MSKS Physiology Lecture 1_Bone and CT

Question 1

What does Clathrin do in osteoclysts?

Answer 1

mediates the formation of secretory vesicles (lysosomes) that release enzymes into the lacuna

Question 2

Describe the WNT/β-catenin pathway

Answer 2

WNT proteins produced by osteoprogenitor cells bind to the LRP5 and LRP6 receptors on osteoblasts and thereby trigger the activation of β- catenin and the production
of OPG ( !bone, "osteoclast)

Question 3

What doe Osx affect

Answer 3

it typically affects the formation of collegen in bone. deffects in Osx leads to Osteogenesis imperfecta (brittle bone syndrome)

Question 4

What happens to a bone without the inorganic portion?

Answer 4

it becomes extreamly flexable

Question 5

What does Paget Disease cause

Answer 5

• Increased osteoclast activity
• Increased levels of serum alkaline phosphatase, urinary hydroxyproline and osteocalcin
• Mosaic pattern of lamellar bone

Question 6

How does parathyroid hormone (PTH) effect Ca absorbtion?

Answer 6

PTH enters the osteoblast where it down regulates the production of OPG and upregulates the production of RANKL and macrophage colony stimulating factor (M-CSF) RANKL and M-CSF bind to preosteoclyst and causes it to differentiate into a mature osteoclyst

Question 7

What does RUNX2 affect

Answer 7

it affects the proper formation of bones that grow via Intramembranous ossification. This means that RUNX2 deffects typically affect the bones of the head and the teeth

Question 8

How is the H+ generated for osteoclast activity?

Answer 8

Carbonic Anhydrase reacts OH- with CO2 to make HCO3-. This drives the dissociation of H2O by the law of mass action.

Question 9

Describe the function of Osteoprotegerin (OPG)

Answer 9

OPG is secreted by osteoblasts. OPG binds RANKL and prevents it from binding to RANK. In this way, OPG indirectly prevents the reabsorbtion of Ca

Question 10

What is an ostiogenic cell

Answer 10

It is the stem cell that gives rise to other bone cells

Question 11

what do BMPs do?

Answer 11

bone morphogenic proteins bind to transmembrane serine/ threonine kinase receptors and induce heterotopic* bone formation

Question 12

How does bicarb exit the osteoclast?

Answer 12

via Cl-HCO3 exchangers. This imports Cl- iinto the cell which allows the ClC7 ion chanel to function as well

Question 13

What mediates acid secretion from the osteoclast into the Lacuna?

Answer 13

V-type proton pump and Cl-channel ClC7

Question 14

Describe the function of Integrins and vitronectins

Answer 14

Integrins are on the surface of Osteoclasts. They bind with vitronectins which are a protein on the bone surface. This creates the micro-enviornment for bone to be disolved.

Question 15

Describe RANK/RANKL signaling in the osteoclyst.

Answer 15

RANK binds RANKL which promotes the reabsorbtion of Ca.

Question 16

Describe Appositional growth in bones

Answer 16

it the gowth that increases the diameter of existing bones It does not contribute to the growth of new bones.

Question 17

Describe the Sclerostin pathway

Answer 17

Sclerostin, which is produced by osteocytes, inhibits the WNT/ β-catenin pathway. LRP5/6 (LDL receptor related proteins 5 and 6)

Question 18

What happens to a bone without collegen?

Answer 18

it becomes very brittle and breaks

Question 19

How does Calcitonin effect osteoclyst signaling?

Answer 19

Calcitonin activates a g protein coupled receptor that activates adenylyl cyclase, creates cAMP, activates protein kinase A, which inhibits the reabsorbtion of calcium.