What is PTH?
Parathyroid Hormone (PTH), also known as parathormone or parathyrin, is a vital peptide hormone secreted by the parathyroid glands. It regulates calcium and phosphate levels in the body by acting on bones, kidneys, and the intestines. This hormone plays an essential role in maintaining mineral balance, ensuring proper bone remodelling, and supporting various metabolic functions.
PTH is produced in response to low calcium levels in the blood, activating mechanisms that restore calcium balance. The bones act as a "bank" for calcium, allowing the body to draw on this reserve to meet its physiological needs. Let us delve deeper into its functions, secretion regulation, associated disorders, and measurement methods.
Functions of Parathyroid Hormone (PTH)
Regulation of Serum Calcium
PTH regulates calcium levels by:
Stimulating the release of calcium from bones through osteoclast activation.
Enhancing calcium reabsorption in the kidneys to reduce calcium loss through urine.
Promoting the activation of vitamin D in the kidneys, which boosts calcium absorption in the intestines.
Interestingly, PTH does not directly act on osteoclasts. Instead, it binds to osteoblasts, triggering a cascade of events that promote bone resorption and calcium release.
Regulation of Serum Phosphate
PTH helps maintain phosphate balance by:
Inhibiting phosphate reabsorption in the kidneys, leading to increased excretion through urine.
Facilitating phosphate release from bones and absorption in the intestines.
While calcium absorption depends heavily on activated vitamin D, phosphate absorption is less reliant on it.
PTH Secretion Regulation
The secretion of PTH is tightly controlled by the levels of ionised calcium in the blood through a negative feedback mechanism:
Low Calcium Levels: When calcium levels drop, calcium-sensing receptors on parathyroid cells stimulate PTH release.
High Calcium Levels: Elevated calcium levels suppress PTH secretion, while calcitonin (another hormone) is secreted to counteract the effects of high calcium.
Calcium-sensing receptors are G-protein-coupled and widely distributed across various tissues, including the brain, heart, and kidneys. These receptors mediate PTH secretion by detecting changes in extracellular calcium levels.
Disorders Associated with Parathyroid Hormone
Hyperparathyroidism
Primary Hyperparathyroidism: This condition occurs due to overactive parathyroid glands that secrete excessive PTH, often caused by benign tumours (adenomas). It leads to hypercalcaemia (elevated calcium levels).
Secondary Hyperparathyroidism: A compensatory increase in PTH secretion due to chronic hypocalcaemia, commonly associated with kidney disease or vitamin D deficiency.
Hypoparathyroidism
Characterised by low PTH levels, this condition results from damage or removal of the parathyroid glands during thyroid surgery or due to autoimmune diseases. It causes hypocalcaemia (low calcium levels), leading to muscle cramps, spasms, and neurological symptoms.
Measurement of PTH
PTH levels are measured using blood tests, with various assays detecting different fragments of the hormone, including:
Intact PTH
N-terminal PTH
Mid-molecule PTH
C-terminal PTH
PTH levels are expressed in either picograms per millilitre (pg/mL) or picomoles per litre (pmol/L). The normal ranges for PTH levels vary:
US Standard: 8–51 pg/mL
UK Reference Range: 1.6–6.9 pmol/L
Calcium levels are also measured alongside PTH to diagnose and monitor disorders effectively. The normal plasma calcium range is 8.5–10.2 mg/dL (2.12–2.55 mmol/L).
PTH and its Role in Maintaining Optimal Health
The influence of PTH extends beyond calcium regulation. It supports the remodelling and repair of bones by stimulating osteoclast activity, which breaks down bone tissue to release calcium and phosphate into the bloodstream. This process ensures that bones maintain their strength and density.
Furthermore, PTH contributes to metabolic health by regulating phosphate levels. By reducing phosphate reabsorption in the kidneys, it prevents an imbalance that could lead to mineral deposits in tissues. Proper PTH function is vital for strong bones, a healthy metabolism, and overall physiological well-being.
Conclusion
Parathyroid Hormone (PTH) plays a crucial role in regulating calcium and phosphate levels, supporting bone health, and maintaining overall metabolic balance. By understanding its functions, secretion mechanisms, and disorders, healthcare professionals can diagnose and manage conditions like hyperparathyroidism and hypoparathyroidism more effectively. PTH also regulates vitamin D and phosphorus levels, further highlighting its importance in maintaining physiological homeostasis.
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FAQs on Complete Overview of PTH: Full Form, Functions & Disorders
1. What is PTH (Parathyroid Hormone)?
PTH, also known as parathormone, is a hormone produced by the parathyroid glands that regulates calcium levels in the blood, bones, and other tissues.
2. What is the primary function of PTH?
The primary function of PTH is to maintain optimal serum calcium levels by regulating calcium release from bones, absorption in the intestines, and reabsorption in the kidneys.
3. How does PTH regulate calcium levels in the body?
PTH increases calcium levels by stimulating calcium release from bones, enhancing calcium absorption in the intestines via vitamin D activation, and reducing calcium excretion in the kidneys.
4. How is PTH secretion regulated?
PTH secretion is regulated through negative feedback. Low blood calcium levels stimulate PTH release, while high calcium levels inhibit its secretion.
5. What are the disorders related to abnormal PTH levels?
Disorders include:
Hyperparathyroidism: Excess PTH production, leading to high blood calcium.
Hypoparathyroidism: Insufficient PTH production, causing low blood calcium.
6. What is hyperparathyroidism, and how does it occur?
Hyperparathyroidism is a condition with abnormally high PTH levels. It can be caused by:
Primary hyperparathyroidism: Overactive parathyroid glands.
Secondary hyperparathyroidism: A reaction to chronic low calcium levels.
7. How does PTH affect phosphate levels in the body?
PTH decreases phosphate levels in the blood by reducing phosphate reabsorption in the kidneys, causing it to be excreted in urine. However, it increases phosphate uptake in the gut and bones.
8. How is PTH measured, and what are normal levels?
PTH is measured through blood tests. The normal range is typically:
PTH levels: 8–51 pg/mL (US) or 1.6-6.9 pmol/L (UK).
Calcium levels: 8.5–10.2 mg/dL.
9. What are the symptoms of abnormal PTH levels?
High PTH levels (hyperparathyroidism): Bone pain, kidney stones, fatigue, and excessive thirst.
Low PTH levels (hypoparathyroidism): Muscle cramps, tingling in extremities, and seizures.
10. Why is PTH important for bone health?
PTH plays a key role in bone remodelling by stimulating osteoclast activity, which releases calcium into the blood. This process ensures calcium availability for critical bodily functions.
