Part 19: Calcium Homeostasis Flashcards
the thyroid gland makes ___, which is important to Ca homeostasis
calcitonin
where are the parathyroid glands found?
on either side of the thyroid gland
are the parathyroid glands regulated separately than the thyroid gland?
yes
what hormone is made by the parathyroid glands?
parathyroid hormone
bone is primarily made up of ___ and ___ arranged in a mineral matrix, making a strong skeletal structure and storing these minerals
Ca and phosphate
foods high in phosphates include:
meat and nuts
depending on the amount of Ca and PO4 in the body, what 2 things can happen to these minerals when eaten?
- if the body already has enough, the excess will be excreted from the body in feces
- if the body could use more, they will be reabsorbed into the blood through the intestine
the absorption of PO4 and Ca in the intestine is regulated by which vitamin?
vitamin D
once Ca and PO4 are absorbed in the blood, they can be used in what 2 ways?
- can be used immediately for cellualr processes
2. stored in bone
what happens with the absorbed Ca and Po4 is regulated by ____, ____ and ____
vitamin D, parathyroid hormone and calcitonin
any absorbed excess Ca and PO4 is excreted by the ____
kidneys
the adult human contains about ___kg of Ca and ___% is deposited in the bones and teeth
1; 99%
t/f Ca and PO4 are cycled in the body due to their involvement in many cellular processes
t
calcium is critical to cardiac muscle ___
contraction
phosphate is used in the biosynthesis of ____
ATP
the levels of Ca needed to initiate cellular processes is ____ (low/high) and demand changes ____ (slowly, rapidly)
low; rapidly
bone remodelling is a ____ process and occurs continually throughout life
dynamic
parathyroid hormone and vitamin D are involved in both ___ and ____ of bones to keep balance
formation and breakdown
the stimulation of ____ and ___cells happens in parallel to allow bone tissue to be balanced and maintained
osteoclasts & osteoblasts
an imbalance of osteoclast/osteoblast stimulation can lead to bone overgrowth (______) and breakdown (______)
osteopetrosis; osteoporosis
____ stimulates osteoblasta results in the secretion of ____, which increases activation of osteoclasts
PTH; RANKL
how do osteoclasts breakdown bone?
acidify the extracellular space around the bone, resulting in demineralization of Ca & PO4 from the bone surface
osteoblasts make new mineral deposits from ____
remaining serum Ca and PO4
PTH is secreted when Ca levels are ___ (high/low)
low
there are Ca sensing receptors on the surface of the ____cells so the parathyroid gland knows how much Ca is in the blood
parathyroid
when the Ca sensing receptors are activated, this activates the _____ pathway , resulting in the production of ____ within PT cells
arachidonic acid; leukotrienes
leukotrienes in the Pt cells promote the breakdown of ____, which prevents its release
PTH
when PTH is secreted, it acts at the bone to increase___
demineralization and release of Ca and PO4 into the blood
PTH ____ (lowers/increases) the activation of vitamin D in the kidney
increases
vitamin D acts in several ways to ____ (increase/decrease) circulating levels of calcium and helps _____(build-up/breakdown) ca and PO4 stored in bone tissue
increase; build up
PTH and vitamin D ___ (decrease/increase) bone resorption and make Ca and PO4 ____ (more/less) readily available for cellular processes
increases; more
vitamin D acts in the GI tract to ____ (increase/decrease) the absorption of Ca and PO4 from food and _____ (increases/decreases) renal excretion
increase; decrease
in what 2 ways can we get vitamin D?
- precursors from our food (or supplement)
2. made from cholesterol in the skin by UV light
what is the active form of vitamin D?
1,25–dihydroxy vitamin D
1,25–dihydroxy vitamin D is made from 2 metabolic steps, one in the ___ and the second in the ___
liver; kidney
1,25–dihydroxy vitamin D is also called ___
calcitriol
vitamin D is an important negative modulator of ____ to help maintain homeostasis
PTH
vitamin D can increase both bone __ and __
formation and resorption
how does vitamin D inhibit parathyroid hormone synthesis and release?
destablizing the hormone mRNA, preventing its translation into a functional hormone protein
when the ca sensor pathway is activated, the secretion of ____ is reduced, which prevents excessive resoprtion and bone mineral loss
PTH
calcitonin is a ____ (negative/positive) regulator of the actions of PTH and reduces bone mineral resorption
negative
calcitonin is made by the ___
thyroid gland
calcitonin is secreted in response to ___
high levels of circulating ca
calcitonin release acts to inhibit ____ (bone cell) activity, which ____ (increases/decreases) the demineralization of the bone surface and ____(promotes/inhibits) the renal excretion of Ca and PO4 to prevent too high levels
osteoclast; decreases; promotes
estrogen and growth hormone are ____ (negative/positive) modulators of bone formation
positive
what happens to bone mass when estrogen decreases during menopause?
decreases
low levels of growth hormone during development can lead to ___
dwarfism
patients with _____ (hyper or hypo thyroidism) are at greater risk of developing osteoporosis
hyperthyroidim
t/f physical forces on bones can affect bone remodelling
t
give 2 examples of physical forces that can be used
- braces
2. weight-bearing exercises to reduce risk of osteoporosis
an area of bone having force applied towards to it has a high level of activity of which bone cells?
osteoclasts (makes space for tooth to move to)
braces reposition the ____ bones to straighten the teth
alveolar
an area of bone having force pulled away from it has a high level of ____ (bone cell) activity
osteoblast (fill in space behind the moving tooth)
what is osteoporosis?
a condition where the balance between bone resorption and formation tips toward a greater proportion of bone being broken down by osteoclasts
____ can be used to slow the progression of osteoporosis
bisphosphates
t/f hormone replacement can be given to help improve bone remodelling in menopasue
t
what class does alendronate belong to?
bisphosphonates
bisphosphonates are relatively simple molecules that have ___(#) ionically charged phosphate groups that bind to ___ on the surface of bone
2; Ca
bisphosponates are also taken up by _____ (bone cells), reducing their activation
osteoclast
bisphosphonates ____ (increase/decrease) bone remodelling
decrease
bisphosphonates ____ (reduce/increase) reabsorption of bone mineral
reduce
why do bisphosphonates have a long half life?
they bind ionically to bone mineral
what is the usual dosing of bisphosphonates?
usually once weekly oral dosing
how is bisphosphonates removed from the body?
excreted unchanged in the urine
does the excretion of bisphosphonates require metabolizing enzymes?
no
bisphosphonates have ____ (many /few ) drug interactions
few
