1. The Skeletal System
Chapter 6

2. Skeletal System
Introduction
Functions of the skeleton
Framework of bones
The skeleton through life

3. Composition of the Skeletal System
Cartilage: embryonic forerunner of most bones and covers many joint surfaces
Ligaments: hold bone to bone at joint
Tendons: attach muscles to bone

4. Functions of the Skeleton
Support
Protection
Movement
Storage areas
Minerals
Lipids
Hemopoiesis
Red marrow

5. Histology of Bones Bone = osseous tissue (connective tissue) Cells
Osteoblasts
Osteocytes
Osteoclasts
Matrix
2/3 inorganic
hydroxyapatite crystals
Calcium carbonate
Other minerals
1/3 organic
Mostly collagen fibers

6. Histology of Bones Bone = osseous tissue (connective tissue) Matrix
2/3 inorganic
hydroxyapatite crystals
Calcium carbonate
Other minerals
1/3 organic
Mostly collagen fibers

7. Shape of Bones
Long
Short
Flat
Irregular

8. General Features of Bones
Compact (dense) bone
Dense
White tissue that acts as outer shell
¾ of skeleton
Spongy (cancellous) bone
Loosely organized
Spaces between bone tissue
¼ of skeleton

9. Human Anatomy, 3rd edition
Anatomy of a Long Bone
Diaphysis – shaft
Epiphysis – extremity of bone
Articular cartilage – covers epiphysis
Periosteum – covering around surface of bone
Nutrient Foramina
Blood vessels penetrate into bone
Medullary cavity – marrow cavity in diaphysis
Endosteum – lines medullary cavity
Human Anatomy, 3rd edition
Prentice Hall, © 2001

10. Human Anatomy, 3rd edition
The Periosteum
Two layers
Fibrous layer
Osteogenic layer
Osteoblasts
Human Anatomy, 3rd edition
Prentice Hall, © 2001

11. Human Anatomy, 3rd edition
The Endosteum
Single layer
Osteoclasts
Osteoblasts
Human Anatomy, 3rd edition
Prentice Hall, © 2001

12. General Features of Bones
Pores
Living cells
Channels for blood vessels
Decrease weight of bone
Degree of porosity
Spongy (cancellous) bone
Loosely organized
25% of skeleton
Compact bone
Dense
75% of skeleton
General Features of Bones
Human Anatomy, 3rd edition
Prentice Hall, © 2001

13. Human Anatomy, 3rd edition
Compact Bone
Haversian system (Osteon)
Volkmann’s canals
Haversian (central) canals
Lamellae
Lacunae
Canaliculi
Human Anatomy, 3rd edition
Prentice Hall, © 2001

14. Human Anatomy, 3rd edition
Spongy Bone
Composed of trabeculae
Spaces filled with bone marrow
Penetrated by blood vessels from periosteum
Human Anatomy, 3rd edition
Prentice Hall, © 2001

15. Bone Marrow Soft tissue Two types Location in adults Medullary cavity
Spaces in trabeculae
Large central canals
Two types
Red marrow
Hemopoietic
Yellow Marrow
Replaces red as we age
Turns to mainly fat
Location in adults
Red marrow: skull, vertebrae, sternum, ribs, parts of pelvic girdle, and proximal heads of humerus and femur
Yellow marrow: rest of skeleton

16. Ossification Embryo skeleton 2 types Begins as cartilage & membrane
Bone formation begins about 6 weeks after fertilization
2 types
Intramembranous ossification
Endochondral ossification

17. Ossification
1st stage – embryonic mesenchyme cells migrate into future bone sites
Become chondroblasts or
Become osteoblasts

18. Intramembranous Ossification
Mostly in flat bones
Osteoblasts in the fibrous membrane secrete intercellular substances (matrix)
Matrix becomes mineralized
Formation of spongy bone
Original layer of connective tissue remains as periosteum

19. Intramembranous Bone Development

20. Endochondral Ossification
Occurs within a hyaline cartilage model
Occurs in most bones of the body
Periosteum forms at about week 8
Calcification begins in center of diaphysis
Primary ossification center
Secondary ossification centers at epiphyses
Medullary cavity forms

21. Endochondral Ossification
FG05_07A.JPG
Title: Endochondral Ossification
Notes: Steps in the formation of a long bone.
Keywords: chondrocytes, matrix, epiphysis, diaphysis, osteogenic, marrow, periosteal, spongy bone, metaphysis, ossification

22. Fetus. 10 weeks

23. Fetus, 16 weeks

24. Remaining Cartilage Articular cartilage Epiphyseal plate
Bone grows in length

25. Homeostasis Remodeling Factors affecting bone growth
Different rates in body
Balance between osteoclasts and osteoblasts
Wolff’s law of bone
Factors affecting bone growth
Calcium & phosphorus in diet
Vitamins A, C, & D
Hormones
Growth hormone, thyroxine
Calcitonin
Parathyroid hormone
Sex hormones

26. Human Anatomy, 3rd edition
Disorders
Human Anatomy, 3rd edition
Prentice Hall, © 2001

27. Rickets Defective mineralization in children - insufficient sunlight
- insufficient vitamin D
- dietary deficiency of calcium or
phosphate
- liver or kidney diseases

28. Osteoporosis “Porous bones” - lack of estrogen
- postmenopausal white women
are at greatest risk
- By age 70, average white
woman has lost 30 – 50% of
bone mass

29. Fractures Stress fracture Pathological fracture
Caused by abnormal trauma to bone
Pathological fracture
Due to weakening of the bone caused by disease or osteoporosis
Can be classified according to direction of fracture line or whether or not skin is broken
Closed reduction
Bone fragments in place
No surgery
Open reduction
Surgery
Plates, screws or pins
Traction
Aligns bone fragments
Children not adults
Heals in 8-12 weeks typically

30. Bone Fractures

31. Fracture Repair Hematoma formation
Formation of fibrocartilagenous callus
Formation of bony callus
Remodeling of bony callus