Give a detailed info about thyroid gland and its secretion and antithyroid agent

1. By:
Ankit SharmA
M.Pharma 2nd Sem
PharmacologY
Bhupal Noble’s University
Udaipur (Rajasthan)
2018-2019

2. :Endocrine System:
 :INTRODUCTION:
 A system inside the consisting all types of endocrine
glands is known as, “Endocrine Gland”
 Endocrine means,“Glands without duct” i.e. such
type of glands secretes their secretions directly in
blood stream
 All these glands perform their expected action on
target site by aid of chemical messenger called,
“The Hormone”

4. :Categories Of Hormones:
 : 6 Categories of Hormones are as :
 1. Amino Acid Derivatives: eg: NA,Adr,Thyroxine etc.
 2. Short Peptide : eg: oxytocin, Vasopressin, MSH etc.
 3. Long Peptide : eg.: insulin, ACTH, calcitonin etc.
 4. Proteins : eg.: gonadotrpic,Somatotropic Hormones
 5. Steroids :eg.: cortisol, aldosterone, testosterone etc.
 6. Fatty Acid Derivatives : eg.: prostaglandins etc.

5. Thyroid Gland
 The butterfly-shaped thyroid
gland is located just inferior to
the larynx (voice box). It is
composed of right and left lateral
lobes, one on either side of the
trachea, that are connected by an
isthmus
 It is Largest gland in the Body
 It is Endodermal in origin.
 Approx. weight is 25 to 35gm in
humans

6. Location of Thyroid Gland

7. :Blood network in Thyroid:

8. T.S. of Thyroid Gland

9. Thyroxine (Thyroid Hormone)
 It is a Amino Acid Derivatives type of Hormones
 There are 4 types of thyroid hormone i.e. T1,T2,T3,&T4
 T4 (tetra iodo thyronine) is originally, “Thyroxine”
 Thyroid is the only gland that stores its secreation
inside its follicles in inactive form till its release,
named “Thyroglobulin” which is a glycoprotein in
nature

10. Steps involved in Synthesis of ThyroxinE
 There are total 4 steps involved in Synthesis:
 1. Iodide Trapping: when KI taken up by follicular cells
 2. Oxidation of Iodide: KI reduces to I2 by enzyme
“Peroxidase”
 3. Organification: Tyrosine + I2 MIT & DIT
 4. Coupling: MIT+DIT T3 & DIT+DIT T4
MIT: mono iodo tyrosine; DIT: di iodo tyrosine
T3: tri iodo thyronine(20%) (Liothyronine)
T4: tetra iodo thyronine (80%) (Thyroxine)

11. 1.Pinocytosis and digestion of colloid. Droplets of colloid reenter
follicular cells by pinocytosis and merge with lysosomes. Digestive enzymes
in the lysosomes break down TGB, cleaving off molecules of T3 and T4.
2.Secretion of thyroid hormones. Because T3 and T4 are lipidsoluble,
they diffuse through the plasma membrane into interstitial fluid and then
into the blood. T4 normally is secreted in greater quantity than T3, but T3 is
several times
more potent. Moreover, after T4 enters a body cell, most of it is converted to
T3 by removal of one iodine.
3.Transport in the blood. More than 99% of both the T3 and the T4
combine with transport proteins in the blood, mainly thyroxine-binding
globulin (TBG).
:Secretion of Thyroxine:

12. Synthesis & Secretion of ThyroxinE

13. Mechanism of action : Thyroxine

14. Mechanism of action : Thyroxine
Cellular Level

15. Control of Thyroid Hormone
SecretioN
 Thyrotropin-releasing hormone (TRH) from the
hypothalamus and thyroid-stimulating hormone
(TSH) from the anterior pituitary
 stimulate synthesis and release of thyroid
hormones
 ●1 Low blood levels of T3 and T4 or low
metabolic rate stimulate the hypothalamus to
secrete TRH.
 ●2 TRH enters the hypophyseal portal veins
and flows to the anterior pituitary, where it
stimulates thyrotrophs to secrete TSH.
 ●3 TSH stimulates virtually all aspects of
thyroid follicular cell activity
 ●4 The thyroid follicular cells release T3 and
T4 into the blood until the metabolic rate returns
to normal.
 ●5 An elevated level of T3 inhibits release of
TRH and TSH
 (negative feedback inhibition).

16. Summary of Thyroid hormones

17. :Actions of Thyroid Hormones:
 Increase BMR (basal metabolic rate)
 Regulate development and growth of nervous tissue
and bones
 Enhance some actions of catecholamines (NA,Adr)
 Stimulate lipolysis
 Stimulate protein synthesis
 Increase body temperature (calorigenic effect)
 Stimulate synthesis of Na+/K+ ATPase
 Increase the use of glucose and fatty acids for ATP
Production

18. Irregularities of Thyroid GlanD
 Hypothyroidism: occurs due to def. of iodine and it
causes Cretinism and may also cause abnormal
skin,deaf-mutism and irregular M.C. in women
 Hyperthyroidism: glands shows enlargement and
secrets large amount of thyroxine which causes rise in
BMR,heart rate,b.p., It may cause following disorders:
 Grave’s Disease: deposition of mucous beneath the
eyeball takes place so that eye ball look enlarged. It is
an autoimmune disorder
 Plummer Disease: thyroid gland doesn’t show even
growth nd formation of tumours on thyroid (Toxic
adenoma)

22. :Anti-Thyroid Agents:
 These are drugs used to lower the functional capacity of the
hyperactive thyroid gland.
 All antithyroid drugs are quickly absorbed orally, widely
distributed in the body, enter milk and cross placenta; are
metabolized in liver and excreted in urine primarily as
metabolites.
 Antithyroid drugs bind to thyroid peroxidase and prevent
oxidation of iodide/iodotyrosyl residues, thereby;
 (i) Inhibit iodination of tyrosine residues in thyroglobulin
 (ii) Inhibit coupling of iodotyrosine residues to form T3
and T4.

23. :Classification of Antithyroids:

24. :Mechanism of Action: