Calcium Flashcards
What percent of calcium is free? What percent is bound to proteins?
50% free, 50% bound
As pH decreases, there is (more/less) bound calcium or __________.
less
hypercalcemia
As pH increases, there is (more/less) bound calcium or ____________.
more
hypocalcemia
As pH increases, the total calcium amount is the same but calcium replaces some of what molecule?
H+
Calcium and what other molecule maintain relatively constant free concentrations since they are inversely proportional?
phosphate (phosphorus)
PTH will (increase/decrease) calcium and (increase/decrease) phosphate.
increase
decrease
(T/F) More calcium is lost than is rebuilt in the adult.
False - equal amount
How is calcium obtained for rebuilding of bone?
through diet –> GI tract –> ECF –> kidneys (reabsorbed) –> bone
What 3 major hormones control calcium levels?
PTH
calcitonin
calcitriol (vitamin D3)
What is the source of parathyroid hormone (PTH)?
chief cells in parathyroid gland
What is the source of calcitonin?
parafollicular cells (C cells) in thyroid gland
What is the source of calcitriol?
skin, activated in kidney
What are the 3 major targets for calcium control?
- GI tract
- kidneys
- bone
Two actions of PTH in bone
up calcium resorption (stim osteoclasts)
up phosphate resorption (but less than Ca)
In the kidney, PTH acts to (increase/decrease) calcium reabsorption, (increase/decrease) phosphate reabsorption, and (increase/decrease) bicarbonate reabsorption.
increase
decrease
decrease
______ converts vitamin D to its active form in what organ?
PTH
kidney
As PTH increases the circulating calcium, it is absorbed the intestines and the calcium increase (stimulates/inhibits) production of PTH via (positive/negative) feedback.
inhibits
negative
(T/F) High enough calcium levels will stop PTH production.
False - never completely stops
Vitamin D is a _______ which can be obtained through UV light of skin as (D2/D3) or by food as (D2/D3).
steroid
D3
D2
Vitamin D begins as a steroid, is converted to ________ in the liver and then a ________ in the kidney.
secosteroid
hormone
In the GI tract, vitamin D (increases/decreases) calcium absorption and (increases/decreases) phosphate absorption.
increases
increases
How does vitamin D increase calcium absorption in the GI tract?
activates calcium channel proteins
What action does vitamin D have on bone?
increases osteoclasts –> calcium resorption
What action does vitamin D have on the kidney?
increases calcium reabsorption
List the last 3 steps in the synthesis of vitamin D hormone and where it takes place.
- skin: 7-dehydrocholersterol in skin exposed to UV light –> cholecalciferol –> blood
- liver: 25-hydroxylase enzyme adds OH group –> 25-hydroxycholicalciferol
- kidney: PTH activates 1-a-hydroxylase which adds another OH group = calcitriol
What is the structure of calcitonin? What unique link does it have which forms a loop?
32-amino acid polypeptide
cysteine-cysteine link
In bone, calcitonin acts to (increase/decrease) calcium resorption and (increase/decrease) phosphate resorption.
decrease
decrease
In the kidney, what happens to calcium and phosphate resorption in response to calcitonin?
decrease calcium resorption
decrease phosphate resorption
Calcitonin acts on the kidney to increase the breakdown of what?
vitamin D
What 2 actions does calcitonin cause in the GI tract?
- decrease gastrin secretion
- decrease calcium reabsorption
Calcitonin binds to a receptor on ______ to inhibit its activity. What does this mean is the main driver?
osteoclast
osteoblasts (use calcium to build bone, reduce circulating calcium)
What is the half-life for each?
- calcitonin
- PTH
- vitamin D (active)
- 5 min (short)
- <10 min (short)
- 4-6 hours (long)
________ receptors are used for PTH and calcitonin while _______ receptors are used for vitamin D.
transmembrane
nuclear superfamily
