Exam 3- Mineral Metabolism Flashcards
what properties of calcium and phosphate make them well suited to altering the conformation and functional properties of proteins?
calcium: positive charge
phosphate: negative charge
what form of calcium is biologically active and what percentage of the total calcium in blood does it make up?
ionized calcium
about 50%
true/false: the amount of calcium in interstitial fluid bound to proteins is higher than the amount in blood
false: very little protein in interstitial fluid to begin with
free intracellular calcium concentrations must remain ______
low
what abnormality causes an increase in free, ionized calcium in blood?
acid-base abnormalities
what do changes in plasma protein concentration do to calcium levels in plasma?
increase total plasma calcium concentration, but not ionized calcium concentration
how do changes in anion concentration affect calcium?
change fraction complexed with anions: raises phosphate concentration, increasing calcium complexed to phosphate, decreasing the amount of free, ionized calcium
where is most of the phosphate that is not stored in bones located?
intracellularly
what happens to plasma phosphate in the kidney?
freely filtered and more than 85% reabsorbed
how do plasma phosphate concentrations trigger hormonal regulation?
decreased phosphate leads to calcitriol
what three organ systems take part in calcium homeostasis?
gastrointestinal tract
bone
kidney
what is the main determinant of intestinal absorption of calcium?
calcitriol (active vitamin D)
how does parathyroid hormone impact calcium homeostasis?
lower plasma calcium levels leads to release
increases bone resorption and decreases bone deposition
increases reabsorption calcium in the kidneys
increases absorption calcium in gastrointestinal tract through activation vitamin D
where is most of the body’s calcium stored?
in the skeleton: about 99%
how is 99% of the bone calcium and phosphate stored?
calcium phosphate crystals: hydroxyapatite
important structural component of bone
where is the rest of the calcium and phosphate in bone stored?
salts in equilibrium with interstitial fluid
how much of the skeleton does cortical/compact bone make up?
80%
cortical bones is composed of repeating units called __________
osteons
where is extracellular fluid stored in bone?
canaliculi between lacunae (osteocytes within)
what are the four types of cells in bone tissue?
osteoblasts
osteocytes
osteogenic stem cells
osteoclasts
what cells take part in bone remodeling?
osteoblasts build up and osteoclasts resorb
from where are osteoclasts derived?
monocyte/macrophage lineage (not osteogenic precursor cells)
how do osteoclasts resorb bone?
release organic acids which dissolve crystals of calcium phosphate and proteolytic enzymes which dissolve collagen
what does the bone cells layer have?
osteocytes
has calcium and phosphate transporters which are hormonally regulated
how is calcium absorbed from the intestinal lumen (what routes)?
paracellular and transcellular
how is calcium absorbed transcellularly?
Ca-ATPase pump and Ca/Na exchanger
where is calcium reabsorbed in the kidney and is it regulated?
60% in proximal tubule: paracellular and unregulated
distal convoluted tubule: transcellular and regulated
true/false: calcium bound to protein is handled by the kidneys
false: only ultrafilterable
what does parathyroid hormone do to activate or inactivate vitamin D?
stimulates 1-alpha hydroxylase in the epithelial cells of the proximal tubule of the kidney to form biologically active form of vitamin D
what cells release parathyroid hormone?
chief cells of the parathyroid gland
how does parathyroid hormone affect phosphate handling?
indirectly decreases plasma phosphate levels
what causes a release of calcitonin?
increased plasma calcium
what does calcitonin do?
inhibits osteoclasts and bone resorption
true/false: the concentration of calcium in milk is 3-4x higher than plasma
true
what is calcium important in?
excitable cells
role in blood coagulation
role in regulating function of enzymes and secretion of hormones
component of 2nd messenger systems
what is phosphate important in?
structural component of nucleic acids and phospholipids
inorganic phosphate needed for synthesis organic phosphates- ATP
many biological pathways
kinases are enzymes that attach phosphate groups
phosphatases are enzymes that remove phosphate groups
how do the ratios of calcium bound to proteins, bound to complexes, and free, in plasma and interstitial fluid compare?
most in both is free
a lot in plasma is bound to proteins too
more, but still small, bound in complexes in interstitial fluid
how does an intracellular calcium signal arise?
ion channels in cell membrane
endoplasmic reticulum releases
where are lacunae and what is in them?
between concentric lamellae
osteocytes
what are osteoblasts formed from?
osteogenic stem cells
what do osteocytes do?
maintain bone tissue
what separates the bone fluid from the plasma?
osteocyte layer with calcium and phosphate transporters that are hormonally regulated
where is calcium reabsorbed in the kidney passively and paracellularly? what percent?
proximal tubule
60%
what is the reabsorption of calcium in the distal convoluted tubule like?
transcellular and regulated
true/false: about 5% of filtered calcium is excreted in urine
false: 1-3%
what does the active form of vitamin D do?
binds to intracellular receptors in target tissues to regulate transcription of genes related to Ca++ transport
what does parathyroid hormone do to phosphate blood levels?
lowers them
do mammary epithelial cells have a lot of free calcium in the cytosol?
no
what do kinases do?
attach phosphate groups
what do phosphatases do?
remove phosphate groups
how much of the calcium in blood is free and ionized?
50%
how can calcium move across membranes?
primary or secondary active transport
how do acid-base abnormalities change free ionized calcium?
changes amount bound to albumin: increased H+ means less calcium bound to albumin means increased free ionized calcium
what is the most important effect of calcitriol?
increases absorption of calcium from the intestine
