F2-PARATHYROID Flashcards
(112 cards)
1
Q
How many parathyroid glands are typically present in humans?
A
Four+ sometimes 3+ 4+ or 5
2
Q
What is the typical size and shape of parathyroid glands?
A
Ovoid or bean-shaped+ approximately 3 mm in size
3
Q
Which parathyroid glands are smaller+ superior or inferior?
A
Superior glands are smaller
4
Q
What specialized receptors do parathyroid glands have?
A
Calcium-sensing receptors (CSRs)
5
Q
How do parathyroid glands respond to hypercalcemia?
A
Decrease parathyroid hormone secretion
6
Q
How do parathyroid glands respond to hypocalcemia?
A
Increase parathyroid hormone secretion
7
Q
What are the main target organs of parathyroid hormone (PTH)?
A
Bone and kidneys
8
Q
What are the three main effects of PTH on the kidneys?
A
Increase reabsorption of renal tubular calcium + increase phosphate excretion + enhance 1α-hydroxylation of 25-hydroxyvitamin D
9
Q
What enzyme does PTH stimulate in the kidneys?
A
1α-hydroxylase
10
Q
What is the active form of vitamin D produced by 1α-hydroxylase?
A
1,25-dihydroxyvitamin D (calcitriol)
11
Q
How does calcitriol aid calcium homeostasis?
A
Increases calcium absorption from the intestines
12
Q
How does PTH affect bone?
A
Indirectly activates osteoclasts via osteoblast-mediated signaling to increase bone resorption and release calcium and phosphate into the bloodstream
13
Q
What is the source of Vitamin D3 (cholecalciferol)?
A
Animal sources like liver+ seafood+ milk+ egg yolks+ multivitamins
14
Q
What is the source of Vitamin D2 (ergocalciferol)?
A
Edible mushrooms
15
Q
Where in the skin is Vitamin D3 synthesized?
A
Epidermal layer containing 7-dehydrocholesterol
16
Q
What converts 7-dehydrocholesterol to Vitamin D3?
A
UV B radiation exposure
17
Q
Where does the first hydroxylation of Vitamin D3 occur?
A
Liver by 25-hydroxylase converting it to 25-hydroxyvitamin D
18
Q
Where does the second hydroxylation of Vitamin D occur?
A
Kidneys by 1α-hydroxylase converting 25-hydroxyvitamin D to 1,25-dihydroxyvitamin D (calcitriol)
19
Q
What are the effects of 1,25-dihydroxyvitamin D (calcitriol)
A
Induces gastrointestinal calcium absorption + regulates mineralization + reduces PTH secretion by parathyroid gland
20
Q
What happens to PTH secretion when blood calcium rises (hypercalcemia)?
A
PTH release is suppressed
21
Q
What happens to bone resorption and urinary calcium loss during hypercalcemia?
A
Bone resorption decreases + urinary calcium loss increases
22
Q
What happens to 1,25-dihydroxyvitamin D production during hypercalcemia?
A
Decreases+ reducing gastrointestinal calcium absorption
23
Q
What happens to PTH secretion when blood calcium falls (hypocalcemia)?
A
PTH secretion is stimulated
24
Q
What happens to bone resorption and urinary calcium loss during hypocalcemia?
A
Bone resorption increases + urinary calcium loss decreases
25
What happens to 1,25-dihydroxyvitamin D production during hypocalcemia?,
Increases+ enhancing gastrointestinal calcium absorption
26
Which organs work together with PTH and Vitamin D to maintain calcium homeostasis?
Gastrointestinal tract + kidneys + bone
27
What is the primary role of PTH in calcium regulation?
Increase serum calcium by acting on bone+ kidney+ and indirectly on intestines via vitamin D activation
28
How does PTH stimulate osteoclast activity?
Binds osteoblasts to increase RANKL - Receptor Activator of Nuclear Factor-κB Ligand expression which activates osteoclast precursors to resorb bone
29
How does PTH affect phosphate levels?
Increases phosphate excretion by kidneys
30
What is the half-life of PTH?
Approximately 4 minutes
31
Where are PTH receptors located?
Bone and kidney cells (PTH1 receptor) + CNS+ pancreas+ testes+ placenta (PTH2 receptor)
32
How does magnesium affect PTH secretion?
Mild hypomagnesemia stimulates PTH secretion; severe hypomagnesemia inhibits PTH secretion and causes resistance
33
What hormone opposes PTH in calcium regulation?
Calcitonin
34
What cells secrete calcitonin?
Parafollicular (C) cells of the thyroid gland
35
How does calcitonin affect calcium levels?
Decreases blood calcium by inhibiting osteoclasts and stimulating osteoblasts and calcium excretion by kidneys
36
In which populations is calcitonin most important?
Children (bone growth) + pregnancy (reduce maternal bone loss) + prolonged starvation (reduce bone mass loss)
37
Where is Vitamin D3 synthesized in the body?
Skin upon exposure to sunlight
38
From which sources can Vitamin D2 and D3 be obtained?
Fortified foods
39
What is the first hydroxylation process for Vitamin D2 and D3?
Conversion to 25-Hydroxyvitamin D in the liver
40
What is the second hydroxylation process for 25-Hydroxyvitamin D?
Conversion to active 1,25-Dihydroxyvitamin D in the kidneys
41
What is the function of active Vitamin D (1,25-Dihydroxyvitamin D)?,
Stimulates gastrointestinal tract to absorb 150-200 mg of calcium from the diet
42
What serum calcium level is maintained by the body?
8.5-10.2 mg/dL
43
How does the body maintain serum calcium levels?
Gastrointestinal absorption of calcium + bone remodeling + renal reabsorption and excretion of calcium
44
Process where mature bone is resorbed by osteoclasts or formed by osteoblasts
bone remodeling
45
How does hypocalcemia affect bone remodeling?
Parathyroid hormone stimulates bone resorption by osteoclasts to release calcium into the bloodstream
46
How does hypercalcemia affect bone remodeling?
Parathyroid hormone secretion decreases + bone formation by osteoblasts increases to deposit excess calcium
47
How do kidneys respond to hypercalcemia?
Increase urinary loss of calcium
48
How do kidneys respond to hypocalcemia?
Increase tubular reabsorption of calcium
49
How does parathyroid hormone affect renal calcium reabsorption?
Increases renal tubular reabsorption of calcium during hypocalcemia
50
Blood calcium levels above the normal range ?
hypercalcemia
51
What symptoms are associated with severe hypercalcemia?
Lethargy + stupor + coma
52
What symptoms are associated with moderate hypercalcemia?
Intellectual weariness + personality changes + nausea + anorexia + kidney stones + hypertension + ECG changes
53
What is the most common cause of hypercalcemia?
Primary hyperparathyroidism (PHPT)
54
What is the hallmark of primary hyperparathyroidism?
Autonomous overproduction of parathyroid hormone
55
What are common causes of PHPT?
Single adenoma (>80%) + multiple gland hyperplasia (5-10%) + rare parathyroid cancer + MEN types 1 and 2a
56
What glands are affected in MEN 1?
Parathyroid + pituitary + pancreas
57
What glands are affected in MEN 2?
Parathyroid + thyroid + adrenal
58
How is PHPT diagnosed?
Elevated serum calcium or ionized calcium + inappropriately normal or elevated PTH level
59
What is the reference range for PTH?
11-54 pg/mL
60
What biochemical findings are typical in PHPT?
Hypercalcemia + hypophosphatemia + elevated PTH relative to serum calcium + low-normal 25-OH-D + high-normal or elevated 1,25-diOH-D
61
Why does hypophosphatemia occur in PHPT?
Calcium and phosphate are inversely related; PTH increases phosphate excretion
62
Increased chloride reabsorption to maintain electroneutrality due to low phosphate levels CAUSES WHAT?
metabolic hyperchloremic acidosis
63
Why is serum alkaline phosphatase elevated in severe PHPT?
Increased bone resorption releases ALP from bone
64
What is the structure of parathyroid hormone?
Polypeptide of 84 amino acids with biologically active N-terminal residues 1-11
65
How is intact PTH measured?
Sandwich ELISA or electrochemiluminescent assays using antibodies against N- and C-terminal ends
66
What other PTH assays are used?
CAP assay (cAMP inducible PTH) + PTHrP assays + FNAB specimens from parathyroid tumors
67
What is the biological activity of the CAP assay?
Measures biologically active PTH (1-11 amino acid sequence)
68
What is the function of PTH in serum calcium regulation?
Increases serum calcium by stimulating bone resorption + increasing renal calcium reabsorption + promoting vitamin D activation for intestinal calcium absorption
69
What is the primary treatment for primary hyperparathyroidism?
Parathyroidectomy
70
Why is parathyroidectomy the primary treatment?
Because the common cause is a tumor in the parathyroid gland
71
What medical treatments are used for mild primary hyperparathyroidism?
Bisphosphonates + selective estrogen receptor modulators (SERMs) + estrogen + allosteric calcium receptor modulators such as cinacalcet
72
What is the role of bisphosphonates in managing hyperparathyroidism?
Potent inhibitor of bone resorption
73
Why are SERMs and estrogen used in PHPT?
To interact with estrogen receptors in the parathyroid gland to inhibit PTH secretion
74
Binds to calcium sensing receptors (CSR) on parathyroid glands to increase sensitivity and inhibit PTH release
allosteric calcium receptor modulator - cinacalcet
75
Compensatory rise in PTH secretion in response to hypocalcemia
secondary hyperparathyroidism
76
What are biochemical findings in secondary hyperparathyroidism?
Low blood calcium + elevated PTH + low serum phosphate + elevated alkaline phosphatase + hypocalciuria + phosphaturia + vitamin D deficiency or lack of vitamin D effect
77
What causes hypocalciuria in secondary hyperparathyroidism?
Decreased calcium excretion due to PTH effect to increase blood calcium
78
How is secondary hyperparathyroidism treated?
Correct underlying hypocalcemia and/or vitamin D deficiency
79
What causes secondary and tertiary hyperparathyroidism in renal failure?
Diseased kidneys fail to excrete phosphate and produce 1,25-dihydroxyvitamin D
80
Autonomous PTH production despite normalized calcium levels after long-standing secondary hyperparathyroidism ?
tertiary hyperparathyroidism
81
What is the treatment for hyperparathyroidism in chronic kidney disease?
Renal transplantation + vitamin D analogs (calcitriol, doxercalciferol, paricalcitol) + calcimimetics (cinacalcet)
82
Benign condition caused by germline mutation in CSR causing continued PTH production despite hypercalcemia
familial hypocalciuric hypercalcemia
83
What are clinical features of familial hypocalciuric hypercalcemia?
Mild to moderate elevated serum calcium + mildly elevated serum magnesium + mildly elevated PTH + low urine calcium excretion (<100 mg/24h) + fractional excretion of calcium <1%
84
What rare complications can familial hypocalciuric hypercalcemia cause?
End-organ dysfunction especially bones and kidneys
85
How does hyperthyroidism affect calcium and PTH levels?
Increased bone resorption causes hypercalcemia which suppresses parathyroid gland and lowers PTH levels
86
What hormone deficiency characterizes Addison's disease (primary adrenal insufficiency)?
Glucocorticoids (Cortisol)
87
How does decreased cortisol affect calcium levels?
Decreased cortisol leads to increased calcium reabsorption causing hypercalcemia
88
How does hypercalcemia affect parathyroid hormone (PTH) levels in Addison's disease?
High calcium suppresses PTH secretion resulting in low PTH levels
89
Which medications can cause hypercalcemia?
Hydrochlorothiazide (HCTZ) + Lithium
90
How does hydrochlorothiazide cause hypercalcemia?
Enhances distal tubular calcium absorption
91
How does lithium cause hypercalcemia?
Disrupts calcium sensing receptor (CSR) function causing excessive PTH release despite high calcium
92
Excessive vitamin D intake or aberrant extrarenal production of active vitamin D leading to hypercalcemia
hypervitaminosis D
93
A protein secreted by some cancers structurally similar to PTH that causes hypercalcemia
parathyroid hormone-related protein (PTHrP)
94
How does PTHrP cause hypercalcemia?
Stimulates bone resorption and renal tubular calcium reabsorption without feedback inhibition
95
What happens to PTH secretion when PTHrP causes hypercalcemia?
PTH secretion is suppressed due to high calcium sensed by parathyroid glands
96
What is the most common cause of hypoparathyroidism?
Neck surgery
97
What autoimmune diseases can cause hypoparathyroidism?
Type 1 diabetes + Hashimoto's thyroiditis + Addison's disease
98
What is the treatment for hypoparathyroidism?
High doses of vitamin D and calcium
99
Conditions with low vitamin D availability
hypovitaminosis D
100
Inherited resistance to PTH causing hypocalcemia despite elevated PTH
pseudohypoparathyroidism
101
What are biochemical features of pseudohypoparathyroidism?
Markedly elevated PTH + hypocalcemia
102
How is pseudohypoparathyroidism treated?
High doses of vitamin D and calcium
103
What organ system disorders can cause hypocalcemia?
Intestinal disorders causing malabsorption of calcium or vitamin D
104
What diseases result from vitamin D deficiency?
Rickets (children) + osteomalacia (adults)
105
What are features of rickets and osteomalacia?
Fractures + hypocalcemia + abnormal bone mineralization
106
What is the treatment for rickets and osteomalacia?
Calcitriol
107
What is the most devastating consequence of osteoporosis?
Hip fracture
108
What conditions cause glucocorticoid-induced osteoporosis?
Asthma + rheumatoid arthritis + lupus + post-organ transplant
109
What is the treatment for glucocorticoid-induced osteoporosis?
Bisphosphonates (alendronate + risedronate)
110
Which drugs induce low bone mass?
Anticonvulsants (phenytoin) + immunosuppressants (cyclosporin A)
111
How does phenytoin affect bone?
Increases vitamin D metabolism leading to deficiency
112
How does cyclosporin A affect bone?
Promotes increased bone turnover causing faster bone reformation
