Physiology - Bone & Calcium Homeostasis Flashcards
Differentiate bone modeling and bone remodeling
Modeling - bone formation during skeletal growth. Remodeling - skeletal maintenance, repairs old bone
What is the major bone mineral?
60% hydroxyapatite (calcium & phosphate). 30% organic matrix (collagen, other proteins, lipids, glycosaminoglycans)
Osteocytes
Most numerous of bone cells, embedded in bone matrix, key sensor in bone remodeling, detects mechanical damage
Osteoblasts
Bone deposition, principle target for PTH’s action to promote bone growth, secretes OBG
Osteoclasts
Bone resorting, secrete acid proteases in process of bone resorption
Why is Vitamin D considered a hormone?
It’s secreted by cells, travels through the blood, and binds to specific receptors
What major endocrine messenger will function to elevate plasma calcium?
Parathyroid gland senses the calcium levels in the ECF. When levels are low, PTH releases to maintain calcium homeostasis
Chronic elevation of which hormone decreases bone mass?
Cortisol
Which cell in the bone plays a pivotal role in stimulating bone deposition?
Osteoblast
What is the effect of intermittent administration of parathyroid hormone?
Increase in bone mass
Clinical manifestations of hypocalcemia?
Neuromuscular excitability and tetany
What role does the kidney play in promoting calcium homeostasis and bone mass?
Stimulates the second hydroxylation of Vitamin D and secretion of Vitamin D. Also reabsorbs calcium and phosphate
Role of RANKL during bone remodeling
Recruitment of pre osteoclast to promote resorption
Major functions of Vitamin D
Absorption of calcium in the GI tract, stimulate secretion of messengers that activate osteoclasts, and mineralization of the osteoid
What is the function of bone?
Support body, protect organs, house bone marrow, reservoir for calcium, site of attachment for tendons and ligaments
