Podcast
Questions and Answers
Most bones are born through ______ ossification.
Most bones are born through ______ ossification.
endochondral
The original support structure for endochondral ossification is a ______ cartilage model.
The original support structure for endochondral ossification is a ______ cartilage model.
hyaline
The process begins with chondrocytes near the center of the shaft becoming ______.
The process begins with chondrocytes near the center of the shaft becoming ______.
enlarged
As blood vessels penetrate the cartilage, ______ starts producing spongy bone at the primary ossification center.
As blood vessels penetrate the cartilage, ______ starts producing spongy bone at the primary ossification center.
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Capillaries and osteoblasts migrate into the ______ to create secondary ossification centers.
Capillaries and osteoblasts migrate into the ______ to create secondary ossification centers.
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________ hormone promotes osteoblast activity from the pituitary gland at the epiphyseal layers.
________ hormone promotes osteoblast activity from the pituitary gland at the epiphyseal layers.
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________ stimulates cell metabolism and promotes osteoblast activity at the epiphyseal layer.
________ stimulates cell metabolism and promotes osteoblast activity at the epiphyseal layer.
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Calcitriol, produced by the kidneys, is derived from vitamin ______.
Calcitriol, produced by the kidneys, is derived from vitamin ______.
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An articulate cartilage remains exposed to the joint cavity; over time it will be reduced to a thin ______.
An articulate cartilage remains exposed to the joint cavity; over time it will be reduced to a thin ______.
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Calcium and phosphate salts are needed to prevent ______ in children and osteomalacia in adults.
Calcium and phosphate salts are needed to prevent ______ in children and osteomalacia in adults.
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At each metaphysis, an epiphyseal cartilage separates the epiphysis from the ______.
At each metaphysis, an epiphyseal cartilage separates the epiphysis from the ______.
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Vitamin ______ is required for collagen synthesis and stimulates osteoblast differentiation.
Vitamin ______ is required for collagen synthesis and stimulates osteoblast differentiation.
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Postnatal growth of bones involves chondrocytes in the epiphyseal plate continuing to divide and grow, adding length to the ______.
Postnatal growth of bones involves chondrocytes in the epiphyseal plate continuing to divide and grow, adding length to the ______.
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Bone develops from hyaline cartilage, which becomes fully ______ after birth.
Bone develops from hyaline cartilage, which becomes fully ______ after birth.
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Bone growth is under ______ control during development.
Bone growth is under ______ control during development.
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Chondrocytes in the primary ossification site enlarge and stop secreting collagen and other ______.
Chondrocytes in the primary ossification site enlarge and stop secreting collagen and other ______.
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Lateral bone growth is achieved by osteoblasts in the ______ laying down new bone.
Lateral bone growth is achieved by osteoblasts in the ______ laying down new bone.
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Blood vessels grow into ______ transforming it into periosteum containing osteoprogenitor cells.
Blood vessels grow into ______ transforming it into periosteum containing osteoprogenitor cells.
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Mature chondrocytes can not divide and die leaving ______.
Mature chondrocytes can not divide and die leaving ______.
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Osteoblasts in ossification sites produce osteoid and turn into ______ as mineral deposits surround and harden around them.
Osteoblasts in ossification sites produce osteoid and turn into ______ as mineral deposits surround and harden around them.
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Ridges in periosteum create a groove for ______ blood vessel.
Ridges in periosteum create a groove for ______ blood vessel.
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Osteoblasts in endosteum build new concentric ______ inward toward the center of the tunnel.
Osteoblasts in endosteum build new concentric ______ inward toward the center of the tunnel.
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Bone grows outwards as osteoblasts in periosteum build new circumferential ______.
Bone grows outwards as osteoblasts in periosteum build new circumferential ______.
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Osteoblasts lay down bone while ______ break down bone on the inside of the medullary cavity.
Osteoblasts lay down bone while ______ break down bone on the inside of the medullary cavity.
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At puberty, the cartilage in the epiphyseal plate is replaced with ______.
At puberty, the cartilage in the epiphyseal plate is replaced with ______.
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Bone remodeling involves resorption of old bone and deposition of new bone where it is ______.
Bone remodeling involves resorption of old bone and deposition of new bone where it is ______.
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Remodeling occurs in response to bone growth, blood ______ levels, and mechanical stress on the bone.
Remodeling occurs in response to bone growth, blood ______ levels, and mechanical stress on the bone.
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Study Notes
Endochondral Ossification
- Most bones are formed through endochondral ossification.
- Hyaline cartilage serves as the initial support structure.
- Osteoblasts replace dead chondrocytes (cartilage cells).
Steps of Endochondral Ossification
- Step 1: Chondrocytes in the center of the shaft enlarge, the matrix calcifies, and chondrocytes die, leaving cavities.
- Step 2: Blood vessels grow around the cartilage, and the perichondrium (cartilage covering) transforms into periosteum, forming a bone collar.
- Step 3: Blood vessels penetrate the cartilage, and osteoblasts lay down spongy bone at the primary ossification center.
- Step 4: Bone remodeling occurs, creating a marrow cavity. Osteoblasts continue adding bone at the ends of the cavity.
- Step 5: Capillaries and osteoblasts migrate into the epiphyses, creating secondary ossification centers.
- Step 6: Spongy bone fills the epiphyses, with articular cartilage remaining at the joint cavity, eventually thinning.
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Postnatal growth of bones:
- Chondrocytes in the epiphyseal plate divide and grow, lengthening the bone.
- Osteoblasts replace cartilage with bone.
- Bone growth is under hormonal control.
Appositional Growth
- Appositional growth refers to the increase in width or diameter of a bone.
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How it works:
- Ridges in the periosteum create a groove for a blood vessel.
- The ridges fuse, forming a tunnel lined by endosteum.
- Osteoblasts within the endosteum build new concentric lamellae inward.
- New circumferential lamellae are deposited by osteoblasts in the periosteum, leading to outward bone growth.
- The medullary cavity enlarges with increased diameter.
Bone Remodeling
- Bone remodeling occurs throughout life and involves the resorption of old bone and the deposition of new bone.
- Remodeling is influenced by:
- Bone growth
- Blood calcium levels
- Mechanical stress on the bone
Hormonal and Nutritional Requirements For Bone Growth
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Hormonal:
- Growth Hormone: From the pituitary gland, promotes osteoblast activity.
- Thyroid Hormone: Thyroxine, stimulates cell metabolism and promotes osteoblast activity.
- Calcitriol: Produced by kidneys from Vitamin D3, allows calcium and phosphate absorption from the digestive tract.
- Sex Hormones: Estrogen and testosterone, promote growth and accelerate osteoblast activity.
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Nutritional:
- Calcium and phosphate salts: 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: Needed for protein synthesis, particularly for collagen.
Regulation of Bone Remodeling (Hormonal)
- Parathyroid Hormone (PTH): Released from the parathyroid glands in response to low blood calcium levels, stimulates osteoclast activity, increasing calcium absorption from the intestines and decreasing calcium excretion by the kidneys.
- Calcitonin: Released from the thyroid gland in response to high blood calcium levels, inhibits osteoclast activity and increases renal excretion of calcium.
- Both hormones work together to maintain calcium homeostasis.
Bone Remodeling: Response to Mechanical Stress
- Wolff's Law: Bones remodel in response to the forces placed on them.
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How it Works:
- Stress generates electrical currents within bones.
- Osteocytes are mechanosensors and secrete chemicals, influencing osteoblast and osteoclast activity, leading to bone thickening and increased density.
- Net Effect of Wolff's Law: Stressed bones become stronger, while unstressed bones become weaker.
Repair of Fractures
- Fractures are treated by realignment of the broken bone pieces (reduction) and immobilization.
- Open (compound) fracture: The broken bone protrudes through the skin.
Blood Supply to Bone
- The periosteum, endosteum, and bone tissue are richly supplied with blood vessels.
Nerve Supply
- The periosteum, endosteum, and bone tissue have a rich network of sensory nerve endings.
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Description
Explore the fascinating process of endochondral ossification, the primary method by which most bones are formed. This quiz covers the key steps, including the transformation of hyaline cartilage into bone and the role of osteoblasts. Test your understanding of bone development and the changes that occur throughout this process.
