Parathyroid hormone

Definition

Parathyroid hormone (PTH) is a peptide hormone produced by the parathyroid glands that plays a crucial role in regulating calcium levels in the blood. It functions by increasing the concentration of calcium in the bloodstream through several mechanisms, including stimulating bone resorption, enhancing renal tubular reabsorption of calcium, and promoting the activation of vitamin D to increase intestinal calcium absorption. PTH is essential for maintaining calcium homeostasis and influences other hormones within the endocrine system.

5 Must Know Facts For Your Next Test

1. Parathyroid hormone is released in response to low blood calcium levels and acts to increase those levels through various pathways.
2. One of the primary actions of PTH is to stimulate osteoclasts, which are cells that break down bone tissue, releasing stored calcium into the bloodstream.
3. PTH promotes renal tubular reabsorption of calcium, which means that more calcium is retained by the kidneys instead of being excreted in urine.
4. The hormone also aids in converting vitamin D into its active form, calcitriol, which enhances intestinal absorption of calcium from food.
5. Elevated levels of parathyroid hormone can lead to hyperparathyroidism, a condition that can cause bone loss and elevated blood calcium levels.

Review Questions

• How does parathyroid hormone regulate calcium levels in the body?
  • Parathyroid hormone regulates calcium levels by increasing blood calcium concentration when it falls too low. It stimulates osteoclasts to break down bone, releasing calcium into the bloodstream. PTH also enhances renal reabsorption of calcium, preventing its loss through urine, and activates vitamin D to improve intestinal absorption of dietary calcium. These combined actions ensure that calcium homeostasis is maintained.
• Discuss the relationship between parathyroid hormone and vitamin D in maintaining calcium balance.
  • Parathyroid hormone and vitamin D work together to maintain calcium balance in the body. When blood calcium levels are low, PTH is released and promotes the conversion of vitamin D into its active form, calcitriol. Calcitriol increases the absorption of calcium from food in the intestines. Additionally, PTH acts directly on bones and kidneys to raise blood calcium levels, while calcitriol supports these actions by enhancing dietary absorption. This collaboration is essential for maintaining stable calcium levels.
• Evaluate the potential consequences of hyperparathyroidism on overall health and how it relates to parathyroid hormone function.
  • Hyperparathyroidism occurs when there are excessively high levels of parathyroid hormone due to overactive parathyroid glands. This leads to increased bone resorption, resulting in weakened bones and a higher risk of fractures. The elevated blood calcium levels can also cause kidney stones and interfere with heart and brain functions. Understanding how PTH functions helps clarify why these health issues arise; excessive PTH disrupts normal calcium regulation, leading to multiple systemic complications.

Related terms

Calcitonin: A hormone produced by the thyroid gland that lowers blood calcium levels by inhibiting bone resorption and increasing calcium excretion in the kidneys.

Vitamin D: A fat-soluble vitamin that is crucial for calcium absorption in the intestines and is activated by PTH to help maintain proper calcium levels.

Hypoparathyroidism: A condition characterized by insufficient production of parathyroid hormone, leading to low levels of calcium in the blood and potential complications such as muscle cramps and seizures.