CHP7 Bone Tissue

Calcidiol to calcitriol kidney calcitriol steroid

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Unformatted text preview: to open, & neurons/muscles not excited excited • [>12 mg/dL] leads to depressed NS, emotional [>12 disturbances, muscle weakness, slow reflexes, potentially cardiac arrest • Rare condition Changes in [PO43-] has little immediate affects on body Calcium phosphate homeostasis depends on calcitriol, Calcium calcitriol calcitonin & PTH calcitonin PTH Calcitriol Calcitriol Calcitriol= active Vit-D, acts like a hormone to elevate active [blood calcium] Produced by a process including skin, liver, & kidneysProduced • UV rad penetrates epidermal keratinocytes, they convert a UV steroid into previtamin D3 and then to D3 which enters previtamin bldstream bldstream • Liver adds OH- to it, converting it to calcidiol Liver calcidiol • Kidney adds OH- to convert calcidiol to calcitriol Kidney calcitriol • Steroid + lgt=Vit-D3,enters bld to liver; +OH=calcidiol, off Steroid to kidney; +OH=calcitriol, ready to act as a chemical messenger messenger Calcitriol (cont.) Calcitriol Acts as a hormone to: • Stimulate intestine to absorb Ca2+, PO43- & Mg2+ • Inc Ca2+ (& PO43-) resorption by binding to osteoblasts, resorption causing the release of chem messenger to promote production of osteoclasts • Result is an inc of [bld Ca2+] for bone growth, etc. • Weakly promotes urinary reabsorption of Ca2+ • Vitamin since only added to body thru diet…fortified milk Calcitonin Calcitonin Abnormal softness of the bones= rickets in children & Abnormal rickets osteomalacia in adults osteomalacia Calcitonin= secreted by C cells (thyroid gland) when [Ca] too Calcitonin secreted high high 2 ways it lowers [bld Ca]= osteoclast inhibition & stimulation • Osteoclast inhibition= reduces osteoclast activity by as much reduces as 70% in 15 minutes as • Osteoblast stimulation= w/in 1 hr inc # & activity of osteoblasts • Important role in children, but little effect in adults • Deficiencies are not known to cause disease in adults, but may Deficiencies prevent bone loss (preg/lactating) & useful in reducing bone loss in osteoporosis in Parathroid hormone Parathroid Parathyroid hormone (PTH)= iimportant regulator of [bld mportant Ca2+] Ca • Secreted by parathyroid glands when bld-Ca level is too Secreted low low Raises [bld Ca2+] iin 4 ways: n • Inc #’s osteoclasts • Promotes Ca resorption by kidneys (retain Ca but excrete Promotes PO43-) PO • Promotes final step of calcitriol synthesis in kidneys (thus, Promotes accelerates effects of calcitriol) accelerates • Inhibits collagen synthesis so osteoblasts can’t build bone Inhibits Other Factors Affecting Bone Other 20+ hormones, Vit’s & growth factors not well understood • Bone growth especially rapid at puberty/adolescence w/ Bone GH, estrogen, testosterone promoting ossification GH, • Adolescent girls grow faster than boys & reach their full Adolescent height earlier (estrogen has stronger effect), but males grow for longer period…taller for Recall that growth ceases when epiphyseal plate “closes” • Anabolic steroids may cause premature closure of growth plate producing short adult stature Orthopedics= branch dealing w/ prevention & correction of branch injuries & disorders of bone, joints, muscles injuries Osteoporosis Osteoporosis Osteoporosis= porous bones, most common bone disease • Bones lose mass & become brittle due to loss of both organic Bones matrix & minerals; spongy bone most affected matrix • High risk of fractures of hip, wrist & vertebral column; can lead High to fatal complications such as pneumonia due to stress of recovery recovery • Lose height due to vertebrae compressing…can lead to Lose widow’s (dowager’s) hump of spine widow’s Postmenopausal white women at greatest risk • Begin losing ~35 & by age 70, lost ~30% of bone mass Therapies to stimulate bone deposition are still under Therapies investigation investigation • Estrogen replacement drugs & inhibitors of osteoclasts...
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