Exam 4 - Calcium Disorders Flashcards
T/f: >99% of the body’s calcium is in bone with most of the remainder being intracellular, & <0.1% extracellular
true
what biochemical influences impact calcium homeostasis in the body?
PTH
calcitonin
vitamin d
cortisol
aldosterone
thyroxine
what action does PTH have on calcium? how does it work?
goal is to raise serum calcium levels
osteoclast activation & promotes calcium reabsorption in the loop of henle & distal convoluted tubules of the kidneys
what action does vitamin d have on calcium? how does it work?
it is essential for gi uptake of calcium - cholecalciferol has little biological activity & requires sequential hydroxylations
effect on osteoclasts is dose dependent - physiologic doses are inhibitory & toxic levels activate osteoclasts
what action does calcitonin have on calcium? how does it work?
goal is to lower serum calcium
inhibits osteoclasts & inhibits calcium reabsorption in the loop of henle & distal convoluted tubules
limited biologic effect
99% of calcium in bone - _______
hydroxyapatite
how is calcium released from bone?
osteoclasts release stored calcium (they are part of the macrophage family) & are activated by PTH when serum calcium levels are too low
gi calcium uptake is dependent on what?
vitamin d dependent!!!
T/F: calcium is present in gi secretions, so net loss can occur
true
how does the kidney act in the body for calcium homeostasis?
fine tunes calcium levels through balancing through filtration & reuptake
99% of filtered calcium is automatically reabsorbed in the proximal tubules - essentially mimics sodium, is influenced by gfr, but less is reabsorbed if gfr is high
how does PTH & calcitonin affect the kidneys in regards to calcium homeostasis?
PTH increases uptake in the later portions of the nephrons
calcitonin decreases uptake in the later portions of the nephrons
urinary calcium loss is primarily determined by serum calcium levels
what is the basic action of PTH release in the body? where does it act?
increases serum calcium levels & decreases phosphate levels (bone resorption - calcium & p release)
kidney (increases reabsorption & decreases excretion of calcium & decreases phosphate reabsorption while increasing excretion) & bone (vitamin d3 activation)
what is the basic action of vitamin d3 release in the body? where does it act?
increases serum calcium levels & phosphate levels
gut - stimulates absorption of calcium & phosphate from gi tract
bone - promotes PTH’s activity in bone
what is the basic action of calcitonin release in the body? where does it act?
inhibits bone resorption & decreases serum calcium levels
bone
why is PTH an important part of causing release of vitamin d3?
PTH controls 1a-hydroxylase in the kidney
vitamin d3 starts by being hydroxylated in the liver (25-(OH)2 vitamin d3 - first hydroxylation
further hydroxylated in the kidney by 1a-hydroxylase! becomes 1,25-(OH)2 (active form)
where does PTH act at in the body?
bone, intestines, & kidney
bone - osteoclast activation to release calcium
intestines - increases calcium & phosphate absorbed
kidneys - release of 1a-hydroxylase which hydroxylates vitamin d3 into its active form so it can act in the intestines! increases amount of reabsorbed calcium & decreases amount of phosphate reabsorbed
what are some synonymous terms for vitamin d3?
cholecalciferol
calcitriol
1,25 hydroxycholecalciferol
what are the stimuli for release of vitamin d3?
low ECF Ca - increases pth which causes vitamin d3 activation
low ECF P stimulates vitamin d formation
T/F: PTH raises Ca & lowers P while vitamin d raises both Ca & P
true
where does the body get PTH?
parathyroid gland chief cells
where does the body get vitamin d?
either ingested or converted by uv light
where does the body get calcitonin?
thyroid gland - parafollicular c cells
what is the effect of PTH on serum PO4?
decreases serum PO4
what fraction of calcium is biologically active in the body?
free ionized calcium