B6.052 - CBCL Osteoporosis Prework 3 ARF Cycle

Question 1

describe the ARF cycle

Answer 1

hematopoietic stem cells –> pre osteoclasts –> osteoclasts

mesechymal stem cells –> pre osteoblasts –> osteoblasts –> osteocytes

Question 2

describe regulation of osteoclasts by osteoblasts

Answer 2

hormones like PTH an calcitonin and vit D regulate calcium levels through interactions with osteoblasts/clasts
there are NO receptors for PTH, vit D on osteoclasts but there ARE calcitonin receptors

Question 3

effects of PTH

Answer 3

increased bone release of calcium, kidneys conserve calcium, intestine absorbs calcium

Question 4

describe the dual effect of PTH on the bone

Answer 4

binds to osteoblasts which (intermittently) activates osteoblasts and then chronically activates osteoclasts via release of RANKL

Question 5

vitamin D interaction with bone metabolism

Answer 5

in vitamin d deficient state calcium absorption decreases
low calcium causes PTH secretion
Vitamin D receptors on osteoblasts facilitate vitamin D induced proliferation, differentiation and mineralization

Question 6

what do bisphosphonates do

Answer 6

induce apoptosis of osteoclasts

Question 7

interaction between bone cells

Answer 7

osteoblasts secrete M-CSF to induce monocyte differentiation into osteoclast progenitor cell, also secretes RANKL to induce osteoclast progenitor cells to differentiate inot osteoclasts
OPG secreted to inhibit RANKL
calcitonin interacts with osteocyte to inhibit it

Question 8

what does sclerostin do

Answer 8

osteocytes secrete it to inhibit osteoblast activity