Calcium and Phosphate Flashcards
The labile pool is in direct contact with the osteocytic-osteoblastic bone membrane which contains many _________ which is why Ca2+ can be released so quickly into the central canal
PTH activated Ca2+-ATPase pumps
PTH activates vitamin D in the kidney my stimulating _______________ activity
stimulating 1-alpha hydroxylase
In the cells, where is most of the phosphate (more than 80%)?
mitochondria
the rest is in the cytosol
What do patients with Pseudohypoparathyroidism look like?
short stature
short neck
obese
shortened 4th metatarsal and metacarpal
Which “pool” of the bone responds to acute changes and PTH stimulation
labile pool
What enzyme converts vitamin D3 to 25-hydroxyvitamin D3?
By adding what?
25-hydroxylase
OH to Carbon 25
Where is the first step of vitamin D activation?
liver
What % of calcium in the plasma is in the ionized active form?
50%
complications of hypoparathyroidism
- hypocalcemia induced tetany
- hyperreflexia
- spontaneous twitching
- muscle cramps
- convulsions
Effects of excessive PTH-rp on the intestines
no intestinal effect
calcium uptake is not increased in the presence of PTH-rp
increased cortisol or diabetes has what effect on PTH
increased
increased phosphate excretion by the kidney can be measured by measuring ________ in the urine
cAMP
Calcium is excreted mostly by the _____, and partially by the ______
mostly by the GI
partially by the kidney
“stones, bones, and groans” =
primary hyperparathyroidism
complications of Primary hyperparathyroidism
- osteoporosis, osteomalacia
- kidney stones
- muscle weakness
Which “pool” of the bone undergoes resorption– slow breakdown of crystals and liberation of Ca and PO4 into the ECF
stable pool
Effects of excessive PTH-rp
plasma Ca =
plasma PO43- =
plasma PTH =
plasma Ca = increased
plasma PO43- = decreased
plasma PTH = decreased
The addition of ______ to _______ creates inactive vitamin D3
OH to carbon 24
24,25-dihydroxycholecalciferol
What two effects does PTH have on the kidney?
What effect does it have in relation to the kidney that is not a “direct effect”
- stimulates Ca reabsorption
- inhibits PO4 reabsorption
PTH also activates vitamin D by stimulating 1-alpha hydroxylase activity in the kidney
Vitamin D is inactive when it enters the blood from the skin or diet and it is called ___________
Vitamin D3
prohormone
Effects of Pseudohypoparathyroidism
PTH =
serum Ca =
serum PO4 =
PTH = increased… but ineffective
serum Ca = decreased
serum PO4 = increased
increased PTH = increase bone resorption = increased risk of
bone fracture
Parathyroid gland release parathyroid hormone (PTH) from _______ cells
chief cells
of the 1% of Ca2+ in the body that is not in the teeth and bone,
- 9% =
- 1 % =
- 9% = soft tissues, ER, mitochondria, membranes
- 1 % = plasma
(half of plasma is bound, half is free ionized)
Vitamin D action on the bone:
synergizes with PTH to stimulate resorption and remodeling and to mobilize calcium and phosphate
Ca10(PO4)6(OH)2 – hydroxyapatite
which bone “pool”?
stable pool
Roles of phosphate:
- energy related pathways (metabolic)
- cofactors (NAD, etc)
- 2nd messengers
Hypoparathyroidism is usually caused by
inadvertent consequence of thyroid surgery for treatment of cancer or Graves’ disease
Effects of excessive PTH-rp
urine PO4 =
urine Ca2+ =
urine cAMP =
urine PO4 = increased
urine Ca2+ = increased
urine cAMP = increased
what enzyme converts 25-hyroxyvitamin D3 to 1,25-dihydroxyvitamin D3?
By adding what?
1a-hydroxylase
OH to Carbon 1
Primary hyperparathyroidism is most commonly caused by
PTH-secreting adenoma
Vitamin D action on the kidney
calcium reabsorption
phosphate reabsorption
If 1000mg of Ca2+ is ingested in the diet, what is the net absorption of Ca2+ (and eventually excreted by the kidney if Ca2+ levels are normal)
200 mg
which means 800mg is excreted by the GI
What is the active hormone of vitamin D3?
1,25-dihydroxycholecalciferol
or
1,25-dihydroxyvitamin D3
muscle weakness =
muscle tetany/hyperactive =
hypo/hyperparathyroidism?
muscle weakness = hyperparathyroidism
muscle tetany/hyperactive = hypoparathyroidism
PTH on the kidney
plasma PO4 =
urine PO4 =
plasma Ca =
urine cAMP =
plasma PO4 = decrease
urine PO4 = increase
plasma Ca = increase
urine cAMP = increase
Pseudohypoparathyroidism is also called
Albright’s hereditary osteodystrophy
calcitonin decreases plasma Ca and PO4 by inhibiting:
bone resorption
tubular reabsorption
CaHPO4:2H2O – amorphous crystals
which bone “pool”?
labile pool
Phosphate distribution:
85% =
15% =
85% = bone and teeth 15% = muscle
99% of Ca2+ is in ______ form found in the _____
crystalline
teeth and bone (1 and 2 kg)
Primary hyperparathyroidism
Plasma Ca = Plasma PO43 = urine Ca = urine PO43 = urine cAMP =
Plasma Ca = increased Plasma PO43 = decreased urine Ca = increased ---(spills over!) urine PO43 = increased urine cAMP = increased
With normal Ca2+ intake, which form of vitamin D3 is produced?
inactive form
24,25-dihydroxycholecalciferol
The __________ separates the bone itself from the plasma within the canals
osteocytic-osteoblastic bone membrane
Activated vitamin D targets the intestine, bone, and kidney to collectively regulate __________ synthesis, and _____ and _____ levels in the plasma
calbindin synthesis
Ca2+ and PO43- levels in the plasma
What is calbindin?
buffer protein of calcium in the intestines
Total calcium free and bound in the blood =
~10mg/dL
Where does the second step of vitamin D activation occur?
kidney
What is the theorized reason for calcitonin
may protect against excessive bone resorption or when demand for Ca increases in pregnancy, lactation, and growth
Hypoparathyroidism
Plasma PTH =
Plasma Ca =
Plasma PO4 =
Plasma PTH = decreased
Plasma Ca = decreased
Plasma PO43 = increased
phosphate cannot be excreted without PTH
25-hydroxylase converts vitamin D3 to ________
in the liver
25-hydroxyvitamin D3
calcitonin does not have an effect on _____ whereas PTH does
intestines
PTH effect on labile pool of bone
osteolytic osteolysis for fast release of Ca and PO4 liberation into the ECF
Humoral hypercalcemia of is caused by
malignant cell clusters that secrete PTH-related peptide (PTH-rp)
Vitamin D action on the small intestine
increase expression of calbindin
increase calcium absorption
excess vitamin D supplementation has what effect on PTH
decreased
but all the effects of PTH still exist from too much vitamin D
