Parathyroid hormone

Definition

Parathyroid hormone (PTH) is a peptide hormone produced by the parathyroid glands that regulates calcium and phosphate levels in the blood. PTH plays a crucial role in maintaining calcium homeostasis by increasing calcium reabsorption in the kidneys, stimulating the release of calcium from bones, and promoting the conversion of vitamin D to its active form, which enhances intestinal absorption of calcium.

5 Must Know Facts For Your Next Test

1. PTH is released in response to low blood calcium levels, triggering several mechanisms to increase calcium concentration.
2. One of PTH's key actions is to increase tubular reabsorption of calcium in the kidneys, reducing calcium loss in urine.
3. PTH stimulates osteoclast activity in bones, leading to the breakdown of bone tissue and the release of stored calcium into the bloodstream.
4. The hormone also enhances the activation of vitamin D in the kidneys, which increases intestinal absorption of dietary calcium.
5. An imbalance of PTH can lead to conditions such as hyperparathyroidism, which can cause elevated blood calcium levels, or hypoparathyroidism, leading to low blood calcium levels.

Review Questions

• How does parathyroid hormone interact with other hormones to maintain calcium homeostasis in the body?
  • Parathyroid hormone works closely with calcitonin and vitamin D to regulate calcium levels. When blood calcium is low, PTH increases calcium reabsorption in the kidneys and stimulates bone resorption. Meanwhile, calcitonin acts to lower blood calcium when levels are high by inhibiting bone breakdown. Vitamin D enhances intestinal absorption of calcium, creating a synergistic effect with PTH that ensures balanced calcium levels in the bloodstream.
• Discuss the physiological effects of parathyroid hormone on the kidneys and bones, highlighting its role in calcium regulation.
  • Parathyroid hormone has significant effects on both kidneys and bones. In the kidneys, it increases tubular reabsorption of calcium while promoting phosphate excretion. This action helps retain more calcium in the body. In bones, PTH stimulates osteoclasts, which break down bone tissue and release calcium into the bloodstream. Together, these effects elevate blood calcium levels, maintaining homeostasis essential for various bodily functions.
• Evaluate how disorders related to parathyroid hormone can impact overall health and what systems might be affected.
  • Disorders involving parathyroid hormone can significantly impact overall health. Hyperparathyroidism leads to high blood calcium levels, potentially causing kidney stones, osteoporosis, and cardiovascular issues. Conversely, hypoparathyroidism results in low blood calcium, leading to muscle cramps, seizures, and cardiac problems. The interconnectedness of these hormonal pathways highlights how disturbances can affect not only skeletal health but also renal function and neuromuscular systems.

Related terms

Calcium: A vital mineral in the body that is necessary for various physiological functions, including muscle contraction, nerve transmission, and blood coagulation.

Calcitonin: A hormone produced by the thyroid gland that helps lower blood calcium levels by inhibiting bone resorption and promoting calcium excretion by the kidneys.

Vitamin D: A fat-soluble vitamin that plays a key role in calcium and phosphate metabolism and is essential for bone health.