1. Bones, Bones, and more Bones!
Types of Bones
Bones, Bones, and more Bones!

2. Objectives I will be able to:
name the four major classifications of bones.
identify the major anatomical areas of a long bone.
describe the microscopic structure of compact bone.

3. Bones of the Human Body The skeleton has ~206 bones
Two basic types of bone tissue
Compact bone tissue
Dense
Spongy bone tissue
Small needle-like pieces of bone
Many open spaces

4. Vocabulary:
compact bone: dense bone tissue composed of osteons that makes up the outer layer of flat, short, and irregular bones; major component of long bones
spongy bone: internal layer of bone tissue in flat, short, and irregular bones, and in the epiphyses of long bones
Spongy bone is full of open sections called pores.
The pores are filled with marrow, nerves, and blood vessels that carry cells and nutrients in and out of the bone. 
Compact bone tissue makes up 80% and spongy bone tissue makes up 20% of all your bone material.

5. Classification of Bones
Long bones
Typically longer than wide
Have a shaft with heads at both ends
Contain mostly compact bone
Examples: Femur, humerus

6. Classification of Bones
Short bones
Generally cube-shape
Contain mostly spongy bone
Examples: carpals, tarsals

7. Classification of Bones
Flat bones
Thin and flattened
Usually curved
Thin layers of compact bone around a layer of spongy bone
Examples: Skull, ribs, sternum

8. Classification of Bones
Irregular bones
Irregular shape
Do not fit into other bone classification categories
Example: Vertebrae and hip

9.  How many bones does the typical human body have?
What is the difference between compact bone and spongy bone?
Give an example of each major bone type?
~206
compact = dense, spongy = full of pores
Answers will vary

10. Classification of Bones on the Basis of Shape

11. Gross Anatomy of a Long Bone
Diaphysis
Shaft
Made of compact bone tissue
Epiphysis
Expanded ends of long bones
Covered with dense bone tissue
Internal structure is spongy bone

12. Structures of a Long Bone
Periosteum
Outside covering of the diaphysis
Fibrous connective tissue membrane
Arteries
Supply bone cells with nutrients

13. Structures of a Long Bone
Articular cartilage
Covers surface of epiphyses
Composed of Hyaline cartilage
Decreases friction at joint surfaces

14. Structures of a Long Bone
Medullary cavity
Cavity in shaft
Contains yellow marrow in adults
Contains red marrow in infants

15.  What is the difference between the diaphysis and the epiphysis?
What do we find in the pores of spongy bone tissue?
What is the function of articular cartilage?
diaphysis is the shaft and made of compact bone, epiphysis is the ends of long bones, covered with dense bone, internal structure is spongy bone
marrow, nerves, and blood vessels
decreases friction at joint surfaces

16. Vocabulary osteocyte: a mature bone cell
ossification: the process of bone formation
osteoblasts: bone-forming cells
osteoclasts: large cells that reabsorb or break down bone matrix

17. Microscopic Anatomy of Bone

18. Microscopic Anatomy of Bone
At the microscopic level, spongy bone tissue is composed of small needle-like pieces of bone called trabeculae and open space (pores).
The pores are filled with marrow, blood vessels, and nerves.
In compact bone tissue, mature bone cells (osteocytes) are found in the bone matrix in cavities called lacunae.

19. Microscopic Anatomy of Bone
The lacunae are arranged in concentric circles (like tree rings) called lamellae with a canal through the center (Haversian canal).
The Haversian canal carries blood vessels and nerves.
Together, the lamellae and Haversian canal form a tube-like structure called an osteon or Haversian System.
Osteons (Haversian System) are made up of rings of calcium salts and collagen fibers and form the bone matrix.

20. Microscopic Anatomy of Bone

21. Microscopic Anatomy of Bone
Haversian canals run lengthwise through bone matrix carrying blood vessels and nerves.
Radiating from the center canals to the lacunae are the canaliculi (-us).
Tiny canals that form a nutrient transport system for the matrix.

22.  How are lacunae arranged? What is bone matrix composed of?
in concentric circles (like tree rings) called lamellae with a canal through the center
rings of calcium salts and collagen fibers

23. Changes in the Human Skeleton
In embryos, the skeleton is primarily hyaline cartilage
During development (in the womb, and after birth), much of this cartilage is replaced by bone
In adulthood, cartilage remains in:
Anterior portion of the nose
Parts of ribs
Joints
Ears

24. Bone Growth: Intramembranous
“Between membranes”
Compact Bone
Spongy Bone
Trabeculae
Cross-section of a trabecula

25. Bone Formation: Intramembranous
Membranous bones are incomplete at birth
Fontanelles: regions of the skull that remain as membranes
“Little fountains”
Bone formation complete by age ~2

26. Bone Growth & Maintenance
Bone maintenance is an ongoing process.
Our bones are not static but living tissue undergoing constant cellular respiration like other cells in our bodies.
Bone matrix undergoes constant rebuilding.

27. Bone Growth & Maintenance
The cells involved in this process include:
Osteocytes
Mature bone cells (bone maintenance)
Osteoblasts
Bone-forming cells
Osteoclasts
Bone-destroying cells
Break down bone matrix for remodeling and release of calcium

28. Bone Growth: Endochondral
Steps in Bone Growth – Embryo to Child:
1) Beginning in the first month of pregnancy, a cartilage model is produced by chondrocytes.
It is surrounded by a membrane, the perichondrium.
Ossification begins at about the 6th week.
2) By the 3rd month, a bone “collar” is produced by osteocytes.
The perichondrium of the diaphysis is now termed periosteum.

29. Bone Growth: Endochondral
3) Chondrocytes hypertrophy (enlarge) and cartilage is calcified.
4) A primary ossification center forms.
Blood vessels and osteoblasts invade the calcified cartilage
Osteoblasts lay down bone matrix
Trabeculae are formed

30. Bone Growth: Endochondral
5) Around the time of birth, secondary ossification centers form in the epiphyses
Bone formation is incomplete at birth
The skeleton is not complete until the late teens (females) or early twenties (males)

31. Bone Growth: Endochondral
Epiphyseal plates allow for growth of long bone during childhood.
New cartilage is continuously formed
Older cartilage becomes ossified
Cartilage is broken down
Bone replaces cartilage

32. Long Bone Formation and Growth

33. Bone Growth: Endochondral
Bones are lengthened until growth stops.
Bones are remodeled continually in response to two factors:
The Ca+ level in the blood and
The pull of muscles and gravity on the skeleton (stress).

34. Bone Growth: Endochondral
Bones change shape (how? genetic instructions)
Bones grow in width (osteoblasts lay down new bone matrix on the outside of the bone and osteoclasts remove bone from the inner face of the diaphysis).
Bone remodeling is done by both osteoblasts and osteoclasts.

35.  How does your pediatrician know when you are done growing?
When do your bones typically stop growing?
When the epiphyseal plates close
the late teens (females) or early twenties (males)

36. Websites Crash Course – Skeletal System Part 2