Thyroid Stimulating Hormone (THS).ppt

TSH ( THYROID STIMULATING HORMONE)

1. Thyroid Stimulating Hormone (THS)
Introduction
–Thyroid Stimulating Hormone, also known as
Thyrotropin,is an anterior pituitary hormone.THS
increases the secretion of thyroxine and
triiodothyronine by the thyroid gland.
Chemistry
–THS is glycoprotein that contains 211 amino acids
residues.It is made up of two subunits,designated à
and β.

2. Half-Life And plasma Level:
–The biologic half-life of human TSH is about
60 minutes.The normal plasma level of TSH is
approximately 2u/ml.
Activation:
–Activation of the second messengercyclic
adenosine monophosphate (cAMP) system of
the cell.

3. •The first event in this activation is binding
of TSH with specific TSH receptors on the
basal membrane surfaces of the thyroid
cell.This then activates adenylyl cyclase in
the membrane,which increases the
formation of cAMP inside the
cell.Finally,the cAMP acts as a second
messenger to activate protein
kinase,which causes multiple
phosphorylations through the cell.

4. •The result is both an immediate increase in
secretion of thyroid hormone and prolonged
growth of the thyroid glandular tissue itself.
Effects on the thyroid glands
–Increases proteolysis of the thyroglobulin that has
already been stored in the follicles,with resultant
release of the thyroid hormones in to the circulating
blood.
–Increased iodination of tyrosine to form the the thyroid
hormones.

5. –Increased activity of the iodide pump, which
increases the rate of Iodide Trapping in the
glandular cells.
–Increased size and secretory activity of the
thyroid cells.
–Increased the number of the thyroid
cells,cuboidal in nature and,then it converts
them into columnar cells and causes the
development of thyroid follicles.

6. Regulation of secretion of TSH
–Anterior pituitary secretion of TSH is
controlled by a hypothalamic hormone,
Thyrotropin-releasing hormone (TRH),which
is secreted by nerve endings in the median
eminence of the hypothalamus.
–TRH has been obtained in pure form.It is a
simple tripeptide amide.TRH directly affects
the anterior pituitary gland cells to increase
their output of TSH.

7. Feedback Control
–Increased thyroid hormone in body fluids
decreases secretion of TSH by the anterior
pituitary.
–When the rate of thyroid hormone secretion
rises to about 1.75 times normal,the rate of
TSH secretion falls essentially to zero.Almost
all this feedback depressant effect occurs
even when the anterior pituitary has been
separated from the hypothalamus.