Bone Flashcards
What are three basic qualities of bone that can help explain its histology?
Its alive
Its light
It has high tensile strength
What are the two shape classifications of bone?
Flat
Long
What are the two mechanisms of bone formation?
Intramembranous
Endochondral
What does intramembranous formation mean?
Mesenchymal CT CHANGES INTO bone
What does endochondral formation mean?
Cartilage is REPLACED by bone
How can inferences about the bone’s age be made?
By examining its microscopic structure
What features of bone would suggest youth/immaturity?
Woven or immature bone
What features suggest a mature/older bone?
Lamellar
Spongy/Compact
What are some qualities of woven bone?
Very cellular
Irregular matrix
Low mineral content
What are some qualities of lamellar bone?
Matrix is arranged in layers
Bone can be spongy or compact
What is the only way bone Grows?
Appositional
What are the three regional divisions of a long bone?
Diaphysis/Shaft
Epiphysis/Rounded End
Epiphyseal Plate
What is the structural makeup of the long bone diaphysis?
Compact bone on outside, marrow cavity inside
What is the term for blood cell formation?
Hematopoiesis
Where in the bone does hematopoiesis take place?
In the red marrow
What is yellow marrow filled with?
Adipose CT
What is the structural makeup of the epiphysis?
Compact bone on outside, spongy bone on inside
What two regions does the epiphyseal plate separate?
It separates the diaphysis from the epiphysis
Where is the periosteum found?
It covers the entire exterior of the bone except for articular surfaces
What are the two primary layers of periosteum?
Outer layer of Dense Fibrous CT
Inner Osteogenic layer
Where is the endosteum found?
It lines the marrow cavity,
aka all internal surfaces of the long bone
What makes up the endosteum?
A single layer of osteoblasts or osteogenic cells
What type of cartilage makes up the articular cartilage?
Hyaline
How do blood vessels get into the mature bone layers?
Periosteal vessels are “trapped” as the periosteum lays down new bone
What do Nutrient vessels supply?
Long bone marrow
Where do the nutrient vessels enter?
The diaphysis compact bone
What are the function of epiphyseal vessels?
To supply the epiphysis
Where do epiphyseal vessels enter?
Near the epiphyseal plate
Where is there an abundance of nerve cells
In the periosteum, not in the “bone” cells
How do the vasomotor nerves get inside the bone?
They run alongside the blood vessels
What are the components of flat bone?
Inner and Outer Tables of thick compact bone
Diploe layer
Periosteum
What is the diploe of flat bone?
Spongy bone between the tables
Where is the periosteum found in the cranial flat bones?
On the outer surface
Inner surface is dura mater
What are the 3 primary histological components of bone?
Osteoblasts
Osteoclasts
Osteocytes
Where do you find osteoblasts
They (or their precursors) form a row of cuboidal cells of the surfaces of bone on both the periosteal and endosteal surfaces
What is the nucleus of the osteoblast like?
Its usually on the side of the cell away from the bone
It has a prominent nucleolus
Why is the osteoblast cytoplasm so basophilic?
Because of the large amount of RER
Besides the basophilic RER, what else is notable about the osteoblast cytoplasm?
Negative image golgi
Lots of mitochondria
When depositing new bone, what is the first thing synthesized by an osteoblast?
Osteoid
What are the two components of the Osteoid?
Type I collagen
Ground Surface: Condroitin sulfate
What do the osteoblasts secrete to ossify the osteoid?
Alkaline phosphatase
What does the alkaline phosphatase do?
Causes the calcification of the osteoid along the collagen fibers
What do osteocytes look like?
Flattened ovoid with long processes extending from it through caniculi in the bone towards other osteocytes. They are joined by gap junctions
What is the function of the osteocyte?
They transport materials between blood and bone to maintain the surrounding matrix
How many nuclei can osteoclasts have?
Up to 15-20!
Where are osteoclasts located?
Surface of bone, frequently in depressions called Howship’s lacunae
What are the precursors for Osteoclasts?
Monocytes in the bone marrow
How do they resorb bone?
Primarily with proteolytic enzymes (acid phosphatase)
How can the cytoplasm of osteoclasts be described?
frothy of vacuolated
contain granules of acid phosphatase
surface facing bone is ruffled
What percent of the dry weight is the organic portion of bone?
35%
What organic component makes up 90% of the bone matrix?
Type I collagen
What feature identifies Type I collagen
banding
What is the other major portion of the organic bone matrix?
Glycosaminoglycans
What do the GAGs do?
Cement collagen fibers together
Why is the matrix more acidophilic than cartilage?
There are less chondoitin sulfates
What is the function of the organic matrix
Gives bone great toughness and resiliency
What makes up the inorganic portion of bone?
Crystals like Hydroxyapaptite
Calcium ions
Phosphate ions
Citrate & Carbonate
What do the deposition needles look like physically?
Slender needles along collagen fibers
What is the function of the inorganic portion
Hardness
What are the three types of Lamella?
Haversian System
Inner and Outer circumferential lamellae
Interstitial Lamellae
