8 Questions
How many amino acids are present in the preproPTH molecule?
115
Which region of the PTH molecule is primarily responsible for receptor binding?
25-34
Which action is NOT a function of PTH on calcium homeostasis?
Decreasing intestinal calcium absorption
In prolonged dietary calcium deficiency, how does PTH prevent hypocalcemia?
At the expense of bone substance
Which mineral is typically released from bone along with calcium due to PTH activity?
Phosphate
What is the role of 1.25 (OH)2 D3 in the calcium homeostasis maintained by PTH?
Increasing intestinal calcium absorption
How does PTH affect renal phosphate clearance?
Increases it
Which phase(s) of bone does PTH act upon to increase the ECF calcium concentration?
Both organic and inorganic phases
Study Notes
Chemistry of PTH
- PTH consists of 84 amino acids
- Formed by parathyroid glands from a precursor molecule called preproPTH (115 amino acids)
- PreproPTH forms proPTH (90 amino acids), which then forms PTH
- PTH is stored in the parathyroid gland to be released on need
- PTH 1-34 amino acids has full biologic activity
- Region 25-34 of PTH is primarily responsible for receptor binding
Function of PTH
- Net effect of PTH on bone and kidney is to increase ECF calcium concentration
- Net effect of PTH on bone and kidney is to decrease ECF phosphate concentration
Effects of PTH on Calcium Homeostasis
- In acute hypocalcemia, PTH restores normal ECF calcium concentration
- PTH acts indirectly on the intestinal mucosa through stimulation of 1.25 (OH)2 D3
- PTH acts directly on the kidneys and bone
- PTH reduces the clearance or excretion of calcium, increasing ECF concentration
- PTH increases the rate of dissolution of bone, moving Ca+2 ions into ECF
- PTH increases the efficiency of absorption from the intestine by promoting the synthesis of 1.25 (OH)2 D3
- In prolonged dietary Ca deficiency, PTH prevents hypocalcemia at the expense of bone substance
PTH Affects Phosphate Homeostasis
- Phosphate is released with calcium from bone whenever PTH dissolves the mineral matrix
- PTH increases renal phosphate clearance
This quiz covers the chemistry and function of Parathyroid Hormone (PTH), including its formation, storage, and biological activity in the body.
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