Download MBBS Parathyroid Hormone Lecture PPT

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