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ELM3 - endocrine > parathyroid hormone > Flashcards

parathyroid hormone Flashcards

1
Q

What form is calcium stored as in bone?

A

Calcium carbonate, in the hydroxyapatite matrix

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2
Q

What is the role of parathyroid hormone?

A

Regulates calcium and phosphate homeostasis

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3
Q

What are the 3 main targets of PTH?

A

Bone, Kidneys, Intestines

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4
Q

What is the action of PTH on bone?

A

Stimulates osteoclast activity, to break down bone and release stored calcium and phosphate into the blood stream

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5
Q

What is the action of PTH on the kidneys?

A

Reduces phosphate reabsorption/increases urinary excretion, increases calcium reabsorption.
Also stimulates calcitriol production.

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6
Q

What is the action of PTH on the intestines?

A

Calcitriol released in response to PTH activity in the kidneys enhances gut calcium and phosphate absorption

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7
Q

What is the net effect of PTH on phosphate levels?

A

Net decrease in phosphate - although bone breakdown and gut absorption increase levels, the increased renal clearance has a greater effect and lowers phosphate

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8
Q

What are the negative feedback loops controlling PTH secretion?

A

High calcium levels due to PTH action on bone/kidneys/intestines provides negative feedback to the parathyroid gland

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9
Q

What is the function of calcitonin?

A

Function is poorly understood in mammals, but role is generally to decrease calcium levels by reducing bone turnover and increasing renal excretion

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10
Q

How does calcium travel in the blood?

A

Bound to albumin

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11
Q

Why is it important to measure albumin levels in a patient with calcium dysfunction?

A

Calcium in the body is bound to albumin. A low albumin will make the calcium appear lower than it really is and vice versa.

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12
Q

What is primary hyperparathyroidism?

A

Excessive, uncontrolled secretion of PTH from the parathyroid glands, usually due to an adenoma/carcinoma

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13
Q

What is secondary hyperparathyroidism?

A

Low calcium levels from CKD, vitamin D deficiency or malabsorption syndromes stimulate an excessive PTH production.

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14
Q

What is tertiary hyperparathyroidism?

A

Long standing secondary hyperparathyroidism and low calcium causes the parathyroid galnds to become autonomous and overactive, so they continue to secrete excess PTH, even once calcium levels are corrected.

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15
Q

How does chronic kidney disease cause secondary hyperparathyroidism?

A

The damaged kidneys are unable to activate calcitriol, so there will be reduced calcium uptake from the gut. Renal phosphate excretion will be impaired so levels will be high. Together, this will trigger release of PTH, which will be inadequate to correct calcium due to the damaged kidneys

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16
Q

What is the pathophysiology of secondary hyperparathyroidism caused by vitamin D/calcium deficiency?

A

Low levels of calcium due to gut absorption or inadequate vitamin D activation will increase PTH levels to compensate.

17
Q

What are the symptoms of hyperparathyroidism?

A

Bone pain, bone fractures, muscle weakness, fatigue, cystic bone lesions, kidney stones, polyuria, constipation, cognitive disturbances, arrhythmias

18
Q

What are the relative phosphate and calcium levels in primary hyperparathyroidism?

A

Calcium will be high, phosphate will be low

19
Q

What are the relative phosphate and calcium levels in secondary hyperparathyroidism caused by CKD?

A

Calcium will be decreased, phosphate will be increased

20
Q

What are the relative phosphate and calcium levels in secondary hyperparathyroidism caused by Ca/Vit D deficiency?

A

Decreased calcium, decreased phosphate

21
Q

What are the relative phosphate and calcium levels in tertiary hyperparathyroidism?

A

Increased calcium, decreased phosphate

22
Q

What are the results of a 24 hour urinary calcium excretion test in the different types of hyperparathyroidism?

A

Calcium excretion is elevated in primary and tertiary hyperparathyroidism, low/normal in secondary hyperparathyroidism

23
Q

What are some of the investigations that can be used to diagnose hyperparathyroidism?

A

Bloods testing calcium, phosphate, albumin, PTH. Bone density scan may show osteoporosis or osteopenia, ultrasound may show parathyroid tumo

24
Q

What are the treatment options for primary hyperparathyroidism?

A

Removal of tumour, surgical parathyroidectomy

25
Q

What are the treatment options for secondary hyperparathyroidism?

A

Vitamin D/calcitriol supplements

26
Q

What are the treatment options for tertiary hyperparathyroidism?

A

Complete parathyroidectomy

27
Q

What are the causes of hypoparathyroidism?

A

Thyroidectomy/parathyroidectomy, autoimmunity, congenital abnormality of parathyroid glands, pseudo-hypo-parathyroidism (not technically hypoparathyroidism)

28
Q

What are the symptoms of hypoparathyroidism?

A

muscle cramps/spasms, paraesthesia, irritability, anxiety, seizures, prolonged QT interval, hypotension, osteosclerosis

29
Q

What are the relative calcium and phosphate levels in hypoparathyroidism?

A

low calcium, high phosphate

30
Q

What is a possible abnormality seen on ECG in hypoparathyroidism?

A

Prolonged QT interval

31
Q

What are the treatment options for hypoparathyroidism?

A

calcium supplementation, calcitriol/vitamin D supplementation, recombinant PTH therapy, phosphate binders

32
Q

What is the Parathyroid Rule?

A

In primary parathyroid conditions, calcium and phosphate will be opposite (one raised, one low).
In secondary parathyroid conditions, calcium and phosphate will trend the same way (both increase or decrease) - except in CKD

33
Q

What is pseudo-hypoparathyroidism?

A

A condition where tissues become resistant to the action of PTH, resulting in symptoms of low calcium/low PTH, despite high plasma levels of PTH

34
Q

What are the relative calcium and phosphate levels in pseudo-hypoparathyroidism?

A

Decreased calcium, increased phosphate

ELM3 - endocrine (10 decks)

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