A&P-Bone Remodeling & Blood Calcium Regulation
Explain the relationship b/w PTH and calcium
When the calcium in our blood goes too low, the parathyroid glands make more PTH. Increased PTH causes the body to put more calcium into the blood. Increased PTH causes the bones to release their calcium into the blood.
Explain the effect of mechanical stress on bone remodeling
mechanical stress occurs in the form of weight-bearing movement and exercise, and it's required for normal bone remodeling. stress is detected by osteocytes and communicated to osteoblasts.
Identify the hormones that influence bone growth and remodeling, and describe their effects
-growth hormone & IGF both directly stimulate growth of cartilage in the epiphyseal plate -thyroid hormone stimulates bone growth by influencing the metabolic rate of bone cells -sex hormones accelerate bone growth. increase the rate of both cartilage growth and bone formation w/in the epiphyseal plate
Compare and contrast the five zones of the epiphyseal plate, and describe how growth in length occurs there
-zone 1: zone of resting cartilage -zone 2:zone of proliferating cartilage -zone 3: zone of hypertrophic cartilage -zone 4: zone of calcified cartilage -zone 5: zone of ossification
Explain how parathyroid hormone and calcitriol function together to regulate blood calcium levels
Blood calcium levels are closely regulated by a negative feedback mechanism that involves the parathyroid gland, calcitriol, and various effectors (bone, kidneys, and small intestine). A low blood calcium level is the initial stimulus for the parathyroid glands to release parathyroid hormone. Together, PTH and calcitriol target various effectors to ultimately instigate a rise in blood calcium levels and return to homeostasis.
Discuss the homeostatic system involving the hormone calcitonin and its effect on blood calcium levels
High blood calcium stimulates the release of calcitonin from the thyroid gland. Calcitonin acts on its effectors (bone & kidneys) to lower blood calcium to homeostatic levels
Discuss the release of parathyroid hormone
Parathyroid hormone (PTH) is secreted and released by the parathyroid glands in response to reduced blood calcium levels. the final enzymatic step converting calcidiol to calcitriol in the kidney occurs more readily in the presence of PTH.
Describe the steps of appositional growth
in this process, osteoblasts in the inner cellular (compact bone) layer of the periosteum produce and deposit bone matrix w/in layers parallel to the surface. as they increase in number, the structure increases in diameter. thus, the bone becomes wider as new bone is laid down at its periphery. as the new bone is being laid down, osteoclasts along the medullary cavity resorb (destroy) bone matrix, creating an expanding medullary cavity.
Define bone remodeling, and give examples of how it varies in different bones and in different portions of the same bone
the constant, dynamic process of continual addition of new bone tissue (bone deposition) and removal of old bone tissue (bone resorption).occurs at both the periosteal and endosteal surfaces of a bone.
