The thyroid gland is located in the anterior neck, spanning from the C5 to T1 vertebrae. It consists of two lobes connected by an isthmus, wrapping around the cricoid cartilage and trachea. The thyroid gland produces the hormones thyroxine (T4), triiodothyronine (T3), and calcitonin, which regulate metabolism, growth and development, body temperature, heart rate, and energy production. Thyroid hormone synthesis involves iodine being transported into follicular cells and binding to tyrosine residues on thyroglobulin, forming T3 and T4 which are then cleaved and released.

1. Thyroid Gland
By Akanksha Wagh

2. Anatomical Location
Anatomy
The thyroid gland is an endocrine structure located in the neck. It plays a key role in regulating the metabolic rate of
the body.
In this article, we shall look at the anatomy of the thyroid gland – its position, blood supply, and clinical correlations.
The thyroid gland is located in the anterior neck and spans the C5-T1
vertebrae. It consists of two lobes (left and right), which are connected by a
central isthmus anteriorly – this produces a butterfly-shape appearance.
The lobes of the thyroid gland are wrapped around the cricoid cartilage and
superior rings of the trachea. The gland is located within
the visceral compartment of the neck (along with the
trachea, oesophagus and pharynx). This compartment is bound by
the pretracheal fascia.

3. The thyroid gland consists of two lobes connected by a central
isthmus. It is wrapped around the cricoid cartilage and trachea
anteriorly.

4. Anatomical
Relations
The thyroid gland is closely associated with numerous other
structures in the anterior neck:
•Anteriorly – infrahyoid muscles, namely the sternothyroid,
superior belly of the omohyoid and sternohyoid
•Laterally – carotid sheath, containing the common carotid artey,
internal jugular vein and vagus nerve
•Medially –
• Organs – larynx, pharynx, trachea and oesophagus
• Nerves – external laryngeal and recurrent laryngeal
Transverse section of the neck, showing the pretracheal fascia in
red.

5. •Participation in Metabolism: The thyroid gland actively participates in regulating the body's metabolism. It accomplishes this
by controlling the rate at which cells use oxygen and calories to produce energy.
•Hormone Production: The thyroid gland produces thyroid hormones, primarily thyroxine (T4) and triiodothyronine (T3). These
hormones play a crucial role in influencing metabolism, energy production, and overall cellular activity.
•Regulation of Body Temperature: One of the physiological functions of the thyroid gland is to help regulate body temperature.
Thyroid hormones play a role in maintaining temperature homeostasis by affecting heat production and dissipation in the body.
•Heart Rate Regulation: The thyroid gland impacts heart rate by influencing cardiac function. Thyroid hormones help control
how fast the heart beats and how effectively it pumps blood.
•Influence on Growth and Development: In children, the thyroid gland is essential for normal growth and development. It is
crucial for the development of various tissues and organs, including the central nervous system.
•Control of Energy Production: The thyroid gland regulates the conversion of oxygen and calories into usable energy. It
affects how efficiently cells produce and use energy, which is fundamental for overall bodily functions.
Physiology of the Thyroid Gland
Participation

6. Functions of Thyroid Gland
The thyroid gland produces three hormones:
1.Triiodothyronine, also known as T3
2.Tetraiodothyronine, also called thyroxine or T4
3.Calcitonin
Physiology of thyroid hormones:
•T3 and T4 are the only proper thyroid hormones, they are made in follicular epithelial cells of the thyroid
gland.
•The third hormone produced by the thyroid gland calcitonin is made by c-cells.
•Iodine is the building block of both T3 and T4. Hence, dietary intake of this trace mineral iodine is vital.
• The amount of thyroid hormone required by the human body at a particular time varies; and to make the
perfect quantity of thyroid hormone at any given time, the human body needs help from the pituitary
gland.
Thyroid hormones affect you:
1.T3 and T4 increase the basal metabolic rate.
2.T3 and T4 promote physical and mental growth in children.
3.Calcitonin is involved in calcium and bone metabolism.
4.Thyroid hormones activate the nervous system which improves concentration.
5.Thyroid hormone affects your: body temperature and circulation, appetite, energy levels, growth and
bone development, muscle tone and suppleness, heart rate, blood sugar levels, central nervous system
and bowel function, cholesterol levels, fat, carbohydrate and protein metabolism.
6.The higher the amount of T3 and T4 in the body, the higher the body’s metabolism. If the level of T3 and

7. Functions of Thyroid Gland

8. Thyroid Hormone
Synthesis
There are six steps in the synthesis of thyroid hormone, and you can remember them using the mnemonic ATE ICE:
•Active transport of Iodide into the follicular cell via the Sodium-Iodide Symporter (NIS). This is actually secondary active
transport, and the sodium gradient driving it is maintained by a Sodium-Potassium ATPase.
•Thyroglobulin (Tg), a large protein rich in Tyrosine, is formed in follicular ribosomes and placed into secretory vesicles.
•Exocytosis of Thyroglobulin into the follicle lumen, where it is stored as a colloid. Thyroglobulin is the scaffold upon which
thyroid hormone is synthesized.
•Iodination of the Thyroglobulin. Iodide is made reactive by the enzyme thyroid peroxidase. Iodide binds to the benzene ring on
Tyrosine residues of Thyroglobulin, forming monoiodotyrosine (MIT) and then diiodotyrosine (DIT).
•Coupling of MIT and DIT gives the Triiodothyronine (T3) hormone and coupling of DIT and DIT gives the Tetraiodothyronine (T4)
hormone, also known as Thyroxine.
•Endocytosis of iodinated thyroglobulin back into the follicular cell. Thyroglobulin undergoes proteolysis in lysosomes to cleave
the iodinated tyrosine residues from the larger protein. Free T3 or T4 is then released, and the Thyroglobulin scaffold is recycled.
T3 and T4 are the active thyroid hormones. They are fat soluble and mostly carried by plasma proteins – Thyronine Binding
Globulin and Albumin. While T3 is the more potent form, it also has a shorter half-life due to its lower affinity for the binding
proteins. Less than 1% of T3 and T4 is unbound free hormone. At the peripheries, T4 is deiodinated to the more active T3.
T3 and T4 are deactivated by removing iodine. This happens in the liver and kidney. As T4 has a longer half-life, it is used in the
treatment of hypothyroidism over T3 as its plasma concentrations are easier to manage.

9. Thyroid Hormone
Synthesis

10. Thank You