This slide shows the mechanism of secretion of thyroxine. I tried my best to explain this topic.

1. ZOOLOGY PROJECT
LUCKNOW CHRISTIAN DEGREE COLLEGE
KRISHNPRADDHUMNNAME:
CLASS: BSC YEAR- 3, SEM -5
ROLL NO.:
COLLEGE- 53102
UNIVERSITY: 180450605103
ADDRESS: 285/197 DA KAREHATA MILL ROAD
AISHBAGH LUCKNOW
MOBILE NO.: +91-8924806766
SIGN OF HOD

2. CERTIFICATE
This is to certify that KRISHNPRADDHUMN of class B.Sc 3rd
year SEM.5, DEPARTMENT OF ZOOLOGY,
LUCKNOW CHRISTIAN COLLEGE, LUCKNOW has
submitted the project titled THE THYROIDGLANDunder the
supervision of Dr. (Mrs. )DORIS PHILIPS SINGH,
Associate Professor at Lucknow Christian College.
Head of Department Staff Advisor

3. INDEX
1. THE THYROID INTRODUCTION
2. HISTORY OR SCIENTIFIC CONTRIBUTIONS
3. LOCATION
4. DEVELOPMENT AND ORIGIN
5. ANATOMY
6. HISTOLOGY AND ELECTRON
MICROSCOPY
7. HORMONES
8. SECRETIONS
9. THYROID FUNCTIONS
10. THYROID DISORDERS

4. THE THYROID GLAND
 The Thyroid gland is a butterfly or H- shaped, bilobbed
endocrine gland.
 It was termed by anatomist THOMAS WHARTON. in 1656
named them glandulae thyroidaeae (Thyroid glands)
because of their anatomic proximity to thyroid cartilage.
 Thyroid gland is endodermal origin.
 Microscopically the functional unit of the thyroid gland is
THYROID FOLLICLES.
 It is related with secretion of hormones that controls
metabolism.

5. HISTORY
In1500 Leonardo Da Vinci firstly illustrated the
thyroid gland.
Andreas Vesalius in 1543 gave the first anatomic
discription and illustration.
The term thyroid gland was given by Thomas
Wharton (in 1656).
Thyroxine was synthesised by Harrington And
Barger in 1927 for the first time.

6. LOCATION
The Thyroid Gland is located below larynx (the adam’s
apple), in the neck region.
It is attached on the trachea with the help of
CRICOTHYROID MUSCLE, and median CRICOTHYROID
LIGAMENT (form the front).

8. ORIGIN AND DEVELOPMENT
 The Thyroid Gland develops in the floor of the pharynx at the base of the
tongue at 3–4 weeks gestation; ultimately over the next few weeks, it migrates
to the base of the neck.
 During migration, the thyroid remains connected to the tongue by a narrow
canal called the thyroglossal duct.
 The thyroid gland is the first endocrine gland to develop in the embryo.
 It appears as a median endodermal thickening in the floor of the primordial
pharynx between tuberculum impar and copula.
 The site from which it originated persists as the foramen cecum at the base of
the tongue.
 At the end of the fifth week the thyroglossal duct degenerates, and over the
following two weeks the detached thyroid migrates to its final position.
Ref. web: 1.2

9. Ref. Web: 2.0

10. Fig. 1: to show the development of thyroid gland
Ref. Web: 2.0

11. ANATOMY
 The thyroid gland is highly vascularized organ located
anteriorly in the neck between the C5 and T1 vertebrae.
 The thyroid weighs 15–20 g and weighs more in men than in
women; the thyroid weighs approximately 1 g in a newborn and
increases by about 1 g/year until age 15.
 It is an H-shaped, soft, and reddish parenchymal organ,
consisting of two lobes (left and right) and one isthmus that
binds them together (Fig. ).
 Each lobe – 2cm x 2cm x (2 to 3)cm
 Isthmus – 2cm x 2cm x (2 to 6 mm)
Ref.: E-BOOK 1.1

12. Fig.2: THE THYROID GLAND
Image Ref.: E-BOOK 1.1

13. Histology
 Histologically the thyroid gland consists numerous rounded
structures called thyroid follicles.These Thyroid follicles may
vary in size and locations.
 The macro thyroid follicles are present peripherally, whereas the
micro thyroid follicles towards centre (as shown in fig.).
 These thyroid follicles are surrounded by the connective tissues
and are present in the form of blood vessels.
 There are also the specialised cells present in the histological
observations called Parafollicular cells or C-cells.
 A Thyroid follicle consists of cuboidal epithelial cells which
forms lumen inside it.
 Lumen contains colloids or coagulum.
Ref.: E-BOOK 1.1

14. Electron microscopy of thyroid follicles
 The thyroid follicles contains cuboidal epithelial cells.
 Each cuboidal epithelial cell opens into lumen by
inward by its membrane.
 And surrounded by a blood vessel from outside.
 The membrane towards blood vessels contains Iodine
receptors for intake of iodine from blood, and TSH
receptors at TSH binding site, there are also many
other important receptors binding sites on these
membranes.
Ref. Web: 1.4

16. Fig.4: electron microscopy of thyroid follicle
(a) (b)

17. HORMONES OF THYROID
 The thyroid gland consists of Thyroid follicular cells
and Parafollicular cells or C-cells.
 The Thyroid follicular cells are related with synthesis
and secretion of 2 iodinated hormones ie. T3 and T4.
 Parafollicular cells are related with synthesis and
secretion of a non-iodinated hormone called
Thyrocalcitonin, this hormone is hypocalcaemic in
nature, related with Lowering the blood calcium ions.

18. Secretion
 The thyroid gland stores it’s hormone in the form of colloid or
coagulum.
 These coagulum contains Thyroglobulin proteins which are
formed with the help nucleus, RER, Golgi Bodies and Secretory
V. of cuboidal epithelial cells, and also contains the iodide ions
and thyroid peroxidase enzymes (strong oxidizing agent).
 In the presence of this enzyme there will be formation of T1 and
T2 which under the stimulation of TSH binds together and
becomes active ie. T3 and T4.
 Which are then secreted to the blood vessel and transported to
the target tissue or organ.

20. Fig.5: .Synthesis of thyroid hormones. Iodine is actively concentrated by thyroid cells. An enzyme called thyroperoxidase catalyses the
addition of iodine to the tyrosine residues in thyroglobulin, a large protein, rich in tyrosine residues, which is synthesized in thyroid cells. The
iodinated thyroglobulin is stored in the thyroid in the form of ‘colloid’. In response to TSH stimulation, portions of the colloid are taken back into
the thyroid cell by phagocytosis and pairs of iodinated tyrosine residues (thyroxine) are released into the circulation. Anti-thyroid drugs, such as
carbimazole, act by inhibiting thyroperoxidase activity. AC, adenylyl cyclase; cAMP, cyclic adenosine monophosphate.
See reference (1.1)

21. Functions of Thyroid
 The thyroid hormones are important for metamorphosis in larvae of all
vertebrates.
 The thyroid hormones Controls the metabolism of the liver .
 It controls the heart rate indirectly.
 It also related with homeostasis of thermoregulation.
 It also affects the CNS Nerve construction works.
 It also affects the GI tract metabolism.
 It also affects the cells of adipose tissues .
Ref. Book: 1.2

22. Thyroid disorders
 Since, the thyroid gland is only endocrine gland that stores its
hormones, there might be abnormalities in its hormone secretion.
The thyroxine secretion may be caused in 2 ways:
1. Hyposecretion (Leads to hypothyroidism):
Hypothyroidism is a disorder in which thyroid gland is
underactive and does not produce or release enough thyroid
hormones or thyroxin.
The undersecretion of Thyroxine may cause:
 Simple Goitre: Leads to enlargement of the thyroid
gland in adults and becomes visible as a swelling in the neck.

23. Cont…
 Cretinism (upto 15 years of age): This condition is observed in children.
Retardation in the growth of the infant.
 Myxoedema (gull's disease): Caused by the Hyposecretion of Thyroxine in
Adulthood.
Mucus Accumulation in Subcutaneous tissue, BMR retardation. falling of hair and
teeth, cracking of skin and form of albinism called leucoderma and vitligo.
 Hashimoto’s disease: Suicide of the Thyroid Gland or Autoimmune
Thyroiditis.
In special form of hypothyroidism called hashimoto's disease, antibodies develop
against own thyroglobulin.
The disease is inherited as a Mendelian dominant characterstic. It is an instance of auto-
immune disease.

24. Cont...
2. Hyperthyroidism:
 Thyrotoxicosis: This may be genital,provoked by
chronic infection, large dosage of drugs.
 Exophthalamic Goitre: There is overactive
of cells of a normalgland, it leads to
enlargement of gland (Assymmetrically).

25. THYROGLOSSAL CYST
 A thyroglossal cyst is a fibrous cyst that forms from a
persistent thyroglossal duct.
 Thyroglossal cysts can be defined as an irregular neck
mass or a lump which develops from cells and tissues left
over after the formation of the thyroid gland during
developmental stages.
 Thyroglossal cysts are the most common cause of midline
neck masses and are generally located caudal to (below)
the hyoid bone.
 Thyroglossal cysts develop at birth.

26. Fig. 1 : Image to show Thyroglossal cyst
Ref.: Image web: 1.3

27. Conclusions
 The thyroid gland is the only endocrine gland which stores
hormones.
 The thyroid gland is responsible for the heart beat by
relating it with neural hormones.
 The thyroid gland acts synergistically with somatotropin .
 Sometimes the Thyroid hormone (T3) is related with
gastric disease like Diarrhoea, Constipation.