1. Essentials of Human Anatomy The Skeletal System 1
Chapter 5
Dr Fadel Naim
Ass. Prof. Faculty of Medicine
IUG 1

2. Bone Bones are organs Bones are composed of all tissue types.
Their primary component is osseous connective tissue.
The matrix is sturdy and rigid due to calcification (also called mineralization).

3. Function of Bones
Support: form the framework that supports the body and cradles soft organs
Protection: provide a protective case for the brain, spinal cord, and vital organs
Movement: provide levers for muscles
Mineral storage: reservoir for minerals, especially calcium and phosphorus
Blood cell formation: hematopoiesis occurs within the marrow cavities of bones
Energy storage (fat in yellow marrow)

4. Support and Protection
Bones provide structural support and serve as a framework for the entire body.
Bones protect many delicate tissues and organs from injury and trauma.

5. Movement Muscles attach to the bones of the skeleton
contract and pull on bone
functions as a series of levers.

6. Storage of Mineral and Energy Reserves
More than 90% of the body’s reserves of the minerals calcium and phosphate are stored and released by bone.
Calcium: needed for
muscle contraction
blood clotting
nerve impulse transmission.
Phosphate: needed for
ATP utilization
structure of nucleic acids (DNA, RNA)

7. Hematopoiesis Blood Cell Formation
Blood cell production in red bone marrow
located in some spongy bone.
Red bone marrow contains stem cells
form all of the blood cell types.

8. Bone Classification Long Bones Short Bones Flat Bones Irregular Bones
Sesamoid (Round) Bones

9. Classification of Bones: By Shape
Long bones – longer than they are wide (e.g., humerus)

10. Classification of Bones: By Shape
Short bones
Cube-shaped bones of the wrist and ankle
Bones that form within tendons (e.G., Patella)

11. Classification of Bones: By Shape
Flat bones – thin, flattened, and a bit curved (e.g., sternum, and most skull bones)

12. Classification of Bones: By Shape
Irregular bones – bones with complicated shapes (e.g., vertebrae and hip bones)

13. Classification of Bones
Axial skeleton – bones of the skull, vertebral column, and rib cage
Appendicular skeleton – bones of the upper and lower limbs, shoulder, and hip

14. Bone Structure - External
Cartilage protection for joints

15. Bone Structure - External
Epiphyses
Expanded ends of long bones
Exterior is compact bone, and the interior is spongy bone
Joint surface is covered with articular (hyaline) cartilage
location of red bone marrow
Epiphyseal line separates the diaphysis from the epiphyses
Epiphyse

16. Bone Structure - External
Diaphysis
Tubular shaft that forms the axis of long bones
Composed of compact bone that surrounds the medullary cavity
Yellow bone marrow (fat) is contained in the medullary cavity
Diaphysis

17. Bone Structure - Internal
Spongy Bone- red marrow

18. Bone Structure - Internal
Compact bone

19. Compact and Spongy Bone

20. Bone Structure - Internal
Medullary Cavity-yellow marrow

21. Bone Structure - Internal
Epiphiseal Plate
“Growth Plate”

22. Parts of a Long Bone epiphysis diaphysis compact bone spongy bone
distal
proximal
diaphysis
compact bone
spongy bone
articular cartilage
periosteum
endosteum
medullary cavity
trabeculae
marrow
red
yellow

23. Structure of Short, Irregular, and Flat Bones
Thin plates of periosteum-covered compact bone on the outside with endosteum-covered spongy bone on the inside
Have no diaphysis or epiphyses
Contain bone marrow between the trabeculae

24. Bone Membranes Periosteum – double-layered protective membrane
Outer fibrous layer is dense regular connective tissue
Inner osteogenic layer is composed of osteoblasts and osteoclasts
Richly supplied with nerve fibers, blood, and lymphatic vessels, which enter the bone via nutrient foramina
Secured to underlying bone by Sharpey’s fibers
Endosteum – delicate membrane covering internal surfaces of bone

25. Blood and Nerve Supply of Bone
Periosteal arteries
Supply periosteum
Nutrient arteries
Enter through nutrient foramen
Supplies compact bone of diaphysis & red marrow
Metaphyseal & epiphyseal aa
Supply red marrow & bone tissue of epiphyses

26. Bone Markings: Tuberosity – rounded projection
Projections ( Sites of Muscle and Ligament Attachment)
Tuberosity – rounded projection
Crest – narrow, prominent ridge of bone
Trochanter – large, blunt, irregular surface
Line – narrow ridge of bone

27. Bone Markings: Tubercle – small rounded projection
Projections ( Sites of Muscle and Ligament Attachment)
Tubercle – small rounded projection
Epicondyle – raised area above a condyle
Spine – sharp, slender projection
Process – any bony prominence

28. Bone Markings: Head – bony expansion carried on a narrow neck
Projections That Help to Form Joints
Head – bony expansion carried on a narrow neck
Facet – smooth, nearly flat articular surface
Condyle – rounded articular projection
Ramus – armlike bar of bone

29. Bone Markings: Depressions and Openings
Meatus – canal-like passageway
Sinus – cavity within a bone
Fossa – shallow, basinlike depression
Groove – furrow
Fissure – narrow, slitlike opening
Foramen – round or oval opening through a bone

30. The Histologic Types: Compact bone ( cortical)
Spongy bone ( cancellous)
Lamellar bone: regular – mature
Woven bone: irregular – immature – fetus - fracture
Osteoid
Callus: fracture healing

31. Compact Bone:
Haversian system, or osteon – the structural unit of compact bone
Lamella – weight-bearing, column-like matrix tubes composed mainly of collagen
Haversian, or central canal – central channel containing blood vessels and nerves
Volkmann’s canals – channels lying at right angles to the central canal, connecting blood and nerve supply of the periosteum to that of the Haversian canal

32. Compact Bone Osteocytes – mature bone cells
Lacunae – small cavities in bone that contain osteocytes
Canaliculi – hairlike canals that connect lacunae to each other and the central canal

33. Compact Bone:

34. Spongy (cancellous) Bone
Does not contain osteons.
trabeculae surrounding red marrow spaces

35. Cell Types of Bone 4 types of cells in bone tissue
Osteoprogenitor cells:
Undifferentiated cells
Can divide become osteoblasts
Found in inner layer of periosteum and endosteum
Osteoblasts:
Form matrix & collagen fibers but can’t divide
Osteocytes:
Mature cells that no longer secrete matrix
Osteoclasts:
Huge cells from fused monocytes (WBC)
Function in bone resorption at surfaces such as endosteum

36. Bone Development The process of bone tissue formation, which leads to:
Osteogenesis and ossification:
The process of bone tissue formation, which leads to:
The formation of the bony skeleton in embryos
Bone growth until early adulthood
Bone thickness, remodeling, and fracture repair

37. Bone Growth - Ossification
Cartilage template laid down.
Osteoblasts (bone building cells) located in Ossification Centers.

38. Bone Growth - Ossification
Primary Ossification Center in diaphasis.
Secondary Ossification Centers in epiphisis.

39. Bone Growth - Ossification
Grow toward one another, cartilage remains between them.
As long as cartilage remains undamaged, growth can occur.

40. Formation of the Bony Skeleton
Begins at week 8 of embryo development
Intramembranous ossification – bone develops from a fibrous membrane
Endochondral ossification – bone forms by replacing hyaline cartilage

41. Endochondral Ossification
Begins in the second month of development
Uses hyaline cartilage “bones” as models for bone construction
Requires breakdown of hyaline cartilage prior to ossification

42. Stages of Endochondral Ossification
Formation of bone collar
Cavitation of the hyaline cartilage
Invasion of internal cavities by the periosteal bud, and spongy bone formation
Formation of the medullary cavity; appearance of secondary ossification centers in the epiphyses
Ossification of the epiphyses, with hyaline cartilage remaining only in the epiphyseal plates

43. Stages of Endochondral Ossification
Formation of bone collar around hyaline cartilage model. 1 2 3 4
Cavitation of the hyaline cartilage within the cartilage model.
Invasion of internal cavities by the periosteal bud and spongy bone formation. 5
Ossification of the epiphyses; when completed, hyaline cartilage remains only in the epiphyseal plates and articular cartilages
Formation of the medullary cavity as ossification continues; appearance of secondary ossification centers in the epiphyses in preparation for stage 5.
Hyaline cartilage
Primary ossification center
Bone collar
Deteriorating cartilage matrix
Spongy bone formation
Blood vessel of periosteal bud
Secondary ossification center
Epiphyseal blood vessel
Medullary cavity
Epiphyseal plate cartilage
Spongy bone
Articular cartilage

44. Long Bone Growth and Remodeling
Growth in length – cartilage continually grows and is replaced by bone
Remodeling – bone is resorbed and added by appositional growth

45. Bone Growth in Length Epiphyseal plate or cartilage growth plate
Cartilage cells are produced by mitosis on epiphyseal side of plate
Cartilage cells are destroyed and replaced by bone on diaphyseal side of plate
Between ages 18 to 25, epiphyseal plates close
Cartilage cells stop dividing and bone replaces the cartilage (epiphyseal line)
Growth in length stops at age 25

46. Remodeling Occurs all the time. Stresses change, bones adapt.
Osteoclasts remove bone, Osteoblasts build bone, Osteocytes maintain bone
Mineral deposits in Spongy Bone form to hold the stress best.
5-10% bone / year.

47. Osteoclast in lacuna;

48. Control of Remodeling Two control loops regulate bone remodeling
Hormonal mechanism maintains calcium homeostasis in the blood
Mechanical and gravitational forces acting on the skeleton

49. Developmental Aspects of Bones
The embryonic skeleton ossifies in a predictable timetable that allows fetal age to be easily determined from sonograms
At birth, most long bones are well ossified (except for their epiphyses)
By age 25, nearly all bones are completely ossified
In old age, bone resorption predominates

50. Fracture
A disruption in the integrity of a living bone involving injury to:
Bone
Bone marrow
Periosteum
Adjacent soft tissues

51. Types of Fractures green stick fissured comminuted transverse oblique
spiral
Pathologic
Stress
Occult

53. Fracture Healing
Bone is the only tissue in the human body other than liver that heals by regeneration instead of by scarring.
For regeneration to occur the bone must be immobilized to allow uninterrupted formation of new bone.

54. Fracture Healing Primary healing Secondary healing
Non displaced fractures, fractures with compressive fixation across the fracture site
Osteoblasts traverse the fracture site and lay down lamellar bone without forming immature bone when there is direct contact between cortical bone ends
Secondary healing
No compression across fracture site, motion can occur
Fracture callus forms to stop motion, stage of consolidation and remodeling

55. Primary Bone Healing

56. Secondary Bone Healing
Fracture hematoma
(72 hours)
Granulation tissue
(3-14 days)
Callus formation
(7-14 days)
Ossification
(3 weeks- 6 months)
Consolidation
Remodeling
(Up to 1 year)

57. Rickets a generalized metabolic bone disorder
characterized by a failure of or delay in calcification of the cartilaginous growth plate in children whose epiphyses have not yet fused.
it is primarily a disease affecting endochondral calcification
manifests clinically and radiographically with widening and deformation of the metaphyseal regions of long bones

58. THE END