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Physiology II Exam III > Calcium Balance > Flashcards

Calcium Balance Flashcards

1
Q

What are the effects of hypercalcemia?

A

-increases in Ca above normal progressive depression of the nervous system
+symptoms appear when the bloof Ca level rises above 12mg/dL
+reflex activities of the nervous system are sluggish
+there is constipation and lack of appetite

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2
Q

Decreases in calcium concentration causes the nervous system to become more __________.

A

Excited

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3
Q

What is the distribution of calcium stored in the body?

A
  • 0.1% in extracellular fluid
  • 1% in the cells and organelles
  • rest is stored in the bones
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4
Q

How is phosphate storied in the body?

A
  • 85% in bones
  • 14-15% cells
  • less than 1% in extracellular fluid
  • extracellular phosphate conc is not nearly as well regulated as that of Ca
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5
Q

What are the two forms of phosphate in the plasma?

A

HPO4- and H2PO2-

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6
Q

What can hypocalcemia do in the body?

A
  • causes nervous system excitement and tetany
    • nervous system is more excitable due to increased neuronal permeability to Na+

-hypocalcemia may also causes seizures
+first signs of tetany typically occurs in the hand, resulting in capopedal spasm

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7
Q

When does tetany typically occur?

A
  • when blood conc of Ca falls below normal level of 9.5mg/dL to 6mg/dL (35% below normal Ca conc)
  • usually lethal at 4mg/dL
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8
Q

How much calcium is typically taken into the body? How is it absorbed?

A
  • 1000mg/day
  • usually divalent ions are poorly absorbed but vitamin D promotes Ca absorption by the intestines, so 35% if ingested Ca is absorbed
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9
Q

Calcium excretion

A

-Ca not absorbed is excreted in the feces
+250mg/day enter intestines via secreted GI juices and sloughed mucosal cells
+90% of daily intake is excreted

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10
Q

Renal excretion of calcium and phosphate

A
  • about 100mg/day (10%) of the ingested Ca is excreted in the urine
  • 41% of plasma Ca bound to plasma proteins is not filtered by glomerular capillaries
  • the rest is combined with anions or ionized and filtered through the glomeruli
  • renal tubules reabsorb 99% Ca in filtrate
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11
Q

What can increase phosphate excretion?

A

-PTH

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12
Q

Hydroxyapatite crystals fail to precipitate in normal tissues except in what? What prevents this precipitation?

A
  • Bones

- pyrophosphate

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13
Q

What are the initial calcium salts deposited in the bone?

A

CaHPO4- * 2H2O + Ca3(PO4)

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14
Q

What happens when soluble calcium is injected intravenously?

A
  • Ca+2 conc may increase immediately to high levels

- within 30-60mins, the Ca+2 conc returns to normal

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15
Q

How can calcium concs be maintained so well in the body?

A
  • bone contains exchangeable calcium that is always in equilibrium with the Ca+2 in the extracellular fluids
  • small amount of exchangeable Ca is found in tissue cells, especially in highly permeable types of cells such as those of the liver and GI tract
  • exchangeable Ca provides a rapid buffering system
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16
Q

What is the active form of vitamin D?

A

1,25-dihydroxycholecalciferol

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17
Q

What is the importance of vitamin D?

A

-causes kidneys, intestines, and bones to increases absorption of Ca adn P into the extracellular fluid and contribute to feedback regulation of these substances

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18
Q

Where are vitamin D receptors found? What do they do?

A

-present in most cells in the body and are located mainly in the nuclei of target cells
+hormone and DNA binding domains
+can suppress transcription

19
Q

How does vitamin D promote intestinal absorption of Ca?

A

-by increasing, over a period of 2 days, formation of calbindin (Ca binding protein) in epithelial intestine cells
+functions in brush border to transport Ca into the cell cytoplasm

  • Ca moves through the basolateral membrane of the cell by facilitated diffusion
  • calbindin remains in the cell for weeks after the vitamin D has been removed
20
Q

Vitamin D also promotes Ca absorption through the formation of what?

A
  • a Ca stimulated ATPase in the brush border of the epithelial cells
  • an alkaline phosphate in the epithelial cells
21
Q

Vitamin D also increases Ca and P reabsorption in the renal tubules

A

Weak effect

22
Q

What happens when there is an excess of vitamin D?

A
  • causes absorption of bone

- in the absence of vitamin D, the effect of PTH in causing bone formation Iis greatly reduced or prevented

23
Q

How can vitamin D in smaller quantities promote bone calcification?

A

-increasing Ca and P absorption from the intestines

24
Q

Excess activity of the parathyroid gland causes rapid absorption of ________ from the bones.

A
  • Ca salts -> results in hypercalcemia

- hypo function of parathyroid causes hypocalcemia

25
Q

Outline the synthesis of PTH.

A
  • synthesis occurs in ER and Golgi
  • hormone is packaged in granules
  • most of the hormonal activity is caused by 34 aas adjacent to the N terminus of the molecule
26
Q

What effects does the parathyroid hormone have on the bone?

A

-rapid phase begin in mins and increases for several hours
+phase results from activation of the osteocytes to promote calcium and phosphate absorption

-slower phase
+requires several days of weeks
+results from proliferation of osteoclasts, followed by greatly increased osteoclast is reabsorption of the bone not just calcium phosphate salts from the bone

27
Q

How does PTH affect osteoblasts and osteocytes?

A
  • have receptors for PTH

- PTH can activate Ca pumps and cause rapid removal of Ca PO4 salts from amorphous bone crystals that low near the cells

28
Q

How are osteoclasts affected by PTH?

A
  • does not have a receptor for PTH, activated osteoblasts and osteocytes send secondary signals to the osteoclasts
  • secondary signal is osteoprotegrin ligand which activates receptors on pre osteoclasts cells and transforms them into mature osteoclasts that remove bone over a period of weeks of months
29
Q

What are the 2 stages of osteoclastic activation?

A
  1. Immediate activation of osteoclasts that are already formed
  2. Formation of new osteoclasts
30
Q

What are the effects of PTH on renal calcium reabsorption?

A
  • rapid loss of phosphate in the urine
  • increases renal tubular reabsorption of Ca
  • diminishes phosphate reabsorption
  • increases the rate the reabsorption of Mg and H
  • decreases the reabsorption of Na, K, and aas
31
Q

What happens without the effect of PTH on the kidneys?

A

-urine would eventually deplete extracellular fluid and bones of calcium

32
Q

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

A

[Ca]

33
Q

What mediates PTH on target organs?

A

-cAMP

34
Q

What causes the parathyroid gland to increase the rate of secretion?

A

-slight decrease in Ca ion conc in the extracellular fluid

35
Q

What are some conditions that decrease Ca ion conc?

A
  • Rickets
  • pregnancy
  • lactation
36
Q

What conditions increase the Ca+2 conc above normal? What does this result in?

A
  • reduced size of the parathyroid glands
  • excess quantities of Ca in the diet
  • increased vitamin D in the diet
  • bone absorption caused by other factors such as disease
37
Q

What are some characteristics of calcitonin?

A
  • peptide hormone
  • secreted by the thyroid gland
  • tends to decrease plasma calcium conc
  • synthesized in and secreted by parafollicular cells (C cells)
  • has a weak effect on plasma calcium conc in the adult human
  • any initial reduction of the calcium in conc caused by calcitonin leads within hours to a powerful stimulation of PTH secretion
38
Q

In certain bone disease, such as Paget’s disease, what happens?

A

-osteoclatic activity is greatly accelerated and calcitonin has a more potent effect of reducing calcium absorption

39
Q

What is hypoparathyroidism?

A

-parathyroid glands do not secrete sufficient PTH

40
Q

What happens physiologically during hypothyroidism?

A
  • osteoclasts become almost totally inactive
  • calcium reabsorption from the bones is so depressed that blood calcium levels decrease
  • when he parathyroid glands are removed suddenly, the calcium level in the blood falls from the normal 9.4 mg/dL to 6-7mg/dL within 2-3 days and the blood phosphate conc may double
  • signs of tetany begin to develop at this level -> laryngeal muscles sensitive
41
Q

What is the typical cause of death for hypothyroidism?

A

-spasms of the respiratory muscles obstruct respiration

42
Q

What is primary hyperparathyroidism?

A
  • an abnormality, usually a tumor, of the parathyroid glands that causes excess PTH secretions
  • this is more prevalent in women bc pregnancy and lactation stimulate the parathyroid glands and predispose to the development of such a tumor
43
Q

What is secondary hyperparathyroidism?

A
  • high levels of PTH occur as a compensation for hypocalcemia
  • can be caused by vitamin D deficiency, which can lead to osteomalacia

Physiology II Exam III (9 decks)

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