Calcium is required for a variety of important physiologic processes, including neuromuscular functioning; thus, blood calcium levels are closely regulated. The parathyroid glands are small structures located on the posterior thyroid gland that produce parathyroid hormone (PTH), which regulates blood calcium levels. Low blood calcium levels cause the production and secretion of PTH. In contrast, elevated blood calcium levels inhibit secretion of PTH and trigger secretion of the thyroid hormone calcitonin. Underproduction of PTH can result in hypoparathyroidism. In contrast, overproduction of PTH can result in hyperparathyroidism.
hyperparathyroidism
disorder caused by overproduction of PTH that results in abnormally elevated blood calcium
hypoparathyroidism
disorder caused by underproduction of PTH that results in abnormally low blood calcium
parathyroid glands
small, round glands embedded in the posterior thyroid gland that produce parathyroid hormone (PTH)
parathyroid hormone (PTH)
peptide hormone produced and secreted by the parathyroid glands in response to low blood calcium levels
1. When blood calcium levels are low, PTH stimulates ________.
A) urinary excretion of calcium by the kidneys
B) a reduction in calcium absorption from the intestines
C) the activity of osteoblasts
D) the activity of osteoclasts
D
2. Which of the following can result from hyperparathyroidism?
A) increased bone deposition
B) fractures
C) convulsions
D) all of the above
B
1. Describe the role of negative feedback in the function of the parathyroid gland.
The production and secretion of PTH is regulated by a negative feedback loop. Low blood calcium levels initiate the production and secretion of PTH. PTH increases bone resorption, calcium absorption from the intestines, and calcium reabsorption by the kidneys. As a result, blood calcium levels begin to rise. This, in turn, inhibits the further production and secretion of PTH.
2. Explain why someone with a parathyroid gland tumor might develop kidney stones.
A parathyroid gland tumor can prompt hypersecretion of PTH. This can raise blood calcium levels so excessively that calcium deposits begin to accumulate throughout the body, including in the kidney tubules, where they are referred to as kidney stones.