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Questions and Answers
Estrogen and testosterone are sex hormones that promote osteoblast activity and can lead to narrower epiphyseal plates.
Estrogen and testosterone are sex hormones that promote osteoblast activity and can lead to narrower epiphyseal plates.
True
Vitamin A is primarily required for calcium absorption from the digestive tract.
Vitamin A is primarily required for calcium absorption from the digestive tract.
False
The hormone calcitriol is produced by the liver and plays a key role in bone growth by allowing the absorption of Ca++ and PO4 ions.
The hormone calcitriol is produced by the liver and plays a key role in bone growth by allowing the absorption of Ca++ and PO4 ions.
False
Growth hormone stimulates osteoblast activity exclusively at the bone's surface.
Growth hormone stimulates osteoblast activity exclusively at the bone's surface.
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Vitamin C is not involved in osteoblast differentiation and collagen synthesis.
Vitamin C is not involved in osteoblast differentiation and collagen synthesis.
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The diaphysis of a bone contains spongy bone that surrounds the medullary cavity.
The diaphysis of a bone contains spongy bone that surrounds the medullary cavity.
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Trabecular bone is avascular and has a branching structure.
Trabecular bone is avascular and has a branching structure.
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Flat bones, such as the carpal bones, contain a medullary cavity.
Flat bones, such as the carpal bones, contain a medullary cavity.
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Both the epiphysis and metaphysis consist predominantly of compact bone.
Both the epiphysis and metaphysis consist predominantly of compact bone.
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Red bone marrow is indicated by a red color in spongy bone.
Red bone marrow is indicated by a red color in spongy bone.
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Collagen constitutes roughly 30% of the bone's weight.
Collagen constitutes roughly 30% of the bone's weight.
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Spongy bone contains a network of osteons with central canals.
Spongy bone contains a network of osteons with central canals.
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Water makes up approximately 15% of the organic components in bone.
Water makes up approximately 15% of the organic components in bone.
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The organic matrix of bone, known as osteoid, is primarily made up of collagen and sugar compounds.
The organic matrix of bone, known as osteoid, is primarily made up of collagen and sugar compounds.
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Osteocytes are considered immature bone cells.
Osteocytes are considered immature bone cells.
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Trabeculae in spongy bone are oriented to withstand forces from multiple directions.
Trabeculae in spongy bone are oriented to withstand forces from multiple directions.
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Collagen is weaker than steel and lacks flexibility.
Collagen is weaker than steel and lacks flexibility.
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Canaliculi in bone serve to diffuse nutrients necessary for the survival of bone cells.
Canaliculi in bone serve to diffuse nutrients necessary for the survival of bone cells.
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Spongy bone cannot be cut to observe its internal structure.
Spongy bone cannot be cut to observe its internal structure.
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Both osteoblasts and osteoclasts are involved in the maintenance of bone health.
Both osteoblasts and osteoclasts are involved in the maintenance of bone health.
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Study Notes
Blood Supply to the Bone
- The periosteum, endosteum, and the bone itself are richly supplied with sensory nerve endings.
Hormonal and Nutritional Requirements for Normal Bone Growth
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Hormonal Requirements:
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Growth Hormone:
- Secreted by the pituitary gland.
- Promotes osteoblast activity at the epiphyseal layers.
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Thyroid Hormone:
- Thyroxine is secreted at the epiphyseal layer.
- Stimulates cell metabolism and promotes osteoblast activity.
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Calcitriol:
- Produced by the kidneys, derived from vitamin D3.
- Enables normal absorption of calcium and phosphate ions from the digestive tract.
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Sex Hormones:
- Estrogen and testosterone promote growth and accelerate osteoblast bone production.
- Increased sex hormone production during puberty causes epiphyseal plates to narrow.
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Growth Hormone:
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Nutritional Requirements:
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Calcium and Phosphate Salts:
- Essential for bone growth, preventing rickets in children and osteomalacia in adults.
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Vitamin C:
- Required for collagen synthesis.
- Stimulates osteoblast differentiation.
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Vitamin A, E, and K:
- Stimulate osteoblast activity.
- Vitamin K and B12 are essential for protein synthesis required for normal bone formation, particularly collagen.
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Calcium and Phosphate Salts:
Bone Structure
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Bone Types:
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Compact Bone/Cortical Bone:
- Dense and solid, found in diaphysis (shaft) of long bones.
- Provides strength and rigidity.
- Contains osteons, which are cylindrical units containing a central canal with blood vessels and nerves.
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Spongy Bone/Cancellous Bone:
- Lighter and less dense than compact bone, found in epiphysis of long bones.
- Contains trabeculae, which are branching structures filled with bone marrow.
- Trabeculae are avascular but provide strength and support.
- Spongy bone is found in short, irregular, and flat bones, such as carpal bones, vertebrae, and cranial bones.
- Spongy bone and medullary cavity reduce bone weight, allowing for efficient movement and providing space for red and yellow marrow.
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Compact Bone/Cortical Bone:
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Bone Structure:
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Periosteum:
- Tough, fibrous membrane that surrounds the outer surface of all bones.
- Houses blood vessels, nerves, and osteoprogenitor cells that contribute to bone growth and repair.
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Endosteum:
- Thin, cellular membrane that lines the inner surface of the medullary cavity and the trabeculae of spongy bone.
- Contains osteoprogenitor cells and osteoblasts.
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Medullary Cavity:
- Hollow space within the diaphysis of long bones that contains bone marrow.
- Red marrow is responsible for blood cell formation, while yellow marrow serves as fat storage.
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Periosteum:
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Bone Composition:
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Mineral Crystals:
- Primarily calcium phosphate (hydroxyapatite) and other minerals, accounting for 55% of bone weight.
- Responsible for bone hardness and rigidity.
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Collagen:
- Strong fibrous protein, responsible for bone flexibility and tensile strength.
- Accounts for 30% of bone weight.
- Part of osteoid, the organic matrix of bone.
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Water:
- Makes up 15% of bone weight.
- Essential for bone metabolism and hydration.
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Organic Components:
- Cells (2%) and osteoid (90%) consisting of protein (collagen) and sugar compounds.
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Mineral Crystals:
Bone Growth
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Longitudinal Growth:
- Occurs at the epiphyseal plates, which are cartilaginous growth plates located between the epiphysis and diaphysis.
- Chondrocytes in the epiphyseal plates divide and produce new cartilage.
- Osteoblasts in the metaphysis convert cartilage into bone, lengthening the bone.
- Growth in length is primarily influenced by growth hormone, thyroid hormone, and sex hormones.
- At puberty, increased sex hormone production causes the closure of the epiphyseal plates, ending longitudinal growth.
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Appositional Growth:
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Formation of New Osteons:
- Ridges in the periosteum create a groove for blood vessels.
- Periosteum ridges fuse, forming an endosteum-lined tunnel.
- Osteoblasts in the endosteum build new concentric lamellae inwards, forming a new osteon.
- Bone grows outwards as osteoblasts in the periosteum build new circumferential lamellae.
- Osteon formation repeats as new periosteal ridges fold over blood vessels.
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Expansion of Medullary Cavity:
- Osteoclasts dissolve bone on the inner surface of the medullary cavity, while osteoblasts deposit bone under the periosteum.
- This expands the medullary cavity and increases bone diameter.
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Formation of New Osteons:
Bone Remodeling
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Continuous Process:
- Bone remodeling occurs throughout life, involving the resorption of old bone and the deposition of new bone in response to various factors.
- It helps maintain bone strength, shape, and calcium homeostasis.
- Remodeling is influenced by mechanical stress, blood calcium levels, and bone growth.
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Hormonal Regulation:
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Parathyroid Hormone (PTH):
- Released from the parathyroid glands in response to low blood calcium levels.
- Stimulates osteoclast activity, increasing calcium release from bones.
- Increases intestinal calcium absorption and decreases renal calcium excretion.
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Calcitonin:
- Released from the thyroid gland in response to high blood calcium levels.
- Inhibits osteoclast activity, reducing calcium release from bones.
- Increases renal calcium excretion.
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Parathyroid Hormone (PTH):
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Mechanical Stress:
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Wolff's Law:
- Bones adapt to the forces placed upon them.
- Mechanical stress stimulates osteocytes, which act as mechanosensors and release chemicals that influence osteoblast and osteoclast activity.
- This leads to increased bone density and thickness in areas subjected to greater stress.
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Unstressed Bones:
- Remodeled to become weaker due to reduced osteoblast activity and increased osteoclast activity.
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Bone Strength:
- Bones used under stress become stronger, with trabeculae shaped to withstand specific forces.
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Wolff's Law:
Bone Repair
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Fractures:
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Treatment:
- Reduction: Aligning broken bone fragments.
- Immobilization: Reducing movement to allow for healing.
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Open (Compound) Fracture:
- Broken bone protrudes through the skin.
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Treatment:
Additional Information
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Orientation of Trabeculae:
- Withstands forces from multiple directions due to their structural design.
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Blood Vessels:
- Perichondrium transforms into periosteum, containing osteoprogenitor cells that differentiate into osteoblasts.
- Osteoblasts secrete osteoid, forming a bone collar against the shaft of the cartilage model.
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Mature Chondrocytes:
- Cannot divide and die, leaving cavities.
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Osteoid:
- Produced by osteoblasts at ossification sites and eventually turn into osteocytes as mineral deposits harden around them.
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Canaliculi:
- Tiny channels through bone matrix, allowing diffusion of nutrients and oxygen to osteocytes.
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Osteocytes:
- Mature bone cells responsible for maintaining bone tissue.
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Osteoblasts:
- Bone-forming cells that synthesize and secrete osteoid.
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Osteoclasts:
- Large, multinucleated cells that break down bone tissue (bone resorption).
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Red Bone Marrow:
- Found primarily in spongy bone and medullary cavity, responsible for blood cell production (hematopoiesis).
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Yellow Bone Marrow:
- Found primarily in the medullary cavity of long bones and serves as fat storage.
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Description
This quiz explores the blood supply to bones and the hormonal and nutritional requirements necessary for normal bone growth. Understand how hormones like growth hormone and sex hormones contribute to bone development, along with the essential dietary factors involved. Test your knowledge on these fundamental aspects of bone physiology.
