Please help me! Please answer all, this is the last question I have for the mont

Question

Please help me! Please answer all, this is the last question I have for the month

Osteoblasts produce, and then subsequently secrete, most of the materials that make up bone ECM. Osteoclasts degrade the ECM of bone.

• Obviously we must have bone-forming cells to make bone in the fetus and to allow bones to continue to increase in size until we stop growing. Why is it important to also have cells specialized to degrade the ECM of bone? Incorporate into your answer two distinctly different normal situations in which degradation of the ECM of bone is necessary.

• In what ways is an osteoclast specialized to degrade the ECM of bone? [Note: In your answer you need not provide all the details of osteoclast activity, but you must address specializations – properties not displayed by cells in general – that permit osteoclasts to degrade bone ECM.]

• Osteoclast activity is under very tight control by signal molecules. In what general way does such tight control make sense? Indicate two avenues for control of osteoclast activity by signal molecules; for each, mention the source of the signal molecule and whether the signal molecule inhibits or enhances osteoclast activity.

Explanation / Answer

Osteoclasts are cells of bone which is specialized to degrade bone tissue. Degradation of bone or bone resorption process is necessary to maintain, repair and remodelling of bones.Bone ECM is composed of hydroxyapatite crystals and colagen protein. Osteoclasts breaks down bone tissue and release the minerals present in the bone and thus release the calcuim of bones to blood. In human, bones are constantly remodelled to replace old bone parts with newly formed matrix which is necessary for bone strength maintainance and ion homeostasis.Bone remodelling is required in situaiton like healing of fractured bone or micro damage occured due to normal day to day activity. Remodeeling also required for adaptation of skeleton for mechanical work.

Osteoclast posess multiple nucli and also have numerous mitochondria and lysosomes. Osteoclasts are situated in the outer layer of the bone and degrades bone ECM by secreting spacial proteolytic enzymes like cathepsin-K and MMP-9. Cathepsin-K degrades most of the type II collagen on other non collagen present in the bone whereas MMP-9 is required for osteoclast migration. Additionally osteoclasts also secrets acids which help to convert calcium salt into solouble mode and release in the blood.

Differentiation and activity of osteoclasts are regulated by two cytokines like macrophage colony-stimulating factor or M-CSF and receptor activator of nuclear factor-B ligand or RANKL. M-CSF and RANKL generally binds to their specific receptor known as c-Fms and RANK which ae expressed on the surface of osteoclasts and thereby activates the differentiation process through a conrtolled signallig system.

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