Physiology of Bone - Brownell Flashcards
What are some of the functions of bone?
- Protection
- shape–>social identification
- movement
- sensory processing (ear)
- hemopoesis (blood cell and platelet production)
- mineral storage
What is the difference in density and turnover in compact vs. trabecular bone?
compact: high density, low turnover
trabecular: low density, high turnover
What are osteoblasts derived from and what is their function?
derived from stromal (bone marrow) stem cells
- secrete osteoid (collagen fibers + glycoproteins + hydroxyapotite)–> build new bone
- control osteoclastogenesis through releasing RANK-L and OPG upon sensation of mechanical stress of bone–> stimulate osteocytes to make new bone (can be affected by emotion and SNS
- OPG blocks osteoclast differentiation
(only 15% differentiate into osteocytes and the rest undergo apoptosis)
What are osteocytes derived from and what is their function?
mature osteoblasts, make up > 90% of bone cells
- Embedded in mineralized bone matrix
- Intracellular communication via canaliculi
- Load sensing, molecular mechanism unknown
What are osteoclasts derived from and what is their function?
- Derived from hemopoietic stem cells in the bone marrow (not osteoblasts!)
- Resorb bone
- Multinucleate
What are the important regulators of osteoblast/osteoclast interactions? (3)
- RANKL: receptor activator from osteoblasts acting to excite osteoclast activity
- OPG: inhibits RANKL actions
- DKK: a WNT antagonist that blocks osteoblast proliferation
- feedback interaction*
RANKL and OPG are secreted by osteoblasts and develop the relationship between osteoblasts and osteoclasts
How is prostate cancer related to osteoblast cells?
+ feedback loop between prostate cancer and osteoblasts
Cancerous cells release factors that destabilize (commonly promote) osteoblast proliferation and activity
osteoblast growth factors can also stimulate prostate cell proliferation
What do osteoclast growth factors cause during bone remodeling?
osteoblast differentiation
osteoclast apoptosis
What are the functions of PTH and Calcitonin? What is the [Ca2+] in the extracellular fluid?
PTH: mobilization of Ca2+ from the bone into circulation
Calcitonin: moves Ca2+ from circulation into the formation of new bone
2.5 mmol Ca2+ in the ECF
What do PTH and Vitamin D doto plasma [Ca2+]?
increase it!
What 2 things are essential for the formation of Vitamin D?
kidney and PTH
How do FSH and Estrogen regulate osteoclast activity?
FSH stimulates osteoclast resorption activity
Estrogen blocks pre-osteoclast formation (by blocking FSH)–> when estrogen levels are low, preosteoclasts can become osteoclasts and break down bone.
estrogen also induces OPG which causes osteoclast apoptosis and promotes one formation
What effects does PTH have on bone remodeling? (3)
Increases extracellular [Ca2+] by…
- Increasing Ca2+ reabsorption in kidneys
- Activation of vitamin D3 in kidneys
- Promoting activation of osteoclasts
What effects does Vitamin D3 have on bone remodeling?
- Increases dietary Ca2+ absorption
- Requires PTH, UV light for biosynthesis
What is Achondroplasia?
Dwarfism
FGF R3 is hyperactive –> inhibit chondrocytes and elongates endochondral bone but NOT membranous bone (skull, face-> normal size head)
