of long bones. Stronger and lighter than compact bone. Structure is different from compact bone.
Structure of cancellous bone:
Contains no Haversian systems. Instead, it is composed of trabeculae an irregular latticework of thin plates of bone.
spaces between the trabeculae are filled with red bone marrow that produces blood cells.
the osteocytes in trabeculae are capable of division

15. Nerve Vein Lamellae Artery Central canal Canaliculus Osteocyte Lacunae
in a lacuna
Lacunae
(b)
Figure 6.3b

16. Bones are classified according to shape and location
Bone Shapes
1. Long bones: have a greater length than width (arms and legs)
One diaphysis
2 epiphyses
slightly curved for strength
2. Short bones: roughly equal length and width (carpals and tarsals)
Made mostly of spongy bone covered by a thin layer of compact bone
3. Flat bones: 2 parallel plates of compact bone enclosing a layer of spongy bone (cranial bones, sternum, scapula)
Thin bones
Provide protection
Provide extensive areas of muscle attachment

17. 5. Wormian bones: small bones found only in the skull
4. Irregular bones: shapes are complex and they very in amounts of compact and spongy bone (vertebrae and facial bones) 
5. Wormian bones: small bones found only in the skull
found between the parietal and occipital bones
6.Sesamoid bones: small bones located in tendons where high degrees of pressure develop (patella)

18. Figure 6.2

19. Bone Location I. Axial Skeleton
a. Bones of the skull, vertebral column and pelvis.
b. Skull bones are classified as
i. Cranial: bones that enclose the brain and organs of hearing and sight. There are 8 cranial bones
1. cranial bones are held together by sutures: immovable joints. There are 4 sutures in the skull
a. coronal suture: located between the frontal bone and parietal bones
b. saggital suture: located between the 2 parietal bones
c. lambdoidal suture: located between the 2 parietal bones and the occipital bone
d. squamosal suture: located between the 2 parietal bones and the temporal bone

20. 2. Fontanel: membrane filled spaces between the cranial bones at birth
2. Fontanel: membrane filled spaces between the cranial bones at birth. A baby’s “soft spots”.
a. Bone formation is incomplete at fontanels
b. Allow the skull to compress as it passes through the birth canal
c. There are 6 fontanels
1. Anterior: Becomes the coronal suture. Closes mo
2. Posterior: Becomes lambdoidal suture. Closes 2 mos
3. Anterolateral (2): Where frontal, parietal, temporal and sphenoid bones meet. Closes 3 mos
4. Posterolateral (2): Where parietal, occipital and temporal bones meet. Closes 12 mos

22. ii. Facial: make up the face There are 14 facial bones
Vertebra: Contains 26 vertebra that protect the spinal cord and support the head
i. attachment points for muscle
ii. protect spinal nerves
iii. there are 4 curves of the spinal column
cervical (neck)
thoracic (chest)
lumbar (lower back)
sacral (above tailbone)
iv. There are three types of vertebra
cervical (7)
thoracic (12)
lumbar (5)

23. Bone Fractures Partial: incomplete break across a bone
A fracture is defined as any damage to the skeletal system. A bone does not have to be broken to be fractured.
Types of Fractures
Partial: incomplete break across a bone
Complete: bone is broken into 2 pieces
Simple: broken bone does not break the skin above the break
Compound: broken end of a bone protrudes from the skin
Comminuted: bone splinters at point of impact. Small fragments of bone exist between the two ends of the bone. Commonly referred to as “shattered”.

24. Greenstick: Ragged break to a bone that is not fully ossified
Greenstick: Ragged break to a bone that is not fully ossified. Seem most frequently in children. Caused because the bone is flexible and not rigid
Spiral: Bone is twisted until it breaks
Transverse: break is perpendicular to the long axis of the bone
Impacted: one end of a bone is driven into the other end
Displaced: anatomical alignment of the bone is not preserved
Nondisplaced: anatomical alignment of the bone is preserved
Pott’s: fibula is broken at the distal end (lateral malloelus). Michael Vick’s ankle injury.
Colles’: radius is broken at the distal end. Radius is displaced posteriorly

25. Fracture Repair
Some bones can require up to 6 months to heal (femur) because
Ca2+ is deposited gradually
Bone cells reproduce slowly
Blood supply to a bone decreases when it is broken

26. Steps of fracture repair:
1. Formation of a fracture hematoma: blood clot forms at the site of the fracture
begins to form 6-8 hrs after injury
2. Callus formation. New bone tissue (spongy bone) begins to form at the site of the break
forms a bridge between the two edges of the break
callus originates from cells in the periosteum and endosteum
begins 48 hrs after injury
3. Remodeling. Dead bone tissue (a result of the injury) are broken down by osteoclasts
compact bone replaces spongy bone at the point of injury
All new bone tissue is formed by osteoblasts
Longest stage