Lecture 4 (FIRST MIDTERM) Flashcards
Spongy bone is able to resist stress because of the…
trabeculae
think of the analogy of the rolled up magazine
Stress lines are thickest in what regions?
where stress is the highest
What is the periosteum?
the outside covering of bone; fibrous outside, cellular inside; functions in growth and repair
What is the endosteum?
the inside covering (the marrow cavity); functions in growth and repair
How many layers of periosteum?
Two
What are the layers of periosteum?
Fibrous outside (dense irregular connective tissue) and cellular inside
Compared to the periosteum, what does the endosteum lack?
the fibrous outside covering
The cellular layer of the periosteum and the endosteum contain what kind of cells?
osteoprogenitor cells
Two modes of bone formation:
Endochondral ossification and intremembranous ossification
How does the cellular layer of periosteum connect so strongly to the bone?
Perforating fibers go deeply into the bone from the periosteum; when osteoprogenitor cells turn into osteoblasts, they secrete osteoid around the fibers and they become bone. The fibers are actually embedded in bone.
Intramembranous ossification is also called what?
Dermal ossification
because bone develops directly inside the dermis
Endochondral ossification:
- bone that forms inside cartilage
- cartilage is converted to bone (by bonding minerals to cartilage)
Endochondral ossification has a ___________ ______________.
cartilaginous precursor
Endochondral ossification is typical of the formation of what bones?
irregular
2 ways bones grow with the method of endochondral ossification:
Interstitial growth and appositional growth
Epiphyseal growth is another way to refer to…
interstitial growth
The way bones grow with intermembranous ossification:
with bony spicules that spread out.
-common in flat bones (many in the skull)
In the cartilage during endochondral ossification, what starts growing larger and larger and creates big spaces, which eventually “kills” itself but cutting off nutrition to itself?
chondrocytes
The spaces left from the “dead” chondrocytes is invaded by what?
blood vessels
What differentiates into the first osteoblasts?
fibroblasts
What migrates in with the blood vessels?
fibroblasts
The primary center of ossification is located where?
inside of the diaphysis
During ossification, perichondrium now turns into…
periosteum
Secondary centers of ossification are located where?
epiphyses
Where does interstitial (epiphyseal) growth occur?
metaphysis
How does appositional growth occur?
The cells of the inner layer of the periosteum differentiate into osteoblasts and deposit bone matrix to outside.
Osteoclasts from inside the bone are slowly removing bone matrix from the inner surface.
Bone eventually increases in diameter.
How can they tell how much more you’re gonna grow?
Look at the amount of cartilage still there among the bones
Where does appositional growth occur?
at the periosteum
How does intramembranous ossification occur?
Mesenchymal cells aggregate and form clusters that become osteoblasts and start forming osteoid
Where does intramembranous ossification occur?
inside the dermis
Endochondral bone comes from cartilage, so it’s from mesoderm. HOWEVER, intramembranous (dermal) bone comes from…
neural crest cells
Since intramembranous bone forms in the dermis, there is no cartilaginous precursor. Is there a perichondrium? Periosteum?
Neither, UNTIL the very end when there is already some bone (a plate) formed
Mesenchymal cells that form in intramembranous ossification condense to form what?
an ossification center
Bone as a dynamic tissue increases bone formation by…
- Exercise
- Estrogen/testosterone (more hormone, more bone. less hormone, less bone)
- Growth hormone
As you get older, your ________ activity slows down while your __________ activity doesn’t really slow down.
osteoblast, osteoclast
Difference between osteopenia and osteoporosis:
Osteopenia: lack of bone; normal with age
Osteoporosis: porous ; not normal
