About Endocrine Hormones: Parathyroid Hormone

Parathyroid hormone (PTH), one of the most important hormones in the body, is secreted by the main cells of the parathyroid glands and regulates blood calcium and phosphorus mainly through the kidneys, bones and intestines, with the functions of raising blood calcium, lowering blood phosphorus and regulating bone metabolism.

1. Three ways in which parathyroid hormone regulates calcium and phosphorus

(1) Regulation by the kidney: parathyroid hormone antibody promotes the reabsorption of calcium in the distal convoluted tubules and collecting ducts of the kidney, reduces urinary calcium excretion, and increases blood calcium. PTH inhibits the reabsorption of phosphorus in proximal and distal tubules, promotes the excretion of urinary phosphorus, and reduces blood phosphorus.

(2) Regulation through bone: Bone is the largest calcium storehouse in the body, so parathyroid hormone can improve the biological activity of osteoclasts, promote the process of bone resorption, release bone calcium into the blood, and increase blood calcium; increase osteogenesis cell number, increase the production and release of osteoblasts, increase the ability of bone growth factors, promote bone formation and increase bone mass.

Rapid effect: Within a few minutes, the calcium ion pump is activated to increase blood calcium;

Delayed effect: after several days and weeks, due to increased osteoclast activity, there is osteolysis, as well as increased blood calcium and blood phosphorus.

(3) Regulation through the small intestine: PTH promotes the absorption of calcium and phosphorus in the small intestinal mucosa by activating 1ɑ-hydroxylase in the kidney.

2. Characteristics of secretion and regulation of parathyroid hormone

(1) The secretion of PTH fluctuates rhythmically, with the highest concentration at 6:00 in the morning and the lowest concentration at 4:00 in the afternoon. It is inactivated in the liver and excreted through the kidneys.

(2) The main physiological function of PTH is to increase blood calcium and reduce blood phosphorus. The concentration of blood calcium and blood phosphorus affects the secretion of PTH through a feedback mechanism. When blood calcium decreases, it will promote the secretion of PTH; when blood calcium increases, it will inhibit the secretion of PTH; and when blood phosphorus increases, it will also promote the secretion of PTH. So calcium, phosphorus and PTH form a complex relationship of mutual interdependence.

(3) Long-term hypocalcemia can cause parathyroid hyperplasia, and long-term hypercalcemia can cause parathyroid atrophy.

Diseases that need to be considered when changes in PTH occur.

3. The increase in parathyroid hormone

(1) Primary hyperparathyroidism: The primary lesions of the parathyroid tissue lead to excessive secretion of parathyroid PTH, resulting in increased renal calcium reabsorption and urinary phosphorus excretion, further resulting in hypercalcemia and hypophosphatemia, kidney stones, etc. There are three types of pathological changes: Adenoma, hyperplasia and adenocarcinoma, of which adenoma is the most common, accounting for about 78% to 90%, mostly single; hyperplasia accounts for about 10% to 20%, often involving 4 parathyroid glands; adenocarcinoma accounts for about 3%, whose development is slow, but there may be lymphatic or distant metastasis.

(2) Secondary hyperparathyroidism: Hypocalcemia caused by various reasons stimulates hyperparathyroidism and hyperplasia, resulting in excessive PTH secretion. Hyperparathyroidism is common in chronic kidney disease, osteomalacia, and intestinal malabsorption syndrome, vitamin D deficiency, etc.

(3) Tertiary hyperparathyroidism: A condition that occurs when the parathyroid glands are stimulated for a long time to form autonomous nodules or adenomas due to the presence of chronic secondary hyperparathyroidism, when PTH is secreted autonomously and is not regulated by blood calcium. When the primary disease is resolved, hyperparathyroidism does not recover. It is common in patients with chronic renal insufficiency and dialysis.

4. The reduction of parathyroid hormone

(1) Hypoparathyroidism: A group of clinical syndromes caused by too little PTH secretion or insufficient effect. Its clinical manifestations include hypocalcemia, hyperphosphatemia and the resulting increased neuromuscular excitability and ectopic calcification of soft tissue. It is more common in thyroid, parathyroid, throat or other neck diseases after surgery, and this state can be diagnosed as permanent hypoparathyroidism more than 6 to 12 months after surgery.

(2) Pseudo-hypoparathyroidism: PHP is a hereditary disease. The patient's parathyroid hormone receptor is abnormal, and the surrounding organs (bone, kidney) do not respond or have a reduced response to parathyroid hormone (PTH resistance), so the clinical manifestation of the patient is parathyroidism, and the biochemical manifestation is lower blood calcium and higher blood phosphorus, but parathyroid hormone is elevated.

When abnormal calcium and phosphorus ions are found in the body, attention should be paid to monitor the PTH concentration in time. When abnormal PTH occurs, comprehensive consideration should be given. In addition to the lesions of the parathyroid gland itself, it is also necessary to consider the renal system, skeletal system, tumor and other problems, carry out relevant examinations as soon as possible, clarify the cause, and carry out fundamental treatment for the primary disease.