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Questions and Answers
Which hormone is primarily responsible for stimulating epiphyseal plate activity during infancy and childhood?
Which hormone is primarily responsible for stimulating epiphyseal plate activity during infancy and childhood?
What is the role of thyroid hormone in bone growth?
What is the role of thyroid hormone in bone growth?
What effect do testosterone and estrogens have during puberty regarding bone growth?
What effect do testosterone and estrogens have during puberty regarding bone growth?
What triggers the production of parathyroid hormone (PTH)?
What triggers the production of parathyroid hormone (PTH)?
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What is a characteristic of a displaced fracture?
What is a characteristic of a displaced fracture?
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In which type of fracture is the skin penetrated?
In which type of fracture is the skin penetrated?
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How does calcitonin function in relation to blood calcium levels?
How does calcitonin function in relation to blood calcium levels?
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What is the consequence of an excess or deficit of hormones on skeletal growth?
What is the consequence of an excess or deficit of hormones on skeletal growth?
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What is the primary function of osteogenic cells in bone tissue?
What is the primary function of osteogenic cells in bone tissue?
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Which layer of the periosteum contains osteogenic stem cells?
Which layer of the periosteum contains osteogenic stem cells?
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How does the structure of flat bones differ from that of long bones?
How does the structure of flat bones differ from that of long bones?
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What type of bone is characterized by a lack of a defined marrow cavity?
What type of bone is characterized by a lack of a defined marrow cavity?
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Which of the following bone cells is primarily involved in the resorption of bone tissue?
Which of the following bone cells is primarily involved in the resorption of bone tissue?
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What primarily composes the osteoid secreted by osteoblasts?
What primarily composes the osteoid secreted by osteoblasts?
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What is the outer layer of the periosteum primarily composed of?
What is the outer layer of the periosteum primarily composed of?
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Which structure covers the internal surfaces of bone?
Which structure covers the internal surfaces of bone?
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What is the primary function of osteocytes?
What is the primary function of osteocytes?
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What distinguishes osteoclasts from other bone cells?
What distinguishes osteoclasts from other bone cells?
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Which structure serves as the basic functional and structural unit of compact bone?
Which structure serves as the basic functional and structural unit of compact bone?
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What role do lamellae play in the osteon structure?
What role do lamellae play in the osteon structure?
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How does the central canal in an osteon differ from perforating canals?
How does the central canal in an osteon differ from perforating canals?
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What purpose do canaliculi serve within bone tissue?
What purpose do canaliculi serve within bone tissue?
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What characteristic feature do osteoclasts possess to enhance their function?
What characteristic feature do osteoclasts possess to enhance their function?
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Which of the following structures do not contain osteocytes?
Which of the following structures do not contain osteocytes?
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What is the primary structural component that provides strength to spongy bone?
What is the primary structural component that provides strength to spongy bone?
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Which of the following is NOT a component of the organic matrix of bone?
Which of the following is NOT a component of the organic matrix of bone?
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During which process does bone replace hyaline cartilage?
During which process does bone replace hyaline cartilage?
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What percentage of bone mass is made up of hydroxyapatites?
What percentage of bone mass is made up of hydroxyapatites?
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What occurs during the process of ossification?
What occurs during the process of ossification?
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Which of the following best describes intramembranous ossification?
Which of the following best describes intramembranous ossification?
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Which component is crucial for supplying nutrients to spongy bone?
Which component is crucial for supplying nutrients to spongy bone?
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Which stage of bone development begins in the second month of embryonic development?
Which stage of bone development begins in the second month of embryonic development?
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What is the main sequence of events in endochondral ossification?
What is the main sequence of events in endochondral ossification?
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Which bones are formed primarily through intramembranous ossification?
Which bones are formed primarily through intramembranous ossification?
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What primarily controls the increase in thickness of bones during growth?
What primarily controls the increase in thickness of bones during growth?
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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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How does the body adjust bone density in response to physical activity?
How does the body adjust bone density in response to physical activity?
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When does the process of endochondral ossification primarily begin during development?
When does the process of endochondral ossification primarily begin during development?
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What role do osteoclasts play in the growth of bones?
What role do osteoclasts play in the growth of bones?
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Which factor is least likely to lead to an increase in bone thickness?
Which factor is least likely to lead to an increase in bone thickness?
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Study Notes
Hormonal Regulation of Bone Growth
- Growth hormone is crucial for stimulating epiphyseal plate activity during childhood.
- Thyroid hormone regulates the activity of growth hormone, ensuring proper proportions.
- Testosterone (males) and estrogen (females) promote adolescent growth spurts, but eventually induce closure of the epiphyseal plates, ending bone lengthening.
- Excesses or deficits in any of these hormones can lead to abnormal skeletal growth.
Control of Remodeling
- Parathyroid hormone (PTH) is released by the parathyroid glands in response to low blood calcium levels.
- PTH stimulates osteoclasts to resorb bone, releasing calcium into the bloodstream.
- This process continues until calcium levels reach homeostasis.
- Calcitonin is produced by the parafollicular cells of the thyroid gland in response to high blood calcium levels.
- Calcitonin inhibits osteoclast activity, decreasing bone resorption and lowering blood calcium levels.
Bone Repair
- Fractures are classified based on the position of bone ends, completeness of the break and whether the skin is penetrated.
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Position:
- Nondisplaced: Bone ends remain in their normal position.
- Displaced: Bone ends are out of alignment.
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Completeness:
- Complete: Break extends through the entire bone.
- Incomplete: Break does not extend through the entire bone.
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Skin Penetration:
- Open (compound): Skin is penetrated by the fractured bone.
- Closed (simple): Skin is not penetrated.
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Position:
Gross Anatomy: Long Bone
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Membranes:
- Periosteum: Double-layered membrane covering the external surface of bone, excluding joints.
- Fibrous layer: Outer layer composed of dense irregular connective tissue with Sharpey's fibers that secure to bone matrix.
- Osteogenic layer: Inner layer containing osteogenic stem cells that give rise to most bone cells.
- Endosteum: Delicate connective tissue membrane lining the internal bone surface.
- Contains osteogenic cells.
- Periosteum: Double-layered membrane covering the external surface of bone, excluding joints.
Gross Anatomy: Flat Bone
- Flat, irregular, and short bones have thin plates of spongy bone covered by compact bone.
- Compact bone is sandwiched between periosteum and endosteum.
- Bone marrow is scattered throughout the spongy bone; there is no defined marrow cavity.
Microscopic Anatomy of Bone: Cells
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Osteogenic cells: Mitotically active stem cells in periosteum and endosteum.
- Differentiate into osteoblasts.
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Osteoblasts: Bone-forming cells that secrete osteoid, an unmineralized bone matrix composed of collagen and calcium-binding proteins.
- Collagen makes up 90% of bone protein.
- Osteocytes: Mature bone cells housed in lacunae that maintain bone matrix and act as stress sensors.
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Osteoclasts: Giant, multinucleate cells derived from hematopoietic stem cells.
- Involved in bone resorption.
- Reside in depressions called resorption bays, featuring ruffled borders for enhanced enzyme degradation of bone.
Microscopic Anatomy of Compact Bone
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Osteon (Haversian system): Structural unit of compact bone.
- Elongated cylinder running parallel to the long axis of the bone, acting as weight-bearing pillars.
- Composed of lamellae, rings of bone matrix containing collagen fibers oriented in different directions for stress resistance.
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Canals and canaliculi:
- Central (Haversian) canal: Runs through the core of the osteon, containing blood vessels and nerve fibers.
- Perforating (Volkmann’s) canals: Perpendicular to central canal, lined with endosteum.
- Lacunae: Small cavities housing osteocytes.
- Canaliculi: Hairlike canals connecting lacunae to each other and to the central canal.
Microscopic Anatomy of Spongy Bone
- Spongy bone is organized along lines of stress for optimal resistance.
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Trabeculae: Irregular lattice-like bony struts that resist stress.
- Contain irregularly arranged lamellae and osteocytes interconnected by canaliculi.
- No osteons are present in spongy bone.
- Capillaries in the endosteum supply nutrients to spongy bone.
Chemical Composition of Bone
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Organic Component: One-third of organic bone matrix is osteoid, secreted by osteoblasts.
- Osteoid is composed of ground substance and collagen fibers, granting bone flexibility and tensile strength.
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Inorganic Component:
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Hydroxyapatites (mineral salts): Account for 65% of bone mass.
- Tiny calcium phosphate crystals located in and around collagen fibers, responsible for bone hardness and resistance to compression.
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Hydroxyapatites (mineral salts): Account for 65% of bone mass.
Bone Development
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Ossification (osteogenesis): Bone tissue formation.
- Embryonic ossification: Begins during month 2 of development.
- Postnatal ossification: Continues until early adulthood.
- Bone remodeling and repair: Lifelong processes.
Embryonic Bone Growth
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Endochondral ossification: Bone formation by replacing hyaline cartilage.
- Responsible for formation of most bones in the body, except for some skull bones and clavicles.
- Requires breakdown of hyaline cartilage prior to ossification.
- Starts at the primary ossification center in the shaft of long bones.
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Intramembranous ossification: Bone formation directly from fibrous membranes.
- Forms flat bones of the skull and the clavicle.
Postnatal Bone Growth
- Longitudinal growth: Occurs at the epiphyseal plate, allowing bones to lengthen.
- Appositional growth: Bones increase thickness by adding bone matrix on the external surface.
- Bone growth ceases during adolescence, except for slow, continued growth of some facial bones throughout life.
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Description
This quiz covers the essential hormones responsible for bone growth and remodeling. It explores the roles of growth hormone, thyroid hormone, and sex hormones in skeletal development during various life stages. Additionally, it examines the mechanisms of calcium homeostasis and the impact of parathyroid hormone and calcitonin on bone health.
