Which of the following glands controls the biological clock of the body?

Appeared in: CIP Ranchi 2023

Explanation

The pineal gland, a small neuroendocrine gland in the brain, is the primary regulator of the body's biological clock.
It secretes the hormone melatonin, which is responsible for controlling circadian rhythms, most notably the sleep-wake cycle.
Melatonin secretion increases in darkness, inducing sleepiness, and decreases in the presence of light, promoting wakefulness.
This light-mediated response allows the pineal gland to function as the body's internal clock.

Option A: The adrenal gland secretes hormones like adrenaline and cortisol, which are primarily involved in the stress response ('fight or flight'), metabolism, and blood pressure regulation, not the daily biological clock.
Option B: The thymus gland is a primary lymphoid organ essential for the immune system. It is responsible for the maturation of T-lymphocytes (T-cells) and has no endocrine function related to the circadian rhythm.
Option C: The thyroid gland regulates the body's overall metabolic rate, growth, and development by secreting thyroid hormones (T3 and T4). It does not control the sleep-wake cycle.

Clinical Relevance

Nursing practice connection: This is primarily an exam-oriented knowledge point with limited direct bedside application, so retain Endocrine system and regulation of circadian rhythm as background academic context rather than a clinical decision trigger.
Understanding the pineal gland's function is crucial for advising patients on sleep hygiene, as exposure to light (especially blue light from screens) at night can suppress melatonin production and disrupt sleep.
Nurses may encounter patients with sleep disorders like insomnia or those experiencing jet lag. Educating them on maintaining a regular sleep schedule and managing light exposure can help reset their biological clock.
Melatonin supplements are often used to treat sleep disorders. Nurses should be aware of their use, potential side effects, and interactions with other medications.

How to Approach the Question

First, identify the key phrase in the question: 'biological clock of the body'.
Recall the functions of the major endocrine glands listed in the options.
Associate the term 'biological clock' or 'circadian rhythm' with the hormone melatonin.
Remember that the pineal gland is responsible for producing melatonin.
Eliminate the other glands based on their primary functions: Adrenal (stress response), Thymus (immunity), and Thyroid (metabolism).
Select the option that correctly links the gland to the regulation of the biological clock.

Concept Tested & Keywords

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E6 Physiology Essentials Sembulingam 10e Part 2 p. 88-90

E6 Anatomy Applied Ashalatha 4e p. 223-225

E6 Histology Inderbir 11e p. 149-151

Practise the full CIP Ranchi 2023

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