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Bone Development. Human bones grow until about age 25 Osteogenesis : bone formation Ossification : the process of replacing other tissues with bone. Calcification. The process of depositing calcium salts Occurs during bone ossification and in other tissues. Ossification.

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Bone development
Bone Development

  • Human bones grow until about age 25

  • Osteogenesis:

    • bone formation

  • Ossification:

    • the process of replacing other tissues with bone


Calcification
Calcification

  • The process of depositing calcium salts

  • Occurs during bone ossification and in other tissues


Ossification
Ossification

  • The 2 main forms of ossification are:

    • intramembranous ossification

    • endochondral ossification


Intramembranous ossification step 1
Intramembranous Ossification: Step 1

  • Mesenchymal cells aggregate:

    • differentiate into osteoblasts

    • begin ossification at the ossification center

    • develop projections called spicules


Intramembranous ossification step 2
Intramembranous Ossification: Step 2

Figure 6–11 (Step 2)


Intramembranous ossification step 21
Intramembranous Ossification: Step 2

  • Blood vessels grow into the area:

    • to supply the osteoblasts

  • Spicules connect:

    • trapping blood vessels inside bone


Intramembranous ossification step 3
Intramembranous Ossification: Step 3

Figure 6–11 (Step 3)


Intramembranous ossification step 31
Intramembranous Ossification: Step 3

  • Spongy bone develops and is remodeled into:

    • osteons of compact bone

    • periosteum

    • or marrow cavities


Endochondral ossification
Endochondral Ossification

  • Ossifies bones that originate as hyaline cartilage

  • Most bones originate as hyaline cartilage


Endochondral ossification1
Endochondral Ossification

  • Growth and ossification of long bones occurs in 6 steps


Endochondral ossification step 1
Endochondral Ossification: Step 1

  • Chondrocytes in the center of hyaline cartilage:

    • enlarge

    • form struts and calcify

    • die, leaving cavities in cartilage

Figure 6–9 (Step 1)


Endochondral ossification step 2
Endochondral Ossification: Step 2

Figure 6–9 (Step 2)


Endochondral ossification step 21
Endochondral Ossification: Step 2

  • Blood vessels grow around the edges of the cartilage

  • Cells in the perichondrium change to osteoblasts:

    • producing a layer of superficial bone around the shaft which will continue to grow and become compact bone (appositional growth)


Endochondral ossification step 3
Endochondral Ossification: Step 3

  • Blood vessels enter the cartilage:

    • bringing fibroblasts that become osteoblasts

    • spongy bone develops at the primary ossification center

Figure 6–9 (Step 3)


Endochondral ossification step 4
Endochondral Ossification: Step 4

  • Remodeling creates a marrow cavity:

    • bone replaces cartilage at the metaphyses

Figure 6–9 (Step 4)


Endochondral ossification step 5
Endochondral Ossification: Step 5

  • Capillaries and osteoblasts enter the epiphyses:

    • creating secondary ossification centers

Figure 6–9 (Step 5)


Endochondral ossification step 6
Endochondral Ossification: Step 6

Figure 6–9 (Step 6)


Endochondral ossification step 61
Endochondral Ossification: Step 6

  • Epiphyses fill with spongy bone:

    • cartilage within the joint cavity is articulation cartilage

    • cartilage at the metaphysis is epiphyseal cartilage


Endochondral ossification2
Endochondral Ossification

  • Appositional growth:

    • compact bone thickens and strengthens long bone with layers of circumferential lamellae

PLAY

Endochondral Ossification

Figure 6–9 (Step 2)



Epiphyseal lines
Epiphyseal Lines

Figure 6–10


Epiphyseal lines1
Epiphyseal Lines

  • When long bone stops growing, after puberty:

    • epiphyseal cartilage disappears

    • is visible on X-rays as an epiphyseal line


How does the skeletal system remodel and maintain homeostasis, and what are the effects of nutrition, hormones, exercise, and aging on bone?


Remodeling
Remodeling homeostasis, and what are the effects of nutrition, hormones, exercise, and aging on bone?

  • The adult skeleton:

    • maintains itself

    • replaces mineral reserves

  • Remodeling:

    • recycles and renews bone matrix

    • involves osteocytes, osteoblasts, and osteoclasts


Key concepts
KEY CONCEPTS homeostasis, and what are the effects of nutrition, hormones, exercise, and aging on bone?

  • Bone continually remodels, recycles, and replaces

  • Turnover rate varies

  • If deposition is greater than removal, bones get stronger

  • If removal is faster than replacement, bones get weaker


Bone degeneration
Bone Degeneration homeostasis, and what are the effects of nutrition, hormones, exercise, and aging on bone?

  • Bone degenerates quickly

  • Up to 1/3 of bone mass can be lost in a few weeks of inactivity


Key concepts1
KEY CONCEPTS homeostasis, and what are the effects of nutrition, hormones, exercise, and aging on bone?

  • What you don’t use, you lose

  • Stresses applied to bones during physical activity are essential to maintain bone strength and mass


Effects of hormones and nutrition on bone
Effects of Hormones homeostasis, and what are the effects of nutrition, hormones, exercise, and aging on bone?and Nutrition on Bone

  • Normal bone growth and maintenance requires nutritional and hormonal factors


Calcitriol
Calcitriol homeostasis, and what are the effects of nutrition, hormones, exercise, and aging on bone?

  • The hormone calcitriol:

    • is made in the kidneys

    • helps absorb calcium and phosphorus from digestive tract

    • synthesis requires vitamin D3(cholecalciferol)


Vitamins
Vitamins homeostasis, and what are the effects of nutrition, hormones, exercise, and aging on bone?

  • Vitamin C is required for collagen synthesis, and stimulates osteoblast differentiation

  • Vitamin A stimulates osteoblast activity

  • Vitamins K and B12 help synthesize bone proteins


Other hormones
Other Hormones homeostasis, and what are the effects of nutrition, hormones, exercise, and aging on bone?

  • Growth hormone and thyroxine stimulate bone growth

  • Estrogens and androgens stimulate osteoblasts

  • Calcitonin and parathyroid hormone regulate calcium and phosphate levels


Calcium regulation
Calcium Regulation homeostasis, and what are the effects of nutrition, hormones, exercise, and aging on bone?

  • Calcium ions in body fluids:

    • must be closely regulated

  • Homeostasis is maintained:

    • by calcitonin and parathyroid hormone

    • which control storage, absorption, and excretion


Calcitonin and parathyroid hormone control
Calcitonin and Parathyroid Hormone Control homeostasis, and what are the effects of nutrition, hormones, exercise, and aging on bone?

  • Bones:

    • where calcium is stored

  • Digestive tract:

    • where calcium is absorbed

  • Kidneys:

    • where calcium is excreted


Parathyroid hormone pth
Parathyroid Hormone (PTH) homeostasis, and what are the effects of nutrition, hormones, exercise, and aging on bone?

  • Produced by parathyroid glands in neck

  • Increases calcium ion levels by:

    • stimulating osteoclasts

    • increasing intestinal absorption of calcium

    • decreases calcium excretion at kidneys


Calcitonin
Calcitonin homeostasis, and what are the effects of nutrition, hormones, exercise, and aging on bone?

  • Secreted by C cells(parafollicular cells) in thyroid

  • Decreases calcium ion levels by:

    • inhibiting osteoclast activity

    • increasing calcium excretion at kidneys


Fractures
Fractures homeostasis, and what are the effects of nutrition, hormones, exercise, and aging on bone?

  • Fractures:

    • cracks or breaks in bones

    • caused by physical stress

  • Fractures are repaired in 4 steps


Fracture repair step 1
Fracture Repair: Step 1 homeostasis, and what are the effects of nutrition, hormones, exercise, and aging on bone?

Figure 6–15 (Step 1)


Fracture repair step 11
Fracture Repair: Step 1 homeostasis, and what are the effects of nutrition, hormones, exercise, and aging on bone?

  • Bleeding:

    • produces a clot (fracture hematoma)

    • establishes a fibrous network

  • Bone cells in the area die


Fracture repair step 2
Fracture Repair: Step 2 homeostasis, and what are the effects of nutrition, hormones, exercise, and aging on bone?

Figure 6–15 (Step 2)


Fracture repair step 21
Fracture Repair: Step 2 homeostasis, and what are the effects of nutrition, hormones, exercise, and aging on bone?

  • Cells of the endosteum and periosteum:

    • Divide and migrate into fracture zone

  • Calluses stabilize the break:

    • external callus of cartilage and bone surrounds break

    • internal callus develops in marrow cavity


Fracture repair step 3
Fracture Repair: Step 3 homeostasis, and what are the effects of nutrition, hormones, exercise, and aging on bone?

Figure 6–15 (Step 3)


Fracture repair step 31
Fracture Repair: Step 3 homeostasis, and what are the effects of nutrition, hormones, exercise, and aging on bone?

  • Osteoblasts:

    • replace central cartilage of external callus

    • with spongy bone


Fracture repair step 4
Fracture Repair: Step 4 homeostasis, and what are the effects of nutrition, hormones, exercise, and aging on bone?

Figure 6–15 (Step 4)


Fracture repair step 41
Fracture Repair: Step 4 homeostasis, and what are the effects of nutrition, hormones, exercise, and aging on bone?

  • Osteoblasts and osteocytes remodel the fracture for up to a year:

    • reducing bone calluses

PLAY

Steps in the Repair of a Fracture


The major types of fractures

Pott’s fracture homeostasis, and what are the effects of nutrition, hormones, exercise, and aging on bone?

The Major Types of Fractures

Figure 6–16 (1 of 9)


The major types of fractures1
The Major Types of Fractures homeostasis, and what are the effects of nutrition, hormones, exercise, and aging on bone?

  • Comminuted fractures

Figure 6–16 (2 of 9)


The major types of fractures2
The Major Types of Fractures homeostasis, and what are the effects of nutrition, hormones, exercise, and aging on bone?

  • Transverse fractures

Figure 6–16 (3 of 9)


The major types of fractures3
The Major Types of Fractures homeostasis, and what are the effects of nutrition, hormones, exercise, and aging on bone?

  • Spiral fractures

Figure 6–16 (4 of 9)


The major types of fractures4
The Major Types of Fractures homeostasis, and what are the effects of nutrition, hormones, exercise, and aging on bone?

  • Displaced fractures

Figure 6–16 (5 of 9)


The major types of fractures5
The Major Types of Fractures homeostasis, and what are the effects of nutrition, hormones, exercise, and aging on bone?

  • Colles’ fracture

Figure 6–16 (6 of 9)


The major types of fractures6
The Major Types of Fractures homeostasis, and what are the effects of nutrition, hormones, exercise, and aging on bone?

  • Greenstick fracture

Figure 6–16 (7 of 9)


The major types of fractures7
The Major Types of Fractures homeostasis, and what are the effects of nutrition, hormones, exercise, and aging on bone?

  • Epiphyseal fractures

Figure 6–16 (8 of 9)


The major types of fractures8
The Major Types of Fractures homeostasis, and what are the effects of nutrition, hormones, exercise, and aging on bone?

  • Compression fractures

Figure 6–16 (9 of 9)


What are the effects of aging on the skeletal system
What are the effects of aging on the skeletal system? homeostasis, and what are the effects of nutrition, hormones, exercise, and aging on bone?


Age and bones
Age and Bones homeostasis, and what are the effects of nutrition, hormones, exercise, and aging on bone?

  • Bones become thinner and weaker with age

  • Osteopenia begins between ages 30 and 40

  • Women lose 8% of bone mass per decade, men 3%


Effects of bone loss
Effects of Bone Loss homeostasis, and what are the effects of nutrition, hormones, exercise, and aging on bone?

  • The epiphyses, vertebrae, and jaws are most affected:

    • resulting in fragile limbs

    • reduction in height

    • tooth loss


Osteoporosis
Osteoporosis homeostasis, and what are the effects of nutrition, hormones, exercise, and aging on bone?

  • Severe bone loss

  • Affects normal function

  • Over age 45, occurs in:

    • 29% of women

    • 18% of men


Hormones and bone loss
Hormones and Bone Loss homeostasis, and what are the effects of nutrition, hormones, exercise, and aging on bone?

  • Estrogens and androgens help maintain bone mass

  • Bone loss in women accelerates after menopause


Cancer and bone loss
Cancer and Bone Loss homeostasis, and what are the effects of nutrition, hormones, exercise, and aging on bone?

  • Cancerous tissues release osteoclast-activating factor:

    • that stimulates osteoclasts

    • and produces severe osteoporosis


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