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32 Cards in this Set

  • Front
  • Back
Name the physiological processes that involve Ca+?
Muscular contraction
membrane permeability
Endo/Exocrine secretions
Enzyme regulation
How does Ca+ circulate in serum?
40-50% in free ionized form(active)
50-60% bound to plasma proteins or complexed to other ions.
Where is Ca+ stored and app. in what amounts?
How is Ca+ stored in one?
Two thirds as inorganic crystals=hydroxyapatite[Ca10(PO4)(OH),]
One third as organic materials(Ca2PO4)
Name the three organs that play an important role in serum Ca+ regulation?
Bone---resorption and formation
How is Ca+ homeostasis maintained?
Net absorption must be balanced by excretion.
Name the 3 hormones that play an important role in Ca+ homeostsasis?
Parathyroid hormone(PTH)
Calcitriol(1,25 dihydroxyvitamin D)
What is PTH?
A polypeptide hormone that has 84 amino acids, only the first 34 aa are required for biological activity.
Where is PTH synthesized?
Chief cells of the 4 parathyroid glands.
How is PTH synthesized?
What factor regulates PTH secretion?
Serum Ca+(neg feedback)
What happens to PTH secretion when when serum Ca+ is too low/high?
How are the effects of PTH mediated?
Through the PTH receptor
What is the second messenger system of PTH?
cAMP and intracellular Ca+.
Name the actions of PTH on the kidney?
1. Increased Ca+ reabsorption---increased serum Ca+(distal tubule)
2. PO4- reabsorption---increased serum Ca+(proximal tubule)
3. Increased 1-alpha hydroxylase---increased calcitriol production---increased serum Ca+(proximal tubule)
4. Stimulates osteoclasts to increase bone resorption---increased Ca2PO4 in ECF

In bone, it inhibits osteoblasts to further increase bone resorption.
What is Vit D(cholecalciferol)?
A steroid hormone synthesized by skin through a UV radiation reaction.
What is the active form of Vit D?
Calcitriol(1,25 dihydroxycholecalciferol)
What are the inactive forms of Vit D?
1. Cholecalciferol
2. 25-Hydroxycholecalciferol
3. 24,25-hydroxycholecalciferol
Where and how is calcitriol synthesized?
decrease 25 hydroxylase(in liver)---25-hydroxycholecalciferol---decrease 1 alpha hydroxylase(in kidney)---1,25 hydroxycholecalciferol and 24,25-hydroxycholecalciferol
What factors regulate calcitriol synthesis?
Activity of 1 alpha-hydroxylase, which is increased by;
decreased serum Ca+
Increased PTH levels
decreased serum PO4-
How are the effects of calcitriol mediated?
Through the calcitriol receptor.
Name the actions of calcitriol on;
Intestines-Induces Ca+ binding protein---increases Ca+ absorption
2. Increases PO4- reabsorption

Kidney-Increases Ca+ and PO4- reabsorption

Bone-Increase bone resorption---increase serum Ca+ and PO4-
What is Calcitonin?
A polypeptide hormone of 32 amino acids
Where is Calcitonin synthesized and secreted?
Parafollicular cells(C cells) of thyroid gland
What factor regulates calcitonin secretion?
Increased serum Ca+ stimulates secretion.
What is the 2nd messenger system of calcitonin?
cAMP(most likely)
Name the actions of calcitonin?
Decrease bone resorption by osteoclasts
Decrease bone formation by osteoblasts---increases serum Ca+.
Summarize the factors that regulate Ca2+ homeostasis hormone secretion;
PTH--decrease serum Ca+
Calcitriol-Decrease serum calcium/Increases PTH levels/decreases serum PO4-
Calcitonin- increase serum Ca2+
Summarize the actions of the Ca+ homeostasis hormones in the intestines.
PTH; increase Ca2+ absorption through activating calcitriol
Calcitriol; increase Ca2+ and PO4- reabsorption
Calcitonin-no effect
How do Ca2+ homeostasis hormones affect the kidney?
PTH; increase Ca2+ reabsorption and decrease PO4- reabsorption
Calcitriol; increased Ca2+ and PO4- reabsorption
How does the Ca2+ homeostasis hormones affect bone?
PTH- increased resorption
Calcitriol- increased resorption
Calcitonin- decreased resorption
Summarize the net effect of the Ca2+ homeostasis hormones on serum Ca2+ and PO4-
PTH results in an increase of serum Ca2+, and a decrease in PO4-

Calcitriol results in an increase in serum Ca2+, and increase in PO4-

Calcitonin results in a decrease in serum Ca2+.