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Physiology > Lecture 15: Calcium Balance > Flashcards

Lecture 15: Calcium Balance Flashcards

1
Q

What is the most abundant element in body

A

Calcium

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2
Q

What are the forms of Ca2+ in the blood

A

40-45% protein bound
55-60% ultrafilterable
- 5-10% complexed to anions
- 50% ionized Ca2+

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3
Q

What form of calcium is physiologically active

A

Ionized Ca2+ in blood

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4
Q

describe blood coagulation test and role of ca2+

A

Stage 1: injured blood vessel and release of prothrombin activator (PTA)
2. Ca2+ and PTA interact to form thrombin
3. Thrombin—> fibrinogen which forms blood clots

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5
Q

What is hydroxyapatite

A

Biological apatite that makes mineral bone (lots of phosphate)

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6
Q

How can plasma ionized calcium be altered

A

Increase in plasma proteins, increase in anions, acid base refluxes, hormonal exchange between intestine, bone and kidney

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7
Q

How does increase in plasma proteins affect ionized calcium

A

Increase total bound calcium but minimal change to ionized calcium

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8
Q

How does an increase in anions (PO4^3-) affect ionized calcium

A

Decrease ionized Ca2+

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9
Q

How does acid base refluxes affect ionized calcium

A

Protons complete with calcium for albumin binding sites

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10
Q

How does acidemia affect ionized calcium levels

A

Increases

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11
Q

How does alkalemia affect ionized calcium levels

A

Decreases

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12
Q

How is Ca2+ balance maintained in body

A

Slowly, between ECF/bone and intestine and kidney

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13
Q

How is Ca2+ balance maintained in ECF

A

Rapid, between ECF/bone fluid, regulated by hormonal control

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14
Q

When is the extracellular pool in equilibrium

A

When mg of calcium removed from serum by bone growth= mg of calcium liberated from bone and returned to blood

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15
Q

What hormones primarily regulate calcium and phosphate

A

parathyroid hormone and vitamin D

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16
Q

When does parathyroid hormone activate

A

Low plasma Ca2+, high plasma PO4^3-

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17
Q

What is the main regulator of Ca2+ metabolism

A

Parathyroid hormone

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18
Q

When does Vitamin D get activated

A

Low plasma Ca2+

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19
Q

What is the mechanism in which vitamin D increases Ca2+

A

Increases absorption of Ca2+ through the intestine

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20
Q

When does calcitonin get activated

A

High plasma Ca2+, corrects symptoms of hypercalcemia

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21
Q

Ca2+ intake=

A

Absorbed-secreted (=calcium excretion)

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22
Q

Why kind of hormone is parathyroid hormone

A

Peptide hormone

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23
Q

What are chief cells

A

Majority cell type in the parathyroid gland that detect extracellular Ca2+

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24
Q

Describe the mechanism in which chief cells detect increased Calcium and what is the response

A

Increased calcium enters chief cell, cellular signaling activates PKC which inhibits release of PTH

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25
low Serum Ca2+ drives release of what hormone
PTH
26
Osteoblast
Bone builders, deposit the matrix
27
Osteocytes
Former osteoblasts that are now internalized in the bone
28
osteoclasts
Bone demolition, reabsorb the matrix
29
What are osteoclasts derived from
Macrophages
30
What are labile calcium pools
Ca2+ in bone fluid that allows rapid exchange of calcium with blood
31
What are stable calcium pools
Ca2+ in bone matrix that allow storage and slow exchange of Ca2+
32
Where is the site of bone reabsorption
Stable pools
33
Describe the mechanism of fast exchange of Ca2+
Osteoblasts and osteocyte network has labile reserve of Ca2+, PTH activates membrane bound Ca2+ pumps to take in Calcium and then transfer to central canal and into blood
34
What happens to phosphate during fast exchange of Ca2+
Gets left behind
35
Where are PTH receptors located
Osteoblasts
36
Describe the mechanism of slow exchange of calcium
Osteoclast enters mineralized bone with stable pool of Ca2+, and causes bone dissolution through PTH mediated mechanism
37
PTH inhibits bone formation activity of ___
Osteoblasts
38
PTH stimulates osteoblasts to release ___
RANKL
39
What does RANKL do
Binds RANK on nearby macrophage causing them to differentiate into osteoclasts
40
What do osteoclasts release to dissolve the matrix and release calcium and phosphate
HCL and hydrolytic enzymes
41
What two direct effects does PTH have in kidney
1. Conserves calcium 2. Eliminates phosphate
42
How does PTH conserve calcium in kidney
Increases activity of Na+ Ca2+ cotransport in distal tubule of kindey
43
When PTH is increased what happens to urine calcium
Decreases
44
How does PTH eliminate phosphate
Inhibits Na+/ PO4^3- contransport in the proximal convoluted tubule of the kidney
45
What happens to urine phosphate when PTH is stimulated
Increases
46
Why is PO4^3- elimination necessary
To avoid cation-anion complexes and apatite formation in the blood
47
How does PTH activate vitamin D
By stimulating 1alpha hydroxylase converting precursor to active form
48
What is 25-hydroxycholecalciferol
Vitamin D in the liver
49
What is 1,25 dihydroxycholecalcerfol
Vitamin D in kidney
50
What are the effects on Ca2+ and PO4^3- on increase vitamin D
Increase Ca2+ and PO4^4- absorption in intestine
51
What are the three steps of vitamin D synthesis
1. UV dependent proteolysis of 7-dehydrocholesterol to Vitamin D3 2. Activation: in liver CYP27A1 adds OH group to carbon 25 3. PTH dependent activation: in kidney CYP27B1 adds OH group to carbon 1
52
What are 3 sites of action for Vitamin D and what is the main one
Small intestine (main) Kidney Bone
53
How does vitamin D impact the small intestine and what is the mechanism
Increases calcium and phosphate absorption by increasing expression of calcium binding protein, calbindin, Ca2+ goes into cell, binds calbindin and then is actively pumped out via Ca-ATPase into blood *same mechanism for phophsate*
54
How does vitamin D impact the kidney
Vitamin D promotes calcium reabsorption in DT and phosphate reabsorption in PT
55
How does vitamin D impact bone
Synergizes with PTH to stimulate resorption and bone remodeling Stimulates mobilization of Calcium and phosphate
56
What is Ricket’s disease
Vitamin D deficiency that results in insufficient calcium and phosphate. Present as growth failure or skeletal abnormalities
57
What is osteomalacia
Vitamin D deficiency in adults that is a result of impaired ability to absorb calcium and phosphate in intestine Causes bones to become demineralized and soft, resulting in frequent fractures
58
What could cause osteomalacia
Usually a result of intestinal surgery Also malabsorption syndrome, malnutrition, renal failure and Celia disease
59
What directly regulates phosphate
Vitamin D in intestines by increase phosphate absorption
60
What indirectly regulates phosphate
Inverse relationship between plasma phosphate and plasma calcium levels. A fall in phosphate will increase Ca2+ resulting in decrease PTH
61
A decrease in PTH has what affect on phosphate
Increases renal absorption
62
Where is calcitonin produced
Parafollicular C cells in thyroid gland
63
What stimulates release of calcitonin
Hypercalcemia
64
What is the job of calcitonin
Decrease ECF Ca2+, decrease bone resorption, inhibit Ca2+ and PO4^3- reabsorption in kidney
65
Does calcitonin have an effect on vitamin D
No
66
In general, calcitonin opposes ___ system
PTH
67
Humoral hypercalcemia of malignancy causes release of
PTH related peptide and binds to PTH receptor
68
What are the mechanisms of action of PTH-rp (calcium and phosphate)
Increased bone resorption, increased renal calcium reabsorption, inhibition of renal phosphate reabsorption
69
What is the most common cause of hypercalcemia in dogs and cats
Humoral hypercalcemia of malignancy
70
Are PTH levels low or high in humoral hypercalcemia of malignancy
Low inhibited by hypercalcemia
71
PTH hyper secretion caused by primary hyperparathyroidism results in excess PTH which does what to calcium and phosphate levels
Hypercalcemia and hypophosphatemia
72
What are urine levels of calcium and phosphate in cases of primary hyperparathyroidism
Increase in both
73
Horses lack 1alpha hydroxylase and therefore are susceptible to what type of toxicity
Vitamin D
74
in horses, intestinal absorption of calcium is independent of
Vitamin D signaling
75
Equine renal failure may be indicated by
Hypercalcemia due to decreased excretion
76
Equine hypervitaminosis D is caused by what and what happens to calcium and phosphate levels
Iatrogenic or by ingestion of calcinogenic plants Causes hypercalcemia and hyperphopphatemia
77
How does hypoparathyroidism impact PTH, calcium and phosphate levels
Low PTH, hypocalcemia, hyperphosphatemia
78
How are PTH, calcium and phosphate levels effect in pseudophypoparathyroidism
Elevated PTH, hypocalcemia, hyperphosphatemia

Physiology (10 decks)

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