1. The Skeletal System: Bone Tissue Chapter 6

2. Bone Skeletal system Functions:
Defined: Includes all of the bones of the human body (total of 206), and their associated cartilages and joints.
Functions:
Support – supporting framework for body
Protection – protects vital organs (brain and thoracic cavity)
Movement / levers- allows movement and flexion as well as levers for different movements
Mineral storage- calcium and phosphate
Hematopoiesis- principal site for blood cell formation in red marrow of flat bones (e.g. sacrum, sternum, etc.)
Electrolyte balance of calcium and phosphorus
Acid/Base balance buffers the blood calcium phosphate
Detoxification by absorbing heavy minerals

3. Classification of Bones by Shape

4. Bone Composition Two types of Bone: Compact Bone
Bone is living tissue.
solid network of cells and protein fibers surrounded by deposits of minerals.
Components:
32% Organic materials (collagen & bone cells)
43% Minerals (calcium & phosphorous)
25% Water
Two types of Bone:
Compact Bone
Spongy Bone

5. Long Bone Anatomy (Humerus) Diaphysis Epiphysis Metaphysis
-Epiphyseal growth plate
Articular cartilage
-Perforating fibers
Periosteum- covers bone
Medullary cavity
Endosteum- lines bone

6. Cells in bone: Osteocytes = mature bone cells In lacunae
Connected by canaliculi
Osteoblasts synthesize new matrix
Osteogenesis
Osteoclasts dissolve bone matrix
Osteolysis
Osteoprogenitor cells differentiate into osteoblasts

7. Histology of Bone Tissue

8. Figure 6.3a

9. Matrix of Bone Inorganic mineral salts provide bone’s hardness
Organic collagen fibers provide bone’s flexibility
their tensile strength resists being stretched or torn
Mineralization (calcification) is hardening of tissue when mineral crystals deposit around collagen fibers
Bone is not completely solid since it has small spaces for vessels and red bone marrow
spongy bone has many such spaces
compact bone has very few

10. Bone Matrix If mineral removed, bone is too bendable
If collagen removed, bone is too brittle

11. Histology of Bone Tissue
Compact (Dense) Bone- resists stresses produced by weight & movement
Components of compact bone are arranged into repeating structural units called osteons or Haversian systems
Osteons consist of a central (Haversian) canal with concentrically arranged lamellae, lacunae, osteocytes, canaliculi

12. Compact bone terms
Osteon/Haversian System: structural unit of compact bone. Oriented parallel to shaft and forming a group of hollow tubes through which an artery, vein and nerve pass into and through bone. Lacunae: small cavities (halo’s) containing osteocytes Osteocyte: true bone cell, spider shaped and found in lacunae at the junctions of the lamellae Lamellae: layers of the matrix with each layer of collagen fibers going in opposite direction to the adjacent layer ; maybe Concentric (forming rings like a tree)or Circumferential (encircling the entire bone structure). Canaliculi: Hair like canals that connect each lacunae and in turn connect to the central canal. Remove wastes and bring nutrients into osteocytes Volkman’s canal/Perforating canal: Canals running perpendicular to the Haversian canals, but connecting to them. They bring in the artery, vein and nerves to the bone structure.

13. Histology of Bone Tissue
Osteon
Canaliculi connect lacunae, forming a system of interconnected canals
Providing routes for nutrients and oxygen to reach the osteocytes
The organization of osteons changes in response to the physical demands placed on the skeleton

14. Histology of Bone Tissue
Spongy Bone
Lacks osteons
Lamellae are arranged in a lattice of thin columns called trabeculae
Spaces between the trabeculae make bones lighter
Trabeculae support & protect the red bone marrow
Hematopoiesis (blood cell production) occurs in spongy bone
Found in ends of long bones and inside flat bones such as the hipbones, sternum, sides of skull, and ribs.

16. Blood and Nerve Supply of Bone
Bone is richly supplied with blood
Periosteal arteries accompanied by nerves supply the periosteum and compact bone
Epiphyseal veins carry blood away from long bones
Nerves accompany the blood vessels that supply bones
The periosteum is rich in sensory nerves sensitive to tearing or tension

17. Bone development and growth
Ossification = converting other tissue to bone
Intramembranous Ossification
Endochondral Ossification
Calcification = depositing calcium salts within tissues

18. Bone Formation Bone formation follows one of two patterns
Formation of Bone in an Embryo (during 6th week)
Bone formation follows one of two patterns
Intramembranous ossification
-formation of bone directly from mesenchymal cells.
Flat bones of the skull and mandible are formed in this way
“Soft spots” that help the fetal skull pass through the birth canal later become ossified forming the skull
Endochondral ossification
The replacement of cartilage by bone
Most bones of the body are formed in this way including long bones

19. Intramembranous Bone Formation
Mesenchymal cells become osteoprogenitor cells then osteoblasts.
Osteoblasts surround themselves with matrix to become osteocytes.
Matrix calcifies into trabeculae with spaces holding red bone marrow.
Mesenchyme condenses as periosteum at the bone surface.
Superficial layers of spongy bone are replaced with compact bone.

20. Intramembranous Ossification

21. Bone Formation Bone growth begins long before birth.
10 week fetus
Cartilage bone
of the skull
Intramembranous
ossification
produces the
roofing bones
Primary
centers of the
diaphyses
(skeleton of the
lower limb)
Future
hip bone
Bone Formation
Bone growth begins long before birth.
The basic shape of a long bone, such as an arm bone, is first formed as cartilage

22. Bone Formation 12 week fetus 16 week fetus
Ossification begins to take place up to seven months before birth

23. Bone Formation
Babies are born with 350 bones, many are composed almost entirely of cartilage.
Latter the cartilage cells will be replaced by cells that form the bones. (ossification)
The SOFT SPOT of a babie’s skull will fuse around age , but growth of the skull continues until adulthood.
Long bones develop and grow throughout childhood at the centers of ossification (growth plates)

24. Endochondral Bone Formation (1)
Development of Cartilage model
Mesenchymal cells form a cartilage model of the bone during development
Growth of Cartilage model
in length by chondrocyte cell division and matrix formation
( interstitial growth)
in width by formation of new matrix on the periphery by new chondroblasts from the perichondrium (appositional growth)

25. Endochondral Bone Formation (2)
Development of Primary Ossification Center
nutrient artery penetrates center of cartilage model
osteoblasts deposit bone matrix over calcified cartilage forming spongy bone trabeculae
osteoclasts form medullary cavity

26. Endochondral Bone Formation (3)
Development of Secondary Ossification Center
blood vessels enter the epiphyses around time of birth
spongy bone is formed but no medullary cavity
Formation of Articular Cartilage
cartilage on ends of bone remains as articular cartilage.

27. 1
Development of
cartilage model
primary ossification
center
the medullary
cavity
Growth of 2 3 4
Hyaline
cartilage
Calcified
matrix
Periosteum
(covering
compact bone)
Uncalcified
Medullary
Nutrient
artery and vein
artery
Perichondrium
Proximal
epiphysis
Distal
Diaphysis
Primary
ossification
Secondary
Epiphyseal
artery and
vein
Development of secondary
ossification center 5
Spongy
bone 1
Articular cartilage
Spongy bone
Epiphyseal plate
Secondary
ossification
center
Nutrient
artery and vein
Uncalcified
matrix
Epiphyseal
artery and
vein
Formation of articular cartilage
and epiphyseal plate
Development of secondary
ossification center
Development of
cartilage model
primary ossification
the medullary
cavity
Growth of 2 3 4 5 6
Hyaline
cartilage
Calcified
Periosteum
(covering
compact bone)
Medullary
artery
Perichondrium
Proximal
epiphysis
Distal
Diaphysis
Primary
Spongy
bone 1
Hyaline
cartilage
Calcified
matrix
Periosteum
(covering
compact bone)
Uncalcified
Medullary
cavity
Nutrient
artery and vein
artery
Perichondrium
Proximal
epiphysis
Distal
Diaphysis
Development of
cartilage model
primary ossification
center
the medullary
Growth of
Primary
ossification 2 3 4
Spongy
bone 1
Development of
cartilage model
primary ossification
center
Growth of 2 3
Hyaline
cartilage
Uncalcified
matrix
Calcified
Nutrient
artery
Perichondrium
Proximal
epiphysis
Distal
Diaphysis
Periosteum
Primary
ossification
Spongy
bone 1
Development of
cartilage model
Growth of 2
Hyaline
cartilage
Uncalcified
matrix
Calcified
Perichondrium
Proximal
epiphysis
Distal
Diaphysis 1
Development of
cartilage model
Hyaline
cartilage
Perichondrium
Proximal
epiphysis
Distal
Diaphysis

28. Bone Growth During Infancy, Childhood and Adolescence
Growth in Length (Interstitial Growth)
The growth in length of long bones involves two major events:
1) Growth of cartilage on the epiphyseal plate
2) Replacement of cartilage by bone tissue in the epiphyseal plate

29. Zones of Growth in Epiphyseal Plate
Zone of resting cartilage
anchors growth plate to bone
Zone of proliferating cartilage
rapid cell division (stacked coins)
Zone of hypertrophic cartilage
cells enlarged & remain in columns
Zone of calcified cartilage
thin zone, cells mostly dead since matrix calcified
osteoclasts removing matrix
osteoblasts & capillaries move in to create bone over calcified cartilage
Closure of epiphyseal plate (age 18-25)
– bone stops growing – epiphyseal line

31. Bone Growth During Infancy, Childhood and Adolescence
Growth in Thickness(Appositional Growth)
Bones grow in thickness at the outer surface
Remodeling of Bone
Bone forms before birth and continually renews itself
The ongoing replacement of old bone tissue by new bone tissue
Old bone is continually destroyed and new bone is formed in its place throughout an individual’s life

32. Appositional Bone Growth

33. Factors That Affect Bone Growth and Maintenance
1. Hereditary
2. Nutrition
3. Hormones
4. Exercise or “stress”—for bones, exercise means bearing weight

34. Factors Affecting Bone Growth and Bone Remodeling
Minerals
Large amounts of calcium and phosphorus and smaller amounts of magnesium, fluoride, and manganese are required for bone growth and remodeling
Vitamins
Vitamin A stimulates activity of osteoblasts
Vitamin C is needed for synthesis of collagen
Vitamin D helps build bone by increasing the absorption of calcium from foods in the GI tract into the blood
Vitamins K & B12 are needed for synthesis of bone proteins

35. Factors Affecting Bone Growth and Bone Remodeling
Hormones
During childhood, the hormones most important to bone growth are growth factors (IGFs), produced by the liver
IGFs stimulate osteoblasts, promote cell division at the epiphyseal plate, and enhance protein synthesis
Thyroid hormones also promote bone growth by stimulating osteoblasts
Insulin promotes bone growth by increasing the synthesis of bone proteins
Sex Hormones cause a dramatic effect on bone growth
-Cause of the sudden “growth spurt” that occurs during the teenage year
-promote changes in females, such as widening of the pelvis
-Shut down growth at epiphyseal plates
Parathyroid hormone, calcitriol, and calcitonin are other hormones that can affect bone remodeling

37. Fracture and Repair of Bone
Fracture Types
Open (compound) fracture
The broken ends of the bone protrude through the skin
Closed (simple) fracture
Does not break the skin
Comminuted fracture
The bone is splintered, crushed, or broken into pieces
Greenstick fracture
A partial fracture in which one side of the bone is broken and the other side bends
Impacted fracture
One end of the fractured bone is forcefully driven into another
Pott’s fracture
Fracture of the fibula, with injury of the tibial articulation
Colles’ fracture
A fracture of the radius in which the distal fragment is displaced
Stress fracture
A series of microscopic fissures in bone

38. Fracture and Repair of Bone

39. The Major Types of Fractures
Comminuted fractures

40. Displaced
Colles’
Greenstick
Compression
Figure 6–16 (4 of 9)

41. Fracture and Repair of Bone
Calcium and phosphorus needed to strengthen and harden new bone after a fracture are deposited only gradually and may take several months
The repair of a bone fracture involves the following steps
1) Formation of fracture hematoma
Blood leaks from the torn ends of blood vessels, a clotted mass of blood forms around the site of the fracture
2) Fibrocartilaginous callus formation
Fibroblasts invade the fracture site and produce collagen fibers bridging the broken ends of the bone
3) Bony callus formation
Osteoblasts begin to produce spongy bone trabeculae joining portions of the original bone fragments
4) Bone remodeling
Compact bone replaces spongy bone

42. Spongy bone
Osteoblast
Osteoclast
New compact
bone
Bony callus formation
Bone remodeling
Osteocyte 3 4
Compact bone
Periosteum
Fracture hematoma
Fracture
hematoma
Bone
fragment
Red blood
cell
Blood vessel
Formation of fracture hematoma
Phagocyte
Osteon 1
Fibroblast
Fibrocartilaginous
callus
Collagen fiber
Chondroblast
Cartilage
Fibrocartilaginous callus formation 2
Bony callus
Bony callus
Spongy bone
Osteoblast
Bony callus formation
Osteocyte 3
Compact bone
Periosteum
Fracture hematoma
Fracture
hematoma
Bone
fragment
Red blood
cell
Blood vessel
Formation of fracture hematoma
Phagocyte
Osteon 1
Fibroblast
Fibrocartilaginous
callus
Collagen fiber
Chondroblast
Cartilage
Fibrocartilaginous callus formation 2
Phagocyte
Osteoblast
Fibroblast
Fibrocartilaginous
callus
Collagen fiber
Chondroblast
Cartilage
Fibrocartilaginous callus formation 2
Compact bone
Spongy bone
Periosteum
Fracture hematoma
Fracture
hematoma
Bone
fragment
Osteocyte
Red blood
cell
Blood vessel
Formation of fracture hematoma
Osteon 1
Compact bone
Spongy bone
Periosteum
Fracture hematoma
Fracture
hematoma
Bone
fragment
Osteocyte
Red blood
cell
Blood vessel
Formation of fracture hematoma
Phagocyte
Osteon 1

43. Bone’s Role in Calcium Homeostasis
Bone is the body’s major calcium reservoir
Levels of calcium in the blood are maintained by controlling the rates of calcium resorption from bone into blood and of calcium deposition from blood into bone
Both nerve and muscle cells depend on calcium ions to function properly
Blood clotting also requires Ca2+
Many enzymes require Ca2+ as a cofactor

44. Bone’s Role in Calcium Homeostasis
Actions that help elevate blood Ca2+ level
Parathyroid hormone (PTH) –from parathyroid gland -regulates Ca2+ exchange between blood and bone tissue
PTH increases the number and activity of osteoclasts
PTH acts on the kidneys to decrease loss of Ca2+ in the urine
PTH stimulates formation of Calcitriol, a hormone that promotes absorption of calcium from foods in the gastrointestinal tract
Calcitonin – from thyroid gland
- effects opposite that of PTH

47. Exercise and Bone Tissue
Bone tissue alters its strength in response to changes in mechanical stress
Under stress, bone tissue becomes stronger through deposition of mineral salts and production of collagen fibers by osteoblasts
Unstressed bones diminishes because of the loss of bone minerals and decreased numbers of collagen fibers
The main mechanical stresses on bone are those that result from the pull of skeletal muscles and the pull of gravity
Weight-bearing activities help build and retain bone mass

48. Aging and Bone Tissue
The level of sex hormones diminishes during middle age, especially in women after menopause
A decrease in bone mass occurs
Bone resorption by osteoclasts outpaces bone deposition by osteoblasts
Female bones generally are smaller and less massive than males
Loss of bone mass in old age has a greater adverse effect in females

49. Aging and Bone Tissue
There are two principal effects of aging on bone tissue:
1) Loss of bone mass
Results from the loss of calcium from bone matrix→osteoporosis
2) Brittleness
Results from a decreased rate of protein synthesis
Collagen fibers gives bone its tensile strength
Loss of tensile strength→ very brittle bones & susceptible to fracture

50. Spinal Osteoporosis

51. Compact Bone

52. Spongy Bone (Cancellous)

53. Hyaline Cartilage

54. Adipose Tissue