Unit Two Flashcards
What percentage does bone tissue weight in the human body?
18%
What are the functions of Bone?
- Support
- Protection
- Movement
- Mineral Homeostasis - Stores minerals (like calcium and phosphorus) and releases minerals into blood when other organs and muscles need them
- Blood Cell Production - Hemopoiesis (production of RBCs, WBCs, and platelets) occurs in red bone marrow inside bone
- Triglyceride Storage - Triglycerides are high energy source and stored in yellow bone marrow (consists of high concentration of adipose cells) and found within the bone
Regions of long bones:
Diaphysis - Central shaft of the bone
Epiphysis - The distal and proximal ends of the bone
Metaphysis - Regions where diaphysis meets the epiphysis (contains epiphyseal plate of hyaline cartilage responsible for growth and becomes epiphyseal line when bone stops growing)
Structures of long bones:
Articular Cartilage - Hyaline cartilage covering epiphysis, reduce friction and absorbs shock in the joint
Periosteum - Dense irregular tissue surrounds bone surface.
Medullary Cavity - Space in the Diaphysis that contain fatty yellow bone marrow in adult long bones and red marrow in flat bones
Endosteum - Thin membrane of bone forming cells that lines the medullary cavity
Functions of Periosteum
Allow bone to grow in width, protection, nourishment, and an attachment point for ligaments and tendons
Sharpy’s fibers are collagen fibers that attach the periosteum to the bone
What is the extracellular matrix of bone tissue made of?
25% water, 25% collagen (flexibility), and 50% crystallized mineral salt
(calcium phosphate salts - reason for hardness)
Process of calcification:
Mineral salts are deposited in the framework formed by the collagen fibers, then crystallize causing the tissue to harden
What does a bone’s hardness depend on?
The crystallized mineral salt
What does a bone’s flexibility depend on?
The collagen fibers
What are the cells of the bone?
Osteogenic cells
Osteoblasts
Osteocytes
Osteoclasts
What are Osteogenic cells
Unspecialized stem cells that undergo mitosis and differentiation and become osteoblasts
Where do you find Osteogenic cells?
Mostly in endosteum but also a little in periosteum
What bone cells undergo cell devision?
Osteogenic cells
What are Osteoblasts?
Bone-building cells that synthesize collagen to build the extracellular matrix and initiate calcification
They become trapped in extracellular matrix and develop into osteocytes
What are Osteocytes?
Mature bone cells that maintain the bone metabolism and nutrient/waste exchange with the blood
(Keep bone tissue healthy)
What are Osteoclasts?
Large cells produced from the fusion of around 50 monocytes (type of WBC)
Responsible for resorption of bone (breakdown of bone’s extracellular matrix for development, growth and repair)
Where are Osteoclasts found?
Endosteum
What is bone remodelling?
Interaction where osteoclasts breakdown bone and osteoblasts build new bone
What is the strongest form of bone tissue?
Compact bone
What percentage of compact bone makes up the skeleton?
80%
Where is compact bone found?
Outer portion of the bone, under the periosteum
What are the structures of compact bone?
Haversian Canal - tubes where arteries and veins pass through
Concentric Lamellae - calcified extracellular matrix surrounding the haversian canal
Lacunae - spaces between the lamellae that house the osteocytes
Canaliculi - small canals that connect the lacunae and eventually lead to the haversian canal (so osteocytes can communicate and nutrient/waste can travel through)
Interstitial lamellae - Areas between osteons (concentric lamellae) that has been broken down by osteoclasts
Circumferential Lamellae - Lamellae that encircle the medullary cavity just beneath the periosteum
What type of bone does not contain osteons?
Spongy bone
What is the lamellae in spongy bone called?
Trabeculae
What surrounds the trabeculae?
Spaces
Are there lacunae and canaliculi in the trabecula?
Yes
Function of the space between trabeculae?
Makes bone lighter and contains red bone marrow which feeds the osteocytes directly with blood from the marrow
Where do you find spongy bone?
Abundant in flat and irregularly shaped bones
Bones that are not heavily stressed
What is a Bone Scan?
Radiological diagnostic procedure where the body is injected intravenously with a small amount of radioactive tracer (dye). Then body is scanned by a gamma camera to measure the amount of radiation emitted from the bones.
What are “cold spots” indicated by in bone scans and what can they mean?
Lighter areas - decreased metabolism/blood flow
Can indicate osteoporosis, infections, and inflammatory arthridities (rheumatoid arthritis)
What identifies normal bones after doing a bone scan?
Gray color - indicates a uniform uptake of the tracer by the bone
What are “hot spots” indicated by in bone scans and what can they mean?
Darker spots - areas of increased metabolism/blood flow
Can indicate bone cancer, fractures, or abnormal growth
Why are bones so abundant with blood vessels?
- Accommodate the constant metabolism, remodeling and growth of the bone
- To deliver the newly manufactured blood out from the red marrow to the rest of the body
What are periosteal arteries?
Arteries accompanying nerves that travel through the Volkman’s canals (nutrient foramen) into the diaphysis, supplying the periosteum and the outer compact bone
Where are nerves and free nerve endings abundant within bone?
The periosteum
(reason why fractures and bone tumors are so painful)
What are the terms for bone formation?
Ossification or osteogenesis
What does Osteogenesis involve?
Either the replacement of preexisting connective tissue with bone or the replacement of cartilage with bone
What are the two methods of osteogenesis?
Intramembranous and endochondral ossification
Where does intramembranous ossification occur?
Flat bones and skull bones
What are the steps of Intramembranous ossification?
- Development of the ossification center
- Calcification
- Trabeculae Formation
- Periosteum Development
What occurs during the development of the ossification center for Intramembranous Ossification?
During fetal development: mesenchymal cells (tissue from which all CT arises) cluster together, forming the ossification center. These cells then differentiate into osteogenic cells then into osteoblasts. The osteoblasts start secreting the extracellular matrix
What occurs during the calcification step in Intramembranous Ossification?
After the extracellular matrix formation stops, the osteoblasts mature and become osteocytes. After a few days the calcium and mineral salts are deposited and the extracellular matrix calcifies and hardens
What occurs during the Trabeculae formation step in Intramembranous Ossification?
As the extracellular matrix forms, it develops into trabeculae forming spongy bone. Blood vessels grow in the spaces between the trabeculae and form red bone marrow
What occurs during the Periosteum Development step in intramembranous Ossification?
On the outside of the bone, mesenchymal cells condense and form the periosteum
What is Endochondral Ossification?
Replacement of cartilage by bone
What type of bone undergoes Endochondral Ossification?
Long bones
What are the steps for Endochondral Ossification?
- Development of the Cartilage model
- Growth of the Cartilage model
- Development of the primary ossification center
- Development of the medullary cavity
5.Development of the secondary ossification centers - Formation of the articular cartilage and the epiphyseal plate
What occurs during the development of the cartilage model in Endochondral Ossification?
During fetal development: mesenchymal cells form the shape of the future bone and differentiate into chondroblasts.
Chondroblasts are immature cartilage cells that secrete hyaline cartilage and produce a cartilage model of the long bone.
Also, a membrane called the perichondrium develops around the cartilage model.
What occurs during the growth of the cartilage model in Endochondral Ossification?
Chondroblasts mature and become chondrocytes. The chondrocytes
undergo continual mitosis causing the cartilage model to increase in length (interstitial growth)
The cartilage model increases in width by continual mitotic activity of chondroblasts in the perichondrium. (Appositional growth)
As the cartilage model continues to grow, chondrocytes grow in size and the surrounding cartilage extracellular matrix begins to calcify.
Soon the chondrocytes begin to die
because nutrients cannot diffuse across the calcified matrix and reach the chondrocyte. As the chondrocytes die, lacunae form.
What occurs during the development of the primary ossification center in Endochondral Ossification?
A nutrient artery penetrates the perichondrium and travels to the middle of the cartilage model. The blood supply stimulates the osteogenic cells in the perichondrium to become osteoblasts. The perichondrium starts to form bone and becomes the periosteum.
In the middle of the cartilage model, the nutrient artery branches into capillaries and fills the already disintegrating calcified cartilage, forming the primary ossification center. This is the region where bone tissue will start being deposited over remnants of calcified cartilage, forming spongy bone trabeculae.
What occurs during the development of the medullary cavity in Endochondral Ossification?
As the primary ossification center
expands toward the ends of the bones,
osteoclasts start to break down some of
the newly formed spongy trabeculae.
This leaves a central cavity in the
diaphysis which becomes the medullary
cavity that will contain the marrow.
What occurs during the development of the secondary ossification centers in Endochondral Ossification?
This occurs at the time of birth. Branches of the
epiphyseal artery enters the epiphyses, where the sites of the secondary ossification centers are located. The blood supply stimulates the formation of osteogenic cells that quickly differentiate into osteoblasts. The osteoblasts start to deposit bone tissue over the remnants of calcified cartilage forming spongy bone.
What occurs during the formation of the articular cartilage and the epiphyseal plate in Endochondral Ossification?
The hyaline cartilage of the preexisting cartilage
model remains over the epiphyses and
becomes the articulating cartilage.
Hyaline cartilage also remains between
the diaphysis and the epiphysis forming
the epiphyseal plate, responsible for the
lengthening of long bone.
What is the difference between primary and secondary ossification centers?
The primary ossification center occurs in the diaphysis and forms the medullary cavity.
The secondary ossification centers occurs in the epiphyses, the spongy bone remains and is not replaced by the
medullary cavity
What is the Epiphyseal plate?
A layer of hyaline cartilage in the metaphysis of long bones
What are the Zones of the Epiphyseal plate?
- Zone of resting cartilage
- Zone of proliferating cartilage
- Zone of Hypertrophic Cartilage
- Zone of Calcified Cartilage
What is the Zone of Resting Cartilage?
A layer of small chondrocytes that is closest to the epiphysis and functions to anchor the epiphyseal plate
What is the Zone of Proliferating Cartilage?
Layer of larger chondrocytes that divide to replace dead chondrocytes at the diaphyseal side of the epiphyseal plate
What is the zone of Hypertrophic Cartilage?
Layer of large, maturing chondrocytes arranged in columns
What is the Zone of Calcified Cartilage?
Layer of mostly dead, calcified chondrocytes. Osteoclasts will dissolve the calcified cartilage while osteoblasts and vessels from the diaphysis invade the area and lay down new bone.
Where does the length of the bone increase?
The diaphyseal end of the epiphyseal plate
Explain Appositional Growth:
- Cells in the periosteum differentiate into osteoblasts. The osteoblasts secrete collagen and extracellular matrix until they become surrounded by it. They then become osteocytes. This process forms bone ridges on either sides of a periosteal blood vessel, which continues to grow forming grooves for the vessel.
- Eventually the ridges fold over the vessel and fuse, causing the groove to become a tunnel that encloses the blood vessel. The former periosteum becomes the endosteum that line the tunnel.
- Osteoblasts in the endosteum lays down more bony matrix forming new concentric lamellae around the vessel. This continues until the vessel is firmly anchored, forming the osteon.
- Osteoblasts under the periosteum deposit new outer circumferential lamellae, increasing the width of the bone.
Where do osteoclasts destroy bone tissue?
In the Medullary cavity
Why is Bone remodeling important?
Allows for increased growth of a bone
Also removes injured bone, replacing with a new stronger and thicker bone, that is more fracture resistant
What can happen if there is too much activity from osteoclasts and too little activity from osteoblasts?
Excessive loss of calcium and mineral content leading to osteoporosis, rickets, and osteomalasia
What can happen if there is too much activity from osteoblasts and too little activity from osteoclasts?
Lead to abnormally thick and heavy bones or the formation of osteophytes (bone spurs)
What are factors that can affect bone growth?
Minerals
Vitamins
Hormones
What Vitamin is essential for collagen formation?
Vitamin C
What Vitamins are needed for bone protein synthesis?
Vitamin K and B12
What Vitamin stimulates osteoblastic activity?
Vitamin A