Bone Flashcards
What is bone mostly composed of?
Calcified ECM. Made up of type 1 collagen fibers and hydroxyapatite minerals.
What is the difference between the outside of the bone and the inside?
Outside hard, cortical compact bone. Very dense, hard to penetrate. Inside spongy trabecula bone - forms a lattice.
What are the different types of bone cells?
Osteoclasts (reabsorb bone), Osteoblasts (form bone), Osteocytes (load sensing cells) and Lining Cells (line the bone matrix).
What is the bone matrix composed of?
Collagen - gives tensile strength.
Non-collagenous proteins.
Bone mineral.
How is new bone made?
Osteoclasts come from monocyte - cells become pre-osteoclasts which bind together and donate their nuclei to become osteoclast. Attaches to bone and a ring of actin protein vacuum seals to bone. Releases enzymes that chop up collagen and acid - reduces pH under vacuum seal which dissolves bone minerals. Calcium is released. Growth factors also released - recruit pre-osteoblasts - lines create new bone - secrete type 1 collagen - hydroxyapatite crystals create new bone. Build bones around themselves.
How is bone resorption regulated?
Paracrine. Osteoblast expresses RANK ligand on their surface which have receptor - signals monocytes to form osteoclasts. Osteoblast can also make OPG as a decoy receptor for RANK ligand when don’t want this to happen.
What would happen should there be no osteoprotegerin or no rank ligand?
Osteo- too little bone as too many osteoclasts (osteoporosis)
Rank- too much bone as no osteoclasts (osteopetrosis)
What are endocrine factors?
Secreted hormones produces in endocrine organ - effect any cell with receptor for it.
What are the parathyroid glands?
On the thyroid gland - detect calcium levels as they are covered with calcium sensing receptor. Release parathyroid hormone.
What is the role of parathyroid hormone?
Control of serum calcium. PTH binds to a receptor in the tubules of the kidney and increases activation of 1, 25D (vit D) goes to the gut and increases absorption of phosphate and calcium from the diet. Acts also on RANK ligand to stimulate osteoclasts to get calcium from bone.
What are the sex steroids?
Estrogens and androgens.
What is the role of estrogen in bone mass?
Acts on osteoclasts to stimulate apoptosis. If lack of estrogen get more rapid bone remodeling and breakdown but not extra rebuilding.
