End 11 - Calcium Metabolism

Question 1

How many parathyroid glands are in the thyroid gland and where are they located?

Answer 1

There are 4 parathyroid glands located on the posterior surface of the thyroid gland: 2 inferior and 2 superior.

Question 2

Where do the parathyroid glands come from?

Answer 2

From the brachial apparatus: from the 3 and 4th brachial pouches.

Question 3

What are the 2 main cell types of the parathyroid glands and what do they do?

Answer 3

Chief cells: AKA principal cells, they produce PTH. Oxyphil cells: unknown function, they are packed w/ mitochondria, appear at puberty and increase with age.

Question 4

How is parathyroid glands controlled?

Answer 4

The cervical sympathetic ganglia control the flow of blood into the parathyroid.

Question 5

What does the Parathyroid hormone do?

Answer 5

It increase serum calcium in 3 different ways: Ramp up osteoclasts by binding into osteoblasts to release RANKL which stimulate osteoclasts. It increases Ca2+ reabsorption in the distal convoluted tubule and upregulates 1-alpha hydroxylase which converts vitamin D to calcitriol. Calcitriol acts to increase Ca2+ absorption in the gut. Also reduces serum phosphate: osteoclasts dump phosphate into the blood, and the kidneys secrete phosphate into the urine.

Question 6

What stimulates PTH release?

Answer 6

Low serum calcium. Magnesium: if low, it secretes PTH but if low for prolonged or severely low, the it decreases PTH secretion.

Question 7

What would cause low Magnesium levels?

Answer 7

Diuresis. Alcohol. Diarrhea. Aminoglycosides.

Question 8

Which cell produces Calcitonin?

Answer 8

By the parafollicular cells (or C-cells) of the thyroid.

Question 9

What is the embryologic origin of Parafollicular cells?

Answer 9

Neural crest cells.

Question 10

What does Calcitonin do?

Answer 10

It decreases bone reabsorption of Ca2+. Doesn’t play a role in Ca2+ metabolism.

Question 11

What kind of cancer is a parafollicular cell tumor?

Answer 11

Medullary Thyroid carcinoma.

Question 12

What are the 90% of causes of Hypercalcemia?

Answer 12

90% are due to Primary hyperparathyroidism (95% solitary parathyroid adenoma, 5% parathyroid hyperplasia) or Malignancy (squamous cell cancers like the lung via PTH-related peptide, renal cell carcinoma, breast metastasis, multiple myeloma via local osteolytic factors).

Question 13

What are the 10% of the causes of Hypercalcemia?

Answer 13

Excess vitamin D ingestion. Excess antacid ingestion (milk-alkali syndrome). Granulomatous disease (excess vitamin D due to sarcoid or TB). Increased bone turnover (hyperthyroidism, vitamin A intox, immobilization). Thiazide diuretics (leads to decreased renal excretion of calcium).

Question 14

What is primary hyperparathyroidism?

Answer 14

The parathyroid gland is making excess PTH just by itself. 95% is due to solitary parathyroid adenoma. 5% is due to parathyroid hyperplasia. High Alk Phos because of increased bone turnover.

Question 15

Which syndrome is associated with parathyroid adenomas? Which one for parathyroid hyperplasia?

Answer 15

MEN 1 is associated w/ parathyroid adenomas. MEN 2A is associated w/ parathyroid hyperplasia.

Question 16

What is secondary hyperparathyroidism? What lab values does it present?

Answer 16

Where you have Chronic hypocalcemia (maybe due to chronic renal disease where you can’t make calcitriol, and w/o calcitriol, you can’t absorb much Ca2+ in the gut). This increases PTH secretion, which causes osteodystrophy. Low calcium, high phosphate (Cant throw away phosphate due to renal failure), high PTH. High Alk Phos because of increased bone turnover.

Question 17

What is Terciary Hyperparathyroidism?

Answer 17

Chronic renal disease and parathyroid hyperplasia (working autonomously), but instead of elevation of PTH response to low Ca2+, now the PTH is high even if Ca2+ is high.

Question 18

What are the 4 causes of hypoparathyroidism?

Answer 18

Parathyroidectomy (from dmg during thyroidectomy). Autoimmune destructionof parathyroids. Pseudohypoparathyroidism (kidneys unresponsive to PTH). DiGeorge syndrome.

Question 19

What are the four causes of Hypocalcemia?

Answer 19

Hypoparathyroidism. Poor calcium intake. Vit D deficiency (nutritional deficiency and paucity of sunlight, chronic renal failure). Acute pancreatitis.

Question 20

What are the 2 classic signs of hypocalcemia?

Answer 20

Chvostek’s sign (tap the CHeek, which stimulate the facial nerve and causes contraction of the facial muscles). Trousseau’s sign (Tighten a BP cuff on the arm causing Carpopedal spasms).

Question 21

What are the 3 functions of vitamin D?

Answer 21

Increase dietary absorption of Ca2+. Increase dietary absorption of phosphate. Increases bone resorption of Ca2+ and phosphate.

Question 22

How does PTH affect calcium?

Answer 22

PTH affects calcium by increasing bone resorption of calcium and increasing renal reabsorption of calcium.

Question 23

How does PTH affect phosphate?

Answer 23

PTH thrashes phosphate: it pulls phosphate from the bone and excretes it in the urine.

Question 24

RFF: Most common cause of hypercalcemia.

Answer 24

Primary hyperparathyroidism.

Question 25

RFF: most common cause of primary hyperparathyroidism.

Answer 25

Parathyroid adenoma.

Question 26

RFF: Most common cause of secondary hyperparathyroidism.

Answer 26

Chronic renal failure.

Question 27

RFF: Most common cause of hypoparathyroidism.

Answer 27

Accidental Parathyroidectomy.

Question 28

RFF: Facial muscle spams when tapping on the cheek.

Answer 28

Chvostek’s sign.

Question 29

RFF: Parathyroid, pancreatic, and pituitary tumors.

Answer 29

MEN 1.