1. section 1, chapter 7
The Skeletal System

2. The science of bones is called osteology
Functions of bone
Support & protect organs
The brain is protected by the skull and the heart and lungs are protected the ribs & sternum
Movement
Muscles attach to skeleton
Inorganic salt storage
Stores calcium and phosphate
Blood cell production
Red bone marrow forms new blood cells

3. Components of bone
The extracellular matrix of bones is composed of
1. hydroxyapatite – a calcium phosphate salt that provides
the hardness of bones
2. collagen fibers – provides bone with some pliability
The cells associated with bones include:
Osteocytes = cells that maintain bone
Osteoblasts = cells that deposit new bone. Once mature, osteoblasts become osteocytes.
Osteoclasts = cells that dissolve bone. Osteoclasts originate from white blood cells and they secrete an acid that dissolves the inorganic salts of bone.

4. Bones may be classified by their shape.
Long bones = elongated diaphysis
humerus radius ulna
femur tibia fibula
metatarsals metacarpals phalanges
Short Bones = cube-shaped
carpals
tarsals
Flat Bones = plate-like
sternum ribs scapula
parietal and frontal bones

5. Bone Classification continued
Irregular bones = variety of shapes
vertebrae
mandible maxilla
ethmoid bone sphenoid bone
sesamoid (or round) bone = develops within tendons
patella

6. Parts of a long bone Diaphysis = shaft of long bone
Lined with compact bone
Epiphysis = expanded ends of bone
Filled with spongy bone
Proximal epiphysis & distal epiphysis
Sites of articulation (joint)
Epiphyseal plates
Remnants of bone growth
Articular cartilage
Hyaline cartilage
Covers epiphyses

7. Parts of a long bone Medullary Cavity Cavity within diaphysis
Filled with bone marrow, blood vessels and nerves
Endosteum
Membrane that lines medullary cavity
Contains osteoblasts
Periosteum
Tough membrane covering bone
Continuous with tendons and ligaments
Osteoblasts, blood vessels, and nerves

8. Parts of a long bone Compact bone Lines the Diaphysis
Composed of osteons
Spongy bone
Fills the epiphyses
Trabiculae = thin bony plates
Osteocytes lie within trabiculae
Figure 7.3

9. Compact Bone Osteon = Structural & functional unit of compact bone
Lamella = concentric rings of bone
Central Canal = blood vessels and nerves
Lacunae = bony chamber that contains an osteocyte
Canaliculi = canals with cellular processes
Pathway for nutrient and waste diffusion
Figure 7.5 Scanning electron micrograph of a single osteon in compact bone.

10. Osteon continued
Perforating Canal = conveys blood from periosteum towards individual osteons

11. Figure 7.4 Compact bone is composed of osteons cemented together by bone matrix.
Figure 7.4c Canaliculi allow nutrients and waste to diffuse between the central canal and individual osteocytes.

12. Bone Development and Growth
Parts of the skeletal system begin to develop during the first
few weeks of prenatal development
Bone formation = ossification
Bones replace existing connective tissue in one of two ways:
As intramembranous bones
As endchondral bones

13. Intramembranous Bones
Broad, flat bones of the skull
Formed by replacing layers of
connective tissue (mesenchyme)
with bone
Osteoblasts within mesenchyme
deposit bony matrix in all directions
Osteoblasts become osteocytes
once surrounded by bone

14. Endochondral Bones Endochondral Bones
Most of the bones in the skeleton are endochondral
Bone formation begins with a hyaline cartilage model
Cartilage decomposes and is replaced by bone.
Figure 7.6a stained bones of a 14-week fetus showing intramembranous and endochorndal bones.

15. Endochondral Ossification
Hyaline cartilage forms model of future bone
Cartilage degenerates and periosteum surrounds bone
Osteoblasts from periosteum invade the degenerating tissue
Osteoblasts beneath periosteum form compact bone at diaphysis = primary ossification center
Later, Osteoblasts form spongy bone at epiphyses = secondary ossification center

16. Endochondral Ossification continued
Figure 7.8 Major stages of endochondral ossification. (a-d fetal, e child, f adult)

17. Endochondral Ossification
Two areas of endochondral bone retain cartilage after ossification.
Articular cartilage
surrounds the epiphyses for joints
Epiphyseal plates
retain cartilage for bone growth
Articular cartilage

18. Growth at the Epiphyseal Plate
Band of hyaline cartilage that remains
between the two ossification centers
Bone growth continues at epiphyseal
plates until adulthood.
New cartilage is added towards the epiphysis
and cartilage is ossified towards diaphysis
Once the epiphyseal plates ossify the
bones can no longer be lengthened

19. 4 Layers (zones) of growth at epiphyseal Plate
Zone of resting cartilage
Cartilage cells near epiphysis
Do not participate in bone growth
Anchor epiphyseal plate to epiphysis
Zone of proliferating cartilage
Young chondrocytes undergoing mitosis
Adds new cartilage to plate

20. 4 Layers (zones) of growth at epiphyseal Plate
Zone of hypertrophic cartilage
Older cells enlarge and thicken the epiphyseal plate
Osteoblasts invade and calcify the cartilaginous matrix.
Zone of calcified cartilage
Dead cells & calcium matrix
Ossified bone
Osteoclasts dissolve and phagocytize
the matrix
Osteoblasts invade the region and
deposit new bone.
(b)
End of Section 1, Chapter 7
Figure 7.9a

21. Section 2, Chapter 7
Bone Homeostasis

22. Homeostasis of Bone Tissue
Calcium is constantly exchanged between the blood and bone.
Bone resorption = Osteoclasts breakdown bone releasing calcium into the blood. Bone resorption occurs when blood [Ca2+] is low and it’s stimulated by parathyroid hormone (PTH).
Bone deposition = Osteoblasts deposit new bone from calcium in the blood stream. Bone deposition occurs when blood [Ca2+] is high and it’s stimulated by the hormone calcitonin.

23. Nutrients that effect bone homeostasis
Vitamin D – promotes Ca2+ absorption in small intestine
Vitamin D deficiency = softened and deformed bones
Osteomalacia in adults
Rickets in children
Vitamin A – balances bone resorption and deposition
Vitamin A deficiency = retards bone development
Vitamin C – is required for collagen synthesis.
Vitamin C deficiency = results in fragile bones

24. Hormones that affect bone homeostasis
Calcitonin
Secreted from thyroid gland
Promotes bone deposition
Parathyroid Hormone (PTH)
Secreted from parathyroid glands
Promotes bone resorption
Figure 7.13 Hormonal regulation of blood calcium and resorption

25. Hormones that affect bone homeostasis
Growth Hormone (GH)
Secreted from pituitary gland
Promotes bone growth at epiphyseal plates
Pituitary Gigantism
over secretion of GH during childhood
Pituitary Dwarfism
insufficient GH during childhood
Acromegaly
Over secretion of GH as an adult
Occurs after epiphyseal plates have sealed
Enlargement of hands, feet, nose

26. Hormones that affect bone homeostasis
Sex Hormones (testosterone & estrogen)
Promotes long bone growth at puberty
Sex hormones also stimulate ossification at epiphyseal plates.
Effects of Exercise on bone homeostasis
Contracting muscles pull on bones and promotes bone thickening
Figure 7.12 The thickened bone on the left is better able to withstand forces from muscle contractions.

27. Bone Fractures Incomplete Fractures Greenstick fracture Fissured

28. Bone Fractures Complete Fractures Transverse fracture Oblique fracture
Comminuted
fracture
Spiral
fracture

29. Repair of a fracture Step 1. hematoma formation
When a bone breaks blood vessels rupture and the periosteum tears.
The repair of a broken bone occurs in 5 general steps.
Step 1. hematoma formation
Blood soon forms a hematoma (blood clot).
Hematoma in foot

30. Repair of a fracture Step 2. temporary spongy bone
Osteoblasts invade from periosteum and deposit temporary spongy bone.
Step 3. cartilaginous callus
Fibroblasts deposit a mass of fibrocartilage “cartilaginous callus”
&
Phagocytes remove hematoma
Osteoclasts remove bony debris

31. Repair of a fracture Step 4. bony callus Step 5. bone remodeling
Osteoblasts replace the cartilaginous callus with bone, forming a bony callus
Step 5. bone remodeling
Osteoclasts remove excess bone, remodeling the bone the bone close to its original shape.

32. Disorders of Bone
Over time, osteoclasts outnumber osteoblasts, and more bone is resorbed than can be deposited. Bone mass decreases as a result.
Bone loss is rapid in menopausal women due to reduced estrogen
Osteopenia “low bone mass”
Progresses towards osteoporosis
Osteoporosis “porous bone”
Bones develop spaces and canals
Bones are fragile and easily broken
Common in menopausal women
(from the low estrogen levels)

33. End of Chapter 7, Section 2 Ways to delay or prevent osteoporosis:
Exercise daily.
Consume enough calcium and vitamin D every day.
Do not smoke.
End of Chapter 7, Section 2