The thyroid gland, located in the neck, produces hormones including thyroxine (T4), triiodothyronine (T3), and calcitonin, which regulate metabolic rate and calcium levels. Its structure consists of spherical follicles composed of follicle cells that synthesize thyroglobulin and parafollicular cells that produce calcitonin. Thyroid disorders include hyperthyroidism and hypothyroidism, with goiter signifying an enlarged thyroid.

1. THYROID GLAND PHYSIOLOGY
By : Dr. Iqra Bano Chandio

2. The Thyroid Gland
•Thyroid gland is located at anterior portion of neck on
trachea just inferior to larynx
•Consisting of Two lateral lobes and an isthmus

3. Thyroid Gland
•This is the normal
appearance of the thyroid
gland on the anterior
trachea of the neck..

4. The Thyroid Gland
•Produces three hormones
•Thyroid hormone: tyrosine based with 3 or 4 iodine
molecules
•T4 tetraiodothyronine (T4; usually called thyroxine)
•Triiodothyronine (T3)
•Calcitonin involved with calcium and phosphorus
metabolism .

5. The Thyroid Gland
• Thyroid is composed of spherical follicles
• Follicle cells: produce thyroglobulin, the precursor of thryoid
hormone (thyroxin)
• Colloid lumen is of thyroglobulin
• Parafollicular “C” cells: produce calcitonin

7. The Thyroid Gland – Histology
Gland is composed of hollow spheres, called colloid follicles.
Squamous epithelial cells, cuboidal cells (follicle cells)
Follicle cells produce thyroglobulin ----→ TH
I
Colloid fills the follicle cavities

8. Normal thyroid seen microscopically consists of follicles
lined
by a cuboidal epithelium and filled with pink,
homogenous colloid

9. • Thyroxine (T4)
• Triiodothyronine (T3)
Both control metabolic rate and cellular
oxidation
• Calcitonin (from parafolicular cells)- lowers
blood CA ++ levels and causes CA++
reabsorption in bone
Thyroid gland selectively uptakes iodine
to produce T3 & T4

10. Actions of Thyroid Hormone
•Required for GH and prolactin production and
secretion
•Required for GH action
•Increases intestinal glucose reabsorption (glucose
transporter)
•Increases(ATP production)
•Increases activity of adrenal medulla
•Induces enzyme synthesis
•Result: stimulation of growth of tissues and
increased metabolic rate.
• Increased heat production (calorigenic effect)

11. The Effects of Calcitonin
• Secreted from thyroid parafollicular (C) cells when blood
calcium levels are high
• Calcitonin lowers Ca++ by slowing the calcium-releasing activity
of osteoclasts in bone and increasing calcium secretion by the
kidney

12. - Hyperthyroidism (Grave’s, Goiter):
increased level of thyroid hormones.
- Hypothyroidism (Cretinism, Myxedima):
decreased level of thyroid hormones.
Thyroid Disorders

16. Goiter
• Goiter simply means enlarged thyroid

17. Goiter in animals

18. Goiter in animals

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