L19-20 Calcium And Phosphate Regulation Flashcards
Free calcium fluctuates (hardly at all/a lot)
Hardly at all. Changes less than 2%
99% of calcium in your body is in what form?
Crystalline form in teeth and bone
If you eat 1000mg of calcium, how much do you poop and pee out that day?
1000mg
(You absorb about 350 mg, but you also secrete 350mg of your body’s calcium back into the intestine and urine. Plus 650mg from diet didn’t even get absorbed)
How much of plasma calcium is in the ionized active form
50%
What is the normal plasma concentration of calcium
10mg/dL
What is required to absorb calcium from the intestine and from the bone
1,25-Dihydroxycholecalciferol aka Vitamin D
What effect does calcitonin have on bone resorption?
Inhibits it
What are the target organs of parathyroid hormone
Bone
Intestine
Kidney
What causes PTH to be released
DROP IN BLOOD CALCIUM*****
PTH then acts on kidney, bone and intestine to normalize blood calcium levels
What cells in the parathyroid release PTH?
Chief cells**
Does the parathyroid have any follicular cells
/
No
What is the effect of PTH on vitamin D?
Promotes the activation of Vitamin D to increase calcium absorption from food
What is the affect of PTH on bone
Activated osteoclasts to release calcium and phosphate into blood
What are the 2 calcium pools in your bones?
Stable pool
Labile pool
What kind of bone is in the stable pool?
Mature mineralized bone composed primarily of hydroxyapatite
What kind of bone is in the labile pool?
Bone fluid composed primarily of amorphous crystals
Which pool releases calcium And phosphate into the blood faster?
Labile pool
Which pool would your body use if you needed to make a quick small adjustment to blood calcium
Labile pool
How do calcium and phosphate get from the labile pool into the blood
The pool undergoes osteolytic osteolysis and then there is a rapid exchange with the ECF
Within the bone, what separates the bone itself from the plasma within the canals?
Ostocytic-osteoblastic bone membrane
This has a large surface area and a small movement of calcium= large influx of calcium and phosphate into the plasma from the bone fluid
What are the 2 effects of PTH on the kidney?
- Stimulates calcium reabsorption
- Inhibits PO4 reabsorption
(Calcium IN, Phosphate OUT)
Elimination of PO4 in the kidney also causes what other substance to increase in the urine?
Urine cAMP
because you need cAMP to eliminate PO4
What lab value could you measure to track a patient’s PTH status?
cAMP levels in the urine
increase PTH= increased cAMP in the urine
How does PTH activate vitamin D?
Stimulates 1-α hydroxylase activity in the kidney
What are the 2 steps required for vitamin D to become activated?
- Addition of (OH) on carbon 25 in the liver via the enzyme 25-hydroxylase
- Addition of (OH) on carbon 1 in the kidney via the enzyme 1α-hydroxylase
Results in 1,25-dihydroxycholecalciferol
STEP 2 ONLY HAPPENS IF YOU DON’T GET ENOUGH CALCIUM FROM YOUR DIET**
Is vitamin D3 considered a prohormone?
Yes
What are the 2 names for active vitamin D3
1,25-dihydroxyvitamin D3
1,25-dihydroxycholecalciferol
If you have an adequate amount of calcium in your diet, what happens to the Vitamin D3 you eat/your skin makes
- Vitamin D3 goes to Liver.
- (OH)group is added to carbon 25 by 25-hydroxylase
- Goes to kidney
- (OH) group is added to carbon 24***
- Produces inactive 24,25-dihydroxycholecalciferol
What effect does Vitamin D have on the bones?
It synergizes with PTH to remodel the bone and to mobilize calcium and PO4.
True or false:
Vitamin D + PTH are required for bone growth
True
What effect does vitamin D have on the kidney?
Reabsorption of calcium
Reabsorption of Phosphate**!!!
(It has the opposite effect on PO4 reabsorption as PTH)
What effect does Vitamin D have on the small intestine?
It makes more Calbindin, which then allows the body to absorb more calcium from the diet
What is calbindin
It is inside small intestine cells and it absorbs calcium out of the foods you eat
What effect do glucocorticoids have on PTH?
They increase PTH secretion
Too much corticosteroids= lots of bone resorption=fracture risk
Type II diabetics and obese people have lots of cortisol. Why does this put them at in increased fracture risk?
Corticosteroids increase the secretion of PTH which can cause too much bone resorption and put them at risk
What effect does Vitamin D have on PTH secretion?
Decreases it
What are the possible risks of taking too much vitamin D?
Fracture risk
Hypercalcemia
What does calcitonin do?
Decreases plasma calcium and PO4
How does calcitonin decreases plasma Calcium and PO4?
Inhibits bone resorption
Inhibits tubular reabsorption in Kidney
What effect does calcitonin have on the intestine?
NONE*!!!**!!
Calcitonin does the opposite of PTH except in what organ?
In the small intestine.
PTH causes increased calcium reabsorption
Calcitonin has NO EFFECT on the small intestine.
What causes calcitonin release?
Increased plasma calcium
Why do we have calcitonin
We dont really know
- when we don’t have calcitonin, we don’t get hypercalcemia
- excessive calcitonin does not produce hypocalcemia
- may prevent hypercalcemia after a meal?
What is the only time we think calcitonin might have an important role?
In pregnancy
What disease:
“Stones, bones and groans”
Primary hyperparathyroidism
What is the most common cause of primary hyperparathyroidism?
A PTH-secreting tumor
If your patient has primary hyperparathyroidism, what do you expect to see in
Plasma:
Urine:
Plasma; hypercalcemia and hypophosphatemia
Urine: increased phosphate, cAMP, and hypercalciuria
What are the complications of hyperparathyroidism?
Muscle weakness **
Kidney stones
Osteoporosis, ostemalacia (bones)
Constipation (groans)
What causes hypoparathyroidism?
Thyroid surgery
What is Trousseau’s Sign and in what condition might you see it?
It is spasms of the hand when you inflate a BP cuff around the arm.
Seen in hypoparathyroidism (low calcium)
Low calcium causes muscle (weakness/hyperactivity)
Hyperactivity
If you have a tumor that is secreting PTH-related peptide, what will happen to calcium and phosphate levels?
Hypercalcemia
Hypophosphatemia
(Same thing as if it was real PTH)
If you have a tumor that is secreting PTH-related peptide, what will PTH levels be?
Low**
PTH secretion is inhibited by hypercalcemia
“PTH resistance” describes what condition?
Pseudohypoparathyroidism
aka
Albright’s hereditary osteodystrophy
What is pseudohypoparathyroidism?
An autosomal dominant disorder where PTH binds to its receptor, and then nothing happens due to defective signal transduction
In pseudohypoparathyroidism, what are the levels of:
PTH:
Calcium:
Phosphate:
PTH: high
Calcium: low
Phosphate: high
What will someone with pseudohypoparathyroidism look like?
Short
Short neck
Obese
Short 4th finger and 4th toe
Primary hyperparathyroidism effect on:
PTH:
Vitamin D:
Bone resorption:
Urine:
Calcium:
Phosphate:
PTH: high
Vitamin D: high (effect on 1α-hydroxylase)
Bone resorption: high
Urine: high PO4, Ca, and cAMPT
Calcium: high
Phosphate: low
Surgical hypoparathyroidism effect on:
PTH:
Vitamin D:
Bone resorption:
Urine:
Calcium:
Phosphate:
PTH: low
Vitamin D: low (effect on 1α-hydroxylase)
Bone resorption: low
Urine: low PO4 and cAMP
Calcium: low
Phosphate: high
Pseudohypoparathyroidism effect on:
PTH:
Vitamin D:
Bone resorption:
Urine:
Calcium:
Phosphate:
PTH: high
Vitamin D: low
Bone resorption: low
Urine: low PO4 and cAMP
Calcium: low
Phosphate: high
Humoral hypercalcemia (tumor that secretes PTH-related peptide) effect on: PTH:
Vitamin D:
Bone resorption:
Urine:
Calcium:
Phosphate:
PTH: Low
Vitamin D: no effect** calcium uptake not increased in presence of PTH-rp
Bone resorption: high
Urine: increased PO4, Ca, and cAMP
Calcium: high
Phosphate: low
What causes rickets?
Deficiency of vitamin D in childhood
What is osteomalacia?
Deficiency of vitamin D in adulthood
Either due to diet or intestinal surgery that affects absorption
What muscle effects would you expect to see in rickets or osteomalacia?
Hypocalcemic Tetany
Why would low vitamin D cause you to break your bones a lot (rickets/osteomalacia)
No vitamin D= no calcium absorption and high levels of PTH due to the hypocalcemia = bone resorption
