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Bone Physiology

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imissyou419's version from 2017-03-27 19:15

Section

Question Answer
_________% of body calcium is stored in bones99
Parathyroid hormoneregulate level of Ca2+ in ECF; acts on distal convoluted tubule to reabsorb Ca2+ more when low
Calcitrol (vitamin D) affects absorption of Ca2+ in GI tract
Ca2+ stored ashydroxyapatite crystals (calcium and phosphate salts) in bone to prevent large changes in plasma calcium levels; hydroxyapatite crystals provide strength
Which way are most bones formed by?endochondral ossification
Endochondral ossification vs intramembranous ossificationEndochondrial is long bodies of body, intramembranous is flat bones of skull
Endochondral bone formation1. Chondrocytes (cells that make up cartilage) secrete an extracellular matrix containing type II collagen (provide structure) and proteoglycans (provide cushion)
2. Chondrocytes in the centre of the template differentiate into hypertrophic chondrocytes
3. Hypertrophic chondrocytes secrete type X collagen and less proteoglycans
4. Localized hypoxia triggers secretion of angiogenic factors, recruitment to hypertrophic chondrocytes (metabolically active, secreting type X collagen, not able to get enough nutrients through diffusion through ECF)
5. Hypertrophic chondrocytes mineralize the surrounding matrix and undergoes apoptosis
6. Invading blood vessels bring in osteoblast and osteoclasts to this mineralized zone (primary ossification)
7. Osteoclasts remove the hypertrophic chondrocytes extracellular matrix
8. Osteoblasts replace the mineralized cartilage matrix with bone matrix (mostly type I collagen)
9. Chondrocytes on either side of primary ossification centre are actively proliferating
10. Secondary ossification occurs in most condyles (epiphysis). In humans, mostly occurs postnatally (hypertrophic condrocyte, hypoxia so release angiogenic factors, blood vessels bring osteoclast and osteoblast to replace codyle with bone matrix)
11. A cartilage region between the 2 ossification centres is called the growth plate
12. Longitudinal growth is achieved by the active proliferation and hypertrophy of growth plate chondrocytes
To get long boneschondrocyte proliferation, large size hypertrophic chondryctes (volume change due to movement of ions and water in cells - push proliferative chondrocytes further away from primary ossification centre)
Drugs that disrupt growthless condrocytes able to contribute to longitudinal growth of growth plate or drugs that affect the size of hypertrophic chondrocytes
Osteoclasts and osteoblastmodified monocytes, circulate in blood, escaped from blood when blood vascular came to remodelling matrix; multinuclear, active, secrete acid (dissolve hydroxyapatite) and enzymes (breakdown collagen), forms tunnels and die, release signal for osteoblast to come in and replace holes with collagen matrix which mineralize into hydoxyapatite; osteoclasts on periosteal surface originally
Osteocyteosteoclasts that get trapped in compact and trabecular bone, give information about how much mechanical stress exerted on bone -> trigger osteoclast/osteoblast action
Bone remodellingability to adjust strength depending on use, bone shape can be rearranged if mechanical forces are altered, bone matrix becomes brittle with age so a new organic matrix needs to be deposited
Osteoporosis causesimbalance of osteoblast and osteoclast activity (more resorption and less bone formation)
Who is at greater risk for osteoporosis?post-menopausal women due to decline in estrogen levels (important for coordination of osteoblast/osteoclast activity), Treatment: estrogen replacement, osteoclast killers (bisphosphate chelate Ca2+ and kills osteoclast when it ingest it), Ca2+ supplement with vitamin D. Prevention: weightlifting exercises
Osteoarthritisarticular cartilage (persistent cartilage) is composed mostly of ECM (type II collagen and proteoglycans) and some chondrocytes that secrete and maintain that matrix, problem with matrix maintenance and production inhibition, or chondrocytes become hypertrophic
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