1. Path 1 Flashcards
What is the periostium of a bone?
Membrane of the bone that covers the outer surface of bone: contains blood vessels and nerves.
What is the cortical bone?
“Compact bone” that makes up the hard exterior of the bone
What is the trabecular bone?
Spongy bone with ALOT of surface area that is soft and flexible, found at the ends of long bones
What is the medullary cavity of bones?
Contain marrow: makes RBC.
Osteoblasts
Located on surface of matrix.
- Make bone matrix, by laying down osteiod
- Regulates mineralization
Osteoclasts
Specialized MO, derived from circulating monocytes, that secrete acid (H+) and proteases => resorb bone matrix
Osteocytes
- Inactive osteoblasts burried in bone matrix that become osteocytes:
- 1. Control Ca2+ and phosphate levels.
- Mechanotransduction: detect mechanical forces and translate them into biological activity
What is the bone matrix?
How is it made and what makes it up?
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Extracellular component of bone made by osteoblasts.
- 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.
What makes up osteoid??
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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.
What makes the bone hard?
Hydroxyapatite, which holds 99% of body calcium; 85% phosphorus.
Located in bone matrix.
Woven vs Lamellar Bone
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
What regulates levels of Ca2+ and phosphate in blood and bone?
- Vitamin D => adds Ca2+ and phosphate to bone
- PTH ==> removes Ca2+ and phosphate to bone
When is PTH secreted?
↓ blood Ca2+:
When to ↓ blood Ca2+, what happens?
↓ 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:
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↑ 1-a-hydroxylase activity =>
- ↑ active vitamin D
- ↑ absorption of Ca2+ from gut
- ↑ Ca2+ resorption from kidneys
↓ Phosphate reabsorption from kidneys => ↑ excretion
Levels of what = inadequate mineralization?
- ↓ VitD
- ↓ Ca2+
- ↓ Phosphate