What type of tissue is bone?
Connective
What are the components of bone?
Cells and Extracellular Matrix (Bone Matrix)
What cells make up bone?
- Osteoblasts
- Osteoclasts
- Osteocytes
- Bone lining Cells
- Osteoprogenitor Cells
What makes up Bone Matrix?
- Fibers
2. Ground Substance
What is general fibrous structure of bone and why is it like that?
Fibers are aligned parallel but are oriented in different directions.
Adds strength.
What gives bone its strength?
A calcified bone matrix
What cells help “maintain” the bone matrix?
Osteocytes
How does the osteocyte gets its nutrients and get rid of waste?
Canaliculi
What happens in the canaliculi?
Exchange of nutrients and waste products that travel down cell to cell of dendritic processes of osteocytes
What structure aids w/ transfer of nutrients from one osteocyte to another?
Gap Junctions
2 General Types of Bone Structure
- Compact Bone
2. Cancellous Bone (AKA spongy or trabecular bone)
Is compact bone and cancellous bone made of the same material?
Yes. Both Lamellar bone. Organized differently.
Where do osteoblasts come from?
Bone lining cells or osteoprogenitor cells.
Steps of the bone remodeling cycle (3).
- Osteoclast (apoptosis)
- Osteoblast Secretes bone matrix (osteoid - unmineralized bone)
- Mineralization
Where does bone remodeling occur?
- On the surface of bone
2. In the middle of bone
How does bone modeling occur in the middle of bone?
- Clasts come through blood vessel, start working to make a connecting canal
- Blasts stay on surface (bone lining cells) and fill in canal with bone (surround blood vessels)
- Cytes sit in lacuna and maintain matrix and stim remodeling cycle from stress
What is osteoporosis?
- Decreased bone mass per unit volume of anatomical bone.
2. After 35, clast > blast
Biphosphonates can help limit osteoporosis, but osteonecrosis may be a side effect, why?
Biphosphonates disrupt bone remodeling. When there is continual stress on the bones, they have a limited capacity for healing
Different kinds of osteogenesis (2)
- Intramembranous Ossification
2. Endochondral Ossification
Most flat bones develop via _______ ossification.
Intramembranous
Steps of intramembranous ossification (4)
- Mesenchymal cells in CT membrane or sheet form clusters
- Cluster differentiates into osteoblasts = ossification center
- Osteoblasts secrete osteoid
- Becomes mineralized
What is condensed mesenchyme?
Mesenchyme that is more cellular
What kind of bone is intramembranous bone?
Primary bone or Woven Bone = SPONGY
*NOT LAMELLAR BONE or secondary bone
What are trabeculae made of and how is it oriented?
Collagen Fibers
Oriented Randomly
What happens during the remodeling of woven bone?
Where can you find this kind of bone?
It become lamellar bone, with collagen fibers oriented in parallel.
Flat bones like in the skull.
What does endochondral ossification mean?
Cartilage that turns to bone.
Steps of endochondral ossification.
- Mesenchymal Cells Condense during fetal development
- Develop into chondrocytes
- Cartilage is developed into the shape of the bone that it will form (surrounded by perichondrium)
- Cartilage deteriorates and becomes primary ossification center (woven bone), has blood vessel of periosteal bud
- Secondary Ossification Centers develop at the ends of the bone
Why is epiphyseal cartilage important?
It allows you to get taller
Zones of epiphyseal growth plate (5)
Zone 1 - Hyaline Cartilage (resting zone)
Zone 2 - Proliferation - making more chondrocytes
Zone 3 - Hypertrophy
Zone 4 - Calcification - osteoblasts come in and lay down bone
Zone 5 - Ossification
What happens to chondrocytes at the epiphyseal growth plate? (7)
- Hypertrophy of chondrocytes
- Compress surrounding cartilaganous matrix
- Chondrocytes die (apoptosis)
- Carilage matrix become more calcified (basophilic)
- Blood vessels and osteoblasts invade the tissue
- Lay down Osteoid
- Mineralized to bone
What type of bone will initially be formed at the growth plate?
Woven bone. Later remodeled into lamellar bone.
When is full stature obtained?
When the epiphyses have fused (fully ossified, no more cartilage there)
Which type of bone would you see in a new fracture and healed fracture?
- Woven Bone
- Lamellar Bone
* Fractures heal quickly, woven bone is layed and remodeled
What general things affect bone formation/turnover?
- Major Systemic Regulators
2. Stress on the bone
What are the major systemic regulators of bone formation/turnover? (7)
- Parathyroid Hormone (PTH)
- Calcitrol (vit. D)
- Calcitonin
- Growth hormone/ IGF - 1
- Glucocorticoids
- Thyroid Hormones
- Estrogen/androgens
* First 3 are most important*
* *Remember PCC**
What is the main function of Vitamin D?
Increase Ca absorption from the gut
Main function of PTH?
Released when serum Ca low
*Stimulates osteoclast activity to raise serum Ca
What would a happen with deficiency of PTH?
Remodeling process would not be stimulated
What does excess growth hormone in an adult result in and why?
Acromegaly
Periosteal growth happens b/c you do not have endochondral ossification as an adult
What does excess growth hormone in a child result in and why?
Gigantism
Endochondral ossification at the epiphyseal plate
What does insufficent growth hormone in a child result in?
Dwarfism
What are the components of the joint capsule?
- Fibrous Layer
2. Synovial Membrane
What is the orientation of collagen fibers in Articular Cartilage?
Curved fibers. Perpendicular to surface near the bone and parallel to surface neaer the surface.
What is the advantage of curved fibers in articular cartilage?
Pressure is more evenly distributed, helps protect the chondrocytes from deformation.
Where do chondrocytes in articular cartilage get their nutrients?
Synovial fluid.
*When you stand and squish cartilage, the water is pushed out into synovial fluid, and when you sit back down, water goes back in and brings O2 and nutrients with it.
