Parathyroid Gland Physiology

Question 1

What three hormones regulate body Ca2+ levels?

Answer 1

• PTH
• Vitamin D
• Calcitonin

Question 2

Calcium metabolism

Answer 2

Question 3

Parathyroid gland chief cell release of PTH is regulated by a ____________.

Answer 3

Ca-sensing receptor (CaSR)

NOTE: Active Vitamin D3 supresses PTH synthesis and stimulates CaSR synthesis. CaSR inhibits PTH. PTH blockage occurs in two places. It block the gene from being transcibed and its released from stored vesicles is also blocked when calcium is high.

Question 4

What effect does PTH have on bone?

Answer 4

• Stimulates bone osteoblasts to increase growth and metabolic activity
• Stimulates bone resorption and releases calcium and phosphate into blood

Question 5

What effect does PTH have on the kidneys?

Answer 5

• Increases calcium reabsorption and reduces reabsorption of phosphate
• Stimulates synthesis of Vitamin D3
• Inhibits resorption of Na+ and bicarbonate in the proximal tubule and stimulates a Na+-H+ exhanger

NOTE: The kidneys are the only place we can really make adjustment in the levels of calcium and phosphate

Question 6

What effect does PTH have on the intestine?

Answer 6

Increases calcium and phosphate reabsorption via vitamin D

Question 7

In osteons, there is a ________ where blood vessels are coming in.

Answer 7

Central canal

Question 8

Osteocytes make contact with the cytoplasmic processes of their counterparts via a network of small transverse canals, or ________.

Answer 8

canaliculi

Question 9

Describe the fast exhange of bone Ca2+

Answer 9

• Moved from the labile pool (in canaliculi) in the bone fluid into the plasma by means of PTH-activated Ca2+ pumps located in the osteocytic-osteoblastic bone membrane

Question 10

Describe the slow exchange of bone Ca2+

Answer 10

• Ca 2+ is moved from the stable pool in the mineralized bone into the plasma by means of PTH-induced dissolution of bone (via osteoclasts)

Question 11

Which cells secrete calcitonin?

Answer 11

Parafollicular (C cells) of the thyroid gland

*It is synthesized as the preprohormone and released in response to high plasma calcium

NOTE: Parathyroid hormone pretty much maintains physiological balance. If we ger really far out of the physiological range and have high high levels of calcium then calcitonin will respond.

Question 12

Feedback regulation of the Synthesis and Secretion of PTH & Calcitonin

Answer 12

Question 13

What is the principal action of Vitamin D?

Answer 13

Increased intestinal absorption of Ca2+ and (PO4)3-

Question 14

Which enzyme is required to create the active form of Vitamin D?

Answer 14

1-alpha-hyroxylase

*1-alpha-hyroxylase is stimulated by PTH and suppressed by Vitamin D

Question 15

What effect does Vitamin D3 have on plasma phosphate levels?

Answer 15

It increases (PO4)3- levels

Question 16

PTH acts __________ (indirectly/directly) on the intestine.

Answer 16

Indirectly

Question 17

What effect does a decrease in plasma phosphate have on PTH levels?

Answer 17

A decrease in in plasma phosphate leads to an increase in plasma calcium, which would lead to a decrease in PTH.

NOTE: A decrease in plasma phosphate also leads to an increase in Vitamin D3.

Question 18

Primary hyperparathyroidism causes:

Answer 18

• Hypercalcemia
• Hypophosphatemia
• Hypercalciuria
• Kidney stones

Question 19

Secondary hyperparathyroidism causes:

Answer 19

• Slowly developing renal failure generated by hyperphosphospahtemia and hypocalcemia
• Accelerated bone resorption

Question 20

Symptoms of hypoparathyroidism

Answer 20

• Increased neuromascular excitability
• Numbness
• Tingling sensations
• Tetanic muscle contractions
• Seizures