1. Path 1

Question 1

What is the periostium of a bone?

Answer 1

Membrane of the bone that covers the outer surface of bone: contains blood vessels and nerves.

Question 2

What is the cortical bone?

Answer 2

“Compact bone” that makes up the hard exterior of the bone

Question 3

What is the trabecular bone?

Answer 3

Spongy bone with ALOT of surface area that is soft and flexible, found at the ends of long bones

Question 4

What is the medullary cavity of bones?

Answer 4

Contain marrow: makes RBC.

Question 5

Osteoblasts

Answer 5

Located on surface of matrix.

1. Make bone matrix, by laying down osteiod
2. Regulates mineralization

Question 6

Osteoclasts

Answer 6

Specialized MO, derived from circulating monocytes, that secrete acid (H+) and proteases => resorb bone matrix

Question 7

Osteocytes

Answer 7

• Inactive osteoblasts burried in bone matrix that become osteocytes:
  
  • 1. Control Ca2+ and phosphate levels.
  • 2. Mechanotransduction: detect mechanical forces and translate them into biological activity

Question 8

What is the bone matrix?

How is it made and what makes it up?

Answer 8

• Extracellular component of bone made by osteoblasts.
  
  • 1. Osteoblasts lay down: Osteoid, organic, non-mineralized protein made up of type 1 collagen and smaller amounts of GAG, like osteopontin (osteocalcin)​, which helps w bone formation, mineralization and Ca2+ homeostasis
  • Later, it is mineralized with Ca2+ and phosphate.

Question 9

What makes up osteoid??

Answer 9

• Osteoid is made up of mainly type 1 collagen and a smaller amount of glycoaminolgycans, like osteopontin (aka osteocalcin).
  
  • Osteopontin helps with: bone formation, mineralization and Ca2+ homeostasis.

Question 10

What makes the bone hard?

Answer 10

Hydroxyapatite, which holds 99% of body calcium; 85% phosphorus.

Located in bone matrix.

Question 11

Woven vs Lamellar Bone

Answer 11

Woven bone (primary or immature) is the FIRST type of bone formed.

• • Made rapidly in fetal development
• • Disorganized collagen fibers and weaker.
• • ABNL to see in adults: but can be seen in adults after injury

Woven bone is LATER remodeled into lamellar bone.

• • Made slowly with parallel collagen
• • Stronger

Question 12

What regulates levels of Ca2+ and phosphate in blood and bone?

Answer 12

1. Vitamin D => adds Ca2+ and phosphate to bone
2. PTH ==> removes Ca2+ and phosphate to bone

Question 13

When is PTH secreted?

Answer 13

↓ blood Ca2+:

Question 14

When to ↓ blood Ca2+, what happens?

Answer 14

↓ blood Ca2 => PTH is secreted => (+) osteoclasts indirectly, by ↑ RANKL on osteoblasts => RANKL on osteoblasts binds to RANK-R on osteoclasts => (+) osteoclasts => bone resorption => ↑ blood Ca2+ and phosphate. Also:

• ↑ 1-a-hydroxylase activity =>
  
  • ↑ active vitamin D
  • ↑ absorption of Ca2+ from gut
  • ↑ Ca2+ resorption from kidneys

↓ Phosphate reabsorption from kidneys => ↑ excretion

Question 15

Levels of what = inadequate mineralization?

Answer 15

1. ↓ VitD
2. ↓ Ca2+
3. ↓ Phosphate