The thyroid gland is the largest endocrine gland located in the neck. It regulates metabolism and plays a role in growth and development through its secretion of hormones like triiodothyronine (T3) and thyroxine (T4). The thyroid has two lobes connected by an isthmus and is typically around 25g. It receives blood supply from the superior and inferior thyroid arteries. Conditions like goiter can result if there is insufficient iodine intake needed to produce thyroid hormones. Hyperthyroidism and hypothyroidism occur when hormone levels are too high or low, respectively.

1. Thyroid Gland
Dr. Aamir
DPT (AIMC), M.Phil.
Lecturer, Quaid-e-Azam Educational Complex, Sahiwal

5. What is Thyroid Gland
It is largest endocrine gland in the body,
Lying in the lower part of front and sides of the neck.

6. What is important about it?
By means of its secretions (Hormones), it
regulates BMR of most of the tissue, causing heat
production.
Normal BMR for male is 1500-1700 calories per
day, for female it is 1400-1600 calories per day.

9. ROLE of Thyroid
Moreover it helps in the brain and body
growth and development.
It plays role in Calcium metabolism

10. Gross Anatomy of Thyroid Gland
It looks like a shield.
It has two lobes
Right Lobe
Left Lobe
A third lobe called as Pyramidal lobe is sometimes present
projects upward from isthmus or from right or left lobes.
Two lobes are joined by means of Isthmus

13. Anatomical Location of Thyroid Gland
Anatomically on the whole, it lies in the lower part of
neck at the level of C5-T1 vertebrae, embracing the
upper part of the trachea.
Right and left lobe extends from middle of thyroid
cartilage to the 4th or 5th tracheal ring.
The isthmus extends from second to 4th tracheal ring.

15. Dimension and weight of Thyroid Gland
Each lobe measures about 5cmx2.5cm while
isthmus is about 1.2cmx1.2cm.
Average weight of thyroid gland is about 25g.
In females it is larger than in males, further
increase in size during pregnancy.

16. Thyroid Capsule
On the external surface of the Thyroid gland
main substance, two types of capsules are
present.
True Capsule
False Capsule

19. True Capsule
Peripheral condensation of connective tissue of
thyroid gland leads to the formation of True
Capsule.
Deep to it lies venous plexus.

21. False Capsule
This capsule is not formed from connective tissue of
the gland.
Instead, deep fascia, of neck region leads to form false
capsule around the thyroid gland.
This capsule forms suspensory ligament of Berry to
connect lobes with cricoid cartilage of larynx

23. Histological Features of Thyroid Gland
When seen under microscope, the gland lobes are
divided into various lobules by tissue septa.
Each lobule has an aggregation of several follicles,
Each follicle is lined from inside by follicular cells.

26. Parafollicular Cells
In addition to follicular cells, another type of cells
are seen in the gland when observed under
microscope, these cells are Parafollicular cells.
These Parafollicular cells also called as C-cells.

27. Colloid Substance
Colloid substance is also present in the
cavity of the follicle. The major constituent
here is glycoprotein.

28. Follicular Cells
The shape of these cells vary according to activity of Gland.
If the gland is in normal average activity, the cells are Cube like 0r
Cuboidal.
If the gland is highly active, the cells become column like or
columnar.
If the gland is completely inactive, the cells become flat or squamous
shaped.

29. Why Do They Exist?

31. What are these Cells For?????
The Follicular cells are responsible for the
production and secretion of
Tri-iodothyonine (T3) (Bound Form).
Tetra-iodothyonine (T4) or Thyroxine (Free
form).

32. Parafollicular Cells
These cells are few in number and lie between
follicles or parallel to follicles so called as
parafollicular cells or C-cells.

33. What are they for????
These cells secrete Thyro-Calcitonin.
This calcitonin promotes deposition of
Calcium in skeletal and other tissue leads to
the production of Hypocalcemia.

34. Blood Supply of Thyroid Gland

35. Blood Supply of Thyroid Gland
Arterial Blood Supply:
Superior Thyroid Artery (A Branch of External Carotid
Artery)
Inferior Thyroid Artery (Arises from Subclavian Artery)
Sometimes in 3% persons another artery exist
Called as Thyroid Ima Artery

38. Venous Drainage
Venous drainage is by
Superior Thyroid Vein
Middle Thyroid Vein
Inferior Thyroid Vein
Fourth thyroid vein (Kocher)

39. Clinical Anatomy

40. Goiter
Any Abnormal Increase in the size of
Thyroid Gland is called as Goiter.

43. Why it Develops?
Synthesis of T3 and T4 requires Iodine.
In dietary deficiency of iodine, TSH level
increases from anterior pituitary.
This TSH cause increase in the proliferation of
thyroid gland tissue.

44. Goiter Effects
It Depends weather Thyroid Hormones level
is normal or not.
It may be associated with Normal Thyroid
Hormones Level.
It may leads to Hyper or Hypothyroidism.

45. Endemic Goiter
Goiter occurs due to deficiency of daily Iodine
Intake
Normal Requirement is 100-200ug/day.
Normal plasma iodine level is 0.15-0.30ug%.

46. Hyperthyroidism
Graves Disease

50. Hypothyroidism
Myxedema (Adults)
Cretinism (New Born)

53. Thyroidectomy
In case of Hyperthyroidism, the removal of thyroid
gland is carried out called as thyroidectomy.
In Subtotal thyroidectomy, the posterior parts of both
lobes are left behind to prevent postoperative
myxoedema.

56. Thank You