LESSON 22 (Bone Structure And Remodelling) Flashcards
What are osteon?
The structural unit of compact bone
What does osteon consists of?
An elongated cylinder that runs PARALLEL to the long axis of bone. Which acts as a tiny weight-bearing pillar
What does the Osteon Cylinder Consists of?
- several rings of bone matrix aka (LAMELLA)
What does Lamellae contain?
Collagen fibers that run in different directions in adjacent rings
Where does the Central (Haversian) canal run through?
The core of the osteon which contains blood vessels and nerve fibres
Where can you find the Perforating (Volkmann’s) canals?
It is lined with Endosteum which occur at right angles to the central canal
- connected to blood vessels and nerves of periosteum, medullary cavity and central canal
What are lacunae?
Small cavities that contain osteocytes
What are canaliculi?
Hairlike canals that connect the lacunae to e/o & to the central canal
Why does osteoblasts secrete bone matrix?
To maintain contact with e/o & other osteocytes (through cell projections with gap junctions)
How does Canaliculi form?
When matrix hardens and cells are trapped
Function of canaliculi
Allow communication between the osteocytes and permit nutrients and waste to flow to and from the central canal
What are Interstitial Lamellae
- Lamellae that are not part of osteon
- some fill gaps between forming osteons
- others are remnants
What are Circumferential Lamellae?
- layers of Lamellae that extend around the entire surface of diaphysis
- they are located deep into the periosteum but superficial to Endosteum
- helps long bones to resist twisting
How are Spongy Bones organized
Along lies of stress to help bone resist any stress
What are Trabeculae and what do they contain?
- they’re like cables on a suspension bridge (strength to bone)
- doesn’t contain Osteons
- but contains irregularly arranged Lamellae and osteocytes that is interconnected by canaliculi
What does Capillaries in the Endosteum do?
Supply nutrients
What are Hydroxyapatite’s and what does it consists?
- aka mineral salts that makes up 65% of bone mass
- consists of tiny calcium phosphate crystals in and around collagen fibres
- responsible for hardness and resist compression
What does bone remodelling consists primarily of and how does it occur?
- consists of both Bone Deposit and Bone Resorption
- occurs at the surface of both the Periosteum and Endosteum
What coordinates the remodelling process of bones?
Packets of adjacent Osteoblasts and Osteoclasts
How is the new bone matrix deposited by?
Osteoblasts
What are osteoid seam?
A band of unmineralized bone matrix that marks areas of new deposition
What is the calcification front?
A transition zone between the osteoid seam and the older mineralized bone
What is Bone Resorption?
A function of Osteoclasts that dig grooves as they break down matrix by secreting Lysosomal enzymes and protons
How is hormonal control of remodelling used?
To maintain blood calcium homeostasis & balances activity of parathyroid hormone & calcitonin
What are Parathyroid Hormone (PHT)
It stimulates osteoclasts to resorb bone
- releases calcium into blood
Why is Calcitonin?
Produced by parafollicular cells of thyroid gland in response to high levels of blood calcium levels