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Questions and Answers
What is the primary function of the nutrient artery in bone anatomy?
Where does the nutrient artery enter the bone shaft?
What do the metaphyseal arteries specifically reinforce?
Which bone structure is primarily supplied by the epiphyseal arteries?
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What is the most abundant mineral salt found in the extracellular matrix of bone tissue?
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What role do osteoblasts play in the process of calcification?
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Which characteristic is NOT associated with the flexibility of bone?
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Where are osteogenic cells primarily found in the body?
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How do osteocytes contribute to bone health?
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What distinguishes osteocytes from osteoblasts?
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What is the primary function of canaliculi in bone tissue?
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Why is spongy bone lighter than compact bone?
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Where is spongy bone primarily located?
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How do trabeculae contribute to the strength of spongy bone?
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What role does spongy bone play in relation to compact bone?
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What is the primary function of canaliculi in compact bone?
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What structures run longitudinally through each osteon?
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Which statement accurately describes interstitial lamellae?
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What is the significance of the direction of collagen fibers in adjacent lamellae?
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What role do perforating canals (Volkmann’s canals) play in bone structure?
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Which of the following is true about lamellae in compact bone?
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What defines an osteon in the context of compact bone?
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Where are lacunae located in the structure of compact bone?
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What initiates the formation of the ossification center during intramembranous ossification?
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In endochondral ossification, what structure replaces the cartilage model?
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During which phase do chondrocytes undergo cell division and secrete cartilage extracellular matrix?
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What happens to osteoclasts during the development of the medullary cavity?
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Which structure is formed last in the process of endochondral ossification?
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What role does the nutrient artery play in the development of the primary ossification center?
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What occurs during the calcification of the matrix in intramembranous ossification?
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What is the primary function of the periosteum formed during intramembranous ossification?
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Which type of growth allows for the increase in length of long bones?
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What characterizes the secondary ossification centers during bone development?
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Study Notes
Bone Blood Supply
- The inner 2/3 of the cortex is supplied by the nutrient artery.
- The nutrient artery enters the shaft through the nutrient foramen.
- It runs through the cortex and divides into ascending and descending branches in the medullary cavity.
- These branches anastomose with epiphyseal, metaphyseal, and periosteal arteries at the metaphysis.
- The nutrient artery nourishes the medullary cavity, the inner 2/3 of the cortex, and the metaphysis.
- Epiphyseal arteries supply the red bone marrow and bone tissue of the epiphyses.
- Metaphyseal arteries directly enter the metaphysis and reinforce metaphyseal branches of the primary nutrient artery.
- Nutrient veins accompany the nutrient artery and exit through the diaphysis.
- Epiphyseal and metaphyseal veins are numerous and exit through the epiphysis.
- Periosteal veins exit through the periosteum.
Bone Tissue Histology
- Bone extracellular matrix surrounds widely separated cells.
- The matrix composition is 15% water, 30% collagen fibers, and 55% crystallized mineral salts.
- The most abundant mineral salt is calcium phosphate (Ca3(PO4)2) which combines with Ca(OH)2 to form hydroxyapatite.
- Hydroxyapatite also combines with other mineral salts, including calcium carbonate (CaCO3), and ions like magnesium, fluoride, potassium, and sulfate.
- Calcification is initiated by osteoblasts; the process of depositing and crystallizing mineral salts in the framework formed by collagen fibers of the extracellular matrix.
- Bone is both hard and flexible: Mineral salts provide hardness while collagen fibers provide flexibility.
Bone Cells
- There are four main types of bone cells: osteogenic cells, osteoblasts, osteocytes, and osteoclasts.
Osteogenic Cells
- Unspecialized bone stem cells derived from mesenchyme.
- They divide and differentiate into osteoblasts.
- They are found in the inner part of the periosteum, endosteum, and canals within bone.
Osteoblasts
- Responsible for building bone.
- They are basophilic, mononuclear, and have a “cuboidal” shape.
- They secrete collagen fibers and other organic components to build the extracellular matrix.
- Osteoblasts surround themselves with extracellular matrix, become trapped, and differentiate into osteocytes.
Osteocytes
- Mature bone cells that are derived from osteoblasts.
- They are ellipsoid cells with few organelles and have mononuclear, dendritic processes.
- Their processes connect via gap junctions for communication and nutrient/waste exchange with the blood.
Circumferential Lamellae
- These are rings of calcified extracellular bone matrix that line the inner and outer surfaces of compact bone.
Osteons (Haversian System)
- The structural unit of compact bone.
- Each osteon is an elongated cylindrical structure consisting of concentric rings of lamellae surrounding a central canal.
- Osteons are usually parallel to each other along the long axis of the bone.
Central Canal (Haversian Canal)
- Channels that run through the core of each osteon.
- They run longitudinally through the bone and facilitate the passage of neurovascular structures (blood vessels and nerve fibers).
Interstitial Lamellae
- Areas of incomplete lamellae present between osteons.
- They are formed from fragments of old osteons that have been partly destroyed during bone resorption or growth.
Perforating Canals (Volkmann’s Canals)
- Transverse channels that lie at 90 degrees to the central canals and long axis of the bone.
- They connect the blood and nerve supply of the periosteum with the neurovascular supply of the central canals and medullary cavity.
Compact Bone Histology
- Compact bone is densely packed and forms the outer shell of bones.
General Features
- Concentric lamellae are the calcified extracellular matrix arranged in rings.
- Lacunae are tiny cavities between the lamellae housing osteocytes.
- Canaliculi are hair-like canals filled with extracellular fluid that radiate from lacunae to connect lacunae with each other.
Spongy (Cancellous) Bone
- Spongy bone is much lighter than compact bone.
- It consists of branching and anastomosing bars and plates of osseous tissue called trabeculae.
- Spongy bone is found in the majority of epiphyses in long bones and in the interior bone tissue of short, flat, and irregularly shaped bones.
- Spongy bone is typically found in bones that undergo a small amount of stress.
Spongy Bone Characteristics
- Spongy bone contains osteocytes in lacunae within the trabeculae.
- The lacunae and osteocytes are found in a lattice-like network of matrix spikes called trabeculae.
- The trabeculae form along lines of stress to provide strength to the bone.
Intramembranous Bone Formation
- Bone forms directly from mesenchymal cells.
- This type of bone formation occurs in flat bones of the face, most cranial bones, mandible, and clavicles.
Intramembranous Ossification Stages
- Development of ossification center: Chemical messages cause mesenchymal cells to cluster and differentiate into osteoprogenitor cells then osteoblasts.
- Calcification of matrix: Osteoblasts secrete extracellular matrix, becoming trapped as osteocytes. Extracellular matrix ossifies.
- Formation of trabeculae: Mesenchyme condenses to form the periosteum.
Endochondral Ossification
- Bone formation within hyaline cartilage that develops from mesenchyme.
- It replaces the cartilage model with bone.
Endochondral Ossification Stages
- Development of cartilage model: Chemical messages cause mesenchymal cells to crowd together and differentiate into chondroblasts that secrete cartilage extracellular matrix.
- Growth of cartilage model: The cartilage model grows in length (interstitial/endogenous) via chondrocyte division and secretion of extracellular matrix, and in width (appositional/exogenous) by deposition of extracellular matrix on the cartilage surface.
- Development of primary ossification center: A nutrient artery penetrates the perichondrium, stimulating osteoprogenitor cells to differentiate into osteoblasts. Periosteal capillaries infiltrate the disintegrating calcified cartilage. Bone replaces most of the cartilage in the primary ossification center.
- Development of the medullary (marrow) cavity: Osteoclasts breakdown newly formed spongy bone, creating a cavity.
- Development of the secondary ossification centers: An epiphyseal artery enters, forming a secondary ossification center. The secondary ossification center expands outward.
- Formation of articular cartilage & the epiphyseal plate: These structures form at the ends of the bone and epiphysis.
Bone Growth During Infancy, Childhood & Adolescence
- The growth in length of long bones involves two major events:
- Interstitial growth: occurs at the epiphyseal plate.
- Appositional growth: occurs at the periosteum.
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Description
Explore the intricate blood supply of bone, including the nutrient artery and its branches, as well as the vascular structures associated with epiphyseal and metaphyseal arteries. Additionally, delve into the histology of bone tissue, focusing on the extracellular matrix and its significance. Test your knowledge on these essential topics in bone biology.
