Parathyroid hormone (PTH) is a single-chain 84 amino acid peptide produced by the parathyroid gland in response to a decrease in the extracellular concentration of ionized calcium. Its main role is to increase the level of calcium in the serum. It does this by stimulating the release of calcium from the bones and renal reabsorption in the distal tubules. In the proximal tubules, PTH stimulates the synthesis of calcitriol, which in turn increases the absorption of calcium in the intestines and creates an endocrine feedback loop on PTH secretion at the level of the parathyroid gland. Parathyroid hormone also reduces phosphate reabsorption in the proximal tubules of the kidneys, thereby reducing the amount of phosphate in the serum.
Disorders of the parathyroid gland lead to an increase or decrease in blood calcium levels (hypercalcemia or hypocalcemia), which is caused by a change in parathyroid gland secretion.
Excessive production of parathyroid hormone is called hyperparathyroidism.
Types include:
•
Primary hyperparathyroidism
: Often caused by a benign tumor (adenoma) on one of the parathyroid glands. Other causes include enlarged glands (hyperplasia) or, rarely, parathyroid gland cancer.•
Secondary hyperparathyroidism
: Occurs as a response to low blood calcium levels due to chronic renal failure, vitamin D deficiency, or extremely high levels of phosphate. The parathyroid glands produce excess PTH, attempting to restore calcium balance.•
Tertiary hyperparathyroidism
: Develops when secondary hyperparathyroidism continues for a long time, leading to autonomous hyperactivity of the glands, even when calcium levels return to normal.Underproduction of parathyroid hormone is called hypoparathyroidism.
The causes of hypoparathyroidism are
:• Damage, accidental removal, or destruction of the parathyroid glands during neck or thyroid surgery
• Autoimmune diseases
• Low magnesium levels
• Radiation therapy to the head or neck
• Rarely, congenital absence of glands or functional defects
Symptoms of hyperparathyroidism are
:• Fatigue and general weakness (the most common symptom)
• Bone and joint pain, osteoporosis, brittle bones, and fractures
• Muscle weakness
• Kidney stones and possible kidney disease or renal failure
• Memory problems, difficulty concentrating, depression, anxiety, and mood swings
• Increased thirst and frequent urination
• Gastrointestinal problems such as nausea, vomiting, loss of appetite, constipation, and abdominal pain
• Insomnia or difficulty sleeping
• Headaches
• Heart-related symptoms such as high blood pressure, arrhythmias, and atrial fibrillation
Symptoms of hypoparathyroidism are
:• A tingling or burning sensation in the fingers, toes, lips, and around the mouth (paresthesia)
• Muscle aches, spasms, and cramps, sometimes affecting the hands, feet, face, and throat
• Fatigue, weakness, exhaustion
• Headaches and problems with memory or concentration
• Abdominal pain
• Dry skin, brittle nails, dry hair, brittle teeth
• Cataracts
• Anxiety, irritability, and mood swings
• In severe cases, convulsions
Sometimes the symptoms are mild or absent, and parathyroid gland problems are detected through routine blood tests.