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Endocrine > Osteoporosis > Flashcards

Osteoporosis Flashcards

1
Q

What are the Hormones involved in Ca homeostasis?

A
  1. Parathyroid Hormone (PTH)
  2. Calcitonin
  3. Vitamin D (Calcitriol)
  4. Thyroid hormones, growth hormone, androgens, estrogens, and glucocorticoids play a secondary role.
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2
Q

How is Parathyroid hormone involved in Ca homeostasis?

A
  1. Secreted in response to DECREASE in Ca or INCREASE in Phosphate.
  2. Secreted by parathyroid glands in thyroid.
  3. Mobilizes Ca from bone, Increases intestinal absorption (increase Vit. D synthesis). and decreases renal excretion.
  4. Suppresses Calcitonin release.
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3
Q

How is Calcitonin involved in Ca homeostasis?

A
  1. Secreted in response to HIGH blood Ca.
    - Secreted by parafollicular C cells of thyroid.
  2. Inhibits osteoclast-mediated bone resorption.
  3. Increases renal phosphate and Calcium excretion.
  4. Suppresses PTH release.
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4
Q

How is Vitamin D involved in Ca homeostasis?

A
  1. Promotes Ca absorption in intestine.

2. Promotes bone resorption.

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5
Q

What is the daily requirement for Ca in an adult?

A

1000 mg/day

Less than 1/3 is absorbed (~300mg)

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6
Q

What is the daily requirement for Ca in Women over 50 and Men over 70?

A

1200 mg/day

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7
Q

What is the daily requirement for Ca in adolescents?

A

1300 mg/day

-Median intake is 750 mg/day!

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8
Q

What are the upper limits for Ca intake?

A

3 g/day adolescents
2.5 g/day adults
2 g/d for elderly.

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9
Q

Where is most Ca obtained from?

A

75% obtained from dairy products.

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10
Q

What is the Bone turnover of Ca?

A
  1. 300 mg/day
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11
Q

How much Ca is lost in the urine and in the feces?

A

150 mg is lost in urine
-Can be increased by loop diuretics (furosemide)
150 mg is lost in feces, including as bile and sloughed cells.

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12
Q

How is Ca absorbed?

A

In proximal duodenum by active Vit D-Dependent transport.
-Can increase Ca absorption by 2 fold (up to 600 mg/day)
In all of small intestine by facilitated transport
-Accounts for majority of Ca uptake.

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13
Q

Where is most of the Phosphate in the body found?

A

80% of body phosphate is found in the bone.

-Complexed with Ca as hydroxyapatites (Ca10(PO4)6(OH)2)

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14
Q

Where is Phosphate absorbed?

A

Phosphate is absorbed in the intestine.

  1. Abundance in food prevents inadequate intake
  2. 2/3 of intake is absorbed
  3. Uptake is active transport, facilitated by Vit. D.
  4. Circulates in blood as NaH2PO4/Na2HPO4
  5. PO4 is excreted in urine
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15
Q

What increases phosphate excretion?

A

PTH increase excretion.

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16
Q

What plays an important role in Phosphate homeostasis?

A

FGF-23

-Secreted by osteoclasts in response to high phosphate.
-Promotes phosphate clearance by kidney
(inhibits reabsorption)
-Inhibits Vit D activation (1 alpha hydroxylation)

17
Q

What doe elevated levels of FGF-23 cause?

A

Hypophosphatemic Rickets

  • Impaired bone mineralization
  • Low blood phosphate levels –> treat w/ vit D and oral phosphate.
18
Q

What is the most common cause of primary hyperparathyroidism?

A
  1. Hypercalcemia
19
Q

What is hyperparathyroidism?

A
  1. Hypersecretion of PTH due to parathyroid adenoma or hyperplasia.
  2. Characterized by hypercalcemia, osteoporosis, kidney stones, osteitis fibrosa cystica (replacement of bone with CT), Fatigue, weakness, depression –> seizures.
  3. Often hypophosphatemia.
  4. Frequently associated with low Vit D levels
  5. Currently treated by parathyroidectomy.
20
Q

What is Familial Benign Hypercalcemia?

A
  1. Defect in Ca sensor.
  2. Very low Ca excretion in urine.
  3. PTH levels normal to slightly high.
  4. Relatively benign in most cases; not treated.
21
Q

What are other causes of Hypercalcemia?

A
  1. Systemic malignancies that secrete PTH analogs, or promote bone resorption, or overproduce calcitriol.
  2. Granulomatous diseases
  3. Hypercalcemia of malignancy
22
Q

What are Granulomatous Diseases?

A
  1. Tb, Sarcoidosis cause excess calcitriol synthesis by mononuclear cells.
  2. Leads to increased Ca absorption.
  3. Oral phosphate binds Ca; glucocorticoids also decreases ectopic calcitriol.
23
Q

What is a Hypercalcemia of malignancy?

A
  1. Breast cancer metastatic to bone.

2. Treated by decreasing dietary Ca absorption; increasing urinary Ca; inhibiting bone resorption.

24
Q

How is Acute Hypercalcemia treated?

A
  1. Treated by saline diuresis: IV saline + Ca wasting diuretic (furosemide)
  2. Long-term management w/ Bisphosphonates (pamidronate or zoledronate) and Calcitonin.

Endocrine (9 decks)

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