1. The Skeletal System

2. The Skeletal System Parts of the skeletal system Bones (skeleton)
Cartilages
Ligaments
Articulations (joints)

3. Functions of Bones Support of the body
Protection of soft organs (like the brain)
Movement due to attached skeletal muscles
Storage of minerals and some fat
Blood cell formation (erythropoiesis)

4. Bones of the Human Body The skeleton has 206 bones
Two basic types of bone tissue
1. Compact bone
● hardened bone
2. Spongy bone
small needle-like pieces of bone
many open spaces

5. Classification of Bones
Long bones
Found on the limbs
Have a shaft (a long part) with knobby structures called heads at the ends
The shaft is compact bone surrounding a hollow center, and the heads are filled spongy bone
Examples: femur, humerus

6. Classification of Bones
Short bones
Found on the hand and foot
Generally cube-shape bones that fit snuggly into one another
Thin layer of compact bone filled with spongy bone
Examples: carpals, tarsals

7. Classification of Bones on the Basis of Shape

8. Classification of Bones
Flat bones
Thin and usually curved
Two thin layers of compact bone with a layer of spongy bone in between
Examples: skull, ribs, sternum

9. Classification of Bones
Irregular bones
Odd shaped
Do not fit into other bone classification categories
Usually have a “hole” and have parts that project out
Example: vertebrae and sacrum

10. Classification of Bones on the Basis of Shape

11. Gross Anatomy of a Long Bone
Diaphysis
AKA: Shaft
Composed of compact bone surrounding a medullary cavity
Epiphysis
Ends of the bone
Composed mostly of spongy bone
epiphysis
diaphysis
epiphysis

12. Structures of a Long Bone
Periosteum
Tough membrane covering the outside of the diaphysis
Present when bone is living
Endosteum
● Membrane that lines the medullary cavity
Arteries
Supply bone cells with nutrients
Figure 5.2c

13. Structures of a Long Bone
Articular cartilage
Covers the external surface of the epiphyses
Made of hyaline cartilage
Decreases friction at all joint surfaces

14. Structures of a Long Bone
Medullary cavity
Cavity in the shaft
Contains yellow marrow (mostly fat) in adults
Contains red marrow (for blood cell formation) in infants
Epiphyseal plate
Figure 5.2a

15. Changes in the Human Skeleton
In embryos, the skeleton is primarily cartilage
During development, much of this cartilage is replaced by bone
In adults, cartilage remains in isolated areas
The nose
Parts of ribs
At point of contact at the articulations

16. Bone Growth
Epiphyseal plates on long bones allow for growth during childhood
New cartilage is continuously formed just inside of the growth plate
The cartilage causes bone to increase in length
Eventually, bone replaces cartilage (ossification)

17. Long Bone Formation and Growth

18. Bone Growth Bones are lengthened until growth stops
After that, bones can only grow in width
Bones can change shape somewhat, usually due to disease

19. Bone Homeostasis
Bone is constantly being broken down and rebuilt. This is known as bone remodeling
Minerals from bone are removed when they are needed by the body.
Minerals are deposited into bones when they are found floating in the bloodstream.

20. Osteoclasts break down and dissolve osseous tissue
Osteoblasts produce new osseous tissue

21. Physiology of Bone Growth
Osteocytes are bone cells that form when an osteoblast becomes embedded within the matrix that it secretes.
These are found within an osteon, the functional unit of compact bone

22. Physiology of Bone Growth
Lamellae are the thin layers of bone that surround lacunae
Lacunae are the indentations or spaces within a bone where osteocytes are located

23. Physiology of Bone Growth
Haversian canals are the tubes within the osteon that contain blood vessels.
These tubes form the osteon, also called the Haversian System.
Bone canaliculi are microscopic canals between the lacunae of compact bone.
Filled with osteocytes and a fluid, filled with particles too large to be transported through the gap junctions

24. Physiology of Bone Growth
Volkmann’s canals are microscopic spaces that connect the Haversian System (osteons).