Download MBBS (Bachelor of Medicine and Bachelor of Surgery) Latest Parathyroid Hormone Lecture PPT
Parathyroid hormone from parathyroid glands
Anatomy
Humans have 4 parathyroid glands.
? 2 in superior pole of thyroid and 2 in its inferior pole.
? Contain 2 distinct cells
chief cells: contains golgi apparatus +ER + secretory
granules.
? Secreates PTH.
Oxyphil cells : contains numerous mitochondria +oxyphil
granules.
? Seen before puberty and no. es with age.
? Function unknown
Parathyroid hormone
?Polypeptide hormone
?Secreted by parathyroid glands
Preprohormone (110 A.As)ER
prohormone (90 A.As)Golgi apparatus
hormone (84 A.As - ---->packed in secretory
granules)
?Normal level of PTH in plasma 10-55pg/ml.
Half life approx. 10 min , removed by liver.
Physiological actions
plasma calcium level (by its effect on bone, kidney,
intestine)On bone :-
?Stimulates osteoclastic activity (indirect action)
bone resorption.
?PTH stimulates precursor
cells(monocyte,macrophages,etc;)into osteoclast.
?Hydroxyproline excretion in urine is an index of
osteoclastic activity
?fast Ca2+ efflux into the plasma from the small
labile pool
Contd.
? Stimulation of osteolysis: PTH activate the
process of osteocytic osteolysis.
Ca from bone fluid Osteocyte
ECF Osteoblasts
? PTH also inhibits the synthesis of collagen by
osteoblasts.
?Net effect is in bone mass in low conc. And
in bone mass in high conc.
On kidney
?es Ca2+ reabsorption (late DCT, collecting tubule,
ascending limb of Henle's loop) by regulating the
expression of TRPV5 channels)
?esPO 3-
4 excretion (PCT)---> phosphaturia by
inhibiting Na-Pi II a
enhances the activation of vitamin D by kidney
On intestine
?Indirectly increases both Calcium and Phosphate
absorption from the small intestine by activating
vitamin D.
Final effect :ed plasma calcium;
ed phosphate
Regulation of PTH secretion
Plasma concentration of ionized Calcium .
?Inverse relationship
?parathyroid glands hypertrophy :-rickets,pregnancy,
lactation
?Recently,calcium sensing receptors(CaSR) has been
identified on chief cells.
?CaSR is a G- protein coupled receptor attached to
phospholipase C and on binding to Ca generates IP3
&DAG.
?IP3 & DAG release Ca from cytosolic store and activate
protein kinase C that inhibits PTH secretion.
?Vitamin D : es formation of preproPTH
?Plasma phosphate
Rise in plasma phosphate : stimulates PTH
?Other factors :
cAMP, agonists, dopamine, histamine - level
agonists, prostaglandins - level
Mechanism of action:-
3 receptors:-
1. hPTH/PTHrP receptor. :binds to PTH
&PTHrP,main receptor to regulate plasma
calcium.
2. PTH2 (hPTH2-R) : binds to PTH, but not to
PTHrP . Found in brain, placenta & pancreas
3. CPTH which reacts with the carboxyl
terminal rather than the amino terminal of
PTH.
PTH binds to its receptors and activates both
adenylyl cyclase and phospholipase C pathway
PTHrP
? Another protein with PTH activity..
? Has 140 amino acid, encoded by gene on ch.12
whereas PTH by ch.11.
? Although both bind on same receptor
hPTH/PTrP, yet their physiological actions are
different.
? PTHrP acts close to where it is formed (paracrine
factor).
? Has effect on cartilage ,brain,placenta ,smooth
muscle in utero.
? It is also present in enamel epithelium of teeth.
Applied physiology
Hyperparathyroidism
Hypoparathyroidism
primary
Hyperparathyroidism
secondary
Primary hyperparathyroidism
Tumor of parathyroid gland
Features :-
hypercalcemia, hypophosphatemia, demineralisation of
bone, hypercalciuria, renal stones
Extreme PTH : parathyroid poisoning, metastatic
calcification
?high level of plasma alkaline phosphatase --- an
important diagnostic finding
?Secondary hyperparathyroidism
?Seen in chronic renal disease, rickets.
?In these diseases ,the chronic hypocalcemia causes
PTH secretion.
Hypoparathyroidism
True hypoparathyroidism
- m/c : damage to glands/their blood
supply/inadvertent removal e.g;.during thyroidectomy.
Pseudo-hypoparathyroidism
?PTH level normal/elevated
Defect : receptors/ post-receptor
Features :-
?hypocalcemia (6-7mg/dL)
?Hyperphosphatemia (6-16mg/dL)
Tetany
? Carpopedal spasm
?Laryngeal spasm leading to asphyxia
?Convulsions & seizures
?Paraesthesia
CVS :-
?dilatation of heart
?arrhythmias
?prolonged ST &QT intervals
? hypotension
? heart failure
Latent tetany : subclinical tetany
?Neuromuscular hyperexcitability d/t
hypocalcemia
?Provocative tests:-
Chvostek's sign
Trousseau's sign
Management of hypoparathyroidism
? PTH
?Vitamin D (100,000units/day) along
with calcium (1-2gms/day)
?Injections of calcium salts
??????
? Is parathyroid gland essential for life?
? Why hypoparathyroidism is common after
thyroid surgery and its effects ?
? What is the role of plasma calcium & vit D in the
regulation of PTH secretion?
? Difference between primary and secondary
hyperparathyroidism ?
? In hypocalcemic tetany ,hyperexitibility is due to
.......
? List physiological actions of PTH.
?Hypercalcemia of malignancy?
?Local osteolytic hypercalcemia?
This post was last modified on 30 November 2021