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32 Cards in this Set
- Front
- Back
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Name the physiological processes that involve Ca+?
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Muscular contraction
membrane permeability Endo/Exocrine secretions Enzyme regulation Coagulation |
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How does Ca+ circulate in serum?
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40-50% in free ionized form(active)
50-60% bound to plasma proteins or complexed to other ions. |
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Where is Ca+ stored and app. in what amounts?
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ECF-0.9g
ICF-11grams Bone-1000grams |
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How is Ca+ stored in one?
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Two thirds as inorganic crystals=hydroxyapatite[Ca10(PO4)(OH),]
One third as organic materials(Ca2PO4) |
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Name the three organs that play an important role in serum Ca+ regulation?
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Intestines---absorption
Kidney---excretion Bone---resorption and formation |
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How is Ca+ homeostasis maintained?
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Net absorption must be balanced by excretion.
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Name the 3 hormones that play an important role in Ca+ homeostsasis?
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Parathyroid hormone(PTH)
Calcitriol(1,25 dihydroxyvitamin D) Calcitonin |
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What is PTH?
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A polypeptide hormone that has 84 amino acids, only the first 34 aa are required for biological activity.
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Where is PTH synthesized?
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Chief cells of the 4 parathyroid glands.
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How is PTH synthesized?
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PreproPTH---ProPTH---PTH
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What factor regulates PTH secretion?
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Serum Ca+(neg feedback)
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What happens to PTH secretion when when serum Ca+ is too low/high?
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Low-Increased
High-decreased |
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How are the effects of PTH mediated?
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Through the PTH receptor
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What is the second messenger system of PTH?
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cAMP and intracellular Ca+.
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Name the actions of PTH on the kidney?
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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. |
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What is Vit D(cholecalciferol)?
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A steroid hormone synthesized by skin through a UV radiation reaction.
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What is the active form of Vit D?
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Calcitriol(1,25 dihydroxycholecalciferol)
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What are the inactive forms of Vit D?
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1. Cholecalciferol
2. 25-Hydroxycholecalciferol 3. 24,25-hydroxycholecalciferol |
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Where and how is calcitriol synthesized?
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VitD
decrease 25 hydroxylase(in liver)---25-hydroxycholecalciferol---decrease 1 alpha hydroxylase(in kidney)---1,25 hydroxycholecalciferol and 24,25-hydroxycholecalciferol |
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What factors regulate calcitriol synthesis?
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Activity of 1 alpha-hydroxylase, which is increased by;
decreased serum Ca+ Increased PTH levels decreased serum PO4- |
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How are the effects of calcitriol mediated?
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Through the calcitriol receptor.
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Name the actions of calcitriol on;
Intestines Kidney Bone |
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- |
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What is Calcitonin?
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A polypeptide hormone of 32 amino acids
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Where is Calcitonin synthesized and secreted?
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Parafollicular cells(C cells) of thyroid gland
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What factor regulates calcitonin secretion?
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Increased serum Ca+ stimulates secretion.
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What is the 2nd messenger system of calcitonin?
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cAMP(most likely)
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Name the actions of calcitonin?
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Decrease bone resorption by osteoclasts
Decrease bone formation by osteoblasts---increases serum Ca+. |
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Summarize the factors that regulate Ca2+ homeostasis hormone secretion;
PTH Calcitriol Calcitonin |
PTH--decrease serum Ca+
Calcitriol-Decrease serum calcium/Increases PTH levels/decreases serum PO4- Calcitonin- increase serum Ca2+ |
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Summarize the actions of the Ca+ homeostasis hormones in the intestines.
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PTH; increase Ca2+ absorption through activating calcitriol
Calcitriol; increase Ca2+ and PO4- reabsorption Calcitonin-no effect |
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How do Ca2+ homeostasis hormones affect the kidney?
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PTH; increase Ca2+ reabsorption and decrease PO4- reabsorption
Calcitriol; increased Ca2+ and PO4- reabsorption Calcitonin-noeffect |
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How does the Ca2+ homeostasis hormones affect bone?
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PTH- increased resorption
Calcitriol- increased resorption Calcitonin- decreased resorption |
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Summarize the net effect of the Ca2+ homeostasis hormones on serum Ca2+ and PO4-
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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+. |
