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Questions and Answers
What is the initial support structure that is replaced during endochondral ossification?
What is the initial support structure that is replaced during endochondral ossification?
Which process occurs immediately after the enlargement of chondrocytes in the initial step of endochondral ossification?
Which process occurs immediately after the enlargement of chondrocytes in the initial step of endochondral ossification?
What is the role of osteoclasts during the endochondral ossification process?
What is the role of osteoclasts during the endochondral ossification process?
During which step of endochondral ossification do capillaries and osteoblasts migrate into the epiphyses?
During which step of endochondral ossification do capillaries and osteoblasts migrate into the epiphyses?
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What happens to the cartilage as it enlarges during the ossification process?
What happens to the cartilage as it enlarges during the ossification process?
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What occurs at the epiphyseal plate during postnatal bone growth?
What occurs at the epiphyseal plate during postnatal bone growth?
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Which cell type is primarily responsible for replacing cartilage with bone during growth?
Which cell type is primarily responsible for replacing cartilage with bone during growth?
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What is the primary role of alkaline phosphatase in bone development?
What is the primary role of alkaline phosphatase in bone development?
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What initiates lateral bone growth in mature bones?
What initiates lateral bone growth in mature bones?
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Which event occurs first during the development of the cartilage model?
Which event occurs first during the development of the cartilage model?
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What is the role of osteoprogenitor cells in bone formation?
What is the role of osteoprogenitor cells in bone formation?
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During appositional growth of bone, how is a new osteon formed?
During appositional growth of bone, how is a new osteon formed?
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What happens to mature chondrocytes during the process of bone ossification?
What happens to mature chondrocytes during the process of bone ossification?
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What primarily causes the enlargement of the medullary cavity during appositional growth?
What primarily causes the enlargement of the medullary cavity during appositional growth?
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Which factors influence bone remodeling throughout a person's life?
Which factors influence bone remodeling throughout a person's life?
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Which hormones are primarily responsible for the replacement of cartilage in the epiphyseal plate during puberty?
Which hormones are primarily responsible for the replacement of cartilage in the epiphyseal plate during puberty?
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What occurs when osteoblasts are present in the periosteum during bone growth?
What occurs when osteoblasts are present in the periosteum during bone growth?
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What is the consequence of osteoclast activity within the medullary cavity?
What is the consequence of osteoclast activity within the medullary cavity?
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Why do sharks maintain a skeleton made of cartilage instead of bone?
Why do sharks maintain a skeleton made of cartilage instead of bone?
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What leads to the repeated osteon formation during bone growth?
What leads to the repeated osteon formation during bone growth?
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Study Notes
Endochondral Ossification
- Most bones develop through this process.
- Hyaline cartilage model serves as the initial support structure.
- Osteoblasts replace chondrocytes (dead cartilage cells).
Steps of Endochondral Ossification
- Step 1: Enlarged chondrocytes near the center of the shaft die, leaving cavities in the cartilage.
- Step 2: Blood vessels grow around the cartilage, and the perichondrium cells transform into osteoblasts.
- Step 3: Blood vessels penetrate the cartilage, and osteoblasts begin producing spongy bone at the primary ossification center.
- Step 4: Remodeling occurs, creating a marrow cavity. The shaft bone thickens, and growth increases length and diameter.
- Step 5: Capillaries and osteoblasts migrate into epiphyses, creating secondary ossification centers.
- Step 6: Epiphyses are filled with spongy bone. Articular cartilage remains exposed to the joint cavity, eventually becoming a thin superficial layer. An epiphyseal cartilage separates the epiphysis from the diaphysis.
Postnatal Growth of Bones
- Growth in length occurs through chondrocyte division and growth within the epiphyseal plate.
- Chondrocytes nearest the diaphysis die, and osteoblasts replace cartilage with bone.
- Bone development from hyaline cartilage involves calcification, chondrocyte deterioration, and replacement with osteoid tissue.
- Growth in length is hormonally-controlled, ending after puberty.
- Lateral growth is achieved by osteoblast activity in the periosteum and osteoclast activity in the medullary cavity.
How Osteons and Central Canals Form During Appositional Growth
- Ridges in the periosteum create grooves for periosteal blood vessels.
- Periosteal ridges fuse, forming an endosteum-lined tunnel.
- Osteoblasts in the endosteum create new concentric lamellae inward toward the tunnel center, forming a new osteon.
- Bone grows outward as osteoblasts build new circumferential lamellae.
Enlargement of Medullary Cavity with Increased Bone Diameter
- Appositional growth increases bone diameter.
- Involves both osteoblast and osteoclast activity.
Growth in Width by Appositional Growth
- Osteoblasts in the periosteum lay down bone.
- Osteoclasts break down bone on the inside of the medullary cavity.
- Bone diameter increases, and the cavity enlarges.
Bone Remodeling
- Occurs throughout life, involving resorption of old bone and deposition of new bone.
- Remodeling is essential for bone growth, blood calcium regulation, and response to mechanical stress.
Wolff's Law
- Bones remodel in response to the forces placed on them.
- Stress generates electrical currents in bone.
- Osteocytes are mechanosensors, secreting chemicals that alter osteoblast and osteoclast activity.
- Stressed bones become stronger, while unstressed bones become weaker.
Repair of Fractures
- Realignment of bone pieces is essential to reduce movement.
- Open (compound) fractures occur when the broken bone penetrates the skin.
Blood Supply to Bone
- Periosteum, endosteum, and bone itself are richly supplied with blood vessels and sensory nerve endings.
Hormonal Requirements for Normal Bone Growth
- Growth Hormone (pituitary gland): Promotes osteoblast activity.
- Thyroid Hormone (thyroxine): Stimulates cell metabolism, promotes osteoblast activity.
- Calcitriol (kidneys): Allows for normal calcium and phosphate absorption from the digestive tract.
- Sex Hormones (estrogen and testosterone): Promote growth and stimulate increased osteoblast activity.
Nutritional Requirements for Bone Growth
- Calcium and Phosphate: Essential for bone health, preventing rickets (children) and osteomalacia (adults).
- Vitamin C: Required for collagen synthesis and osteoblast differentiation.
- Vitamin A: Stimulates osteoblast activity.
- Vitamin K and B12: Required for protein synthesis in bone, particularly collagen.
Regulation of Bone Remodeling
- Parathyroid Hormone (parathyroid glands): Released in response to low blood calcium levels, stimulating osteoclast activity, increasing calcium absorption from the intestine, and decreasing renal calcium excretion.
- Calcitonin (thyroid glands): Released in response to high blood calcium levels, inhibiting osteoclast activity, decreasing calcium absorption, and increasing renal calcium excretion.
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Description
This quiz covers the critical steps of endochondral ossification, the process by which most bones develop. It details the transformation from hyaline cartilage to bone through the action of osteoblasts and the sequence of events leading to the formation of the primary and secondary ossification centers.
