Lecture 2 Flashcards
Human skeleton can be divided in two parts
Name them
How many bones do we have in an adult?
How many in a child?
Axial and appendicular skeleton
Appendicular: appendages or bones. Pelvis is part of the appendicular skeleton
Axial: head,spine,thorax
Appendicular:hands and legs
206 in an adult
300 in a baby
How many curvatures do we have in the human body?
The curvatures don’t exist in babies but as they start sitting and gaining head control and things, the curvatures of the spine start coming. True or false
4 curvatures in the spine
1. In cervical area
2.thoracic area
3.Lumbar area
4.Sacrum area
What are long bones
what are the two ways of osteogenesis?
90 long bones.
Long bones are in the limbs
Generally, all Bones are formed by ossification or osteogenesis
Types of ossification or osteogenesis:
Endochondral (long bones) and intramembranous(short bones) ossification
ways:
1. Intramembranous ossification from mesenchyme. Example is it occurring in flat bones
2. Endochondrial ossification (from cartilage primordium; chondroblasts, chondrocytes).
What are flat bones (not round bones)and how are they formed?
State 6 examples of flat bones
Mesenchymal stem cells either differentiate into osteoblasts or chondrocytes or Adipocytes
Have a plate of compact bones forming the outer part and a spongy bone (bone looks like a sponge cuz it’s a network of smaller bones with spaces in between) in the middle.
Like a sandwich with meat in it
J Intramembranous ossification is the process by which bone forms directly from mesenchymal (undifferentiated) connective tissue membranes. This type of ossification primarily occurs during the development of flat bones, such as those in the skull, certain facial bones, and the clavicles. Here’s a detailed explanation of how intramembranous ossification occurs:
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Mesenchymal Cell Condensation:
- Mesenchymal stem cells, which are pluripotent cells derived from mesoderm(this doesn’t mean they are pluripotent cuz they aren’t. They are multipotent)condense and cluster together within the embryonic or fetal connective tissue membrane.
- These mesenchymal cells differentiate into osteoprogenitor cells (preosteoblasts).
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Differentiation into Osteoblasts:
- Osteoprogenitor cells further differentiate into osteoblasts under the influence of various signaling molecules, growth factors (such as BMPs - bone morphogenetic proteins), and transcription factors (like Runx2).
- Osteoblasts are bone-forming cells responsible for synthesizing and secreting the organic extracellular matrix of bone tissue, known as osteoid.
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Osteoid Secretion:
- Osteoblasts begin secreting osteoid, which consists primarily of collagen fibers (mainly type I collagen) and other proteins.
- The osteoid is deposited around the osteoblasts, forming a network or scaffold that will become the future bone tissue.
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Mineralization:
- As osteoid accumulates, mineral salts (mainly calcium and phosphate ions) are deposited within the matrix.
- These mineral salts gradually harden and crystallize the osteoid, transforming it into mature bone tissue.
- This mineralization process is essential for the strength and rigidity of the bone.
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Formation of Trabeculae:
- The mineralized osteoid forms trabeculae (spicules or plates) of woven bone.
- Trabeculae initially develop in a random arrangement but may remodel into more organized lamellar bone over time.
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Bone Development and Remodeling:
- Blood vessels invade the developing bone tissue, bringing in osteoclasts (bone-resorbing cells) and osteogenic cells.
- Osteoclasts remodel the trabecular bone to form compact bone on the surfaces, while osteogenic cells contribute to further bone growth and maintenance.
In summary, intramembranous ossification involves the direct transformation of mesenchymal connective tissue into bone tissue without an intermediate cartilage model. It is responsible for the formation of flat bones and certain parts of the skull. This process is tightly regulated by genetic and molecular signals to ensure proper bone development and function in the skeletal system.
Examples are the
Sternum (1) - Breastbone
• Ribs (24) - Rib Cage(so 12 pairs of bones making 24 in total)
• Skull:
Frontal Bone (1)
Parietal Bone (2)
Occipital Bone (1)
Nasal (2)
Lacrimal (2)
Vomer (1)
• Scapula (2) - Shoulder Blade
There are 36 Flat Bones
State five general functions of the skeleton
-Support against gravity
-Storage:
Calcium, Phosphorous
Lipids (in yellow marrow)
-Blood cell production(in red marrow)
-Protection of soft internal organs
-Lever for muscle attachment and movement
Calcium and phosphorus are primarily stored in the bone matrix. Here’s a detailed explanation:
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Bone Matrix:
- Calcium: The majority of the body’s calcium (about 99%) is stored in bones and teeth. Calcium is present in the form of hydroxyapatite crystals (Ca₁₀(PO₄)₆(OH)₂), which provide hardness and strength to bones.
- Phosphorus: Similarly, around 85% of the body’s phosphorus is stored in bones, also as part of the hydroxyapatite crystals. Phosphorus in bones is crucial for bone strength and structure.
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Red Bone Marrow:
- Found primarily in the flat bones (like the pelvis, sternum, and skull) and in the epiphyseal (ends) regions of long bones.
- Responsible for the production of red blood cells, white blood cells, and platelets.
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Yellow Bone Marrow:
- Found in the medullary cavity (central cavity) of long bones.
- Primarily consists of fat cells and serves as a storage site for fats.
- Can convert to red marrow if the body needs increased blood cell production, such as in cases of severe blood loss.
While yellow marrow is mainly involved in fat storage, it is not a significant site for the storage of calcium and phosphorus. These minerals are integrated into the bone matrix itself.
- Calcium and Phosphorus Storage: Primarily stored in the bone matrix as hydroxyapatite crystals, providing strength and structure to bones.
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Bone Marrow Types:
- Red Marrow: Involved in blood cell production.
- Yellow Marrow: Involved in fat storage and can convert to red marrow if needed.
The bone matrix is the key location for the storage of calcium and phosphorus, while yellow marrow serves different functions
State the types of bones?
What type of bones are the ribs?
What type of bones are the carpal bones?
What type of bone is the humerus ?
What type of bone are the vertebral bones?
Flat-ribs
Short- carpal bones
Irregular- vertebra bone
Long-humerus
How does intra membranous ossification occur?
Where does most intra membranous ossification occur?
What is the periosteum
What is the osteoid
Which type of collagen is usually seen in the osteoid
from mesenchyme(the mesenchyme are multipotent progenitor cells that commit to the osteogenic lineage and differentiates into osteoprogenitor cells or preosteoblasts. The osteoprogenitor cells differentiate into osteoblast cells. Blasts cells are types of cells that are committed to generate a specific type of cells. So osteoblasts are committed to generating osteocytes – osteoblasts, osteocytes) e.g. in flat bones (skull).Most intramembranous ossification happens in utero. Osteoblasts form clusters while leaving spaces in between for some osteocytes to stay in there. This forms the osteoid. So the clusters formed become the osteoids.This becomes the ossification centres. Yes, osteoid is the term used for the bone matrix that is secreted by osteoblasts before it becomes mineralized to form mature bone.Osteoid:
• Composition: Osteoid is primarily composed of collagen fibers (mainly type I collagen)
First tries to form the spongy part of the flat bone. The trabecular which is in the spongy part of the bone, is a mesh work of solid bones with holes in them. These holes are left in there for some of the mesenchyme cells to migrate into the trabeculae to differentiate to form hematopoietic cells.
Every bone has connective tissue that covers the bone. This is called periosteum.
This periosteum has progenitor cells.
The compact bone has osteoblasts that produce osteocytes to spill the spaces before the spongy part of the bone. The compact bone area undergoes mineralization or deposition of calcium (specifically calcium hydroxyapatite) and phosphorus.
So mesenchymal cells
Osteoprogenitor cells
Osteoblasts
Osteoid
Trabecular (spongy bone formed)
Continuing from the formation of osteoblasts and osteoid in intramembranous ossification:
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Osteoblast Formation:
- Mesenchymal Cells: In the initial stages, mesenchymal cells in the embryonic connective tissue (mesenchyme) differentiate into osteoblasts.
- Osteoblasts: These are bone-forming cells that secrete osteoid, the unmineralized bone matrix.
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Osteoid Formation:
- Osteoid: Osteoblasts secrete osteoid, which consists of collagen fibers and ground substance. This matrix forms a scaffold for future bone mineralization.
- Mineralization: The osteoid becomes mineralized as calcium and phosphate crystals (hydroxyapatite) are deposited, transforming the osteoid into mature bone.
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Formation of Trabecular Bone:
- Trabecular Network: As osteoid secretion continues, the trabecular (spongy) bone forms. The trabecular bone is characterized by a lattice-like network of bone with spaces in between.
- Bone Marrow: The spaces within the trabecular bone are filled with mesenchymal cells that differentiate into hematopoietic cells, forming red bone marrow.
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Compact Bone Formation:
- Osteoblasts in Compact Bone: On the outer edges of the trabecular bone, osteoblasts continue to produce osteoid, forming a layer of compact bone.
- Formation of Osteons: In the compact bone, the osteoid is organized into concentric lamellae around central Haversian canals, forming structures known as osteons or Haversian systems.
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Development of the Periosteum:
- Periosteum: A layer of connective tissue called the periosteum forms on the outer surface of the newly formed bone. The periosteum contains osteoprogenitor cells that can differentiate into osteoblasts for bone growth and repair.
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Bone Remodeling:
- Osteocytes: As the bone matures, some osteoblasts become encased in the bone matrix and differentiate into osteocytes, which maintain the bone matrix.
- Bone Remodeling: The bone continues to remodel throughout life, adjusting its structure based on mechanical stress and other factors.
- Osteoblasts: Secrete osteoid, which forms the bone matrix.
- Osteoid: Mineralizes to become bone tissue.
- Trabecular Bone: Forms first and provides structural support and space for marrow.
- Compact Bone: Forms on the outside, creating a dense outer layer.
- Periosteum: Covers the bone and contains cells for growth and repair.
- Osteocytes: Mature osteoblasts that maintain bone matrix.
This process results in the formation of flat bones like those of the skull and clavicles, starting from a mesenchymal template and evolving into a strong, mineralized bone structure.
Formation of compact bone occurs in the diaphysis during endochondrial ossification
Articular cartilage remains as cartilage in the adult bone after endochondrial ossification
Trabecular bone houses bone marrow
Periosteum begins to form during initial ossification during intramembranous ossification
Compact bone forms the outer layer in endochondrial ossification
Woven bone is the type of bone that is forms first during endochondrial ossification in the diaphysis
What Are Osteons?
• Osteons, also known as Haversian systems, are the fundamental functional units of compact bone. They are cylindrical structures that run parallel to the long axis of the bone and are composed of concentric layers, or lamellae, of calcified matrix.
Key Features of Osteons:
• Central Canal (Haversian Canal): The center of each osteon contains a central canal, which houses blood vessels and nerves, supplying the bone cells with nutrients and oxygen. • Lamellae: Surrounding the central canal are concentric rings of bone matrix called lamellae, which give the bone its strength and rigidity. • Osteocytes: Bone cells, called osteocytes, are located in small spaces called lacunae between the lamellae. These cells maintain the bone tissue. • Canaliculi: Tiny channels called canaliculi connect the lacunae, allowing communication between osteocytes and the central canal.
How does endochondrial ossification occur?
What is the difference between periosteum and perichondrium
Where are chondroblasts found in the hyaline cartilage?
What transport process do nutrients get in and out of the cartilage by?
Where does primary ossification occur?
What about secondary ossification?
Note that there is no medullary cavity in intramembranous ossification so the bone marrow is in the trabeculae while in endochondrial, the bone marrow is in the medullary cavity.
State the five different zones in the Epiphyseal growth plate
Hyaline Cartilage is formed first before chondroblasts and then chondrocytes .
Periosteum is the connective tissue covering of the bone while perichondrium is the connective tissue covering of the hyaline cartilage.
The chondroblasts are in the diaphysis of the hyaline cartilage. (The hyaline cartilage forms the basis of the formation of the long bones. So the long bone has epiphysis at each ends of the bone and diaphysis(middle of the bone) hence the hyaline cartilage also has two ends and the middle to form the basis of generation of more blasts to fill the space in the cartilage to get the bone.
The chondroblasts differentiate to form chondrocytes. The bone will start getting vascularized. The cartilage is formed from a network of proteins (collagen and in this case,type II collagen). Nutrients get in and out of the cartilage by diffusion. Osteoblasts lay down osteocytes to keep growing the bone while osteoclasts break down the middle part of the bone to create holes which become the medullary part of the bone for containing the bone marrow which comes to be producing red blood cells. Endochondrial ossification is important for bone elongation.
Endochondral ossification is the process by which most bones in the body are formed, including long bones such as the femur and humerus. It involves the replacement of a hyaline cartilage model with bone tissue. Here’s a detailed explanation of how endochondral ossification occurs:
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Formation of Hyaline Cartilage Model:
- The process begins with the formation of a hyaline cartilage model of the future bone. This cartilage model is produced by chondrocytes, which are cartilage-forming cells derived from mesenchymal stem cells.
- Mesenchymal stem cells differentiate into chondrocytes within the cartilage model.
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Development of Primary Ossification Center:
- Blood vessels invade the perichondrium (the connective tissue membrane surrounding the cartilage model) and bring osteogenic (bone-forming) cells into the area.
- Osteogenic cells differentiate into osteoblasts, which begin to produce bone matrix (osteoid) around the cartilage model.
- This process occurs at the primary ossification center, usually in the diaphysis (shaft) of the bone.
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Replacement of Cartilage with Bone:
- Osteoblasts deposit osteoid around the cartilage model, gradually replacing the cartilage tissue with bone tissue.
- As osteoid accumulates, mineral salts (mainly calcium and phosphate ions) are deposited within the matrix, causing it to harden and mineralize.
- Chondrocytes within the cartilage model undergo hypertrophy (enlargement) and eventually die. This creates cavities within the cartilage matrix.
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Formation of Trabecular Bone:
- The mineralized osteoid forms trabeculae (spongy bone) within the cavities left by the hypertrophied chondrocytes.
- These trabeculae join together to form a primary spongy bone framework.
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Development of Secondary Ossification Centers:
- Secondary ossification centers develop later in the epiphyses (ends) of long bones.
- Similar processes of ossification occur in the epiphyseal regions, forming secondary ossification centers where spongy bone is formed.
- The epiphyseal cartilage (epiphyseal plate or growth plate), located between the diaphysis and epiphysis, continues to grow and elongate bones during childhood and adolescence.
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Epiphyseal Plate Closure:
- As bone growth continues, the epiphyseal plate gradually ossifies and is replaced by bone tissue, marking the closure of longitudinal bone growth (epiphyseal closure).
- The bone continues to remodel throughout life in response to mechanical stress, hormonal changes, and other factors.
In summary, endochondral ossification involves the transformation of a hyaline cartilage model into bone tissue. It is a highly regulated process involving the differentiation of mesenchymal cells into chondrocytes, followed by the gradual replacement of cartilage with bone at primary and secondary ossification centers. This process is essential for the development, growth, and maintenance of most bones in the skeletal system.
Yes, chondrocytes produce the hyaline cartilage model. Here’s a detailed explanation:
Chondrocytes are the cells found within cartilage tissue. They play a crucial role in the formation and maintenance of cartilage.
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Hyaline Cartilage:
- Structure: Hyaline cartilage is composed of a gel-like matrix with embedded chondrocytes. The matrix is rich in collagen fibers (primarily type II collagen) and proteoglycans.
- Function: Provides support and flexibility, and reduces friction between bones in joints.
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During Development:
- Mesenchymal Cells: Initially, mesenchymal stem cells (precursor cells) in the developing embryo differentiate into chondroblasts.
- Chondroblasts: These cells start secreting the extracellular matrix of cartilage, which includes collagen and proteoglycans.
- Chondrocytes: Once the chondroblasts become embedded in the cartilage matrix, they mature into chondrocytes. These cells continue to maintain and produce the matrix of hyaline cartilage.
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Endochondral Ossification:
- Hyaline Cartilage Model: During the process of endochondral ossification, the hyaline cartilage model serves as a template for bone formation. This process is essential for the development of long bones.
- Replacement by Bone: The cartilage model is gradually replaced by bone tissue as development progresses.
- Chondrocytes: Mature cartilage cells that produce and maintain the cartilage matrix.
- Hyaline Cartilage: A type of cartilage formed and maintained by chondrocytes, which serves as a precursor in the development of long bones through the process of endochondral ossification.
Chondrocytes are indeed responsible for producing the hyaline cartilage model, which is a crucial step in the formation of bones during development.
Chondroblasts and chondrocytes are two stages of cells involved in the formation and maintenance of cartilage. Here’s a detailed explanation of where and when each type comes into play:
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Mesenchymal Stem Cells:
- Both chondroblasts and chondrocytes originate from mesenchymal stem cells during embryonic development.
- Mesenchymal stem cells differentiate into chondroblasts under specific conditions.
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Formation:
- Embryonic Development: During the early stages of embryogenesis, mesenchymal stem cells differentiate into chondroblasts in regions where cartilage is needed.
- Cartilage Matrix Production: Chondroblasts begin synthesizing and secreting the cartilage matrix, which consists of type II collagen and proteoglycans.
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Activity:
- Matrix Secretion: Chondroblasts are highly active, producing the extracellular matrix that forms the cartilage.
- Location: Found at the periphery of growing cartilage, in the perichondrium (a layer of dense irregular connective tissue surrounding the cartilage).
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Endochondral Ossification:
- Role: Chondroblasts form the initial cartilage model in the process of endochondral ossification, which is essential for the development of long bones.
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Transition from Chondroblasts:
- Maturation: As chondroblasts continue to produce matrix, they become embedded within it. Once fully surrounded by the matrix, they mature into chondrocytes.
- Lacunae Formation: Chondrocytes reside in small spaces called lacunae within the cartilage matrix.
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Function:
- Maintenance: Chondrocytes maintain the cartilage matrix, ensuring its integrity and function.
- Less Active: Compared to chondroblasts, chondrocytes are less metabolically active but continue to produce and remodel the cartilage matrix as needed.
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Location:
- Within Cartilage: Chondrocytes are found throughout the cartilage tissue, including articular cartilage and the growth plates of long bones.
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Chondroblasts:
- When: Active during early stages of cartilage formation and growth.
- Where: At the periphery of cartilage, in the perichondrium, and within the developing cartilage model in the growth plates.
- Role: Synthesize and secrete the cartilage matrix, contributing to cartilage growth and the formation of the initial cartilage model in endochondral ossification.
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Chondrocytes:
- When: Arise after chondroblasts become embedded in the cartilage matrix.
- Where: Within lacunae throughout the cartilage tissue.
- Role: Maintain and remodel the cartilage matrix, ensuring the tissue remains functional and healthy.
In summary, chondroblasts are the initial, highly active cells responsible for producing the cartilage matrix. Once they become embedded in this matrix, they mature into chondrocytes, which then maintain and remodel the cartilage.
Let’s clarify the process of endochondral ossification with a more accurate step-by-step explanation to address the confusion. Your understanding has some correct points, but the sequence and details need adjustment.
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Formation of Hyaline Cartilage Model:
- Chondroblasts (cartilage-forming cells) produce a hyaline cartilage model that resembles the shape of the future bone.
- These chondroblasts become chondrocytes (mature cartilage cells) as they get embedded in the cartilage matrix.
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Growth of Cartilage Model:
- The cartilage model grows in size through the division of chondrocytes and the secretion of cartilage matrix. This allows the model to elongate and expand.
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Development of Primary Ossification Center:
- Blood vessels penetrate the perichondrium (a membrane surrounding the cartilage) of the diaphysis (shaft of the bone), converting it into periosteum.
- The increased blood supply brings osteoblasts (bone-forming cells) which start producing a thin layer of bone around the cartilage model, forming a bone collar.
- Chondrocytes in the center of the diaphysis enlarge (hypertrophy), and the surrounding matrix calcifies. These chondrocytes eventually die due to lack of nutrients, creating cavities within the model.
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Invasion of Periosteal Bud:
- A periosteal bud (a mix of blood vessels, nerves, osteoblasts, and osteoclasts) invades the cavities formed by the dying chondrocytes.
- Osteoblasts in the periosteal bud begin producing spongy bone by depositing bone matrix on the remnants of calcified cartilage. This forms the primary ossification center in the diaphysis.
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Formation of Medullary Cavity:
- Osteoclasts (bone-resorbing cells) break down some of the newly formed spongy bone in the diaphysis, creating the medullary (marrow) cavity.
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Development of Secondary Ossification Centers:
- Around the time of birth, secondary ossification centers develop in the epiphyses (ends of the bone).
- Blood vessels invade the epiphyses, chondrocytes enlarge and die, and osteoblasts form new bone, similar to the process in the diaphysis.
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Formation of Epiphyseal Plate:
- The remaining cartilage between the diaphysis and epiphyses forms the epiphyseal plate (growth plate).
- This plate is responsible for the lengthwise growth of bones during childhood and adolescence.
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Continued Bone Growth and Remodeling:
- Bones continue to grow in length at the growth plates until adolescence, when the growth plates close and become epiphyseal lines.
- Throughout life, bones are constantly remodeled by the balanced activity of osteoblasts and osteoclasts to maintain bone strength and integrity.
- The primary ossification center forms in the diaphysis (shaft), not in the epiphyses (ends).
- The process begins with the formation of a cartilage model, which is replaced by bone through the actions of osteoblasts and osteoclasts.
- Blood vessels play a crucial role in bringing osteoblasts to the site of ossification.
- The secondary ossification centers form in the epiphyses around the time of birth.
- The growth plate (epiphyseal plate) allows for continued lengthwise growth of the bone until it closes at the end of adolescence.
This more detailed sequence should help clarify the process of endochondral ossification.
In endochondral ossification, after blood vessels invade the cartilage model and bring in osteoblasts, the following steps occur:
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Formation of the Primary Ossification Center:
- The blood vessels penetrate the middle of the cartilage model, usually in the diaphysis (the shaft of the bone).
- The osteoblasts brought in by the blood vessels start to form bone by secreting osteoid over the remnants of calcified cartilage.
- This region where bone starts to form is called the primary ossification center.
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Cartilage Calcification:
- As the osteoblasts lay down bone, the cartilage in the center begins to calcify (harden), which means that it no longer gets nutrients from the blood, leading to the death of chondrocytes (cartilage cells).
- The dying cartilage cells create spaces that allow the osteoblasts to move in and start forming bone.
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Formation of Spongy Bone:
- Osteoblasts continue to deposit bone matrix, forming trabeculae, which are the small, needle-like structures of spongy bone.
- This spongy bone forms in the inner region of the diaphysis.
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Development of the Medullary Cavity:
- As the spongy bone forms, osteoclasts (cells that break down bone tissue) are also active. They resorb the newly formed bone in the center of the diaphysis, creating the medullary (marrow) cavity.
- The medullary cavity will eventually house bone marrow.
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Growth of Bone Toward the Epiphyses:
- Bone formation spreads outward from the primary ossification center toward the ends of the bone (the epiphyses).
- The cartilage at the ends continues to grow, allowing the bone to lengthen.
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Formation of the Secondary Ossification Centers:
- Eventually, blood vessels invade the cartilage at the epiphyses, and similar processes occur to form secondary ossification centers.
- These centers form bone in the epiphyses, leaving a region of cartilage between the diaphysis and epiphysis known as the epiphyseal plate (growth plate).
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Formation of Articular Cartilage and Growth Plates:
- The remaining cartilage at the ends of the bones becomes the articular cartilage, which covers the joint surfaces.
- The cartilage between the diaphysis and epiphyses forms the epiphyseal plate, which is responsible for bone lengthening during growth.
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Bone Maturation and Growth:
- The bone continues to grow in length as long as the epiphyseal plates remain active.
- When a person reaches adulthood, the epiphyseal plates ossify and turn into epiphyseal lines, marking the end of bone growth in length.
This sequence of events allows for the transformation of a cartilage model into a fully formed bone, with distinct areas of compact and spongy bone, as well as a medullary cavity.
The epiphyseal plate and articular cartilage are both composed of hyaline cartilage, but they serve different functions and are located in different areas of a growing bone. Here’s a breakdown of the differences:
- Location: The epiphyseal plate is found between the diaphysis (shaft) and the epiphysis (end) of long bones.
- Function: The primary function of the epiphyseal plate is to allow the bone to grow in length during childhood and adolescence. It is a site of active cell division (proliferation of chondrocytes), where new cartilage is continuously formed on the epiphyseal side and ossified on the diaphyseal side. This process elongates the bone.
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Structure: The epiphyseal plate is divided into different zones:
- Resting Zone: Located closest to the epiphysis, this zone contains small, inactive chondrocytes.
- Proliferation Zone: Chondrocytes divide rapidly, pushing older cells towards the diaphysis.
- Hypertrophic or maturation Zone or zone of maturation: Chondrocytes enlarge and start to accumulate nutrients.
- Calcification Zone: The cartilage matrix calcifies, and the chondrocytes die.
- Ossification Zone: The calcified cartilage is replaced by bone tissue, formed by osteoblasts.
- Fate: Once growth in length is complete, typically at the end of puberty, the epiphyseal plate ossifies and turns into the epiphyseal line, which is a remnant of the growth plate.
- Location: Articular cartilage is found covering the surfaces of bones at the joints, specifically at the ends of the epiphyses.
- Function: The main function of articular cartilage is to reduce friction and absorb shock in the joints. It provides a smooth, slippery surface that allows bones to move freely against each other with minimal resistance.
- Structure: Unlike the epiphyseal plate, articular cartilage is not divided into zones related to growth. Instead, it is designed to be durable and resilient, capable of withstanding the compressive forces of joint movement.
- Fate: Articular cartilage remains throughout life, but it does not regenerate or ossify like the epiphyseal plate. Over time, articular cartilage can wear down, leading to conditions
The maturation zone, also known as the zone of maturation or hypertrophic zone, is located within the epiphyseal plate (growth plate) of growing bones during endochondral ossification.
The epiphyseal plate is divided into several zones, each representing a different stage of cartilage growth and ossification:
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Resting (Reserve) Zone:
- Location: Closest to the epiphysis.
- Function: Contains small, inactive chondrocytes that anchor the epiphyseal plate to the epiphysis.
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Proliferation (Growth) Zone:
- Location: Below the resting zone, toward the diaphysis.
- Function: Chondrocytes in this zone divide rapidly, pushing older cells toward the diaphysis, contributing to bone lengthening.
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Maturation (Hypertrophic) Zone:
- Location: Below the proliferation zone, closer to the diaphysis.
- Function: In this zone, chondrocytes stop dividing and begin to enlarge (hypertrophy). As they enlarge, they secrete matrix that becomes calcified, preparing the area for subsequent ossification.
- Key Features: The cells are larger than in the other zones, and the surrounding cartilage matrix begins to calcify.
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Calcification Zone:
- Location: Below the maturation zone, just above the ossification zone.
- Function: The cartilage matrix becomes fully calcified, and the chondrocytes die due to lack of nutrients.
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Ossification (Osteogenic) Zone:
- Location: Closest to the diaphysis.
- Function: Osteoblasts invade the calcified cartilage, depositing bone matrix to form new bone. This is where cartilage is replaced by bone.
The maturation zone is where chondrocytes stop dividing and begin to enlarge, contributing to the preparation of cartilage for ossification. It plays a crucial role in bone elongation during growth.
The vessel that enters bone at a specific point is typically referred to as
Difference between epiphyseal bud and nutrient artery
The epiphyseal bud is a structure involved in the process of endochondral ossification, which is how long bones grow in length. During this process, the epiphyseal bud refers to the vascular invasion of the cartilage model in the developing bone. Here’s how it works:
- Cartilage Formation: Initially, the future bone is made of hyaline cartilage.
- Primary Ossification Center: The center of this cartilage model begins to calcify, and the cartilage cells (chondrocytes) die off, leaving behind cavities.
- Epiphyseal Bud Invasion: Blood vessels, along with osteogenic cells, invade the cavities in the cartilage model, forming the “epiphyseal bud.” These blood vessels bring osteoblasts (bone-forming cells) into the area.
- Bone Formation: The osteoblasts begin to lay down bone matrix, replacing the cartilage with bone tissue. This process continues at the epiphyseal plates (growth plates) until the bone has reached its full length.
The epiphyseal bud is essential for the proper development and growth of long bones, as it marks the beginning of the replacement of cartilage with bone tissue during growth.
The vessel that enters bone at a specific point is typically referred to as a “nutrient artery” or a “nutrient vessel.”
Nutrient Artery:
- Nutrient arteries are small branches of larger arteries that penetrate compact bone at specific points, usually near the diaphysis (shaft) of long bones.
- They enter through small openings called nutrient foramina (singular: foramen), which are openings in the bone’s cortex (outer layer).
- Nutrient arteries supply oxygenated blood, nutrients, and minerals to the bone tissue.
- Inside the bone, nutrient arteries branch into smaller vessels that supply the medullary cavity (marrow cavity) and the spongy bone.
These nutrient arteries play a crucial role in maintaining the vitality and health of bone tissue by providing essential nutrients and oxygen for cellular metabolism and bone growth.
The epiphyseal bud and the nutrient artery are both involved in the development and nourishment of bones, but they serve different functions and appear at different stages of bone development. Here’s a comparison:
- Role in Ossification: The epiphyseal bud is critical in the process of endochondral ossification, specifically in the formation of secondary ossification centers within the epiphyses (the ends of long bones).
- Formation: The epiphyseal bud forms when blood vessels, along with osteoblasts, osteoclasts, and other cells, invade the cartilage at the epiphyses. This invasion typically occurs later in bone development, after the primary ossification center has already formed in the diaphysis (shaft) of the bone.
- Function: The cells and blood supply brought by the epiphyseal bud initiate the ossification of the cartilage in the epiphyses, leading to the formation of spongy bone in this region. The process results in the development of secondary ossification centers, which are crucial for the continued growth and eventual ossification of the epiphyses.
- Location: The epiphyseal bud specifically targets the epiphyses of long bones during development.
- Role in Bone Nourishment: The nutrient artery is the primary blood vessel responsible for supplying the bone with nutrients and oxygen throughout life.
- Formation: The nutrient artery enters the bone through the nutrient foramen, a small opening in the diaphysis. It typically invades the developing bone early in endochondral ossification, supplying the primary ossification center in the diaphysis.
- Function: The nutrient artery supplies blood to the inner layers of the bone, including the bone marrow, spongy bone, and the inner part of the compact bone. It is essential for the growth, maintenance, and repair of bone tissue throughout life.
- Location: The nutrient artery typically enters the midsection of long bones (the diaphysis) but can have branches that supply other parts of the bone as well.
- Timing: The nutrient artery is involved early in bone development, supplying the primary ossification center. The epiphyseal bud occurs later, during the formation of secondary ossification centers in the epiphyses.
- Function: The epiphyseal bud initiates the formation of spongy bone in the epiphyses, while the nutrient artery provides the ongoing blood supply necessary for the survival and function of the bone tissue.
- Location: The epiphyseal bud is specific to the epiphyses, while the nutrient artery primarily supplies the diaphysis but has a role in nourishing the entire bone.
Explain the Proliferation zone and maturation zone in endochondrial ossification.
Another name for the maturation zone is what zone?
Where is the maturation zone located at?
What is an osteoid
Bones by endochondrial ossification are harder than those formed by intramembranous ossification
Flat bones also have lesser layers of compact bones than long bones. So the compact bone in femur is bulkier than the skull bone.
Proliferation:osteoblasts differentiating into osteocytes
Maturation: where the osteocytes mature
Site of calcification calcified and adds up to part of the bone to help the bone grow.
The terms “proliferation zone” and “maturation zone” refer to specific regions within the epiphyseal plate (also known as the growth plate) of long bones where different stages of bone growth and development occur.
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Proliferation Zone:
- The proliferation zone is the region of the epiphyseal plate closest to the epiphysis (end) of the bone.
- It contains rapidly dividing chondrocytes (cartilage cells) organized into stacks or columns.
- Chondrocytes in the proliferation zone undergo mitosis (cell division), leading to an increase in the number of cells.
- As new chondrocytes are formed, older cells are pushed away from the epiphysis toward the diaphysis (shaft) of the bone.
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Maturation Zone:
- The maturation zone (also known as the hypertrophic zone) is the region of the epiphyseal plate adjacent to the diaphysis.
- Chondrocytes in the maturation zone cease dividing and instead increase in size (hypertrophy).
- These hypertrophic chondrocytes signal the surrounding matrix to calcify (mineralize), which helps prepare the cartilage for eventual replacement by bone tissue.
- Blood vessels invade this zone, bringing osteogenic cells that begin to lay down bone matrix (osteoid) over the calcified cartilage.
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Function and Bone Growth:
- Together, the proliferation and maturation zones of the epiphyseal plate allow for longitudinal bone growth during childhood and adolescence.
- The continual division of chondrocytes in the proliferation zone pushes the epiphysis away from the diaphysis, elongating the bone.
- As bone growth progresses, the maturation zone undergoes transformation into bone tissue through endochondral ossification, where cartilage is replaced by mineralized bone matrix.
In summary, the proliferation zone and maturation zone are distinct regions within the epiphyseal plate where chondrocytes undergo specific stages of proliferation, hypertrophy, and transformation, contributing to bone elongation and growth in length.
The terms “proliferation zone” and “maturation zone” in the context of the epiphyseal plate (growth plate) refer specifically to the stages of chondrocyte activity during the process of endochondral ossification. These zones describe different stages of cartilage cell growth and development, which ultimately lead to bone formation. Here’s how these zones work and how they relate to osteoblasts:
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Resting Zone:
- Located closest to the epiphysis, this zone contains small, inactive chondrocytes.
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Proliferation Zone:
- Chondrocyte Activity: Chondrocytes in this zone undergo rapid mitosis (cell division), forming columns of cells that push the epiphysis away from the diaphysis, lengthening the bone.
- Significance: This is where the growth in length occurs as new cartilage is continuously produced.
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Hypertrophic Zone:
- Chondrocyte Activity: Chondrocytes enlarge and their lacunae (spaces) become bigger. This zone is characterized by the maturation of chondrocytes.
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Calcification Zone:
- Chondrocyte Activity: Chondrocytes die, and the surrounding matrix begins to calcify, leaving behind a framework for new bone formation.
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Ossification (or Osteogenic) Zone:
- Osteoblast Activity: This is where the calcified cartilage is replaced by bone. Osteoblasts invade the calcified cartilage matrix and start forming new bone tissue by depositing bone matrix.
Osteoblasts are not primarily involved in the proliferation and maturation zones. Instead, they are active in the ossification zone, where they perform the following functions:
- Bone Formation: Osteoblasts synthesize and secrete the bone matrix, including collagen and other organic components.
- Mineralization: Osteoblasts promote the deposition of calcium and phosphorus, leading to the hardening of the bone matrix.
- Proliferation Zone and Maturation Zone: These terms specifically refer to the stages of chondrocyte activity in the growth plate, crucial for cartilage growth and subsequent bone lengthening.
- Osteoblasts: Active in the ossification zone, where they replace calcified cartilage with bone tissue.
The bone matrix consists of both the organic and inorganic components of bone tissue, and osteoid specifically refers to the unmineralized, organic portion of the bone matrix. Here’s a more detailed explanation:
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Organic Component:
- Osteoid: The organic part of the bone matrix produced by osteoblasts. It is composed primarily of type I collagen fibers and a ground substance containing proteoglycans, glycoproteins, and other proteins.
- Function: Provides tensile strength and a framework for the deposition of minerals.
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Inorganic Component:
- Mineralized Matrix: Composed mainly of hydroxyapatite crystals (Ca₁₀(PO₄)₆(OH)₂), which are deposited on the osteoid.
- Function: Provides compressive strength and hardness to bone.
- Definition: The osteoid is the newly formed, unmineralized bone matrix produced by osteoblasts.
- Composition: Mainly type I collagen fibers and ground substance.(while type II is found in the hyaline cartilage )
- Function: Serves as a scaffold for subsequent mineralization by hydroxyapatite crystals.
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Osteoblast Activity:
- Osteoblasts secrete the osteoid, which initially lacks minerals.
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Mineral Deposition:
- Calcium and phosphate ions are deposited onto the osteoid, forming hydroxyapatite crystals and resulting in the mineralized bone matrix.
- Bone Matrix: Includes both the osteoid (organic, unmineralized component) and the mineralized matrix (inorganic component).
- Osteoid: The unmineralized, organic portion of the bone matrix produced by osteoblasts, which eventually becomes mineralized to form mature bone tissue.
In summary, while the osteoid is part of the bone matrix, it specifically refers to the organic, unmineralized portion that osteoblasts produce before it becomes fully mineralized.
Why do people stop growing taller?
Difference between intra membranous ossification and endochondrial
Ossification
They stop usually around 20,21 and because People typically stop growing taller when the epiphyseal plates (growth plates) in their long bones close. Epiphyseal plate is mainly formed by hyaline cartilage. When kids get injury to their epiphyseal plate,that bone stops growing longer.
the key points regarding the closure of growth plates:
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Closure of Epiphyseal Plates:
- Epiphyseal plates are made up of hyaline cartilage and are located near the ends (epiphyses) of long bones.
- During childhood and adolescence, these plates contribute to bone growth by continuously producing new cartilage cells that are eventually replaced by bone tissue through endochondral ossification.
- Closure of the epiphyseal plates occurs when chondrocytes in the growth plate stop dividing and the cartilage matrix is replaced by bone tissue
So when there’s no more hyaline cartilage,there’s no way for more osteoblasts to be formed
So instead of new bone being formed, the bone now undergoes strengthening and thickening
Osteoclasts are in the middle of the bone and osteocytes are on the outside of the bone laying more osteocytes and calcification to make bone bigger
Endochondral Ossification
1. Process: • Begins with a cartilage model that is gradually replaced by bone. • Cartilage is first formed by chondrocytes, which is then calcified, and subsequently replaced by bone tissue as osteoblasts lay down new bone matrix. 2. Types of Bones Formed: • Primarily long bones (e.g., femur, tibia, humerus). • These bones must withstand significant mechanical stress and support body weight, requiring greater strength and density.
Intramembranous Ossification
1. Process: • Direct conversion of mesenchymal tissue into bone without a cartilage intermediate. • Osteoblasts differentiate directly from mesenchymal cells and begin to secrete the bone matrix. 2. Types of Bones Formed: • Primarily flat bones (e.g., skull, clavicle, mandible). • These bones provide protection for internal organs and attachment points for muscles, requiring different structural properties compared to long bones.
State four importance of calcification
Calcification is critically important in several biological processes, particularly in the skeletal system and other tissues where mineralization plays a vital role:
- Bone Formation: In bones, calcification refers to the deposition of calcium salts (mainly hydroxyapatite crystals) onto the collagen matrix produced by osteoblasts. This process converts soft osteoid into hard bone tissue, providing strength and rigidity to the skeleton.
- Teeth Development: Calcification is essential for the formation of dental enamel, dentin, and cementum, which are crucial for tooth structure and function.
- Cartilage Mineralization: In cartilage, calcification helps transform the cartilaginous matrix into a more rigid structure, preparing it for eventual replacement by bone during endochondral ossification.
- Metabolism Regulation: Calcium ions released during bone remodeling and turnover help regulate systemic calcium levels, which are vital for muscle function, nerve transmission, blood clotting, and enzyme activity.
- Biomineralization: Beyond skeletal tissues, calcification is involved in the formation of shells in mollusks, exoskeletons in crustaceans, and other biological structures where hardness and structural integrity are essential.
Overall, calcification plays a crucial role in maintaining the structural integrity and function of various tissues and organs in the body, ensuring their proper development and physiological processes.
Note!!!
The types of ossification are very high yield questions so take note of them
State the curvatures of the spine and whether they are lordotic or kyphotic
The human spine (vertebral column) has four natural curvatures that help to distribute mechanical stress, maintain balance, and absorb shock during movement and weight-bearing activities. These curvatures are categorized based on their direction and location along the vertebral column:
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Cervical Curvature:
- Location: Found in the neck region (cervical spine).
- Curve: Cervical vertebrae naturally form a slight lordotic (concave posteriorly) curvature.
- Function: This curvature helps to support the weight of the head, provides flexibility for neck movement, and absorbs shock during activities.
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Thoracic Curvature:
- Location: Situated in the upper and middle back (thoracic spine).
- Curve: Thoracic vertebrae have a kyphotic (convex posteriorly) curvature.
- Function: The thoracic curvature helps to accommodate the rib cage and protect vital organs, such as the heart and lungs. It also assists in maintaining upright posture.
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Lumbar Curvature:
- Location: Found in the lower back (lumbar spine).
- Curve: Lumbar vertebrae exhibit a lordotic (concave posteriorly) curvature.
- Function: The lumbar curvature supports the weight of the body, facilitates movement (such as bending and lifting), and contributes to maintaining the spine’s stability and balance.
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Sacral and Coccygeal Curvature:
- Location: Sacral and coccygeal regions are located at the base of the spine (sacrum and coccyx).
- Curve: The sacrum and coccyx form a slight kyphotic curvature.
- Function: These curvatures help to distribute weight between the pelvis and lower spine, provide support for the pelvic organs, and stabilize the sitting posture.
Developmental Curvatures:
- Initially, the vertebral column appears straight during fetal development.
- Curves begin to develop as a child starts to lift their head, sit, crawl, and walk.
- These curves continue to develop and become more pronounced as the child grows and the spine matures.
In summary, the natural curvatures of the spine (cervical lordosis, thoracic kyphosis, lumbar lordosis, and sacrococcygeal kyphosis) contribute to the spine’s overall flexibility, stability, and ability to absorb shock. These curvatures are essential for maintaining proper posture, balance, and efficient movement throughout daily activities.
Characteristics of the different types of vertebrae
Focus on Spinous and transverse processes of thoracic and cervical vertebrae is
Focus on whether they have transverse foramen or not
Cervical has transverse foramen but thoracic and lumbar don’t have.
Vertebrae are classified into different types based on their location and specific structural features. In the human spine, there are five main types of vertebrae: cervical, thoracic, lumbar, sacral, and coccygeal. Here are the key differences between these types of vertebrae:
Cervical have articulating facets that are held by pedicles and laminar
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Cervical Vertebrae:
- Location: Located in the neck region (upper spine).
- Characteristics: Cervical vertebrae are generally smaller and more delicate compared to other vertebrae types. They have transverse foramina (openings) in their transverse processes for the passage of the vertebral arteries.
- Number: There are seven cervical vertebrae (C1 to C7), including the atlas (C1) and axis (C2) vertebrae, which are specialized for unique functions in supporting the head and facilitating neck movement.
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Thoracic Vertebrae:
- Location: Situated in the upper and middle back (thoracic spine).
- Characteristics: Thoracic vertebrae have long, downward-pointing spinous processes and facets (articulating surfaces) for articulation with the ribs.
- Number: There are twelve thoracic vertebrae (T1 to T12). Each thoracic vertebra articulates with a pair of ribs, contributing to the rib cage structure and protecting internal organs.
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Lumbar Vertebrae:
- Location: Found in the lower back (lumbar spine).
- Characteristics: Lumbar vertebrae are the largest and strongest of the movable vertebrae. They have thick, stout bodies and short, thick spinous processes.
- Number: There are five lumbar vertebrae (L1 to L5). Lumbar vertebrae provide stability and support to the lower back and bear the majority of the body’s weight.
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Sacral Vertebrae:
- Location: Fused into the sacrum, which is located at the base of the spine.
- Characteristics: The sacral vertebrae are fused together to form a single triangular-shaped bone. They have large, robust bodies and are adapted to support the weight of the upper body when sitting.
- Number: There are usually five sacral vertebrae (S1 to S5), but they fuse together during development to form the sacrum.
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Coccygeal Vertebrae:
- Location: Found in the coccyx or tailbone region.
- Characteristics: Coccygeal vertebrae are small, triangular bones that are typically fused together into a single structure. They lack significant vertebral body and spinous processes.
- Number: There are usually three to five coccygeal vertebrae (Co1 to Co5), but the number can vary among individuals.
In summary, each type of vertebra is specialized for its particular location and function within the spine. These differences in structure and characteristics reflect their roles in providing support, flexibility, protection, and mobility throughout the vertebral column.
Where is the medullary cavity or canal located?
Where is the red and yellow bone marrow found in the bone?
What is the Haversian Canal or system
It seems there might be some confusion or miscommunication in your statement. Let’s clarify the process that occurs in the diaphysis (shaft) of long bones during skeletal development and growth:
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Diaphysis and Medullary Canal:
- The diaphysis of a long bone is the cylindrical, tubular portion located between the epiphyses (ends) of the bone.
- Inside the diaphysis is the medullary cavity (or medullary canal), which is a hollow space filled with bone marrow.
- The medullary cavity contains yellow bone marrow in adults, which stores fat, and red bone marrow in children and some adult bones, where blood cells are produced.
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Bone Development:
- During embryonic and fetal development, the diaphysis of long bones forms through the process of endochondral ossification.
- Endochondral ossification begins with a cartilage model of the bone, which gradually ossifies (turns into bone tissue) over time.
- Chondrocytes (cartilage cells) within the cartilage model hypertrophy (enlarge) and produce calcified cartilage matrix.
- Osteoblasts (bone-forming cells) then replace the calcified cartilage with bone tissue (osteoid), starting from the primary ossification center in the diaphysis.
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Haversian Systems and Remodeling:
- As bone continues to grow and develop, osteoclasts (bone-resorbing cells) and osteoblasts remodel the bone tissue within the diaphysis.
- Haversian systems (or osteons) form, consisting of concentric rings of bone tissue around central canals (Haversian canals), which contain blood vessels and nerves.
- This remodeling process helps to maintain bone strength, repair microdamage, and adjust bone structure in response to mechanical stress.
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Medullary Canal Formation:
- The medullary canal is not formed by the diaphysis “dying,” but rather it is a natural part of the bone’s structure.
- As osteoclasts resorb bone tissue from the center of the diaphysis during development, they create the hollow medullary cavity.
- The medullary cavity is essential for reducing the weight of the bone while maintaining strength and providing space for bone marrow.
In summary, the medullary canal forms as a result of the natural processes of bone development and remodeling in the diaphysis of long bones. It is not caused by the diaphysis “dying,” but rather by the resorption of bone tissue and the formation of bone marrow-containing cavities during skeletal growth and maturation.
Vessel that enters into the bone as a point called the bud. Brings what?
Which part of the bone marrow are hematopoietic stem cells found in? Or apart form the bone marrow, which other part
Of the bone is the HSCs found in
Brings hematopoietic stem cells and other progenitor cells to form more cells
hematopoietic stem cells (HSCs) are primarily found in the bone marrow, particularly in the trabecular (spongy) bone of the long bones and flat bones.
It enters at the periosteal bud.
The periosteal bud is a key component in the process of endochondral ossification. It consists of:
1. Blood Vessels: • Provide nutrients and oxygen to the developing bone and bring in other necessary cells. 2. Osteoblasts: • Bone-forming cells that help lay down new bone matrix. 3. Osteoclasts: • Cells involved in bone resorption, helping to shape and remodel the developing bone. 4. Other Cells: • Includes cells that contribute to the formation of bone marrow.
Number of vertebrae in;
Cervical
Thoracic
Lumbar
Sacral
Coccyx
I eat at 7,12,5 and 9(5 sacral 4 coccyx)The number of vertebrae in the vertebral column can vary depending on the species. In humans, the vertebral column typically consists of 33 vertebrae at birth, which later fuse into 26 as some of the vertebrae fuse together. Here is the breakdown:
- Cervical Vertebrae: 7 vertebrae (C1 to C7) in the neck region.
- Thoracic Vertebrae: 12 vertebrae (T1 to T12) in the upper and mid-back region, each articulating with a pair of ribs.
- Lumbar Vertebrae: 5 vertebrae (L1 to L5) in the lower back, supporting the majority of the body’s weight.
- Sacral Vertebrae: 5 vertebrae fused into a single bone called the sacrum (S1 to S5), forming the back part of the pelvis.
- Coccygeal Vertebrae: 3 to 5 vertebrae fused into a single bone called the coccyx (Co1 to Co5), also known as the tailbone.
In summary, the human vertebral column typically consists of 26 vertebrae after fusion during development and adulthood. This number can vary slightly among individuals due to anatomical variations.
