LESSON 22 (Bone Structure And Remodelling)

Question 1

What are osteon?

Answer 1

The structural unit of compact bone

Question 2

What does osteon consists of?

Answer 2

An elongated cylinder that runs PARALLEL to the long axis of bone. Which acts as a tiny weight-bearing pillar

Question 3

What does the Osteon Cylinder Consists of?

Answer 3

• several rings of bone matrix aka (LAMELLA)

Question 4

What does Lamellae contain?

Answer 4

Collagen fibers that run in different directions in adjacent rings

Question 5

Where does the Central (Haversian) canal run through?

Answer 5

The core of the osteon which contains blood vessels and nerve fibres

Question 6

Where can you find the Perforating (Volkmann’s) canals?

Answer 6

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

Question 7

What are lacunae?

Answer 7

Small cavities that contain osteocytes

Question 8

What are canaliculi?

Answer 8

Hairlike canals that connect the lacunae to e/o & to the central canal

Question 9

Why does osteoblasts secrete bone matrix?

Answer 9

To maintain contact with e/o & other osteocytes (through cell projections with gap junctions)

Question 10

How does Canaliculi form?

Answer 10

When matrix hardens and cells are trapped

Question 11

Function of canaliculi

Answer 11

Allow communication between the osteocytes and permit nutrients and waste to flow to and from the central canal

Question 12

What are Interstitial Lamellae

Answer 12

• Lamellae that are not part of osteon
• some fill gaps between forming osteons
• others are remnants

Question 13

What are Circumferential Lamellae?

Answer 13

• 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

Question 14

How are Spongy Bones organized

Answer 14

Along lies of stress to help bone resist any stress

Question 15

What are Trabeculae and what do they contain?

Answer 15

• 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

Question 16

What does Capillaries in the Endosteum do?

Answer 16

Supply nutrients

Question 17

What are Hydroxyapatite’s and what does it consists?

Answer 17

• 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

Question 18

What does bone remodelling consists primarily of and how does it occur?

Answer 18

• consists of both Bone Deposit and Bone Resorption
• occurs at the surface of both the Periosteum and Endosteum

Question 19

What coordinates the remodelling process of bones?

Answer 19

Packets of adjacent Osteoblasts and Osteoclasts

Question 20

How is the new bone matrix deposited by?

Answer 20

Osteoblasts

Question 21

What are osteoid seam?

Answer 21

A band of unmineralized bone matrix that marks areas of new deposition

Question 22

What is the calcification front?

Answer 22

A transition zone between the osteoid seam and the older mineralized bone

Question 23

What is Bone Resorption?

Answer 23

A function of Osteoclasts that dig grooves as they break down matrix by secreting Lysosomal enzymes and protons

Question 24

How is hormonal control of remodelling used?

Answer 24

To maintain blood calcium homeostasis & balances activity of parathyroid hormone & calcitonin

Question 25

What are Parathyroid Hormone (PHT)

Answer 25

It stimulates osteoclasts to resorb bone
- releases calcium into blood

Question 26

Why is Calcitonin?

Answer 26

Produced by parafollicular cells of thyroid gland in response to high levels of blood calcium levels