1. Introduction to the Human Body Chapter 6
Skeletal System
Introduction to the Human Body
Chapter 6

2. Functions Functions Support Protection Assisting in movement
Mineral homeostasis
Hemopoiesis
Triglyceride storage

3. Bone Types Types of Bones Long bones Short bones Flat bones
Irregular bones
Sesamoid bones
Long bones:
Longer than they are wide
Usually have medullary cavity (yellow marrow)
All in the limbs (appendicular only)
Short bones:
Same length in all directions (approximately cuboidal)
Carpals and Tarsals
Flat
Ribs
Skull
Ilium
Irregular
What might be irregular?
Vetebrae
Grab bag
Zygomatic
Mandible
Sesamoid
Bonus bones
Grow within the

4. Macroscopic (long bone)
Diaphysis--
Epiphysis (proximal & distal)
Metaphysis (proximal & distal)
Articular cartilage
Periosteum – dense irregular CT
Medullary cavity
Endosteum

6. Review Name the 4 types of bones. Name the ends of a long bone.
Name the shaft of a long bone.
Name the part between the ends and shaft of a long bone. the 3 types of bone cells.

7. Structure Microscopic 25% water, 25% collagen, 50% mineral salts
Cell types
Osteoblasts
Osteocytes
Osteoclasts
Mineral salts: what minerals?
Cell types: do prefix/suffix analysis
“clast” is new

8. Structure: Compact Bone
Compact bone is made up of round units called osteons
Central (Haversian) canals
Perforating (Volkmann’s) canals
Concentric lamellae
Lacunae
Canaliculi
Intro: There are several kinds of bone. We’re going to focus on two: compact bone and spongy bone
Where found?

9. Compact Bone Compact bone is made up of round units called osteons
Central (Haversian) canals – run longways through bone; center of osteons.
Concentric lamellae- concentric circles
Perforating (Volkmann’s) canals – carry nerves, blood & lymph vessels from the periostium.
Perpendicular to the long axis (aka, perpendicular to the central canal)
Concentric lamellae – rings of matrix
Lacunae – spaces containing osteocytes
Canaliculi – channels connecting lacunae
*Both central and perforating canals have blood vessels
Direct flow of nutrients from vessels through cell processes of osteoblasts and from one cell to the next

11. Structure: Spongy Bone
Made up of trabeculae
Lighter than compact bone.
Supports red marrow in spaces – makes blood
Trabeculae contain lacunae & osteocytes.

12. Figure 6.02b-c Histology of Bone

13. Review How are compact and spongy bone different?
How are osteocytes arranged within compact bone?
How are Volkman’s and Haversian canals similar? How are they different?

14. Ossification Ossification 2 types Intramembranous ossification
Endochondral ossification

15. Ossification Intramembranous Ossification - Flat bones
Development of center of ossification
Center of ossification – site where the bone develops
Mesenchymal cells (stem cells) cluster together and differentiate into osteoblasts
Calcification
The osteoblasts secrete matrix until they are completely surrounded by it.
Secretion stops and the osteoblasts become osteocytes

16. Ossification Formation of trabeculae
As the bone matrix forms it develops into trabeculae that fuse together to form spongy bone
Blood vessels grow into the spaces between the trabeculae and the mesenchyme along the surface
Connective tissue develops into red bone marrow

17. Ossification Development of periosteum
At the periphery of the bone, the mesenchyme condenses and develops into periosteum
The spongy bone eventually grows together into compact bone
Spongy bone remains in the center

18. Intramembranous Ossification

19. Ossification Endochondral Ossification
Replacement of cartilage by bone
Most bones are formed in this way
5 Steps
Development of the cartilage model
Growth of the cartilage model
Development of the primary ossification center – region where bone tissue will replace most of the cartilage

20. Ossification
Development of the secondary ossification center – similar to primary ossification center only spongy bone remains in the center
Formation of articular cartilage and the epiphyseal plate – responsible for the lengthwise growth of long bones

21. Figure 6.03 Endochondral Ossification of the Tibia

22. Endochondral Ossification

23. Review
How are endochondral and intramembranous ossification different?
Describe how are the skeletons of the following different: fetus, young child, adolescent, adult.

24. Homeostasis Homeostasis Minerals (Ca, P, Mg) Vitamins A, C, and D
Growth & maintenance
Bone remodeling replaces old bone with new bone.
4 factors:
Minerals (Ca, P, Mg)
Vitamins A, C, and D
Hormones: human growth hormone (hGH), estrogens, & androgens
Weight-bearing exercise

25. Homeostasis Calcium homeostasis – 99% stored in bone
Parathyroid hormone (PTH) – stimulates osteoclasts, raises blood Ca2+ levels.
Calcitonin (CT) – inhibits osteoclasts, decreases blood Ca2+ levels.

26. Figure 6.04 Negative Feedback System for the Regulation of Blood Calcium

27. Review What are the effects of PTH and Calcitonin on bones?
What 4 factors affect bone growth and maintenance?