1. Chapter 5 The Skeletal System

2. The Skeletal System Parts of the skeletal system Two divisions:
Bones (skeleton) – 206 in Human
Joints
Cartilages
Ligaments
Two divisions:
Axial skeleton
Appendicular skeleton

3. Functions of Bones 1) Support of the body 2) Protection of soft organs
3) Movement due to attached skeletal muscles
4) Storage of minerals and fats
5) Blood cell formation

4. Tissues in the Skeletal System
A. Bone
Mainly consists of hard calcium compounds and flexible collagen fibers, and is innervated and vascular
Two basic types of bone tissue
1) Compact bone
Homogeneous
Solid and smooth
Outer part of the bone
2) Spongy bone
Small needle-like pieces of bone
Many open spaces
Inner part of the bone

5. Tissues in the Skeletal System
B. Cartilage
Mainly consists of firm gel with embedded fibers, and is avascular
Three basic types of cartilage
1) Hyaline Cartilage – tough and flexible, found in ribs, joints, and respiratory tract
2) Elastic Cartilage – very flexible, found in out ear and epiglottis
3) Fibrocartilage – very dense, durable, and tough, found in spinal column, knee, and pubic bone

6. Types of Cartilage

7. Types of Cells in Skeletal System
A. Bone
Osteocytes: mature bone cells, maintain bones
Osteoblasts: bone-forming cells, repair bones
Osteoclasts: bone-destroying cells, remodel bones and release calcium into the blood
B. Cartilage
Chondrocytes: mature cartilage cells

8. Microscopic Anatomy of Bone
Osteon (Haversian System) – individual unit of bone
Contain:
canals that run parallel and perpendicular
canals carry blood vessels and nerves within each osteon and between osteons
cavities that contain mature bone cells
Run parallel along the shaft so they are resistant to damage from mechanical stress

9. Microscopic Anatomy of Bone
Figure 5.3

10. Classification of Bones
a. Long bones
Typically longer than wide
Have a shaft with heads at both ends
Contain mostly compact bone, ends and inside the shaft contain spongy bone
Examples: Femur, humerus

11. Structures of a Long Bone
Arteries - supply bone cells with
nutrients
Articular cartilage - covers the
external surface of the ends of the
bone to decrease friction at the joint
Medullary cavity – cavity in the shaft that
contains marrow
yellow marrow (mostly fat) in adults
red marrow (for blood cell formation) in infants
Figure 5.2c

12. Classification of Bones
b. Short bones
Generally cube-shaped
Contain mostly spongy bone
Examples: Carpals, tarsals

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

14. Classification of Bones
d. Irregular bones
Irregular shape
Do not fit into other bone classification categories
Examples: Vertebrae and hip

15. Classification of Bones on the Basis of Shape

16. Bone Growth In embryos, the skeleton is mainly cartilage
During development, much of this cartilage is replaced by bone (some areas of the skeleton don’t stop growing until the age of 25)
Cartilaginous space between shaft and the ends is called “epiphyseal plate” allows for growth during childhood (cartilage gets replaced by bone)
Bones not only change in length, but in width (cavity gets larger)
Cartilage remains in isolated areas – nose, ribs, joints

17. Bone Remodeling
Every year, 18% of protein and minerals in skeleton are replaced
Osteocytes maintain the bone by removing and replacing calcium
Osteoblasts build osteons, and osteoclasts destroy osteons
Mineral turnover enables the bone to adapt to new stresses

18. Bone Remodeling
Maintains homeostasis by regulating calcium concentrations
Parathyroid hormone and calcitrol increase calcium in blood (osteoclasts are active)
Calcitonin decreases calcium in blood (osteoblasts are active)
Large fluctuations in calcium ion concentration can cause problems with nerve and muscle cells:
unresponsiveness if too low
convulsions if too high

19. Bone Formation and Growth

20. Bone Fractures A break in a bone Types of bone fractures
Closed (simple) fracture – break that does not penetrate the skin
Open (compound) fracture – broken bone penetrates through the skin
Bone fractures are treated by reduction and immobilization
Realignment of the bone

21. Common Types of Fractures
Table 5.2

22. Repair of Bone Fractures
Hematoma (blood-filled swelling) is formed
Break is splinted by fibrocartilage to form a callus
Fibrocartilage callus is replaced by a bony callus
Bony callus is remodeled to form a permanent patch

23. Stages in the Healing of a Bone Fracture

24. Bone Markings Surface features of bones
Sites of attachments for muscles, tendons, and ligaments
Passages for nerves and blood vessels
Categories of bone markings
Projections and processes – grow out from the bone surface
Depressions or cavities – indentations

25. The Axial Skeleton Forms the longitudinal part of the body
Divided into three parts
Skull
Vertebral column
Bony thorax

26. The Axial Skeleton

27. The Skull Two sets of bones Bones are joined by sutures
Cranium
Facial bones
Bones are joined by sutures
Only the mandible is attached by a freely movable joint

28. The Skull

29. Bones of the Skull

30. Human Skull, Superior View
Figure 5.8

31. Human Skull, Inferior View

32. The Hyoid Bone
The only bone that does not articulate with another bone
Serves as a moveable base for the tongue

33. The Fetal Skull
The fetal skull is large compared to the infants total body length

34. The Fetal Skull
Fontanelles – fibrous membranes connecting the cranial bones
Allow the brain to grow
Convert to bone within 24 months after birth

35. The Vertebral Column Vertebrae separated by intervertebral discs
The spine has a normal curvature
Each vertebrae is given a name according to its location

36. Structure of a Typical Vertebrae

37. Regional Characteristics of Vertebrae
Figure 5.17a, b

38. Regional Characteristics of Vertebrae

39. The Bony Thorax
Forms a cage to protect major organs

40. The Bony Thorax
Made-up of three parts
Sternum
Ribs
Thoracic vertebrae

41. The Appendicular Skeleton
Limbs (appendages)
Pectoral girdle
Pelvic girdle

42. The Appendicular Skeleton

43. The Pectoral (Shoulder) Girdle
Composed of two bones
Clavicle – collarbone
Scapula – shoulder blade
These bones allow the upper limb to have exceptionally free movement

44. Bones of the Shoulder Girdle

45. Bones of the Shoulder Girdle
Figure 5.20c, d

46. Bones of the Upper Limb The arm is formed by a single bone Humerus
Figure 5.21a, b

47. Bones of the Upper Limb
The forearm has two bones
Ulna
Radius

48. Bones of the Upper Limb The hand Carpals – wrist Metacarpals – palm
Phalanges – fingers
Figure 5.22

49. Bones of the Pelvic Girdle
Hip bones
Composed of three pair of fused bones
Ilium
Ischium
Pubic bone
The total weight of the upper body rests on the pelvis
Protects several organs
Reproductive organs
Urinary bladder
Part of the large intestine

50. The Pelvis
Figure 5.23a

51. The Pelvis

52. Gender Differences of the Pelvis

53. Bones of the Lower Limbs
The thigh has one bone
Femur – thigh bone

54. Bones of the Lower Limbs
The leg has two bones
Tibia
Fibula

55. Bones of the Lower Limbs
The foot
Tarsus – ankle
Metatarsals – sole
Phalanges – toes

56. Joints Articulations of bones Functions of joints
Hold bones together
Allow for mobility
Ways joints are classified
Functionally
Structurally

57. Functional Classification of Joints
Synarthroses – immovable joints
Amphiarthroses – slightly moveable joints
Diarthroses – freely moveable joints

58. Structural Classification of Joints
Fibrous joints
Generally immovable, joined by fibrous tissue
Example: distal end of tibia and fibula
Cartilaginous joints
Immovable or slightly moveable, joined by cartilage
Example: pubic symphysis, intervertebral joints
Synovial joints
Freely moveable, separated by a fluid-filled cavity

59. The Synovial Joint

60. Types of Synovial Joints Based on Shape

61. Types of Synovial Joints Based on Shape

62. Effects of Aging on the Skeletal System
Less calcium is deposited in bones and they lose density and become more porous
Higher incidence of bone fractures
Decrease in height as the intervertebral disks become compressed
Increased incidence of osteoarthritis, or degeneration of joint tissues