Problem 48 - Objective Biology for NEET

Question

Which of the following is incorrect about thyroid gland? (a) It is composed of follicles and stromal tissues. (b) It secretes tetraiodothyronine or thyroxine \(\left(\mathrm{T}_{4}\right)\) and triiodothyronine \(\left(\mathrm{T}_{3}\right)\), TCT. (c) It consists of 4 lobes. (d) It is stimulated by the hormone TSH.

Step-by-Step Solution

Answer

The incorrect statement about thyroid gland is option (c): It consists of 4 lobes. Actually, a typical thyroid gland consists of two lobes, not four.

Step 1: Identify the features of thyroid gland

The thyroid gland is a butterfly-shaped gland located at the front of the neck, and it is composed of follicles and stromal tissues that produce and store hormones. Therefore, statement (a) is correct.

Step 2: Understand the secretions of thyroid gland

The thyroid gland secretes hormones like tetraiodothyronine or thyroxine \(\left(\mathrm{T}_{4}\right)\) and triiodothyronine \(\left(\mathrm{T}_{3}\right)\). Hence, statement (b) is correct.

Step 3: Examine the structure of thyroid gland

A typical thyroid gland consists of two lobes, not four. It is joined by a narrow isthmus. So, statement (c) is incorrect.

Step 4: Recognize what stimulates the thyroid gland

The secretion of T4 and T3 from the thyroid gland is stimulated by the Thyroid Stimulating Hormone (TSH), which is produced by the pituitary gland. Accordingly, statement (d) is correct.

Key Concepts

Thyroid Hormones

The thyroid gland produces several important hormones, mainly tetraiodothyronine (T4) and triiodothyronine (T3). These hormones play a crucial role in regulating the body's metabolism, heart rate, and temperature.

• Tetraiodothyronine (T4): Also known as thyroxine, makes up the majority of hormones produced by the thyroid. It has four iodine atoms in its structure.
• Triiodothyronine (T3): This hormone, though less abundant, is more potent than T4 and contains three iodine atoms.

Both T3 and T4 are essential for normal growth and development, influencing the speed at which your cells work. When released into the bloodstream, they affect almost every physiological process in the body.
This includes controlling the body's sensitivity to other hormones and stimulating the production of proteins.

Thyroid Structure

The structure of the thyroid gland is unique and efficient in its function. It is a butterfly-shaped organ located in the front of the neck.

• Lobes: The gland typically consists of two lobes, a right and a left, connected by a thin piece of tissue called the isthmus.
• Location: It is positioned below the Adam's apple and along the front of the windpipe.

Its compact and symmetrical design allows it to efficiently produce and release thyroid hormones into the bloodstream. The gland's lobes enable it to cover a larger area, aiding in the regulation of vital body functions. The description of the thyroid having four lobes, as implied in the exercise, is incorrect.

Thyroid Stimulation

Thyroid gland activity is heavily influenced by another hormone: Thyroid Stimulating Hormone (TSH). This hormone is produced by the pituitary gland, located at the base of the brain.

• Role of TSH: It travels through the bloodstream and binds to receptors on the thyroid gland, prompting it to produce T3 and T4.
• Importance: TSH ensures that the levels of thyroid hormones remain balanced, preventing both deficiency and excess.

The regulation of TSH is mediated by a feedback loop involving the hypothalamus, pituitary gland, and thyroid. When the levels of T3 and T4 rise, they signal the pituitary gland to release less TSH, maintaining hormonal balance.

Thyroid Follicles and Tissues

The thyroid gland is composed predominantly of follicles and stromal tissues. These structures play a significant role in the production and storage of thyroid hormones. Thyroid Follicles:

• They are the functional units of the thyroid gland.
• Composed of a layer of epithelial cells, they surround a lumen filled with colloid, the precursor to thyroid hormones.

Stromal Tissues:

• They provide structural support to the gland.
• These tissues house the blood vessels and nerves that facilitate hormone distribution and regulatory signaling.

The intricate design of follicles and stromal tissues ensures the efficient synthesis, storage, and release of thyroid hormones, maintaining the body's homeostasis.