Parathyroid hormone (PTH) is secreted by the parathyroid glands in response to low blood calcium levels. PTH regulates calcium and phosphate concentrations in the body by increasing their absorption in the intestines and kidneys and mobilizing calcium from bones. PTH is synthesized as a precursor protein that is cleaved into the active 84 amino acid hormone. PTH acts to raise blood calcium levels by increasing its resorption from bone, reducing its renal excretion, and enhancing intestinal absorption. Abnormalities in PTH secretion can cause hypo- or hyperparathyroidism, disrupting calcium homeostasis and potentially resulting in symptoms like weakness, pain, and kidney stones.

1. Parathyroid Hormone
Prepared by:
Shahab Ullah Khan
Ayub Medical College
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2. Introduction:
 Secreted by parathyroid glands.
 Also called parathormone or parathyrin.
 Regulates extracellular calcium and phosphate
concentrations
 Methods of Regulation:
Intestinal absorption.
Renal excretion
Exchange btw ECF and bone
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3. Physiological anatomy of parathyroid
glands:
 Four parathyroid glands whose dimensions are:
 Length = 6mm
 Width= 3mm
 Thickness= 2m
 Appearance dark brown fat.
 Normal Level= 9.4mg/dl
 Mol.Weight= 9500
 Removal of two parathyroid glands: No physiological abnormality.
 Removal of 3 parathyroid glands: Transient Hypo parathyroidism.
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4. Secretion of PTH:
 Secreted by parathyroid gland in response to low calcium levels.
 Normal level of calcium in blood is 9.4 mg/dl.
 Low calcium level is detected by Calcium Sensing receptor in Parathyroid
cell membrane.
 Parathyroid Gland has Two types of cells:
 Chief cells.
 Oxyphil cells.
 Chief cells mostly secrete the PTH.
 Oxyphil are modified or depleted form of chief cells.
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5. Chemistry of PTH:
 Synthesized in form of pre pro hormone on ribosome.
 Pre Pro hormone is polypeptide chain of 110 amino acids.
 ER and Golgi apparatus cleave:
 Pre Pro hormone
 Prohormone (90 amino acids).
 Hormone (84 amino acids)
 Final hormone is packaged in secretory granules in cytoplasm.
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6. Actions of PTH:
Effect of PTH on calcium and phosphate conc. In ECF:
 Infusion of PTH :
 Plateau of calcium concentration in 4 hrs.
 Depression of phosphate concentration in 1 to 2 hours.
 Methods of Regulation:
i) Exchange btw ECF and bone
ii) Intestinal absorption.
iii) Renal excretion
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7. Actions of PTH on bone:
 Rapid phase (1-3 hours)- Osteocytic osteolysis.
 Slow phase(12-24 hours)- Osteoclastic osteolysis.
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8. Rapid phase:
 PTH injected in large quantities.
 Calcium concentration in blood rises with in minutes.
 Causing removal of bone salts from two areas.
 Bone matrix in vicinity of osteocytes.
 Bone matrix in vicinity of osteoblast.
But why these two?
 Osteocystic membrane, pumps calcium from bone fluid to ECF.
 Osteolysis occurs without resorption of bone fibrous and gel matrix.
 What's the Role of PTH then ?
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9. Slow phase:
 Osteoclasts are activated.
 Osteoclasts have No membrane receptor proteins for PTH.
 Secondary signals are received from osteoblasts.
 Activation occurs in two phases.
 Immediate activation of already existing in osteoclasts.
 Formation of new osteoclasts.
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10.  No, bone contains calcium 1000 times more than ECF.
 Prolong administration over months or years results in resorption in all bones.
 PTH injection is Administrated where ?
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Does PTH affect bone on few PTH administrations?

11. Action of PTH on Kidneys:
 PTH is administrated.
 Calcium excretion is decreased.
 PTH increases renal tubular reabsorption of calcium.
 Phosphate excretion is increased.
 PTH diminishes tubular reabsorption of phosphates.
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12. Action of PTH on intestine:
 PTH enhances calcium and phosphate absorption from intestine.
 By increasing formation of 1,25 dihydroxycholecalceforal from vitamin D.
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13. Summary of Actions of PTH:
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14. Control of PTH by calcium ion
concentration.
Condition of decreased calcium level:
 Slight decrease in calcium ion concentration causes increase of PTH
secretion.
 If condition persists it may cause hypertrophy of parathyroid gland.
 Rickets.
 Pregnancy.
 Lactation.
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15. Control of PTH by calcium ion
concentration.
Condition of increased calcium level:
 Increase in calcium ion concentration causes decrease of PTH secretion.
 If condition persists it causes parathyroid gland to reduce in size.
 Excess calcium in diet.
 Increase vitamin D in diet.
 Bone resorption due to disuse.
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16. Pathophysiology of PTH
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17. Hypoparathyroidism:
 Parathyroid gland do not secrete sufficient PTH.
 Osteocytic resorption of calcium ion decreases.
 Osteoblast becomes inactive.
 No calcium resorption by bones.
 Conc. Of calcium in body fluid is decreased.
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18. Symptoms of Hypoparathyroidism:
 Paresthesia in finger tips, toes and lips.
 Muscle cramps in leg, feet, abdomen or face.
 Fatigue.
 Painful menstruation.
 Dry skin.
 Anxiety.
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19. Treatment of Hypoparathyroidism:
 Administration of PTH.
 Expensive.
 Antibodies are developed.
 Administration of vitamin D.
 High doses of vitamin D (100,000 units/day).
 Direct administration of 1,25 dihydroxycholecalceforal .
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20. What if parathyroid gland is removed?
 Calcium level in blood falls from normal 9.4mg/dl to 6-7 mg/dl in two three
days.
 With such low level symptoms of tetany develops.
 Most sensitive muscle to tetanic sparsm are laryngeal muscles.
 Spasms of laryngel muscles obstructs respiration.
 Usual cause of death in people with untreated tetany.
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21. Hyperparathyrodism:
 Parathyroid gland secretes more PTH.
 Calcium level increases in blood.
Two types:
 Primary Hyperparathyrodism.
 Secondary Hyperparathyrodism.
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22. Primary Hyperparathyrodism:
 Abnormality of parathyroid gland causes excess secretion of PTH.
 Extreme osteoclastic activity in bones.
 Elevation of calcium ion conc. In ECF.
 Depression of phosphate ions conc. in ECF.
 Often broken bone is the reason for patient to seek medical attention.
 Women are subjected more frequently to primary hyperparathyroidism.
(Pregnancy, lactation)
 Cause:
 Tumor of one of parathyroid gland.
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23. Secondary Hyperparathyrodism:
 Not a primary abnormality of parathyroid gland
 High level of PTH occurs as a compensation for hypocalcemia
CAUSES:
 Vitamin D defiency.
 Chronic renal disease.
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24. Formation of Kidney Stones in
Hyperparathyroidism
 Patients with hyperparathyroidism have extreme
tendency of developing kidney stones.
Reason:
 excess calcium and phosphate must eventually be excreted by kidney
 Thus there is Increase in concentration of calcium and phosphate in urine
 More tendency of crystals of calcium and phosphate to precipitate in
kidney
 Leading to calcium phosphate stones
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25. Symptoms of hyperparathyroidism:
 Kidney stones.
 Excess urination.
 Fragile bones.
 Abdominal pain.
 Bone and joint pain.
 Depression.
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26. Treatment of Hyperparathyroidism:
 Calcimemetics.
 Hormone Replacement theraphy.
 Biophosphonates.
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27.  Reference Book: Medical Physiology by GUYTON AND HALL
THANKS
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