Thyroxine is secreted by?

Appeared in: AIIMS BBSR SNO - 2019

Explanation

The thyroid gland, a butterfly-shaped gland in the neck, is responsible for producing thyroid hormones.
Its follicular cells synthesize and secrete thyroxine (T4) and triiodothyronine (T3).
These hormones are essential for regulating the body's basal metabolic rate, and they play a critical role in growth, development, and protein synthesis.
The process involves converting thyroglobulin into T4 and T3, which are then released into the bloodstream.

Option B: The thymus gland is primarily a lymphoid organ, crucial for the immune system. It secretes thymosin, a hormone that stimulates the development and maturation of T-lymphocytes (T cells).
Option C: The pituitary gland, often called the 'master gland', does not secrete thyroxine. Instead, it secretes Thyroid-Stimulating Hormone (TSH), which acts on the thyroid gland, stimulating it to produce and release thyroxine.
Option D: The hypothalamus is part of the brain that controls the pituitary gland. It secretes Thyrotropin-Releasing Hormone (TRH), which signals the pituitary to release TSH. It is the starting point of the regulatory axis but does not produce thyroxine itself.

Clinical Relevance

Nursing practice connection: This is primarily an exam-oriented knowledge point with limited direct bedside application, so retain Endocrine System: Hormone Secretion as background academic context rather than a clinical decision trigger.
Understanding the source of thyroxine is fundamental for diagnosing and managing thyroid disorders like hypothyroidism and hyperthyroidism.
Nurses play a key role in assessing for signs of thyroid imbalance, administering medications like levothyroxine, and educating patients on their condition.
What if? If a patient has high TSH but low T4 levels, it indicates primary hypothyroidism, meaning the thyroid gland itself is failing, despite receiving stimulation from the pituitary. Conversely, low TSH and high T4 would suggest primary hyperthyroidism.

How to Approach the Question

First, identify the core of the question, which is asking for the origin of a specific hormone (thyroxine).
This is a factual recall question based on knowledge of the endocrine system.
Recall the major endocrine glands and the primary hormones they secrete.
Evaluate each option: The thyroid gland is known for producing thyroid hormones. The thymus is related to the immune system. The pituitary and hypothalamus are involved in regulation but do not produce thyroxine themselves.
Select the option that directly names the gland responsible for producing the hormone in question.

Concept Tested & Keywords

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E6 Pathology- ROBBINS & COTRAN PATHOLOGIC BASIS OF DISEASE 10TH Ed p. 1074-1076

E6 Medicine Harrison 22e Part 2 p. 925-927

E6 Anatomy Applied Ashalatha 4e p. 217-219

Practise the full AIIMS BBSR SNO - 2019

Attempt every question from this paper in a timed mock, then review the full solution for each one.