Calcium metabolism

Question 1

Parathyroid glands

Answer 1

3rd and 4th branchial arch derivatives
Chief cells – principal cells
Produce PTH

Oxyphil cells – packed w/ mt
Appear at puberty and increase w/ age

Innervated by nerves off cervical sympathetic ganglia
-control blood flow

Question 2

Vit D

Answer 2

Increase dietary Ca2+ and PO43- absorption

Regulates bone turnover

Question 3

Calcitonin

Answer 3

Produced by parafollicular (c) cells of thyroid
Neural crest cells

Decreased bone resorption of Ca2+

Question 4

PTH

Answer 4

Increase serum Ca2+ levels
Increase bone turnover – rev up osteoclasts – resorb bone

Osteoblasts have the PTH receptor -> RANKL which activates osteoclasts

Increased resorption of Ca2+ at DCT

Increased 1 alpha hydroxylase in kidney to activate Vit D3 -> calcitriol -> Ca2+ absorption in gut

Question 5

Hypercalciemia – 90%

Answer 5

Primary hyperparathyroidism:
Solitary parathyroid adenoma 90-95%
Parathyroid hyperplasia 5%

Malignancy:
Squamous cell cancers esp lung via PTHrP
Renal cell carcinoma
Breast metastasis
Multiple myeloma –local osteolytic factors

Question 6

Hypercalcemia – 10%

Answer 6

Excess Vit D ingestion
Excess calcium ingestion – milk-alkali sn – antacids
Granulomatous disease – excess vit D d/t sarcoid or TB
Increased bone turnover – hyperthyroidism, vit A intoxication, immobilization
Thizide diuretics -> decreased renal excretion of calcium

Question 7

PTH regulation

Answer 7

Ca2+ suppresses chief cell secretion of PTH
Low Ca2+ stimulates secretion
Mg2+ inhibits PTH secretion
-slightl low Mg2+ cuases PTH secretion
prolonged, severely low Mg2+ causes decreased PTH secretion

low Mg2+: diruetics, etOH, diarrhea, aminoglycosides

Question 8

S/S of primary hyperthyroidism

Answer 8

Stones:
Renal stones MC
Nephrocalcinosis
Polyuria/polydipsia
Uremia

Bones:
Osteoporosis
Osteitis fibrosa cystica
OA

Abdominal groans:
Constipation
N/V
Peptic ulcers (elevated calcium increases gastrin)
Pancreatitis

Psychiatric overtones:
Lethargy and fatigue
Depression
Psychosis
Confusion, stupor, coma

Other:
Proximal m. weakness
Keratitis and conjunctivitis
HTN
Itching

Question 9

Classic signs of hypocalcemia

Answer 9

Chvostek and Trousseau

Question 10

Hypoparathyroidism

Answer 10

Parathyroidectomy from damage during thyroidectomy
Autoimmune destruction of parathyroids
Pseudohypoparathyroidsim – kidney tubules unresponsive to PTH
-GNAS1 mutation

DiGeorge Sn at birth

Question 11

Vit D deficiency

Answer 11

Nutritional deficiency and paucity of sunlight

Chronic renal failure

Question 12

Acute pancreatitis in hypocalcemia

Answer 12

Ca2+ precipitate into abdomen combine w/ fatty acids -> soaps

Question 13

Type 1A – Albright hereditary osteodystrophy

Answer 13

AD
GNAS mutation – codes PTH g protein receptor at kidney

Short stature
Obesity
Underdevelopment of 4th and 5th digits

Severe: osteitis fibrosa cystica

Question 14

Osteitis fibrosa cystica

Answer 14

Subperiosteal bone absorption of middle phalanges radial aspect

Tapering of distal clavicles
Salt and pepper appearance of skull
Bone cysts
Brown tumors of long bone

Question 15

Secondary hyperparathyroidism

Answer 15

Chronic hypocalcemia

• chronic renal dz
• renal osteodystrophy
  labs: elevated BUN/Cr, high phosphate

severe Vit D deficiency – rickets
low Ca2+
high or low phosphate
labs: high PTH, low Ca2+, low or nl phosphate
low vit D

Question 16

Tertiary hyperparathyroidism

Answer 16

Long standing secondary hyperparathyroidism – chronic renal dz
Parathyroid hyperplasia
Autonomously functioning parathyroid

High calcium but keep making PTH anyway

Question 17

Calcium and phosphate levels in primary, secondary and tertiary hyperparathyroidism

Answer 17

Primary: high calcium, low phosphate
Secondary: low calcium, high phosphate
Tertiary: high calcium