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Phys Exam 3 > 22 - Calcium Balance > Flashcards

22 - Calcium Balance Flashcards

1
Q

Excitable cells, such as neurons, are sensitive to changes in _______ ion concentrations.

A

Calcium

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2
Q

(INCREASES/DECREASES) in calcium ion (ABOVE/BELOW) normal cause progressive depression of the nervous system.

A

Increases

Above

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3
Q

Symptoms begin to appear when the blood calcium level rises above 12 mg/dl. Reflex activates of the nervous system are sluggish and there is constipation and lack of ________.

A

Appetite

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4
Q

(INCREASES/DECREASES) in calcium concentration cause the nervous system to become more excited.

A

Decreases

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5
Q

0.1 percent of the total body calcium is in the extracellular fluid, 1 percent is in the cells organelles, and the rest is tired in the _______.

A

Bones

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6
Q

85 percent of the total body ________ is stored in bones, 14 to 15 percent is in the cells, and less than 1 percent is in the extracellular fluid.

A

Phosphate

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7
Q

Inorganic phosphate in the plasma is mainly in two forms, which are…

A

HPO4

H2PO4

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8
Q

Large changes in the level of phosphate in the ECF do not cause major immediate effects on the body, but even slight changes in ECF _______ can cause extreme immediate physiological effects.

A

Calcium

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9
Q

This causes nervous system excitement and tetany. This is due to an increased neuronal membrane permeability to sodium ions. The first sign of tetany typically occurs in the hand, resulting in carpopedal spasm.

A

Hypocalcemia

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10
Q

_______ ordinarily occurs when the blood concentration of calcium falls from its normal level of 9.5 mg/dl to about 6 mg/dl (35 percent below normal calcium concentration).

A

Tetany

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11
Q

What level does blood calcium drop to when it becomes lethal?

A

4 mg/dl

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12
Q

Usual rates of intake are about _______ mg/day each for calcium and phosphorous.

A

1000

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13
Q

Normally, divalent ions are poorly absorbed, but ________ promotes calcium absorption by the intestines, so that about 35 percent of ingested calcium is absorbed.

A

Vitamin D

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14
Q

Calcium that is not absorbed is excreted in the feces. About 250 mg/day of the absorbed calcium enters intestines via secreted GI juices and sloughed mucosal cells. Thus, about _____ percent of the daily intake of calcium is excreted.

A

90

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15
Q

About 100 mg/day (10 percent) of the ingested calcium is excreted in the _______.

A

Urine

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16
Q

The _____ percent of the plasma calcium bound to plasma proteins is not filtered by glomerular capillaries. The rest is combined with anions or ionized and filtered through the glomeruli.

A

41

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17
Q

The renal tubules reabsorb about ______ percent of the calcium in the filtrate.

A

99

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18
Q

______ can greatly increase phosphate excretion.

A

PTH

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19
Q

These fail to precipitate in normal tissues (except in bone). Inhibitors are present in almost all tissues and plasma, to prevent such precipitation.

A

Hydroxyapatite crystals

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20
Q

Bone may secrete a _________ inhibitor to allow hydroxyapatite precipitation.

A

Pyrophosphate

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21
Q

In the initial stage of bone production, ________ secrete collagen monomers which polymerize rapidly to form collagen fibers. The precipitation of calcium along the collagen fibers eventually forms ________ ________.

A

Osteoblasts

Hydroxyapatite crystals

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22
Q

The initial calcium sals to be deposited are in an amorphous (noncrystalline) form. These salts are converted into the ________ _________ over a period of weeks or months. A few percent may remain in the amorphous form. These amorphous salts can be absorbed rapidly when there is need for extra calcium in the ECF.

A

Hydroxyapatite crystals

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23
Q

T/F. Under abnormal conditions, calcium salts do precipitate in other tissues. This presumably occurs when the inhibitor factors that normally prevent deposition of calcium salts disappear from other tissues.

A

True

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24
Q

You can inject soluble calcium salts intravenously and the calcium ion concentration may increase immediately to high levels. However, within _______ minutes, the calcium ion concentration returns to normal.

A

30 to 60

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25
Q

If large quantities of calcium ions are removed form the circulating body fluid, the calcium ion concentration again returns to normal within ______ minutes or so.

A

30

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26
Q

The ability of calcium ion concentration to return to normal quickly result in great part from the fact that the bone contains exchangeable calcium that is always in equilibrium with the calcium ions in the ______.

A

ECF

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27
Q

A small portion of this exchangeable calcium is also found in all tissue cells, especially in highly permeable types of cells such as those of the _______ and _______. The exchangeable calcium provides a rapid buffering mechanism.

A

Liver

GI tract

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28
Q

The active form of ________ is 1,25-dihydroxycholecalciferol. It causes intestines, kidneys, and bones to increase absorption of calcium and phosphate into ECF and contribute to feedback regulation of these substances.

A

Vitamin D

29
Q

Vitamin D receptors are present in most cells in the body and are located mainly in the _______ of target cells.

A

Nuclei

30
Q

The vitamin D receptor has ________-binding and _______-binding domains.

A

Hormone

DNA

31
Q

The vitamin D receptor forms a complex with another intracellular receptor, the _______ _______, and this complex binds to DNA and activates transcription in most instances. Sometimes vitamin D suppresses transcription.

A

Retinoid-X receptor

32
Q

1,25-dihydroxycholecalciferol itself promotes intestinal absorption of by increasing, over a period of about 2 days, formation of ________, a calcium-binding protein, in the intestinal epithelial cells.

A

Calbindin

33
Q

This protein functions in the brush border of the epithelial cells to transport calcium into the cell cytoplasm.

A

Calbindin

34
Q

Once bound to calbindin, then the calcium moves through the basolateral membrane of the cell by _______ _______. Calbindin remains in the cell for weeks after the 1,25-hydroxycholecalciferol has been removed from the body.

A

Facilitated diffusion

35
Q

1,25-hydroxycholecalciferol also promotes calcium absorption through the formation of a calcium-stimulated _______ in the brush border of the epithelial cells and an alkaline ________ in the epithelial cells.

A

ATPase

Phosphatase

36
Q

Vitamin D also increases calcium and phosphate reabsorption by the epithelial cells of the ______ ______. This is a weak effect.

A

Renal tubules

37
Q

The administration of extreme quantities of vitamin D causes absorption of _______.

A

Bone

38
Q

In the absence of vitamin D, the effect of ______ in causing bone absorption is greatly reduced or even prevented.

A

PTH

39
Q

Vitamin D in smaller quantities promotes bone ________ by increasing calcium and phosphate absorption from the intestines.

A

Calcification

40
Q

Excess activity of the ________ gland causes rapid absorption of calcium salts from the bones. This results in hypercalcemia in the ECF. Hypofunction of the ________ glands causes hypocalcemia often with resultant tetany.

A

Parathyroid

Parathyroid

41
Q

PTH is first synthesized on the ________ in the form of a preprohormone with 110 amino acids. This is cleaved first to a pro hormone with 90 amino acids, then to the hormone itself with _____ amino acids by the ER and Golgi. The hormone is finally packaged in granules.

A

Ribosomes

84

42
Q

Most of the PTH hormonal activity is caused by 34 amino acids adjacent to the _____ terminus of the molecule.

A

N

43
Q

Where does synthesis of PTH occur?

A

ER and Golgi

44
Q

A _______ phase begins in minutes and increases progressively for several hours. This phase results from activation of the already existing bone cells (mainly osteocytes) to promote calcium and phosphate absorption.

A

Rapid

45
Q

A _______ phase requires several days or even weeks to become fully developed. This results from proliferation of osteoclasts, followed by greatly increased osteoclastic reabsorption of the bone itself, not merely absorption of the calcium phosphate salts from the bone.

A

Slow

46
Q

The cell membranes of both the osteoblasts and the osteocytes have receptor proteins for binding _____. This can activate the calcium pump and cause rapid removal of calcium phosphate salts from those amorphous bone crystals that lie near the cells.

A

PTH

47
Q

PTH is believed to stimulate this calcium pump by increasing the calcium permeability of the bone fluid side of the osteocytic membrane, thus allowing calcium ions to diffuse into the membrane cells from the bone fluid. Then the calcium pump on the other side of the cell membrane transfers the calcium ions the rest of the way in to the _______.

A

ECF

48
Q

The _______ do not have membrane receptors proteins for PTH.

A

Osteoclasts

49
Q

It is believed that the activated osteoblasts and osteocytes send secondary “signals” to the osteoclasts. A major secondary signal is _________ ligand, which activates receptors on preosteoclast cells and transforms them into mature osteoclasts that remove bone over a period of weeks or months.

A

Osteoprotegerin

50
Q

Administration of PTH causes rapid loss of ________ in the urine due to the effect of the hormone to diminish proximal tubular reabsorption of the ________ ions.

A

Phosphate

Phosphate

51
Q

PTH also increase renal tubular reabsorption of ________. This occurs mainly in the late distal tubules, the collecting tubules, the early collecting ducts, and possible the ascending loop of Henle to a lesser extent.

A

Calcium

52
Q

PTH also increases the rate of reabsorption of ________ ions and ________ ions.

A

Magnesium

Hydrogen

53
Q

PTH also decreases the reabsorption of ________, _______, and amino acid ions.

A

Sodium

Potassium

54
Q

Without the effect of ______ on the kidneys to increase calcium reabsorption, the urine would eventually deplete both the ECF and the bones of calcium.

A

PTH

55
Q

A large share of the effect of PTH on its target organs is mediated by ______.

A

cAMP

56
Q

The slightest (INCREASE/DECREASE) in calcium ion concentration in the ECF causes the parathyroid glands to increase their rate of secretion.

A

Decrease

57
Q

Conditions that decrease calcium ion concentration include…

A

Rickets
Pregnancy
Lactation

58
Q

Conditions that increase the calcium ion concentration above normal (resulting in a reduced size of the parathyroid glands) include:

    • Excess quantities of _______ in the diet
    • Increased _______ in the diet
    • ______ absorption caused by other factors such as disease
A

Calcium
Vitamin D
Bone

59
Q

This is a peptide hormone secreted by the thyroid gland. It tends to decrease plasma calcium concentration.

A

Calcitonin

60
Q

Calcitonin is synthesized in and secreted by ________ cells (C cells).

A

Parafollicular

61
Q

Calcitonin has a weak effect on plasma calcium concentration in adult humans. Any initial reduction of the calcium ion concentration caused by calcitonin leads within hours to a powerful stimulation of ______ secretion.

A

PTH

62
Q

In certain bone disease, such as _______ disease, osteoclastic activity is greatly accelerated, and calcitonin has a more potent effect of reducing calcium absorption.

A

Paget

63
Q

This occurs when parathyroid glands do not secrete sufficient PTH. Osteoclasts become almost totally inactive and calcium reabsorption from the bones is so depressed that blood calcium levels decrease.

A

Hypoparathyroidism

64
Q

When the parathyroid glands are removed suddenly, the calcium level in the blood falls from the normal 9.4 mg/dl to 6-7 mg/dl within 2 to 3 days and the blood ________ concentration may double. Signs of tetany begin to develop at this level.

A

Phosphate

65
Q

The _______ muscle are especially sensitive to tetanic spasms. Spasms of these muscles obstruct respiration, which is the usual cause of death.

A

Laryngeal

66
Q

Primary _________ is due to an abnormality (usually a tumor) of the parathyroid glands that causes inappropriate, excess PTH secretions. This is more prevalent in women because pregnancy and lactation stimulates the parathyroid glands and predispose to the development of such a tumor.

A

Hyperparathyroidism

67
Q

Secondary ________ is due to high levels of PTH that occur as a compensation for hypocalcemia. This can be caused by vitamin D deficiency, which can lead to osteomalacia.

A

Hyperparathyroidism

68
Q

This disease is the most common of all bone disease in adults, especially in old age. It results from diminished organic bone matrix rather than from poor bone calcification.

A

Osteoporosis

69
Q

This disease occurs mainly in children and it results from calcium or phosphate deficiency in the ECF, usually caused by lack of vitamin D. Can be helped by adequate sunlight.

A

Rickets

Phys Exam 3 (10 decks)

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