Question

What do you understand by ductless glands? Describe the structure and functions of thyroid gland.

Answer 1

Any gland that lacks an excretory duct and secretes hormones directly into the bloodstream or lymph is called as ductless gland. Endocrine glands are also known as the ductless glands because of the fact that their secretions are released directly into the blood, not to any tubes or ducts. These glands include Pituitary gland, Pineal body, Thyroid, Parathyroid, Adrenal glands, etc.

Structure of thyroid gland:

It is situated in the neck in front of the larynx and trachea at the level of 5th, 6th and 7th cervical and 1st thoracic vertebrae.

It resembles a butterfly in shape, consisting of two lobes, one on either side of the thyroid cartilage and upper cartilaginous rings of the trachea.

The lobes are roughly cone shaped, about 5cm long and 3cm wide. The lobes are interconnected by isthmus.

Its weight is somewhat variable, but is usually about 30 grams. It is slightly heavier in the female, in whom it becomes enlarged during menstruation and pregnancy.

It is externally surrounded by a thin connective tissue layer called capsule.

Functions of Thyroid gland:

1) Controlling body's metabolism

2) Secretion of hormones that regulate vitals and maintain internal homeostasis

3) Controls breathing and heart rate

4) Monitors body weight

5) Secretion of hormones like Thyroxine, Tri-iodothyronine and calcitonin.