Term
| Where is calcium found in the body? |
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Definition
Bones
Extracellular fluid bound to proteins
Free ions in ECF (mainly heart and GI tract)
In intracellular organelles like the ER and mitochondria |
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Term
| Where is most of the calcium in the body found? In what form? |
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Definition
| In bone as calcium phosphate (Ca)3(PO4)2 |
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Term
| What is “fast time-scale” regulation of calcium concentrations in the plasma? |
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Definition
| It is the shift of Ca2+ onto and off of the bone |
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Term
| What is “slow time-scale” regulation of calcium concentrations in the plasma? |
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Definition
| Altering the absorption and secretion from the GI tract and loss by renal processes |
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Term
| What are the three forms of calcium in the blood? |
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Definition
| 1. freely ionized 2. reversibly bound to plasma proteins 3. complexed to plasma anions like citrate and phosphate |
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Term
| Why is there very little calcium in the cytosol? |
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Definition
| it would cause abnormal cell signalling |
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Term
| What percentage of calcium is not absorbed by the body? |
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Definition
| 90%, the other 10% is mostly absorbed by the gut |
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Term
| What regulates gut absorption of Ca2+? |
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Definition
| The active form of Vitamin D3 = calcitriol |
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Term
| What types of calcium is filterable in the kidney? |
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Definition
| Only free ionized calcium |
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Term
| How much of the filtered calcium is reabsorbed along the proximal tubule, thick ascending limb of Henle’s loop, distal tubule, and collecting duct? |
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Definition
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Term
| What protein is involved in Ca2+ reabsorption? |
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Definition
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Term
| What is the short-term buffer for fast changes in plasma calcium concentrations? |
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Definition
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Term
| How is calcium transported from the epithelial cells to the interstitium? |
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Definition
Calcium ATPase (primary active transporter)
Na/Ca exchanger (secondary active transporter) |
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Term
| What three hormones participate in the regulation of calcium and phosphate levels in the plasma? |
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Definition
Calcitriol (activated Vitamin D3)
Parathormone (PTH)
Calcitonin |
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Term
| Where is parathormone produced? |
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Definition
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Term
| Where is calcitonin produced? |
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Definition
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Term
| Where is Vit D3 activated to calcitriol? |
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Definition
| Proximal tubule cells in the nephron |
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Term
| How does calcitriol react to hypocalcemia? |
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Definition
It recruits calcium and phosphate from GI absorption and bone resorption.
Calcitriol inhibits excretion of calcium and phosphate in the kidneys. |
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Term
| How does PTH react to hypocalcemia? |
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Definition
It recruits calcium and phosphate from bone resorption.
Calcitriol inhibits excretion of calcium in the kidneys but it promotes the excretion of phosphate. |
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Term
| How does calcitonin react to hypercalcemia? |
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Definition
| It stimulates the formation of new bone as Ca3(PO4)2 and increases the excretion of Ca2+ and (PO4)3- from the kidneys |
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Term
| What transporter do thiazides (diuretics) block? |
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Definition
| Na/Cl cotransporter (NCC) in the apical membrane |
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Term
| How might thiazides reduce calcium loss associated with osteoporosis? |
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Definition
| Thiazides promote calcium reabsorption by enhancing the basolateral sodium gradient since the NCC is inhibited. This increases Na/Ca exchange, thus more Ca2+ is transported into the interstitium and back to the blood |
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Term
| What is the normal plasma concentration of calcium? |
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Definition
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Term
| What are the rapid effects of increased PTH release? |
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Definition
| Increased renal calcium reabsorption and increased bone membrane release |
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Term
| What are the slow effects of increased PTH release? |
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Definition
| Increased osteoclastic bone reabsorption and increased calcium absorption |
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Term
| Where is the renal plasma threshold for phosphate set? |
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Definition
| It is just above the normal plasma concentration of phosphate so the kidney is always excreting the “spilled over” phosphate |
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Term
| What hormone decouples calcium phosphate in the kidney? |
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Definition
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