1. Skeletal
System

2. Skeletal System Consists of Connective Tissue
Three types of connective tissue:
1. Bone
Hard elements of the skeleton
2. Ligaments:
Dense fibrous connective tissue
Attach bones to other bones
3. Cartilage:
Specialized connective tissue, fibers of collagen and elastic in a gel-like ground substance

3. Bones Are the Hard Elements of the Skeleton
Bones: hard elements of the skeleton
Five important functions
1. Support
2. Protection
3. Movement
4. Blood cell formation
5. Mineral storage
Calcium
Phosphate

4. Bone Contains Living Cells
Bone: hard inorganic matrix of calcium salts
Compact bone: forms shaft and ends, contains marrow space
Yellow bone marrow (mostly fat) in marrow space
Spongy bone: trabeculae form lattice-like support
Spaces may contain red bone marrow
Cells: osteoblast, osteocytes, osteoclasts
Types: long, flat, irregular
Osteons/Haversian system: cellular arrangement
Periosteum: connective tissue covering

6. The Living Bone

7. How strong is a bone?
When it comes to weight, it is actually stronger than steel!
But that doesn’t mean they are indestructible

8. Ligaments Hold Bones Together
Function: attach bone to bone
Made of dense fibrous connective tissue
Provide strength in joints yet enable movement

9. Cartilage Lends Support
Function: support under pressure
Types
Fibrocartilage
Intervertebral disks between vertebrae
Menisci in knee joints
Hyaline
Forms embryonic structure which later form bone
Covers and protects ends of long bones in joints, providing protection, reducing friction
Elastic cartilage
Flexible, outer ear, epiglottis

10. Bone Development Begins in the Embryo
Early fetal development: cartilage model forms
Formed by chondroblasts (cartilage-forming cells)
Later fetal development: osteoblasts replace cartilage with bone
Childhood: primary and secondary ossification sites formed
Adolescence: elongation at growth plates

11. Bone Development Is Regulated by Hormones
Preadolescence
Growth hormone stimulates bone lengthening
Early Adolescence
Estrogen and testosterone stimulate bone lengthening
Late Adolescence
Estrogen and testosterone cause replacement of cartilage growth plates with bone

12. long bones move farther apart and osteoblast activity continues just
Figure 5.2
Adolescence
Cartilage
growth
plate
Childhood
Fetus: At
2–3 months
Fetus: First
2 months
Developing
periosteum
Compact
bone
containing
osteocytes
Blood
vessel
Chondroblasts
form hyaline
cartilage, creating
a rudimentary
model of future
bone.
The periosteum
begins to develop
and cartilage starts
to dissolve. Newly
developing blood vessels
transport osteoblasts
into the area from the
periosteum.
Osteoblasts secrete
osteoid and enzymes,
facilitating the
deposition of hard
hydroxyapatite
crystals.
The growth plates in
long bones move farther
apart and osteoblast
activity continues just
below the periosteum.

13. Osteoblasts convert cartilage to bone at the inner surface
Figure 5.3
Osteoblasts
convert cartilage
to bone at the
inner surface
Chondroblasts
deposit new
cartilage at the
outer surface
Joint
cartilage
Growth
plate

14. Mature Bone Undergoes Remodeling and Repair
Remodeling: changes in shape, size, strength
Dependent on diet, exercise, age
Weight-bearing exercise increases overall bone mass and strength
Bone homeostasis depends upon balance of osteoblast and osteoclast activity
Osteoporosis: loss of bone mass due to prolonged imbalance of osteoblast and osteoclast activity

15. Cells Involved in the Development and Maintenance of Bone
Chondroblasts: cartilage-forming cells
Osteoblasts: young bone-forming cells
Osteocytes: mature bone cells
Osteoclasts: bone-dissolving cells

16. Bone Cells Are Regulated by Hormones
Parathyroid hormone (PTH):
PTH secretion increases when blood levels of Ca++ fall
Stimulates osteoclasts to secrete more bone- dissolving enzymes
Calcitonin:
Calcitonin secretion increases when blood levels of Ca++ are high
Stimulates osteoblasts to add calcium and phosphate to bone

17. Bones Undergo Repair Bone fracture Hematoma forms at site of fracture
Fibroblasts migrate to area to begin repair process
Tough fibrocartilage callus is formed at site of fracture by chondroblasts
Osteoclasts remove dead damaged bone and remnants of hematoma
Osteoblasts deposit new bone in area of fracture
Repair process takes from weeks to months

18. The Skeleton Protects, Supports, and Permits Movement
206 bones
Four types of bones
Long (bones of limbs and fingers)
Short (wrist bones)
Flat (cranial bones, sternum, ribs)
Irregular (coxal bone, verterbrae)

19. Skeleton Organized into Two Groupings
Axial skeleton—midline of body
Skull, sternum, ribs, vertebral column, sternum
Appendicular skeleton—bones of the appendages and their attachment structures
Pectoral girdle, arms, pelvic girdle, legs

20. The Skull: Cranial Bones
Function: protect the brain
Cranial bones:
Frontal bone
Parietal bones
Temporal bones
Sphenoid bone
Ethmoid bone
Nasal bone
Lacrimal bones
Occipital bone

21. The Skull: Facial Bones
Maxilla
Palatine bones
Vomer bone
Zygomatic bones
Sinuses—air spaces within several cranial and facial bones

22. Axial Skeleton: Vertebral Column
Protects spinal cord
Regions:
Cervical (neck): seven vertebrae
Thoracic (chest): 12 vertebrae
Lumbar (small of the back): five vertebrae
Sacral (sacrum): five fused vertebrae
Coccygeal (coccyx): four fused vertebrae
Intervertebral disks: cushion vertebrae; assist in movement and flexibility

23. Ribs and Sternum: Protecting the Chest Cavity
Protect lungs, heart
12 pair
10 pair are attached to vertebrae in back, sternum in front
Lowest two pair are “floating,” attached to vertebrae but NOT attached to sternum
Sternum
Protects heart
Breastbone

24. Appendicular Skeleton: Pectoral Girdle and Upper Limbs
Pectoral girdle: shoulder
Clavicles (collarbones)
Scapulas (shoulder blades)
Arms
Upper arm: humerus
Forearm: radius, ulna
Wrist: carpal bones (8)
Hand (palm): metacarpal bones (5)
Fingers and thumb: phalanges (14)

25. Appendicular Skeleton: Pelvic Girdle and Lower Limbs
Pelvic girdle (hip):
Coxal bones (2), sacrum, pubic symphysis
Legs
Upper leg (thigh): femur
Knee cap: patella
Lower leg (calf): tibia, fibula
Ankle: tarsal bones (7)
Foot: metatarsals (5)
Toes: phalanges (14)

26. Joints (Articulations) Form Connections Between Bones
Classified by degree of movement
Fibrous joint:
Immovable
Example: joints between flat bones of skull
Cartilaginous joint:
Slightly movable, cartilage connection
Example: joints between adjacent vertebrae
Synovial joint:
Freely movable
Bones separated by fluid-filled cavity

27. Synovial Joints Joint capsule: synovial membrane + hyaline cartilage
Synovial membrane secretes synovial fluid as a lubricant
Hyaline cartilage acts as a cushion
Types of synovial joints
Hinge joint
Ball and socket joint
Tendons—join bone to muscle

28. Ligaments, Tendons, and Muscles Strengthen and Stabilize Joints
Ligaments: attach bone to bone in a synovial joint
Example: ACL (anterior cruciate ligament in the knee)
Tendon: attach muscle to bone
Example: Achilles tendon
Both tendons and ligaments are composed of tough connective tissue containing collagen (strong, flexible)
Muscles further stabilize joints

29. What can our bones tell us?
Male
Female

30. Diseases and Disorders of the Skeletal System
Sprains:
Stretched or torn ligaments
Heal slowly (few cells and poor blood supply)
Bursitis and tendinitis:
Inflammation of bursae or tendons
Arthritis: inflammation of joints
Osteoarthritis
Rheumatoid arthritis
Osteoporosis: excessive bone loss

31. A scanning electron micrograph (SEM) of normal bone.
Figure 5.16
A scanning electron micrograph (SEM) of
normal bone.
SEM of a bone showing osteoporosis.